key: cord-0034428-9b3eazd4
authors: Merzendorfer, Hans; Cohen, Ephraim
title: Chitin/Chitosan: Versatile Ecological, Industrial, and Biomedical Applications
date: 2019-03-07
journal: Extracellular Sugar-Based Biopolymers Matrices
DOI: 10.1007/978-3-030-12919-4_14
sha: 2f6cc3ec2dd37a20999b8cc4b3e8598b2bfd3b78
doc_id: 34428
cord_uid: 9b3eazd4

Chitin is a linear polysaccharide of N-acetylglucosamine, which is highly abundant in nature and mainly produced by marine crustaceans. Chitosan is obtained by hydrolytic deacetylation. Both polysaccharides are renewable resources, simply and cost-effectively extracted from waste material of fish industry, mainly crab and shrimp shells. Research over the past five decades has revealed that chitosan, in particular, possesses unique and useful characteristics such as chemical versatility, polyelectrolyte properties, gel- and film-forming ability, high adsorption capacity, antimicrobial and antioxidative properties, low toxicity, and biocompatibility and biodegradability features. A plethora of chemical chitosan derivatives have been synthesized yielding improved materials with suggested or effective applications in water treatment, biosensor engineering, agriculture, food processing and storage, textile additives, cosmetics fabrication, and in veterinary and human medicine. The number of studies in this research field has exploded particularly during the last two decades. Here, we review recent advances in utilizing chitosan and chitosan derivatives in different technical, agricultural, and biomedical fields.

Chitosan, a polymer of β(1-4)-linked glucosamine (2-amino-2-deoxy-O-glucose) units, is a biopolymer with unique characteristics due to the presence of free amino groups on its backbone. It is obtained by partial deacetylation of chitin, which is found in the cell walls of unicellular and filamenous fungi and in extracellular matrices and skeletal deposits of many protozoan and metazoan organisms including algae, choanoflagellates, sponges, corals, cephalopods, and arthropods. Commercially, chitin is extracted from the waste shells of marine crustaceans such as shrimp and crab. A significant proportion is used to produce chitosan, which, in contrast to chitin, is soluble in water at a slightly acidic pH and is easy to modify chemically to increase solubility at neutral pH and to add new functionalities. Chitosan and its derivatives have many desirable properties such as antioxidative and antimicrobial effects, mucoadhesiveness, biodegradability, and biocompatibility and can be manufactured in various formulations including hydrogels, films, membranes, porous sponges, nanoparticles, and nanofibers. Moreover, chitosan is considered a harmless compound, as it has received the generally recognized as safe (GRAS) status by the US Food and Drug Administration (FDA), and it has been approved as a food additive in several Asian countries ). In the European Union, chitosan is registered as a basic substance, and the use of chitosan hydrochloride is considered by the European Food Safety Authority (EFSA) as having neither harmful effects on human or animal health nor any negative effects on the environment (European Commission 2014). Therefore, chitosan-based materials have been adopted worldwide in numerous applications in water treatment; food, cosmetic, and textile industry; biosensor engineering; plant protection; pharmaceutical industry; and regenerative medicine. They are used as flocculants, ion exchangers, chelating agents, coating materials, drug carriers, and scaffolds for tissue engineering. During the past years, many companies have started to develop chitosan-based products, and some have already successfully launched them for commercial purposes. This review is intended to summarize recent developments in the use of chitosan-based materials for potential and effective applications in different technical, environmental, agricultural, and biomedical fields.

Pollutants in water, industrial wastewater, and reclaimed wastewater for crop irrigation have presented severe environmental and medical problems all over the world. Such contaminants include various heavy metal ions (copper, cobalt, manganese, chromium, mercury, lead, arsenic, cadmium, and nickel), dyes (mainly azo dyes like malachite green, methyl violet, or methylene blue), oil spills, and a variety of pharmaceuticals and endocrine-disrupting compounds. Among the various methods used as remedial measures to treat polluted water and wastewater, the potential of chitosan-based composites as efficient adsorbent, flocculating and chelating agents has been widely investigated. The presence of free hydroxyls and amino groups in many structural forms of chitosan-derived composites facilitates adsorption of pollutants such as dyes, metals, and organic compounds. Chitosan derivatives like carboxymethyl chitosan and graft polymerization are a prevalent strategy to add a variety of functional groups to the composite. Magnetic particles are embedded usually as nanoparticles in the complex core to facilitate regeneration and reuse of adsorbent composites by applying external magnetic field.

was capable to adsorb heavy metals like Cu(II) but also Cd(II) and Pb(II) from aqueous solutions (Peng et al. 2014) . Chitosan-algal biomass composite microbeads (Sargın et al. 2016b ), a binary chitosan/silk fibroin composite (Ramya and Sudha 2013) , and cotton fibers functionalized by triethylenetetramine (TETA) and carboxymethyl chitosan form composites and hybrids for adsorption of Cu (II) from water (Niu et al. 2017) . Microcapsules composed of phytopathogenic (Ustilago sp.) fungal spores immobilized in cross-linked chitosan matrix (Sargın et al. 2016a ) and a binary complex of chitosan and emu egg shells (Anantha and Kota 2016) were shown to remove copper ions from aqueous solutions.

Chitosan complexed with clays, ceramic minerals, and carbon-based materials was used to enhance absorbance of heavy metals from aqueous solutions. A nanocomposite that consisted of chitosan-montmorillonite (Pereira et al. 2013) and silica gel/chitin and chitosan with nano-hydroxyapatite was used as adsorbents for Cu(II) (Rajiv Gandhi et al. 2011) . Nanocomposites containing chitosan-poly (vinyl alcohol)-attapulgite were also used for removal of Cu(II) from aqueous solutions . Furthermore, a recyclable magnetic microsphere composed of cross-linked chitosan-rectorite (a clay mineral) and Fe 3 O 4 was studied for adsorption of Cu(II) and Cd(II) (Xie et al. 2015) , and chitosan-zeolite composite hydrogel beads were examined for Cu(II) sorption (Djelad et al. 2016) .

A particular interesting recyclable composite with chelating capacity consists of core magnetic (Fe 3 O 4 )-silica particles combined with cross-linked chitosan. Its porous and highly specific surface area contributed by activated carbon carrier showed an excellent adsorption capability for Cu 2+ ions . A recyclable nanocomposite with a core xanthated Fe 3 O 4 chitosan grafted on graphene oxide introduced sulfur groups to the composite using carbon disulfide (Liu et al. 2016a) .

Other sorbent composites that were prepared and studied are a recyclable composites containing chitosan grafted on a core of Fe 3 O 4 -hexadecyl trimethoxysilane (Liu et al. 2016b ), a flocculant composed of poly(acrylic acid) grafted on chitosan (Saleh et al. 2017) or beads containing chitosan-poly(vinyl alcohol) and ZnO (Xu et al. 2017a) . A sophisticated composite was prepared by using magnetic nanoparticles on the surface of polystyrene as core, coated with chitosan crosslinked by glutaraldehyde followed by grafting polyethylenimine on the complex surface . This submicron composite is recyclable and exhibits good adsorption capacity for Cu(II) ions.

Highly selective adsorption of copper ions from aqueous solutions was achieved by the ion-imprinting polymer method (Kong et al. 2017) . Microspheres of magnetic cores of Fe 3 O 4 with a shell of cross-linked chitosan and graphene oxide were used to imprint Cu 2+ ions. Zarghami et al. (2014) prepared Cu(II) ion-imprinted membranes composed of cross-linked chitosan/poly(vinyl alcohol) for adsorption of the metal from aqueous solutions. A similar ion-imprinted technique was reported for selective adsorption of Pb(II) from a recycling wastewater unit (Hande et al. 2016 ).

Textile, leather, paper, and food industries discharge a plethora of environmental pollutants such as synthetic dyes. A variety of chitosan-based composites was examined as promising adsorbents of hard to remove industrial dyes. Chitosan per se contains functional groups for interaction with pollutants including dyes. Adding more functional groups by modifying chitosan (cross-linking of chitosan layers, direct chemical modification, or graft polymerizationsee Chapter 3) improves adsorption capability. Molecular imprinting technique was devised as selective adsorbent of pollutants. Composites' core of iron oxide magnetic nanoparticles like maghemite (γ-Fe 2 O 3 ) and magnetite (Fe 3 O 4 ) offers a way to recover the adsorbent scaffolds for reuse. Again, since the published articles are enormous in number, only essential parameters and basic blocks of adsorbing chitosan-based composites are included.

Methyl orange as a model anionic azo dye was adsorbed by films of cross-linked chitosan/nanonized maghemite from aqueous solution (Jiang et al. 2012) . Improved adsorption of the same anionic dye was achieved by preparing a magnetic chitosan grafted with multi-walled carbon nanotubes (Zhu et al. 2010) , and magnetic chitosan grafted with graphite oxide nanocomposite was able to adsorb the toxic azo dye, Reactive Black 5 (Travlou et al. 2013) . Chitosan modified by ethylenediamine (Zhou et al. 2011) or polyaniline (Abbasian et al. 2017) grafting was able to adsorb other anionic azo dyes like Orange 7, Acid Orange 10 acid and red 4 and direct red 23, respectively. A magnetic complex of chitosan and zirconium oxide was a potent adsorbent of food anionic azo dyes like amaranth and tetrazine (Jiang et al. 2013a ). Moreover, a complex composite adsorbent was prepared by grafting chitosan with poly[poly(ethylene glycol) methyl ether methacrylate] (Tsai et al. 2017) . The functionalized groups added to chitosan contributed to improved removal of the azo dye Reactive Orange 16 from water.

Recyclable composite microspheres composed of cross-linked chitosan grafted with glutamic acid and having a core of Fe 3 O 4 nanoparticles coated with silica adsorb cationic dyes like methylene blue, crystal violet, and light yellow 7GL (Yan et al. 2013) . Similarly, an amphiphilic N-benzyl-O-carboxymethyl chitosan composite with a core of iron oxide nanoparticles was prepared for adsorption of methylene blue, crystal violet, and malachite green (Debrassi et al. 2012) . The cyclic oligosaccharide β-cyclodextrin (β-CD) was added to chitosan-based composites as it provides a hydrophobic inner cavity and a hydrophilic exterior. Magnetic chitosan-β-CD with grafted graphene oxide to enlarge surface area exhibited an improved adsorption of methylene blue as a model dye from water (Fan et al. 2013) . Molecular imprinting technique is of interest to selectively remove dyes from aqueous solutions. The molecule or ion used as templates will be subsequently removed, and a recognition site is generated. Alizarin red served as template molecule, and imprinted magnetic chitosan nanoparticles showed improved adsorption of the dye (Fan et al. 2012 ).

Pharmaceutical, endocrine-disrupting compounds and personal care products have become a new class of hazardous environmental pollutants (Grassi et al. 2013) and have emerged as an extensive global concern. They are discharged as municipal and hospital effluents, from manufacturing industries, and found in water, reclaimed wastewater, and even in crops irrigated by reclaimed water (Paltiel et al. 2016) . Pharmaceuticals, endocrine disruptors, and personal care products and their chemical transformation derivatives are characterized as stable, persistent compounds that are biologically active at very low concentrations.

The challenging goal has been to completely remove the above micropollutants from wastewater following conventional cleaning methods. Laboratory research including adsorption by chitosan-based composites has been high on the agenda (Amouzgar and Salamatinia 2015) . Zhang et al. (2014) used a rather simple crosslinked magnetic chitosan-Fe 3 O 4 composite to examine the sorption of three pharmaceutical compounds from contaminated water. The absorbance analysis showed effective sorption of diclofenac (a nonsteroidal anti-inflammatory drug) and clofibric acid (an antilipemic agent) but not of carbamazepine (an antiepileptic medication). Pharmaceuticals in water can be present as cationic, anionic, and neutral forms at different pH values. Thus, Zhang et al. (2016) in a more recent study devised an innovative, more complex three-dimensional chitosan-based scaffold. A magnetic core of chitosan-Fe 3 O 4 was grafted with polymeric arms of either the polycation [poly(2-methyl acryoxyethyl trimethyl ammonium chloride], the polyanion poly (acrylic acid), or the neutral polymer poly(methylmethacrylate). The polycationic extension was cost-effective in removal of diclofenac from water due to charge attraction . Further, magnetic composite pellets with grafted clay (bentonite) and activated carbon were prepared to examine possible cost-effective removal of cationic and anionic pharmaceuticals (Arya and Philip 2016). The composite was effective as a sorbent for the beta-blocker (atenolol), the antibiotic (ciprofloxacin), and the lipid regulator (gemfibrozil).

A variety of chitosan composites have been tested for the removal of other drugs. Cross-linked chitosan grafted with sulfonate or N-(2-carboxymethyl) groups was used as a sorbent to remove the dopamine agonist pramipexole dihydrochloride from polluted water . Chitosan-poly(acrylic acid)-graphite oxide nanocomposite showed adsorption of dorsolamide, a carbonic anhydrase inhibitor for eye treatment (Kyzas et al. 2014) . Adsorption of nonsteroidal anti-inflammatory drugs ibuprofen and ketoprofen was studied using porous composite beads prepared of Chitosan-MIL 101 (Cr) (Zhuo et al. 2017) . Using the antiepilectic carbamazepine as template, the magnetic molecular imprinted technique, based on chitosan-Fe 3 O 4 nanoparticles, was applied for selective sorption of the drug (Zhang et al. 2013c) .

Chlorophenols are endocrine-disrupting chemicals, used inter alia in manufacturing pharmaceuticals that are found in wastewaters (Sin et al. 2012) . Excellent adsorbing capability was demonstrated using a cross-linked chitosan-salicylic acid-β-CD composite. Composites of chitosan-γ-CD were capable of adsorbing the endocrine disruptors, polychlorophenols, and bisphenol A (Duri and Tran 2013) . Composite films prepared by blending microporous carbon fibers with cross-linked chitosan/polyvinyl alcohol were examined as sorbents of bisphenol A from water (Bilgin Simsek et al. 2017) .

Finally, Soares et al. (2017b) proposed an interesting and unusual concept of using low-cost magnetic chitosan-based scaffold for absorbing and removing oil spills following initial skimming from water. In addition, the composite, which had a core of magnetic nanoparticles with a shell of chitosan-silica hybrid, effectively adsorbs nonpolar organic solvents.

Biosensors are essentially analytical devices that convert biological reactions or interactions into measurable signals. Basically, the biosensors' constructs consist of a biological sensing element associated and intimately interfaced with a transducer that converts a signal in one form of energy to a signal of another form. Such signals should be proportional to the amount of analyte within a certain concentration range. Electrochemical biosensor devices, for example, possess advantages as being simple and relatively cheap while offering rapid detection and high sensitivity and further being amenable to miniaturization. Biosensors have been developed not only as analytical tools for medical purposes of clinical detection but also for applications in food industry and environmental monitoring.

Chitosan, and to a much lesser extent chitin, has several advantageous qualities in the design of biosensors. The polysaccharides are biocompatible, have functional groups pliable to chemical modification, and can be easily deposited on the surface of the transducer as adhesive thin films for the immobilization of recognition elements (enzymes, antibodies, DNA, whole cells, and cell organelles). Addition of carbon tubes, graphite, and graphene oxide to the composite increases electron transfer to the transducer and enhanced mechanical strength as well as water permeability and retention. Since there is a vast array of biosensors based on chitosan in their constructs, the following provide only representative devices.

Glucose detection and monitoring is of paramount importance in the medical field. A variety of biosensors, constructed with chitosan and using immobilized glucose oxidase for the detection of glucose levels, were reported. A glucose electrochemical sensor was prepared with glucose oxidase immobilized on the composite of chitosan-carbon nanotubes ). An amperometric glucose biosensor composed of multilayered chitosan biofilms-gold nanoparticles-glucose oxidase on platinum (Pt) electrode was devised ). The biocompatible gold nanoparticles helped in directing the transfer of electrons to the transducer. Yang et al. (2009) devised a different glucose biosensor composed of Pt electrodeglucose oxidase-Fe 3 O 4 -chitosan-nafion. Zhang et al. (2015c) prepared an electrochemical biosensor for glucose with chitosan-graphite composite and the addition of magnetic Fe 3 O 4 nanoparticles on Pt-coated indium tin oxide (ITO) glass electrode. Shrestha et al. (2016) devised a glucose biosensor with a glassy carbon electrode on which a nanocomposite film of glucose oxidase immobilized on chitosan and on which a graft of polypyrrole-nafion and multi-walled carbon nanotubes was deposited.

Electrochemical biosensors using other oxidases and various constructs were fabricated to monitor food and medically important compounds. For instance, a lactate biosensor was generated using lactate oxidase and a nanocomposite structure of chitosan-polyvinylimidazole-Os-carbon nanotubes (Cui et al. 2007) . Glutamate and xanthine oxidases as recognition elements immobilized on chitosan/graphene oxide-polymerized riboflavin were constructed as glutamate and hypoxanthine biosensors (Celiesiute et al. 2017 ). In addition, a xanthine biosensor based on immobilization of xanthine oxidase on chitosan-polypyrrole-gold nanoparticles was fabricated by Dervisevic et al. (2017) . Tkac et al. (2007) developed a selective galactose biosensor with a rather simple configuration of chitosan-single-walled carbon nanotubes and immobilized galactose oxidase. A sensitive amperometric nanocomposite biosensor for cholesterol detection was constructed using a matrix of Pt nanoparticles deposited on multi-walled chitosan-carbon nanotubes complexes with immobilized cholesterol oxidase (Tsai et al. 2008) . A similar construct was proposed by Medyantseva et al. (2014) for the detection of antidepressant monoamine drugs using immobilized monoamine oxidase. Dai et al. (2010) developed an electro-chemiluminiscent biosensor to detect choline by immobilizing choline oxidase on a chitosan/titanate nanotubes composite film. Finally, a biosensor for measuring ethanol was prepared using alcohol oxidase immobilized on chitosaneggshell film (Wen et al. 2007 ). The biosensor monitored the decrease in oxygen level vs ethanol concentration.

A number of electrochemical biosensors were similarly constructed to immobilize various dehydrogenase enzymes (Zhang et al. 2004 ). The nanocomposite scaffold film, attached predominantly to glassy carbon electrodes, consists of chitosan, multi-walled carbon nanotubes, and NAD + as cofactor. The signal current is based essentially on electrooxidation of the formed NADH. Among the large list of enzymes suffice it to mention NAD-dependent alcohol (Lee and Tsai 2009; Zhang and Gorski 2011) , lactate (Tsai et al. 2007 ) and glutamate (Hughes et al. 2015) dehydrogenases, and FAD-dependent glucose dehydrogenase (Monosik et al. 2012) .

In contrast to the above enzyme-based biosensors, a nonenzymatic electrochemical device for monitoring glucose was formulated (Al-Mokaram et al. 2017 ). The construct, which was based on a nanocomposite film composed of polypyrrole-chitosantitanium dioxide nanoparticles on ITO glass electrodes, involved redox reactions and exhibited improved glucose oxidation and high electron transfer kinetics.

Other biosensors detecting and measuring diverse compounds were formulated, for example, nitrite biosensor based on Cu-containing nitrite reductase immobilized on viologen-chitosan that catalyzes the reduction of nitrite (Quan and Shin 2010) . Horseradish peroxidase immobilized on alumina nanoparticles-chitosan composite was devised to detect phenolic compounds . Wang et al. (2003) developed a biosensor to detect and measure glucose, galactose, and glutamate in human blood by using their corresponding oxidases immobilized on chitosan-Prussian blue composite film. The biosensor used Prussian blue as a good catalyst to form hydrogen peroxide by electroreduction. Biosensors to detect catechol as well as other phenolic compounds were based on immobilized tyrosinase on a film of chitosan-nickel nanoparticles . A biosensor for detection of chlorophenol that includes immobilized laccase on ZnO-chitosan nanocomposite was prepared by Mendes et al. (2017) . Nanocomposite of functionalized graphene oxide (enriched with carboxylic moieties)-polypyrrole-chitosan film was constructed to detect hydrogen peroxide using screen-printed carbon electrodes (Akhtar et al. 2017 ). Such a device was able to electro-catalyze the reduction of hydrogen peroxide. Teepoo et al. (2017) constructed an electrochemical biosensor to detect and monitor hydrogen peroxide by using horseradish peroxidase immobilized on a chitin-gelatin nanofiber composite. Another biosensor for hydrogen peroxide that used immobilized catalase on chitosan-β-cyclodextrin (with ferrocene in its cavity) was fabricated by Dong et al. (2017) . It was based on chitosan-functionalized graphene oxide (enriched with carboxylic moieties)-polypyrrole nanocomposite able to electrocatalytically reduce hydrogen peroxide.

Detection and quantification of trace amounts of carcinogenic and toxic metallic ions are of great challenge and importance. A cross-linked chitosan-carbon nanotube sensor was developed for the determination of Cd(II) and Hg(II) (Janegitz et al. 2011) . Sugunan et al. (2005) prepared a biosensor made of chitosan-gold nanoparticles to detect Cu(II) and Zn(II), and Ahmed and Fekry (2013) used a construct of chitosan-α-Fe 3 O 4 nanoparticles sensor to detect Ni(II), As(II), and Pb (II). Biosensors were developed to detect and determine organophosphorus (OP) pesticides as well. For instance, Stoytcheva et al. (2018) prepared a device based on OP hydrolase immobilization on a chitosan-carbon-nanoparticles-hydroxyapatite nanocomposite. A nanocomposite immunosensor to monitor the OP compound, chlorpyriphos, is based on immobilized anti-chloropyriphos monoclonal antibody on multi-walled carbon nanotubes-chitosan-thionine (as electronic mediator) (Sun et al. 2012b ). An intricate electrochemical immunosensor for the detection and monitoring of the fungal hepatocarcinogen, aflatoxin B1, as model antigen was developed by Masoomi et al. (2013) . The construct scaffold involved chitosan-gold nanoparticles, immobilized polyclonal anti-aflatoxin B1, and a magnetite core that can enable regeneration of the immunosensor.

Biosensors based on chitosan/multi-walled carbon nanotubes hybrid films were developed largely by Babaei and colleagues to determine and quantitate drugs and neurotransmitters: acetaminophen and mefenamic acid (Babaei et al. 2010) , dopamine and morphine (Babaei et al. 2011a) , paracetamol (Babaei et al. 2011b ), L-DOPA (Babaei and Babazadeh 2011) , and 5-hydroxytryptamine and dopamine .

The polycationic nature of chitosan films in immunobiosensors is also exploited to immobilize polyanionic polymers such as nucleic acid sequences and proteins. Singh et al. (2013) devised an electrochemical DNA biosensor to detect typhoid which was constructed by surface immobilizing Salmonella typhi single-stranded (ss) DNA on graphene oxide/chitosan/ITO nanocomposite as a bioelectrode. The biosensor was capable of distinguishing between complementary, noncomplementary, and one base mismatch sequences. A similar electrochemical DNA biosensor was developed for the detection of Escherichia coli 0157:H7 . It was prepared with immobilized E. coli ss-DNA using a graphene oxide/chitosan hybrid nanocomposite. An electrochemical immunobiosensor to detect botulism neurotoxin A was reported by Afkhami et al. (2017) . The sensor consisted of a gold nanoparticles/chitosan/graphene nanocomposite with immobilized antibodies to quantify the bound neurotoxin. To detect α-fetoprotein in human serum, an immunosensor was fabricated in which the α-fetoprotein antigen was immobilized on a film of a gold nanoparticles/carbon nanotubes/chitosan nanocomplex to quantify protein levels using a competitive immunoassay format (Lin et al. 2009 ). Giannetto et al. (2017) fabricated a competitive electrochemical immunosensor to detect HIV1-related capsid protein p24 in human serum. The p24 antigen was immobilized on gold-free single-walled carbon nanotubechitosan complex for the interaction with a mouse monoclonal anti-p24, which was used for competitive immunodetection. Liu et al. (2009) developed an immunosensor to detect carcinoembryonic antigen, which is based on corresponding antibodies immobilized on chitosan-gold nanoparticles. Finally, Qiu et al. (2009) reported an immunosensor to detect hepatitis B surface antigen, which was constructed on the basis of a gold nanoparticles/chitosan/ferrocene biofilm with immobilized hepatitis B antibodies.

14.4 Beneficial Properties of Chitosan for Possible Use in Agriculture, Food, and Textile Industry

The wide-ranging antimicrobial, antiviral, and antioxidant activities, induction of defense systems in plants, and stimulation of plant growth by chitosan, chitosan oligomers, chemically modified chitosan and their composites have indicated their potential use in agricultural practices (El Hadrami et al. 2010; Malerba and Cerana 2016) . Pre-and postharvest treatment of coating seeds, fruits, and vegetables by edible chitosan-based films effectively improve germination and plant vigor and prolonged shelf life and storage quality of food products ). Preservation by chitosan-based coating also expanded to include meat, eggs, dairy products, and seafood (Friedman and Juneja 2010). Other promising practices such as delivery and slow and sustained release of chitosan-based encapsulated agrochemicals (fertilizers, micronutrients, pest control agents, and genetic materials) have been widely investigated (Malerba and Cerana 2016) .

There are several comprehensive reviews that summarize the potential use of chitosan, its derivatives, and chitooligosaccharides in agriculture as related to their broad-spectrum antimicrobial and antioxidant activities (Aider 2010; Cota-Arriola et al. 2013; Li et al. 2013a; Xing et al. 2015; Liaqat and Eltem 2018) . Such beneficial activities were demonstrated in a variety of agricultural products like preservation of vegetables, fruits, cereals, dairy products, eggs, meat, and seafood Friedman and Juneja 2010) . Chitosan per se has antimicrobial activity that depends on higher degree of deacetylation, low molecular weight (its oligosaccharides), increased protonation at low pH, and the type of microorganisms (Katiyar et al. 2014) . The antimicrobial efficiency is enhanced by adding essential oils (extracted from lemon, lemon grass, cinnamon, or rosemary) (Duan and Zhang 2013; Xing et al. 2016; Yuan et al. 2016) or by adding metal ions like silver or copper Brunel et al. 2013; Kumar-Krishnan et al. 2015; Choudhary et al. 2017a; Sharma 2017) particularly to chitosan-based nanoparticles (Friedman and Juneja 2010; Cota-Arriola et al. 2013) . The mode of action is mainly attributed to electrochemical interactions between the positively charged chitosan and the negative surface charge of bacterial cells leading to membranes disruption (Xing et al. 2015) . In addition, penetration and binding of nanochitosan with microbial DNA that impact mRNA and protein synthesis were proposed (Rabea et al. 2003, Malerba and Cerana 2016) . Scavenging of free radical and reactive oxygen species by chitosan and its derivatives is responsible for its antioxidative effects (Guo et al. 2005; Ngo and Kim 2014) . Scavenging of superoxide and hydroxyl radicals by chitosan and its derivatives was demonstrated by several studies (Xie et al. 2001; Guo et al. 2005; Yen et al. 2008; Wan et al. 2013) . Furthermore, chitosan acts as a biogenic elicitor of various enzymes that detoxify reactive oxygen species (Malerba and Cerana 2016) and induces the formation of antioxidant and fungicidal phytoalexins (Yamada et al. 1993; Hadwiger 2013; Xing et al. 2015) .

Chitosan and its derivatives were shown to activate plant immunity enzymes (catalase, peroxidase, superoxide dismutase, phenyl oxidase, phenylalanine ammonia lyase) that are capable of detoxifying reactive oxygen species (Hadwiger 2013; Xing et al. 2015; Malerba and Cerana 2016) . Such activation engages different signal transduction pathways that involve a variety of second messengers. Other defense responses include pathogenesis-related proteins, phytoalexins, proteinase inhibitors, lignin synthesis, or callose formation (El Hadrami et al. 2010; Hadwiger 2013) . Induction of programmed cell death and hypersensitivity-associated responses by chitosan and chitooligosaccharides was documented (Zuppini et al. 2004; Vasilêv et al. 2009; Zhang et al. 2012) , as well as activation of plant defense genes via the octadecanoid pathway leading to jasmonate synthesis (Doares et al. 1995; Rakwal et al. 2002) . Chitosan induces hydrolase enzymes such as chitinase and β-1,3 glucanase able to destroy chitin/glucan-containing fungal cell walls (Ma et al. 2013b; Xing et al. 2015) .

Controlled and sustained release of chitosan-encapsulated agrochemical such as fertilizers, micronutrient, pesticides, and genetic materials was demonstrated by a plethora of investigations (Kashyap et al. 2015) . Food products coating by films of edible chitosan derivatives (plus a variety of additives) prolong their shelf life with concomitant improvements in storage quality Yuan et al. 2016) .

A number of examples linked to chitosan-coated pesticides given below indicate the potential of the eco-friendly techniques in plant protection against phytopathogens, insects, and weeds: controlled release of insecticides like the botanicals azadirachtin being encapsulated in the complex carboxymethyl chitosan-ricinoleic acid (Feng and Peng 2012) and rotenone wrapped in oleoyl carboxymethyl chitosan (Kamari and Aljafree 2017); nanoparticulate chitosan-β-cyclodextrin, which encapsulated carvacrol and exhibited high acaricidal and repellency activities (Campos et al. 2018) ; and controlled release of avermectin conjugated to N,O-carboxymethyl chitosan or avermectin coated by silica cross-linked chitosan composite (He et al. 2013) . Encapsulation of the neonicotinoids imidacloprid (Li et al. 2012a; Lim and Ahmad 2017) and acetamiprid (Yan et al. 2014) , malathion, and spinosad (El Badawy et al. 2016 ) by chitosan-alginate capsules exhibited prolonged release of the insecticides. Slow release of the fungicide carbendazim against the phytopathogens Sclerotinia sclerotiorum using chitosan/β-CD-epichlorohydrin (Wang et al. 2017a ) and hexaconazole encapsulated by chitosan nanoparticles against Rhizoctonia solani (Chauhan et al. 2017 ) was demonstrated. Ilk et al. (2017) reported the antifungal and antioxidant activities of kaempferol encapsulated in lecithin-chitosan nanoparticles against Fusarium oxysporum.

In addition to their slow release property, chitosan composites also protect pesticides from photodegradation. Nanoparticles of chitosan-beeswax protected deltamethrin from photodegradation (Nguyen et al. 2012) , and a similar protective effect of avermectin was demonstrated for a silica/chitosan copolymer (He et al. 2013) . Likewise, composites of chitosan with a variety of clays (montmorillonite, attapulgite, bentonite, and kaolinite), safe anionic dyes (Fast Green and Naphthol Yellow S), and photo-stabilized fungal conidia of the insect biocontrol agent Aschersonia spp. were reported (Cohen et al. 2003) . Chitosan composites were found to be useful carriers of herbicides facilitating soil sorption as in the case of paraquat associated with chitosanalginate nanoparticles (Silva Mdos et al. 2011) or slow release of paraquat encapsulated in tripolyphosphate-generated chitosan nanoparticles (Grillo et al. 2014 ). Moreover, encapsulation of metolachlor in blended gel beads of cross-linked carboxymethyl cellulose and carboxymethyl chitosan was effective in slow release of the herbicide as a model compound (Dong et al. 2012) . Finally, slow release of atrazine encapsulated in carboxymethyl chitosan/bentonite gel was demonstrated (Li et al. 2012a ).

The modulated release of encapsulated fertilizers is important for enhanced growth of plants while reducing environmental problems of their excessive use. Experiments were accompanied by swelling rates of composites, fertilizer loads, and kinetics of release. Examples are chitosan-xanthan tablets (Melaj and Daraio 2013) or chitosan-starch beads (Perez and Francois 2016) as carriers of potassium nitrate that serve as model fertilizer; slow release of NPK fertilizers aggregated on chitosan nanoparticles (Corradini et al. 2010 ) and application on leaf surfaces enables translocation via stomata into the phloem (Abdel-Aziz et al. 2016); efficient controlled slow release of water soluble NPK fertilizers coated by chitosan with an additional outer coating by poly (acrylic acid-co-acrylamide) (Wu and Liu 2008) . This composite also exhibited improved water absorption and retention. Noppakundilograt et al. (2015) examined the controlled release of NPK fertilizer granules embedded in a hydrogel composed of poly(vinyl alcohol) and then chitosan and a third layer of acrylamide and acrylic acid following cross-linking of chitosan by glutaraldehyde. Controlled release of urea by a variety of chitosan-based composites was established. Urea dispersed with humic substances in chitosan (Araújo et al. 2017) , urea encapsulated in chitosan-acryamide (Siafu 2017) , urea release from adduct of silk fibroingelatin-chitosan hydrogels (Rattanamanee et al. 2015) , urea smectite clay chitosan composite (Puspita et al. 2017) , and urea-kaolinite mixed with chitosan (Roshanravan et al. 2015) were tested for controlled release of the fertilizer.

Beneficial effects of preharvest chitosan-based seed coating and foliar treatment were reported by El Hadrami et al. (2010) . Chitosan-coated artichoke seeds, for example, induced better germination, stimulated root system growth, and were effective against a number of pathogenic fungi (Ziani et al. 2010 ). Bhaskara Reddy et al. (1999) demonstrated induced resistance to seed-borne Fusarium graminearum followed by improved germination and vigor in wheat seeds coated with chitosan. Soybean seeds coated by chitosan had anti-feeding effects and protected against several insect pests (Zeng et al. 2012) , and coating rice seeds increased antifungal effect, stimulated seeding growth, improved root system, and increased crop yield (Zeng and Shi 2009) . Tomato seeds coated with chitosan resulted in resistance to infection by inducing plant defense mechanisms (Benhamou et al. 1994) . Chickpea seeds treated with chitosan-silver nanoparticles promoted germination and increased biomass, chlorophyll, carotenoids, and protein contents as well as amylase activity and defense enzyme activities (Anusuya and Banu 2016). Similar effects were demonstrated in maize seeds coated with Cu/chitosan nanoparticles (Saharan et al. 2016; Choudhary et al. 2017b ).

The antimicrobial activity of chitosan was targeted for use to improve preservation of a large variety of vegetable and fruit crops as well as of eggs, meat, and dairy products (Devlieghere et al. 2004; Friedman and Juneja 2010; Yuan et al. 2016) . Chitosan with added compounds such as plant materials and animal proteins (formulations of chitosan with additions of tapioca starch, hydroxypropyl cellulose, pectin, and fish gelatin) was used to develop edible films. Such films in addition to their antimicrobial and antioxidant activities also keep food products from loss of moisture and oxygen penetration (Aider 2010; Duan and Zhang 2013) . Postharvest coating of vegetables and fruits with chitosan and additional essential oils (extracts from lemon, rosemary, lemon grass, bergamont, cinnamon, oregano, and thymine), which by themselves exert antimicrobial and antioxidant activities, improved storage quality and prolonged the shelf life of products . Controlling postharvest decay during storage was reported also for additives such as olive oil, glacial acetic acid, green tea extract, and lactic acid Yuan et al. 2016) .

Microbial contaminations are a serious problem in food industry, because foodborne bacteria and fungi are associated with food spoilage and food poisoning leading to economic losses and human health risks. Using appropriate food packaging materials with antimicrobial properties may prevent or at least slow down bacterial and fungal growth. For this reason, a variety of biopolymers has been tested to identify alternative materials to the classical nondegradable plastic packaging materials, which have caused serious environmental issues due to their inappropriate disposal. Optimal alternative materials should be environmentally safe due to biodegradability and biocompatibility. As chitosan-based material combine antimicrobial properties with biodegradability and biocompatibility, they are the focus of research in food packaging. Moreover, chitosan-based materials have food-preserving antioxidant activity and film-forming ability, which allows the production of transparent foils and bags. Different methods have been established during the past decades to fabricate chitosan films including casting, coating, extrusion, and layer-by-layer synthesis, and the resulting materials have been evaluated for their antimicrobial and antioxidant activity and for their optical, mechanical, barrier, and thermal characteristics. Chitosan has also been combined with other functional materials resulting in composite films with tremendous preservative properties that can be utilized for the packaging of different foods such as vegetables, fruit, and meat. For a comprehensive overview on this topic, the reader is referred to an excellent review article published recently by Wang et al. (2018) .

Pure chitosan films are frequently based on dispersions of chitosan nanoparticles (Ali et al. 2014) , to which plasticizers, such as glycol (Leceta et al. 2013) , and/or surfactants, such as Tween 80 (Martins et al. 2012) , are added to modify the mechanical properties and to emulsify auxiliary compounds. In addition, chitosan nanofibers have been fabricated as a packaging material and tested for their antimicrobial activity. For instance, Arkoun et al. (2017) examined the antimicrobial activity of chitosan/polyethylene oxide nanofibers produced by an electrospinning process. They showed that the chitosan nanofibers were efficient in inhibiting growth of E. coli, Staphylococcus aureus, Lysteria innocua, and S. typhimurium, however at pH 5.8, which was below the pKa of chitosan, limiting the applicability to slightly acidic food. Importantly, the authors demonstrated that the antibacterial effects were irreversible, suggesting a bactericidal rather than bacteriostatic mechanism.

Combinations of chitosan and other natural polysaccharides have been frequently used to fabricate functional films with applications in food packaging. These biopolymers comprise of cellulose and various cellulose derivatives, alginate, cyclodextrin, glucan, mannan, pectin, starch, and xylan. Chitosan/cellulose films revealed improved mechanical properties while maintaining excellent antimicrobial properties . Also chitosan/hydroxypropyl methylcellulose (HMPC) films exhibit significant antimicrobial activity. For instance, Möller et al. (2004) examined the antimicrobial effects of chitosan/HPMC films against Listeria monocytogenes and found that bacterial growth was completely inhibited on the film. Similarly, chitosan/carboxymethyl cellulose films showed superb food preservation properties when tested on packaged cheese (Youssef et al. 2016) . Antimicrobial chitosanalginate films have a great potential for food packaging as well, particularly because they show improved gas exchange and water vapor permeability properties when prepared by a layer-by-layer electrostatic deposition approach (Poverenov et al. 2014a ). Martiñon et al. (2014) studied the effectiveness of antimicrobial multilayered coatings consisting of chitosan, pectin, and trans-cinnamaldehyde at different concentrations to extend the shelf life of fresh-cut cantaloupe and found that certain compositions were effective in preventing bacterial growth and spoilage. Lorevice et al. (2016) produced chitosan nanoparticles and combined them with different methyl pectin matrices to generate nanocomposite films and tested the mechanical, thermal, and barrier properties. The results showed that the nanocomposite film improved mechanical characteristics when compared with conventionally produced pectin films, making these novel materials promising for food packaging production. Similarly, chitosan/cyclodextrin films with inclusions of essential oil have been reported to possess desirable mechanical properties for food packaging . Moreover, this material showed significant antimicrobial activities against a variety of pathogenic bacteria.

Chitosan films have been also combined with a variety of proteins including casein (Khwaldia et al. 2014) , gelatin (Poverenov et al. 2014b; Noorbakhsh-Soltani et al. 2018) , collagen , kidney bean protein ), lactoferrin (Brown et al. 2008) , and lysozyme (Yuceer and Caner 2014) , as well as with antibacterial peptides such as nisin . In addition, chitosan was blended with antimicrobial and antioxidant extracts from bee wax (Velickova et al. 2013 ) and plants, such as citrus (Iturriaga et al. 2014) , thyme (Talon et al. 2017) , and maqui berry (Genskowsky et al. 2015) , as well as with essential oils including clove bud oil, cinnamon oil, and star anise oil .

Other approaches in fabricating chitosan-based films employed grafts, blends, or casts using synthetic polymers such as poly(vinyl alcohol) , poly (lactic acid) (Pal and Katiyar 2016) , poly(ethylene) (Reesha et al. 2015) , poly(ethylene oxide) (Kohsari et al. 2016) , poly(styrene) (Lopez-Carballo et al. 2013) , poly(propylene) (Cavallo et al. 2014) , poly(caprolactone) (Alix et al. 2013) , and poly(acrylonitrileco-acrylamide) (Kumar et al. 2018 ) that led to improved mechanical and thermal properties. However, these synthetic polymers are not readily degraded in nature; hence concerns regarding the environmental safety have been raised. Guo et al. (2015) developed new edible antimicrobial films using microemulsions in combination with high-pressure homogenization processing. The films were made of chitosan, allyl isothiocyanide, and barley straw arabinoxylan, which were used as film-forming, antimicrobial, and emulsifying agents, respectively. The material was tested to be efficient in preventing growth of L. innocua.

To improve antibacterial activity, chitosan-based films were synthesized as composites with metals, minerals, and other inorganic compounds. Youssef et al. (2014) produced chitosan-silver and chitosan-gold (CS-Au) nanocomposites films, which showed enhanced antimicrobial activity against Gram-positive (S. aureus) and Gram-negative bacteria (Pseudomonas aerugenosa), fungi (Aspergillus niger), and yeast (Candida albicans). In another study published by Al-Naamani et al. (2016), poly(ethylene) films were coated with zinc oxide/chitosan nanocomposite, which completely inactivated and prevented the growth of food pathogens. In an approach based on a solution cast method, Sanuja et al. (2015) fabricated a chitosan-based nanocomposite film using nano zinc oxide and neem essential oil, which improved mechanical, physical, barrier, and optical properties. Moreover, Zhang et al. (2017) prepared chitosan/titanium dioxide composite films, which were found to possess significant antimicrobial activity against E. coli, S. aureus, C. albicans, and A. niger. Xu et al. (2017c) employed a different strategy by synthesizing chitosan/graphene oxide nanocomposites with titanium dioxide and analyzed their antimicrobial and food-preserving efficacies. They showed that the material effectively prevented Bacillus subtilis and A. niger biofilm formation presumably by disrupting cellular membranes. In addition, they demonstrated that the nano-coating could be applied as a cling film, which delays loss of moisture in fruits and vegetables and inhibits polyphenol oxidase activity and thus enzymatic browning but increases superoxide dismutase activity, which protects against reactive oxygen species. Next to these materials, chitosan-montmorillonite composites, chitosan/nanosilica films, and manifold combinations of chitin, metals, and minerals have been tested. In addition, numerous chemical chitosan derivatives have been explored for their properties to screen for new films suitable in food packaging. These derivatives include carboxymethyl chitosan and quaternized chitosan such as (2-N-Hydroxypropyl-3trimethylammonium chloride) chitosan ).

Due to their versatile and unique physicochemical and biological properties, chitosan, its multiple derivatives, and their adjunct complexes (addition of functional groups) have attracted considerable attention for possible use of eco-friendly materials in the textile industry. They are relatively inexpensive, biocompatible, biodegradable, and nontoxic and readily adhere to textile fabrics and usually demonstrate antibacterial activity. Certain formulations retain moisture as well as impart thermal stability and UV protection.

Chitosan per se or blends of chitosan-based composites deposited onto textiles fabrics were mostly tested for durable antibacterial activity (nearly all antibacterial studies include E. coli and S. aureus that represent correspondingly Gram-negative and Gram-positive bacteria). Coated Thai silk fabric with chitosan using radio frequencies plasma treatment exhibited antibacterial effects (Wongsawaeng et al. 2017) , and polyester/cotton fabric treated with chitosan can be used as an alternative to the antibacterial triclosan (Ranganath and Sarkar 2014) . Chitosan grafted on cotton (Ferrero et al. 2015) or on wool (Periolatto and Ferrero 2013) fabrics using UV irradiation bestowed antibacterial activity after many washing cycles. Chitosan reduced to nanoparticles and applied onto wool fabric imparted durable antibacterial and bestowed shrink proofing (Yang et al. 2010) . Nanonized chitosan applied onto cotton exhibited, in addition to antibacterial activity, also thermal stability, UV protection, as well as improved dye-binding ability (Hebeish et al. 2013 ). Periolatto et al. (2012) demonstrated antibacterial effects and laundry durability of cotton and silk fabrics by UV curing with 2-hydroxy-2-methylpropylpropane-1-one as photoinitiator of the photochemical reaction.

Chitosan possesses abundant potential, in particular, for use in medical textiles and sportswear. For example, a blend of chitosan (short fibers) with cotton (long fibers) yarn by spinning technology is desirable for medical applications (Lam et al. 2017) . Gauze bandages for wound dressing were prepared by electrospinning of chitosan nanofibers and cotton fabric (Nawalakhe et al. 2015) . Plasma treatment was applied to improve adhesion by increased cross-linking between the two fiber systems imparting subsequent durability (Nawalakhe et al. 2015) . Pure chitosan microfibers produced by wet spinning process was aimed for possible stable 3-D scaffold woven or nonwoven textile fabrics to be used in regenerative medicine such as bone and cartilage engineering (Toskas et al. 2013) . Lam et al. (2018) examined a blend of chitin fibrils with cotton jersey fabric and showed reduced rigidity that may provide comfort to patients with epidermolysis bullosa skin disease. Likewise, chitosan-coated textile fabrics improved atopic dermatitis disease by restraining skin microbiome (Lopes et al. 2015) . Sonochemical deposition was used by Petkova et al. (2014) to coat cotton fabrics with a hybrid of chitosan and ZnO nanoparticles. This complex showed improved antibacterial activity, slow release of the metal and washing stability, and postulated as effective treatment for hospital textiles to prevent transfer of pathogens. Similarly, the hybrid of chitosan and silver nanoparticles deposited onto cotton fabric demonstrated antibacterial effects and laundry durability befitting their possible use for medical textiles and sportswear . Ali et al. (2011) proposed to use chitosan nanoparticles that are able to pick and retain silver ions in medical textile applications. A polyester fabric coated with this complex hybrid imparted enhanced antibacterial activity. Nanonized chitosan applied onto cotton exhibited in addition to antibacterial activity, also thermal stability, UV protection as well as improved dye-ability (Hebeish et al. 2013) .

A large number of publications signified and reported beneficial properties of chitosan and chitosan-based formulations with possibly great potential to treat textile fabrics. Such valuable features include protecting a variety of fabrics with emphasis on medical textiles, production of aromatic and flame-retarding fabrics, as well as dye removal and treatment of textile wastewater. Table 14 .1 summarizes inter alia nanochitosan, chitosan nanometal complexes, or chitosan derivative composites with metals and other substances, which were treated onto textile fabrics (notably cotton), and depicts their conceivable potential for the textile industry.

Chitin and, in particular, chitosan and its derivatives provide advantageous properties in the cosmetic area. They are biocompatible and adhere to surface components of the skin and hair, forming elastic films with moisturizing and water retention capabilities. They can serve as vehicles for encapsulated cosmetic ingredients and their controlled delivery and release and formation of gels in mixtures with water and alcohol and have some antimicrobial, antioxidant, and anti-inflammatory activities, with the additional important benefit of low cytotoxicity Jimtaisong and Saewan 2014; Aranaz et al. 2018) .

Chitosan and its derivatives are included in cosmetic formulations and products for mainly care and protection of the skin and hair but inter alia in tooth enamel and tooth lacquer, nail lacquer, lipsticks, cleansing and bath materials, toothpaste, mouthwash, chewing gum, deodorants, and breath refresheners (Dutta et al. 2004 ). Aging of the skin, viewed as wrinkling, dryness, loss of elasticity, dehydration, and hyperpigmentation, is the result of long-term exposure to sunlight UV, which mainly forms reactive oxygen species. Protection from photoaging is a major drive in the cosmetic industry. For example, chitooligosaccharides per se were able to protect UV-irradiated hairless mouse skin from photoaging damage (Kong et al. 2018) . Gel formulation of chitosan microparticles served as a delivery system for the sustained release of the hydrophilic sunscreen, phenylbenzimidazole sulphonic acid (Gomaa et al. 2010) . The cosmetic gel formulation of blended chitosan, collagen, and Aloe vera, with antibacterial and antioxidant effects, proved useful in the regeneration and rejuvenation of the skin using cultured mouse fibroblast (Rajashree and Rose 2017). Microspheres composed of carboxymethyl chitosan/collagen peptides-calcium chloride protected mice skin and thymus lymphocytes from UV-B radiation damage 

Thermally stable blend Grande et al.

(continued) (Liu et al. 2015b) . A cosmetic cream formulation composed of quaternized carboxymethyl chitosan-montmorillonite nanocomposite bestowed good UV protection and additional moisturizing and water retention effects .

There is a possible cosmetic use of neutralized chitosan in citrate buffer film for skin exfoliation (Libio et al. 2016 ). Chitosan and various chitosan derivatives, as active ingredients, were examined in cosmetic hair care products like shampoos, permanent wave agents, hair conditioner, styling lotions, rinses, hair colorant, hair sprays, and hair tonics (Dutta et al. 2004; Aranaz et al. 2018) . They can adhere to the negatively charged hair keratin forming a transparent elastic film that covers hair fibers endowing smoothness, softness, and also mechanical strength (Dutta et al. 2004) . A blend of chitosan and two other biopolymers like collagen and hyaluronic acid that forms a thin film over hair surface provides enhanced mechanical strength and improved conditioning of the treated hair (Sionkowska et al. 2017 ). Chitosan as a targeting vehicle to hair follicles in the skin was demonstrated with entrapped minoxidil, a medication to treat hair loss (Gelfuso et al. 2011; Matos et al. 2015) . Microparticles and nanoparticles of chitosan-encapsulating minoxidil enabled its controlled release.

A large number of possible applications of cosmetic formulations containing chitosan and its derivatives have been patented. It is noteworthy that formulations containing chitosan are already in the busy cosmetic market. 

Removal and degradation of anionic azo dyes Škorić et al. (2016) AB antibacterial effects, CS chitosan, LBL layer by layer deposition, β-CD β-cyclodextrin a Photochemical reaction by UV generating cross-linked polymers

Because chitosan and many of its derivatives are nontoxic, biocompatible, biodegradable, and highly versatile polymers, a large assortment of possible biomedical applications have been explored, of which some were implemented into therapeutic strategies by the pharmaceutical industry. To obtain optimal materials for the delivery of drugs, several factors have to be considered including the stability of the bioactive agents, absorption properties and mucoadhesiveness, gelling properties, particle sizes, permeation and transfection-enhancing properties, efflux pump inhibition, tissue targeting, residual toxicity of the final products, as well as release kinetic profiles. Chitosan derivatives have been developed into different kinds of pharmaceutical excipients used for the production of tablets and capsules (Illum 1998; Werle and Bernkop-Schnurch 2008) , suppositories (Caramella et al. 2015) , sprays (Osman et al. 2013) , ointments (Kang et al. 2016) , eye drops (Basaran and Yazan 2012) , and wound dressings (Bano et al. 2017) . The drugs are usually encapsulated by ionotropic gelation, spray drying, emulsion solvent evaporation, and coacervation (Panos et al. 2008 ). Chitosan-based excipients have been found useful in tablet disintegration and drug dissolution (Illum 1998 ) and in enhancing penetration and absorption properties (Thanou et al. 2001; van der Merwe et al. 2004; Sahni et al. 2008) . Most importantly, certain dosage forms allow the controlled release of drugs (Jennings et al. 2015 ; Fonseca-Santos and Chorilli 2017). These include chitosan-based hydrogels (Knapczyk 1993; Kristl et al. 1993; Berger et al. 2004; Ishihara et al. 2006; Elviri et al. 2017 ) and micro-/nanoparticles for drug delivery (Hamman 2010). Here, we will focus on the applications of chitosan-based matrices in drug delivery for cancer, immune, and gene therapy, and we will summarize some recent advances in tissue engineering ( Fig. 14.1 ). 

Chitosan-based materials can be used in various forms as drug delivery system ( Fig. 14. 2). Tablets are probably the most favorable and accurate dosage form, which are moreover easy to fabricate and handle. A simple method for their production is homogenization of the drug and chitosan and compressing the resulting mixture to tablets. However, it has to be considered that due to the alkaline conditions in the distal intestine, drug absorption is restricted to the more proximal regions of the gastrointestinal tract when pure chitosan is used which precipitates at an alkaline pH (Sakkinen et al. 2004; Dhaliwal et al. 2008) . Therefore, more pH-insensitive formulations using higher-charged chitosan derivatives such as trimethylated chitosans or thiolated chitosan conjugates have improved absorption properties along the gastrointestinal tract. Although there is still a lack of robust data in human volunteers, some studies indicate that tablet formulations using highercharged chitosan derivatives increase bioavailability due to improved mucoadhesiveness and better protection of the drug from degrading enzymes (van der Merwe et al. 2004 ). Chitosan-based tablets have been also examined for their use in vaginal drug delivery, mainly as carriers for antiviral and antifungal therapeutics (El-Kamel et al. 2002; Senyigit et al. 2014; Frank et al. 2017 ). However, the antimicrobial properties of chitosan may negatively affect the vaginal microflora, and hence long-term treatment should be critically evaluated (Raafat and Sahl 2009) .

As chitosan-based hydrogels facilitate equal distribution and increase mucoadhesiveness, permeation, and bioavailability, they are effective formulations for eye drops to administer therapeutic drugs in ophthalmology (Krishnaswami et al. 2018) . Chitosan-based formulations used in eye care include hydrogels, nanoparticles, and liposomal and colloidal systems (De Campos et al. 2001; De Fig. 14.2 Chitosan-based drug delivery systems Campos et al. 2003; Diebold et al. 2007; Gupta et al. 2010) . For similar reasons, they are also in use for nasal drug delivery, which is impaired by high turnover and secretion rates (Illum 2003) . Notably, chitosan-coated lipid micro-and nanoparticles have been developed for nose-to-brain delivery of a variety of therapeutic drugs (Casettari and Illum 2014; Sarvaiya and Agrawal 2015) . Chitosan-based nanoparticles are also a promising carrier for buccal drug delivery, which has the advantage of avoiding the hepatic first-pass metabolism and degradation in the gastrointestinal system (Sandri et al. 2005) . Polymeric carriers generally have the potential advantage of prolonged release times of low-molecular-weight drugs. Because chitosan is additionally susceptible to hydrolysis by lysozyme in the blood serum, which facilitates drug release, and exhibits no toxic or hemolytic effects when applied parenteral (Nordtveit et al. 1994; Richardson et al. 1999) , chitosan-based formulations are also suitable carriers for controlled drug release when administered by intravenous injection (Thanoo et al. 1992 ).

Conventional chemotherapeutics are frequently not very effective in reaching the tumor cells, as solid tumors are not well supplied with blood, and lack lymphatic vessels, which results in and decreased convective flow in the interstitial fluid. To overcome these problems, novel drug delivery systems have been designed. These carriers are capable of encapsulating high concentrations of the cytotoxic compound within a macromolecular matrix that specifically targets the cargo to the tumor cells where the drugs are finally released in a controlled manner. This concept profits from the EPR (enhanced permeability and retention) effect, the phenomenon that macromolecules preferentially accumulate in solid tumors, probably because they have a defective vasculature and lack effective lymphatic drainage (Matsumura and Maeda 1986) . Chitosan-based nanoparticles have many properties that make them suitable carriers for anticancer drugs. Next to their great chemical flexibility, allowing the design of selective carriers, chitosan-based materials evidently exhibit also the EPR effect depending on the tumor microenvironment (Yhee et al. 2017) . Moreover, they are degraded inside the body into fragments which can be cleared by the kidney (Kean and Thanou 2010) , and several studies suggested that chitosan itself has antitumor effects (Qi and Xu 2006; Yao et al. 2013a) , making this polymer a highly suitable supplementary antitumor drug and drug carrier. Indeed, chitosan-based nanocomposites can be used to deliver hydrophilic and hydrophobic drugs such as doxorubicin hydrochloride and paclitaxel, respectively (Kim et al. 2006; Yousefpour et al. 2011 AT anti-tumor effects, CS chitosan, Tu tumor conjugate and examined the antitumor effects in vivo in macrophage tumor cells implanted into BALB/c mice. The authors observed an improved therapeutic efficacy of dextran-doxorubicin loaded chitosan nanoparticles, which is probably due to the prolonged circulation time and/or drug accumulation at the tumor sites. In another study published by Yousefpour et al. (2011) , doxorubicin was conjugated to chitosan using succinic anhydride as a cross-linker. In a second step, the resulting self-assembled chitosan-doxorubicin conjugate nanoparticles were conjugated with trastuzumab, a monoclonal antibody to the human epidermal growth factor receptor 2+ (Her2+), via lysine thiolation and subsequent linking of the derived thiols to chitosan. The Trastuzumab conjugated chitosan-doxorubicin nanoparticles selectively targeted Her2+ cancer cells resulting in enhanced uptake when compared to chitosan-doxorubicin particles and the free drugs. In another study, pluronic F127, a block copolymer of hydrophobic polyoxypropylene flanked by two chains of hydrophilic polyoxyethylene, was grafted onto chitosan to generate a copolymer micelle that can encapsulate doxorubicin (Naruphontjirakul and Viravaidya-Pasuwat 2011) . The resulting chitosan-pluronic micelles carrying doxorubicin showed a high drug loading capacity and revealed a higher cytotoxic activity to MCF7 breast cancer cell lines in vitro than the free drug. Another approach to deliver doxorubicin specifically to cancer cells was reported by Varshosaz et al. (2016) . The research team fabricated dual targeted nanoparticles loaded with doxorubicin and magnetic nanoparticles to treat breast cancer. For this purpose, the nanoparticles were produced via a layer-bylayer technique and functionalized with a bioconjugate of chitosan/poly(methyl vinyl ether maleic acid) and luteinizing hormone-releasing hormone (LHRH) to target corresponding receptors on the surface of MCF7 breast cancer cells, which presumably take up the particles by endocytosis. The targeted nanoparticles increased the cytotoxicity of doxorubicin about twofold in LHRH-positive cancer cells. In a similar approach, folate-grafted chitosan-coated magnetic nanoparticles were loaded with doxorubicin to target human glioblastoma U87 cells in athymic BALB/c nude mice in a subcutaneous tumor model system .

Guiding the injected nanoparticles to the tumor by a magnetic field significantly decreased tumor growth by controlled delivery of doxorubicin to the cancer cells and demonstrated the feasibility of magnetic nanoparticles to direct the localization of drug release. Mesoporous aluminosilicate zeolite (ZSM-5) chitosan core-shell nanodisks loaded with doxorubicin were used as pH-responsive drug delivery systems against osteosarcoma that release the drug after upon endosomal acidification . Recently, Radmansouri et al. (2018) showed that doxorubicin-loaded electrospun chitosan/cobalt ferrite/titanium oxide nanofibers could be used for localized melanoma cancer therapy. The fastest release of doxorubicin from prepared magnetic nanofibers was observed at acidic pH when an alternating magnetic field was applied. As mentioned above, chitosan-based nanoparticles can also be modified to carry hydrophobic drugs such as paclitaxel.

For this purpose, hydrophobic side chains are grafted onto chitosan. For instance, Kim et al. (2006) used glycol chitosan nanoparticles that were hydrophobically modified with β-cholanic acid and incorporated paclitaxel. The resulting nanoparticles showed sustained drug release, and following injection into the tail vein of tumor-bearing mice, tumor growth was impaired. In a subsequent study, the same research team used this system as carrier for cisplatin, which is also poorly soluble in water. The hydrophobically modified glycol chitosan nanoparticles loaded with cisplatin exhibited the EPR effect, as they accumulated in solid tumors, and was proven to have a high antitumor efficacy in a tumor-bearing mice model (Kim et al. 2008) . Paclitaxel was also encapsulated in chitosan-containing glyceryl monooleate core-shell nanoparticles, which were generated by the emulsification/evaporation technique (Trickler et al. 2008) . Using this drug delivery system, the authors observed a 1000-fold increase in cytotoxicity, when determining the IC 50 values in a human breast cancer cell line. Another common hydrophobic anticancer drug is 5-fluorouracil, which has been widely used to treat different kinds of solid tumors. In a study by Zheng et al. (2007) , polyelectrolyte nanoparticles based on chitosan and polyaspartic acid sodium salt were used to encapsulate 5-fluorouracil testing various conditions for nanoparticle preparation such as temperature, ionic strength, pH and cross-linker concentration, and different loading methods. The optimized nanoparticles showed sustained drug release in vitro and in vivo. Rajan et al. (2013) prepared hyaluronidase-5-fluoruracil-loaded chitosan-polyethylenglycol-gelatin copolymers as a targeted drug delivery system and examined particle size, distribution, morphology, and drug loading capacity. The nanoparticles showed less cytotoxicity than free 5-fluorouracil when applied to colon cancer cells for a few hours. Another approach for controlled drug delivery used molecular surface imprinted graft copolymer of chitosan with methyl methacrylate, which was prepared by free-radical polymerization with 5-fluorouracil as template molecule (Zheng et al. 2016 ). The pH dependency and the kinetics of drug release suggested that this chitosan-based carrier is optimal for orally applied colon-specific drug delivery. A similar strategy to achieve colon specificity was used recently by Bashir et al. (2017) . They synthesized pH-responsive semi-interpenetrating network hydrogels of N-succinyl-chitosan via Schiff base mechanism using glutaraldehyde as a cross-linking agent and embedded poly(acrylamide-co-acrylic acid). The hydrogel exhibited a porous structure and pH-dependent swelling properties. The hydrogel was effectively loaded with 5-fluorouracil, and the determined drug release was pH-dependent as well, with high release rates at pH 7.4 and low rates at pH 1.2. In many cases, chitosan nanoparticles have been conjugated with tumor-specific ligands to mediate active targeting of cancer cells, which is expected to increase therapeutic efficacy, accelerate drug release to selected sites, prevent unwanted drug release before arrival at the target sites, and diminish adverse side effects of chemotherapeutic drugs. Active targeting can be accomplished by functionalizing chitosan-based nanoparticles and hydrogels using tumor-targeting ligands, which bind to specific receptors that are specifically present on the surface of cancer cells. Proper ligands of such kind include cytokines, peptides, folic acid, hyaluronic acid, biotin or avidin, and antibodies (Prabaharan 2015) . Here, we will discuss only a one example for each of these ligands to illustrate active targeting. Deng et al. (2011b) synthesized monodispersed and pH-sensitive chitosan-silica hollow nanospheres, loaded them with antitumorigenic tumor necrosis factor α (TNF-α), and conjugated them with an antibody to epidermal growth factor receptor 2, which is overexpressed in about 20% of all women suffering from breast cancer (Owens et al. 2004) . Subsequent drug release studies demonstrated that the nanospheres delivered cytotoxic TNF-α to MCF-7 breast cancer cells and suppressed tumor with high therapeutic efficacy. Due to the acidic microenvironment inside solid tumors, TNF-α is gradually released from the nanospheres, binds to the TNF-α receptor, and activates a signaling cascade which induces programed cell death.

In a study published by Shen et al. (2013a) , doxorubicin and verapamil were combined in chitosan nanoparticles to achieve an integrated treatment for cancer and doxorubicin-induced cardiomyopathy in the process of cancer therapy. For this purpose, chitosan shells coated on magnetic nanoparticles were loaded with both drugs and entrapped into poly(lactic acid-co-glycolic acid) nanoparticles conjugated with a cyclo(Arg-Gly-Asp-D-Phe-Lys) (cRGD) peptide targeting α v β 3 integrin, which is highly expressed on activated endothelial cells of newborn vessels during tumor angiogenesis as well as in some tumor cells . Near-infrared laser irradiation was sufficient to trigger drug release within an acidic microenvironment. Cytotoxicity assays performed in vitro suggested that cRGD-conjugated nanoparticles exhibited a greater growth inhibitory potential in cancer cell lines than the free drug or control nanoparticles likely due to cRGD-mediated targeting of tumor cells. In vivo imaging and biodistribution studies further showed that the nanoparticles preferentially accumulated in the tumor tissue under magnetic guidance. Finally, in vivo data for tumor regression along with electrocardiogram recordings and histopathology observations indicated that the cRGD-conjugated polymer-coated magnetic nanoparticles could have a high therapeutic potential as a dual-drug delivery system for the treatment of both cancer and doxorubicinmediated cardiotoxicity.

Recently, a novel disulfide-linked chitosan-g-methoxy poly(ethylene glycol) copolymer was successfully synthesized, which was suggested to have excellent properties for redox-responsive drug delivery (Antoniraj et al. 2018 ). Redoxresponsive 5-fluorouracil-loaded nanoparticles were synthesized by ionic gelation method, and folic acid was used to functionalize the nanoparticles for receptortargeted drug delivery, as cancer cells commonly express high-affinity folate receptors on their surface. The 5-fluorouracil-free nanoparticles showed improved hemocompatibility, and the 5-fluorouracil-loaded nanoparticles conjugated with folic acid had a high cytotoxicity to MCF7 breast cancer cells, presumably due to intracellular internalization because of folic acid conjugation, which is expected to enhance the cellular uptake of the nanoparticles.

Many types of cancer cells overexpress different isoforms of hyaluronic acid receptors, which leads to enhanced binding and internalization of hyaluronic acid, as reported for instance in breast tumor cells (Bourguignon et al. 2000) . To exploit this fact for targeting tumor cells, Jain et al. (2010) prepared hyaluronic acid-conjugated chitosan nanoparticles loaded with oxaliplatin and encapsulated in Eudragit S100coated pellets for effective delivery to colorectal tumors. In immunodeficient C57BL mice model with HT-29 cancer cells injected into the ascending colon, relatively high local drug concentrations were found in the colon tumors after oral administration of the oxaliplatin nanoparticles, and the concentrations increased with prolonged exposure time. Coupling of hyaluronic acid onto the surface of chitosan nanoparticles was found to make them more specific for delivery of the anticancer drug to the tumor of the colon.

Several studies revealed that also biotin and avidin possess tumor-targeting properties. Biotin receptors are overexpressed in many tumor types characterized by rapid division rates and aggressive growth (Russell-Jones et al. 2004) , and avidin (a highly glycosylated protein) is recognized by lectins expressed on the surface of tumor cells (Yao et al. 1998) . For this reason, Bu et al. (2013) prepared chitosan nanoparticles conjugated with either biotin or both biotin and avidin as tumortargeted carrier system for the delivery of trans-resveratrol. Pharmacokinetic experiments revealed that avidin-biotin-loaded nanoparticles rapidly accumulated in the liver after injection, while the delivery nanoparticles conjugated only with biotin was attenuated. Cytotoxicity assays using HepG2 cells further uncovered that compared to trans-resveratrol solution and unconjugated chitosan nanoparticles, both biotin and avidin-biotin loaded nanoparticles significantly improved anticancer activity, but the latter combination exhibited a higher cytotoxicity. Thus, it was proposed that the synthesized nanoparticles conjugated with avidin and biotin may be a potent drug delivery system particularly to targeting hepatic carcinoma.

Finally, Xiao and Yu (2017) developed a glycol/chitosan nanobioconjugate loaded with gemcitabine and conjugated with anti-EGFR and anti-chitosan antibodies to target pancreatic cancer cells and cause aggregation. Administration of the chitosan conjugates efficiently blocked tumor growth and metastatic spread in human pancreatic cancer cells.

Gene therapy requires the transmission of nucleic acids (DNA or RNA) into the target cell to mediate expression of therapeutic genes or to silence gene expression by RNA interference. However, negatively charged phosphates of nucleic acids impair permeation through the plasma membrane, which is negatively charged as well. In addition, unprotected nucleic acids are highly susceptible to degradation by nucleases. Hence, delivery of nucleic acids into cells relies on non-viral or viral vectors, which drastically improves transfection and protects from enzymatic degradation (Wivel and Wilson 1998) . As viral vectors have the risk of causing adverse side effects such as immune reactions and malignant transformation, many efforts have been made to develop non-viral vectors for gene delivery, among them are ample examples of different chitosan-based nanoparticles.

Actually, unmodified chitosan is not an effective carrier for the transfer of nucleic acids due to its low solubility in water and instability of DNA/RNA chitosan complexes at physiological pH. Thus, chitosan requires chemical modification or grafting to convey appropriate physicochemical properties to the resulting complex. Chitosan modifications that have been used to design chitosan-based carriers for gene or siRNA delivery include quaternization by alkylation of tertiary amines, reaction with 2-chloroethylamine hydrochloride and N,N-dimethyl-2chloroethylamine hydrochloride, conjugation with polyethylene glycol, poly (amidoamine) or RGD dendrimer grafting, modification with phosphatidylcholine, or combinations of these modifications.

Among the quaternized chitosan derivatives, N-trimethyl chitosan and its derivatives have been extensively studied for their suitability in gene delivery, because they are reasonably soluble in water, have comparably little tendency to form aggregates, and exhibit a high loading capacity for nucleic acid under physiological conditions. In a systematic study published by Germershaus et al. (2008) , the physicochemical properties of chitosan, N-trimethyl chitosan, and poly (ethylenglycol)-N-trimethyl chitosan were analyzed and compared. Using cell lines derived from mouse embryonic fibroblasts as a transfection system for plasmid DNA, the authors observed a significant increase in transfection efficiency when N-trimethyl chitosan nanoparticles were used to deliver plasmid DNA instead of chitosan nanoparticles. In addition, grafting poly(ethylenglycol) onto N-trimethyl chitosan further improved transfection efficiency, stabilized the particles, decreased particle size, and reduced cytotoxicity when compared to unmodified N-trimethyl chitosan nanoparticles. Zheng et al. (2009) prepared folate-conjugated N-trimethyl chitosan nanoparticles and compared cellular uptake and transfection of plasmid DNA (pDNA) in vitro with non-conjugated N-trimethyl chitosan nanoparticles using folate overexpressing KB and SKOV3 cells and folate receptor-deficient A549 and NIH/3T3 cells. The folate-N-trimethyl chitosan/pDNA complex showed a decrease in cytotoxicity in comparison to pDNA complexes made of polyethylenimine. Moreover, folate conjugation increased transfection efficiency and folate receptormediated endocytosis by KB cells and SKOV3 cells when compared to non-conjugated N-trimethyl chitosan nanoparticles.

Exploring further possible improvements of N-trimethyl chitosan-based gene delivery systems, Zheng et al. (2015) synthesized arginine, cysteine, and histidinemodified trimethyl chitosan nanoparticles to form complexes with pDNA. Using HEK 239 cells, they evaluated stability, cellular uptake, endosomal escape, release behavior, nuclear localization, and in vitro and in vivo transfection efficiencies. The cysteine-modified N-trimethyl chitosan nanoparticles turned out to be the most promising candidates for gene delivery due to sufficient stability, high cellular uptake, and glutathione-responsive release-favoring mechanism in combination with preferable nuclear distribution. Addition of sodium tripolyphosphate to the cysteine-modified nanoparticles was further effective to compromise certain disadvantageous attributes for pDNA delivery. N-trimethyl chitosan nanoparticles were also employed in drug-siRNA co-delivery using a metastatic breast cancer cell line (Eivazy et al. 2017) . In this study, the authors tested simultaneous delivery of siRNA to silence the gene encoding the high mobility antigen (HMGA-2) and the anticancer drug doxorubicin to boost therapeutic anticancer effects. They found that dual delivery of HMGA-2 siRNA and doxorubicin by trimethyl chitosan nanoparticles significantly inhibited breast cancer cells growth.

A very recent study developed novel strategies in fighting lung cancer by RNA interference mediated gene silencing of the gene encoding the anti-apoptotic protein, Survivin. For this purpose, Ni et al. (2018) designed nanoparticles consisting of baclofen functionalized N-trimethyl chitosan as polymeric carriers, TPP as ionic cross-linker, and siRNA to Survivin. Baclofen was used to target the nanoparticles to non-small lung cancer cells that overexpress the GABA B receptor, which specifically binds baclofen (Zhang et al. 2013b ). The siRNA-loaded nanoparticles increased the uptake of Survivin-siRNA through the interaction with GABA B receptor and efficiently induced apoptosis and gene silencing. The authors further encapsulated the siRNA-loaded nanoparticles into mannitol microparticles for dispersion in the HFA-134a aerosol to allow administration by pressurized metereddose inhalers. Pulmonary delivery of siRNA is expected to avoid serum-induced degradation, reduce systemic side effects, and improve therapeutic efficacy. Zhong et al. (2015) hypothesized that the addition of amino residues to chitosan could improve stable complex formation with negatively charged siRNA enhancing transfection and gene silencing efficiency. For this purpose, they prepared a novel chitosan derivative (MixNCH) combining 2-chloroethylamine hydrochloride and N, N-dimethyl-2-chloroethylamine hydrochloride with chitosan and examined the physicochemical properties of the resulting nanoparticles. Using a hepatocellular carcinoma cell line (HepG2), gene transfection efficiency of MixNCH/midkine-siRNA nanoparticles and inhibition of HepG2 cell proliferation were analyzed. They found that midkine-siRNA delivered by MixNCH nanoparticles was able to significantly reduce both mRNA and protein levels of the midkine growth factor, resulting in a significant decrease of cell proliferation in HepG2 cells.

Guzman-Villanueva et al. (2014) evaluated the capability of different-sized chitosan derivative-based polyplexes to carry, internalize, and release siRNA in human adenocarcinomic epithelial cells. For this purpose, they first prepared Nphthaloyl-chitosan or N-phthaloyl-oligochitosan, reacted them with polyethylene glycol and hydroxybenzotriazole in DMF, and then cross-linked the polymers using ECD. Finally, the N-phthalimido groups were removed by the reaction with hydrazine monohydrate, and the products were purified by dialysis against water and ethanol. Both the chitosan-and oligochitosan-based polyplexes exhibited biodegradability, low cytotoxicity, and resistance to enzymatic degradation up to 24 h. When loaded with siRNA, the oligochitosan-based polyplexes drastically increased cellular internalization of the siRNA and gene silencing compared to naked siRNA. To improve the transfection efficiency of chitosan-based gene delivery systems, Deng et al. (2011a) fabricated a dendronized chitosan derivative using a coppercatalyzed azide alkyne cyclization reaction of propargyl focal point poly (amidoamine) dendron with 6-azido-6-deoxy-chitosan. The resulting dendronized chitosan nanoparticles exhibited higher water solubility and buffering capacity than native chitosan and showed lower cytotoxicity and enhanced transfection efficiency in transformed human embryonic kidney and nasophyryngeal carcinoma cell lines than commonly used polyethyeneimine.

As already mentioned above, the RGD motif can be used for targeting chitosanbased nanoparticles to tumor sites via the interaction with integrin α v β 3 . Utilizing this fact, Kim et al. (2017) produced a dendrimeric RGD peptide/polyethyleneimine grafted chitosan copolymer, which was soluble in water. The copolymer was nontoxic to mammalian cells and erythrocytes in the absence and presence of plasmid DNA. Moreover, it was found to transfect cells involving microtubuledependent macropinocytosis and clathrin-mediated endocytosis. Finally, injecting copolymers complexed with psiRNA-hBCL2 to silence the gene for the human antiapoptotic Bcl2 protein into BALB/c-nu mice carrying a PC3 prostate tumor xenografts, markedly inhibited tumor growth. Thus, the copolymer was suggested to be a good candidate to develop a specific targeted gene delivery system.

To confer membrane-like properties to chitosan-based gene delivery systems, Li et al. (2015) grafted phosphorylcholine and macrocyclic polyamine onto chitosan to obtain water-soluble nanoparticles. Chitosan grafted with both compounds were more efficient in binding and protecting plasmid DNA than chitosan grafted only with phosphorylcholine or macrocyclic polyamine. The authors also demonstrated that phosphorylcholine and macrocyclic, polyamine-grafted chitosan had a positive net charge and can, therefore, wrap DNA to yield nanoparticles of about 100 nm in diameter. Finally, the DNA-loaded nanoparticles significantly increased cellular uptake and transfection rates in transformed human embryonic kidney cells when compared to chitosan/DNA complexes. A similar transfection strategy was published by Picola et al. (2016) , who inserted phosphorylcholine and increasing numbers of diethylaminoethyl (DEAE) groups into the polymer. The resulting chitosan nanoparticles were water soluble at physiological pH and less cytotoxic than lipofectamine, a commonly used transfection reagent. They further could form complexes with plasmid DNA, and the transfection efficiencies of the nanoparticles with high DEAE substitution rates tested in HeLa cells were in the same range as determined for lipofectamine. When the nanoparticles were loaded with siRNA, they were able to induce gene silencing, with efficiencies highly dependent on the N/P ratio.

Chitosan-based materials have been recognized to be potent adjuvants for immunotherapy, because they non-specifically stimulate immune responses in the host organism and therefore have antiviral, antimicrobial, and antitumor properties ). The adjuvant potency of chitosan is comparable to incomplete Freund's adjuvant, and it has stronger immune-stimulatory effect than aluminum hydroxide, which is frequently used in vaccines though it shows adverse side effects such as neurotoxicity (Zaharoff et al. 2007 ). The mechanism of how chitosan triggers immune responses involves phagocytosis-dependent activation of the NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome, which finally induces a robust interleukin-1β response (Bueter et al. 2011 (Bueter et al. , 2014 . Carroll et al. (2016) described another mechanism by which chitosan stimulates the activation of dendritic cells inducing cellular immunity. They found that chitosan promotes the intracellular release of DNA, which involves the cGAS-STING pathway. As a result, type I interferon is secreted activating the expression of interferoncontrolled genes. Due to the release of the cytokines that stimulate dendritic cells, the cellular immune system is elicited. Due to its mucoadhesiveness, chitosan and its derivatives are considered effective for mucosal administration, which includes oral, nasal, as well as ocular antigendelivery routes. However, other routes are also anticipated to be effective in provoking immune response including subcutaneous (Borges et al. 2008; Scherliess et al. 2013) , intraperitoneal (Chang et al. 2010) , intravenous (Shi et al. 2011) , and intratumoral injections (Zaharoff et al. 2010) . Evidently, innate immune responses are stimulated by chitin, chitosan, or derivatives (Peluso et al. 1994; Tokura et al. 1999; Lee et al. 2008; Lee 2009 ). This includes the activation of alveolar macrophages with the release of cytokines such as interleukin (IL)-12, tumor necrosis factor-α, or IL-18, leading to INF-γ production predominantly released by natural killer cells (Shibata et al. 1997a, b) . However, also humoral and cellular adaptive immune responses are triggered by some antigens when co-administered or encapsulated in chitosan-containing micro-and nanoparticles (Tokura et al. 1999; van der Lubben et al. 2001; Arca et al. 2009; Mori et al. 2012) . In particular, Wen et al. (2011) found that the stimulatory effect on the humoral and cellular immune system by chitosan results in a balanced Th1/Th2 response. However, care has to be taken in assessing the properties of chitosan-based adjuvants, as many studies do not provide sufficient data on the chemical and physical characteristics, preparation and formulation procedures, as well as potential impurities (Vasiliev 2015) . This is particularly critical, as immune responses appear to depend on these parameters as uncovered by Scherliess et al. (2013) , who reported that the degree of immune response varied when chitosans of different qualities were used. The immune-stimulatory effect of chitosan is affected by the combination of molecular weight, solubility, particle size, and viscosity as well as deacetylation degree.

Preclinical studies performed predominantly in mice models suggested that chitosan-containing antigen-delivery systems are promising adjuvant platforms for mucosal vaccination against human pathogenic viruses such as influenza (Read et al. 2005; Svindland et al. 2012; Sawaengsak et al. 2014; Liu et al. 2015a) ; hepatitis A, B, and E (Jiang et al. 2007; Tao et al. 2017a; Tao et al. 2017b; Soares et al. 2018 ); human papilloma virus ; and poliovirus (Ghendon et al. 2011 ). (Choi et al. 2016) . Using chitosan nanoparticles targeted to dendritic cells via antibodies to the DEC-205 surface receptor, Raghuwanshi et al. (2012) successfully delivered plasmid DNA carrying the cDNA for the N protein to trigger immunization against the severe acute respiratory syndrome coronavirus (SARS-CoV). Simultaneous comparison of targeted formulations using intramuscular and intranasal routes revealed that intramuscular administration induced a more potent systemic IgG response compared to intranasal administration. Solid evidence substantiating the advantages of chitosan as an efficient adjuvant for nasal vaccination originates from clinical examinations on a norovirus vaccine, which demonstrated the ability of a chitosan/monophosphoryl lipid-based antigen delivery system (ChiSys®) to induce immunity against the gastroenteric norovirus infections after immunization (Smith et al. 2014) .

Chitosan-derived adjuvants were also used in combination with antigens derived from bacterial toxins, such as diphtheria toxoids (McNeela et al. 2000; Schipper et al. 2017) , tetanus toxoids (Ahire et al. 2007; Pirouzmand et al. 2017) , and dermonecrotoxin (Jiang et al. 2004 ). In addition, the potential of various vaccine formulations against anthrax were evaluated in female BALB/c mice (Malik et al. 2018) . Encapsulating protective antigens (PA) in trimethyl-chitosan nanoparticles and administering them by subcutaneous, intramuscular, and intraperitoneal injections resulted in a strong IgG antibody response (Th1-biased) when combined with immune-stimulatory CpG oligodeoxynucleotides or polyinosinic-polycytidylic acids. Interestingly, without the immune-stimulatory nucleic acids, the PA-loaded trimethyl-chitosan nanoparticles led to a Th2-biased immune response.

Many studies have explored the adjuvant properties of chitosan in vaccines against cancer. In a study published by Wen et al. (2011) , the effects of chitosan nanoparticles on the immune response triggered by an ovalbumin antigen in mice were analyzed. As the administration of the chitosan nanoparticles did not only increase cytokine levels of Th1 (IL-2 and IFN-γ) and Th2 (Il-10) cells, but also stimulated natural killer cells, the authors suggested that chitosan is a promising adjuvant for cancer immunotherapy by promoting both humoral and cellular immune responses. This hypothesis was confirmed by Highton et al. (2016) , who demonstrated that immunization with an ovalbumin/chitosan hydrogel had antitumor effects in an intracaecal mice cancer model. After subcutaneous injection of the ovalbumin/chitosan vaccine, the authors detected CD8 + T memory cells specific for ovalbumin and observed decreased tumor growth in contrast to unvaccinated control mice or mice that were vaccinated with dendritic cells and ovalbumin. Zaharoff et al. (2009) analyzed antitumor effects in mice using a bioluminescent orthotopic bladder cancer model, after repeatedly administering chitosan/IL-12 into the bladder and comparing the antitumor efficacy of this treatment with that of an established adjuvant therapy applied to treat bladder cancer based on attenuated mycobacteria (bacillus Calmette-Guerin therapy). Determination of the urinary cytokine spectrum and immunohistochemical analysis resulted in the identification of cytotoxic T cells and natural killer cells as effector cells responsible for tumor regression. In contrast to the Bacillus Calmette-Guerin therapy, chitosan/IL-12 treatment utterly prevented recurrence of the disease.

More recently, Yao et al. (2013b) prepared mannosylated chitosan nanoparticles and loaded it with a plasmid to produce a vaccine against gastrin-releasing peptide (GRP), whose receptor is overexpressed in various cancer cells. The nanoparticles were intranasally administered in a subcutaneous mice prostate carcinoma model to evaluate the efficacy on inhibition of the growth of tumor cells. Cell binding and cellular uptake assays revealed that the mannosylated chitosan nanoparticles facilitate targeting to antigen-presenting cells, promoting receptor-mediated endocytosis via the mannose receptor. Due to antigen representation, enhanced tumor regression was observed as a result of the production of high titers of anti-GRP antibodies. A similar strategy was finally used by Lai et al. (2014) to test an immune therapy against hepatocellular carcinoma in a H22 tumor-bearing mice model. They synthesized folate-conjugated chitosan nanoparticles and loaded them with a plasmidencoding mouse interferon-γ-inducible protein-10 (IP-10). They found that IP-10 plasmid exhibited efficient antitumor activity, prolonging the survival time in H22 tumor-bearing mice. The antitumor effects were likely due to different effects. Next to the secretion of IFN-γ and IP-10, inhibition of regulatory T cells, suppression of angiogenesis, inhibition of cancer cell proliferation, and activation of apoptosis contributed to tumor growth inhibition.

Tissue engineering is an increasingly important interdisciplinary field in regenerative medicine, which aims to create replacements for damaged tissues based on the combined knowledge provided by physicians, biologists, and engineers. Most approaches employ scaffolds made from biocompatible polymers, which are colonized by cells of the respective tissue. Ideally, the scaffold increases adherence, proliferation, and differentiation of colonizing cells. Chitosan and its derivatives offer ample benefits to generate cell and tissue supporting matrices, which include chemical versatility, antimicrobial activity, biocompatibility, biodegradability, and neglible toxicity (Ahsan et al. 2018) . Chitosan can be produced to form sponge-like scaffolds using rather simple phase separation techniques including freeze-drying (Aranaz et al. 2014) , gas foaming (Kaynak Bayrak et al. 2017) , and electrospinning procedures (Qasim et al. 2018) . The presence of a system of interconnected pores with appropriate diameters facilitates vascularization and tissue integration. Moreover, chitosan-based scaffolds can be synthesized in combinations with ample natural and synthetic polymers resulting in matrices exhibiting special characteristics. Due to their positive surface charges they open the possibility to fabricate polyelectrolyte complexes with anionic polymers such as glutamic acid (Fang et al. 2014) , hyaluronic acid (Lalevee et al. 2016) , dextrane sulfate (Kulkarni et al. 2016) , heparin (Almodovar and Kipper 2011) , dermatan sulfate (Rasente et al. 2016) , and chondroitin sulfate (Tsai et al. 2011) . Particularly the presence of glycosaminoglycans, which are naturally found in extracellular matrices, is known to modulate the activity of cytokines and growth factors by binding to the polymers (Zaman et al. 2016) . Otherwise, chitosan-based scaffolds can be loaded with cytokines and growth factors to attract cells and stimulate tissue regeneration (Sun et al. 2012a; Bader et al. 2015; Choi et al. 2015) . Finally, they further open the possibility of controlled degradation and resorption in physiological environments, designing mechanical properties that match the conditions found in the respective tissue, and determination of desired sizes and shape by easy fabrication procedures. Therefore, chitosan-based scaffolds have numerous applications in tissue engineering, and we will review recent progress in using these materials for tissue regeneration and wound healing.

14.6.5.1 Bone, Cartilage, and Tooth Repair Bone defects can either be congenital or result from trauma, infection, cancer, or failed orthopedic surgical procedures (Venkatesan and Kim 2010) . The grafts used to bridge bone defects can be autografts (bone material from other body regions of the same patient) or allografts (bone material from decedents). However, both materials have disadvantages: autografts require bone harvesting from healthy tissues and may cause complications of wound healing and pain, and allografts may result in immunogenic rejection and have the risk of transmitting viral diseases from the donor to the recipient. Due to these concerns, scientists around the world are searching for alternative materials as bone graft substitutes. As described before, chitosan-based materials have valuable properties for orthopedic applications. Chitosan itself has the capacity to increase bone regeneration rates (Muzzarelli et al. 1993b ); however, it cannot fully substitute natural bone material. Therefore, different composite scaffolds have been developed to assure porosity for vascularization and nutrition, facilitate the formation of new bone material (osteoconductivity), guarantee structural integrity during ingrowth at the site of implantation, and orchestrate biodegradation with bone regeneration (Venkatesan and Kim 2010) . In addition, chitosan-based composites can be loaded with cells and growth factors that promote osteoconductivity and hence facilitate bone regeneration. One of the most important chitosan grafting that has been used in bone tissue engineering is hydroxyapatite, which by itself stimulates bone regeneration, provided that the scaffold has a microporous structure (Woodard et al. 2007 ). Hydroxyapatite grafting of chitosan can be easily achieved by coprecipitation from homogeneous mixtures of precursor (Deepthi et al. 2016 , and references therein). One of the first researchers who tested combinations of chitosan and hydroxyapatite was Michio Ito, who examined the use of chitosan-bonded hydroxyapatite paste for treatment of periodontal defects (Ito 1991) . In 2004 , Ge et al. (2004 published a remarkable study, in which they tested different combinations of air-and freezedried chitosan/hydroxyapatite materials that were colonized by osteoblasts and implanted into rats. The material was found to be nontoxic and biodegradable and to stimulate mineralization. The explanted material that was colonized by osteoblasts before implantation showed newly formed bone material containing proliferating osteoblasts that recruited surrounding tissue to grow in. In another study published by Oliveira et al. (2006) , three-dimensional macroporous hydroxyapatite/chitosan bilayered scaffolds of inorganic and organic deposits were produced in a stepwise procedure and examined with regard to their mechanical properties and cytotoxicity to mouse fibroblast-like cells. Moreover, in vitro cell culture studies using goat marrow stromal cells revealed that the macroporous hydroxyapatite/chitosan composite is a suitable material that promotes attachment, proliferation, and differentiation into osteoblasts and chondrocytes. Additionally, three-layered porous materials of collagen, hydroxyapatite, and chitosan were produced and characterized as an artificial bone matrix (Wang et al. 2008b) . When testing murine pre-osteoblast cell line (MC3T3-E1) grown on this matrix, the cells proliferated significantly more rapidly than cells grown on a pure chitosan matrix (Teng et al. 2008 ). In addition, higher levels of alkaline phosphatase (secreted by osteoblasts) were determined, which is indicative for bone regeneration. Similar results were obtained when osteoblasts were cultured on hydroxyapatite/chitosan nanocomposites and osteocalcin as a marker for late osteoblastic differentiation, and mineralized bone matrix formation was determined (Chesnutt et al. 2009 ). Further studies characterized hydroxyapatite/chitosan hybrids with additional blend materials such as montmorillonite (Katti et al. 2008) , polylactic acid ), cellulose and carboxymethyl cellulose (Liuyun et al. 2009; Jiang et al. 2013b) , gelatin (Sellgren and Ma 2012; Maji et al. 2015; Lee et al. 2017) , nylon 66 ), polygalacturonic acid (Khanna et al. 2011 , marine sponge collagen (Pallela et al. 2012) , collagen ), alginate (Jin et al. 2012; Kim et al. 2015; Liao et al. 2018) , chondroitin sulfate (Venkatesan et al. 2012a; ), hyaluronic acid (Hu et al. 2017 , fibroin (Lima et al. 2013; Ran et al. 2016; Ye et al. 2017 ), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (Zhang et al. 2015b) , fucoidan (Lowe et al. 2016) , β-tricalcium phosphate (Shavandi et al. 2015; Oryan et al. 2017) , graphene oxide , β-cyclodextrin (Shakir et al. 2016) , β-1,3-glucan , whitlockite (Zhou et al. 2017a) , zoledronic acid (Lu et al. 2018) , and zirconium dioxide (Balagangadharan et al. 2018) . Also, three-dimensional hydroxyapatite/chitosan-carbon nanotube scaffolds were shown to be promising materials for bone regeneration (Im et al. 2012) . Naturally, many of these combinations have been tested also in the absence of hydroxyapatite (Park et al. 2000a; Jiang et al. 2006; Arpornmaeklong et al. 2008; Venkatesan et al. 2012b; Deng et al. 2013; Azevedo et al. 2014; Dinescu et al. 2014; Listoni et al. 2015; Georgopoulou et al. 2018; Koç Demir et al. 2018) .

Several studies showed that various growth factors such as transforming growth factors (TGFs), vascular endothelial growth factors (VGEFs), bone morphogenic proteins (BMPs), insulin-like growth factors (IGFs), and platelet-derived growth factors (PDGFs) have major impacts on vascularization and osteoblast activities and thus have been employed to stimulate bone regeneration (Yun et al. 2012) . However, there are limitations in maintaining therapeutic concentrations due to the short halflife of the growth factors in vivo. This can be effectively prevented by the controlled release of the growth factors from porous chitosan composite matrices, which have been demonstrated to stimulate bone formation. For instance, PDGF-BB is an important osteogenic growth factor in the process of bone regeneration, as it stimulates mesenchymal cell proliferation and differentiation and mediates chemotaxis of osteoblast. Park et al. (2000a, b ) produced a porous chitosan or chondroitin-4-sulfate/chitosan sponges releasing PDGF-BB to stimulate bone regeneration. The release rate of PDGF-BB increased proportionally with increasing concentrations loaded onto the sponge, and PDGF-BB retained its chemotactic activity regardless of being loaded onto the sponge or added freely to test solution (Park et al. 2000a ). Finally, osteoblast proliferation was found to be stimulated in PDGF-BB-loaded chondroitin-4-sulfate/chitosan sponge compared with that of the unloaded sponge. PGFs have also been used in combination with other growth factors. As VEGF is known to prolong cell survival, osteoblast proliferation, differentiation, and migration next to its effects on angiogenesis, it has been suggested that the combined action of VEGF and PDGF can accelerate the bone healing process even more efficiently. De la Riva et al. (2010) established a system based on brushite-chitosan capable of controlling release kinetics for these two growth factors. After implanting the chitosan scaffolds loaded with the growth factors into rabbits with femur defects, release kinetics and tissue distribution of radiolabeled VEGF and PDGF were determined. Analyzing bone repair histologically revealed that the combined use of VEGF and PDGF promoted bone regeneration most effectively.

Also, the controlled release of IGF-1 and BMP-2 by the enzymatic degradation of the porous chitosan scaffold stimulates bone healing and regeneration in rabbits considerably (Nandi et al. 2013) . When the chitosan particles were loaded only with one of the two growth factors, the effect was found to be more pronounced for IGF-1 than for BMP-2 infiltrated matrices. In a very recent study, chitosan/biphasic calcium phosphate scaffolds functionalized with BMP-2-encapsulated nanoparticles and the RGD tripeptide were produced using a desolvation technique (Gan et al. 2018 ). In vitro cell culture and in vivo implantation tests demonstrated that RGD and BMP-2 synergistically increased cell adhesion and spreading via integrin binding triggering differentiation of osteoblasts. Increased bone healing was also observed, when porous chitosan scaffolds were loaded with resolvin D1, a potent lipid immune modulator derived from both eicosapentaenoic acid, and implanted into rats with a femur defect (Vasconcelos et al. 2018) . Obviously, resolving D1 administration in the acute phase of the innate immune response to the bio-implant had beneficial effects during bone tissue repair. Impairment of the articular cartilage is frequently due to sport-related injury, disease, trauma, and tumor. If not treated successfully, it may result in osteoarthritis, which increasingly affects also younger individuals (Muzzarelli et al. 2012) . In contrast to bone regeneration, cartilage healing is limited by the lack of vascularization and poor proliferation rates of chondrocytes. Injection of hyaluronan into the joints of arthritic patients is known to improve their function, as it restores viscoelasticity and flow of the synovial fluid, helps to normalize hyaluronan production, and finally reduces pain and inflammation. Chitosan easily forms polyelectrolyte complexes with hyaluronan and chondroitin sulfate, which are important building blocks particularly of the hyaline cartilage found on the surface of joints. Therefore, combinations of chitosan and hyaluronan and/or chondroitin sulfate may be useful in cartilage healing. In a first attempt to realize this idea, Kuo et al. (2015) synthesized a highly elastic, macroporous, and chitosan-containing gelatin/chondoitin-6-sulfate/ hyaluronan (GCH) cryogel scaffold, which mimics the extracellular matrix composition of the cartilage. Furthermore, in vitro cell culture studies suggest that chondrocytes proliferate and redifferentiate within the porous matrix of the cryogels. Although chitosan reduces cell proliferation, it stimulates the secretion of sulfated glycosaminoglycans and type II collagen. In addition, they performed in vivo studies culturing chondrocytes on the GCH chitosan cryogel and implanting the material into rabbits with an articular cartilage defect (Kuo et al. 2015) . After 3 months, the defect in the chondrocytes/cryogel group was completely covered with semitransparent tissue, which had similar characteristics as the native cartilage. A large variety of other chitosan-based materials lacking glycosaminoglycans have been suggested as suitable scaffolds for cartilage tissue engineering and some of them have been tested as mesenchymal stem cell carriers. Such materials include scaffolds containing N,N-dicarboxymethyl chitosan (Mattioli-Belmonte et al. 1999) , chitosan/gelatin and/or alginate complex (Xia et al. 2004; Bhat et al. 2011) , poly(L-lactide)/chitosan microspheres (Lao et al. 2008; Haaparanta et al. 2014) , polyethylene oxide/chitin/chitosan scaffolds (Kuo and Ku 2008) , genipin-cross-linked chitosan/silk fibroin sponges Vishwanath et al. 2016) , chitosan/polyester-based scaffolds (Alves da Silva et al. 2010) , chitosan/ collagen type I scaffolds (Gong et al. 2010) , chitosan/poly(epsilon-caprolactone) blend scaffolds (Neves et al. 2011; Filova et al. 2016) , chitosan/poly(l-glutamic acid) scaffolds , polyvinyl alcohol/chitosan composite hydrogels (Dashtdar et al. 2015) , poly(N-isopropylacrylamide)/chitosan hydrogels (Mellati et al. 2016) , viscoelastic silk/chitosan microcomposite scaffolds (Chameettachal et al. 2017) , and chitosan/graphene oxide polymer nanofibers (Cao et al. 2017) .

As in the case of bone repair, strategies using various chitosan-based scaffolds loaded with growth factors such as TGFs (Kim et al. 2003; Choi et al. 2015) , IGFs (Zhao et al. 2010 ), BMPs (Mattioli-Belmonte et al. 1999 , and basic fibroblast growth factor (bFGF) (Tan et al. 2007 ) have been tested for cartilage repair. In an interesting pilot study, Qi et al. (2013) produced an injectable chitosan/polyvinyl alcohol gel and examined its structure and physicochemical properties. The resulting material exhibited low cytotoxicity and good biocompatibility. Next, the gel was mixed with rabbit bone marrow stromal cells (BMSCs) that were transfected with an adenovirus to produce TGF-b1, and rabbits with cartilage defects were injected with this mixture. After 16 weeks, the defects appeared to be fully repaired. The regenerated tissue was almost indistinguishable from the native cartilage. In another study, a demineralized bone matrix was conjugated with mesenchymal stem cell (MSC) E7 affinity peptide (EPLQLKM) and combined with a chitosan hydrogel for cartilage engineering. Cell culture and implantation experiments demonstrated that the developed material has a high chondrogenic capacity facilitating tissue repair of cartilage defects (Meng et al. 2015) . In a more recently published study, the proliferation and differentiation of multipotent dental pulp stem cells into chondrocytes were investigated to generate cartilage-like material. In this case, a porous chitosan-xanthan gum matrix was employed as a scaffold and loaded with kartogenin to promote chondrogenic differentiation (Westin et al. 2017 ). The manufactured scaffold exhibited favorable characteristics for cartilage tissue engineering, such as high porosity, low cytotoxicity, and mechanical properties compatible with those characteristic of cartilage.

Very recently, Agrawal et al. (2018) reported the in vitro generation of cartilage-like material by seeding human mesenchymal stem cells on freeze-dried porous silk fibroin/ chitosan scaffolds and culturing them in a spinner flask bioreactor under dynamic conditions. The team was successful in preparing a cartilage construct of 5 mm thickness, which roughly corresponds to the thickness of a native articular cartilage.

Due to its unique properties, chitosan has also emerged as a scaffold for potential applications in dental medicine. Chitosan-based hydrogels and nanocomposites have been used as anti-erosive and enamel-repairing additives in dentifrices and chewing gums (Shibasaki et al. 1994; Arnaud et al. 2010; Ganss et al. 2011; Ruan et al. 2014) , for reduction of dental bacterial biofilm formation (Jahanizadeh et al. 2017) , for guided tissue regeneration to treat periodontal diseases such as periodontitis Lotfi et al. 2016) , as dentin-bonding agent (Fawzy et al. 2013) , as modification of dental restorative materials and implants (Petri et al. 2007; Ali et al. 2017; Ibrahim et al. 2017a) , and as scaffold for stem cell-based tissue regeneration (Yang et al. 2012b; Asghari Sana et al. 2017; Soares et al. 2017a) . Periodontitis is a chronic inflammation of the gum, which ultimately may lead to the loss of periodontal tissues and teeth (Pihlstrom et al. 2005) . Current therapeutic strategies mainly rely on good oral hygiene (brushing and flossing), plaque removal, and in more severe cases local application of antibiotics and surgical intervention including open flap debridement, osseous surgery, as well as guided tissue and bone regeneration. Chitosan-based materials turned out to be very useful for periodontal tissue regeneration. Such materials comprise methylpyrrolidinone chitosan (Muzzarelli et al. 1993a) , chitosan scaffolds coated with a bioactive hydroxyapatite (Ang et Coimbra et al. 2011; Fraga et al. 2011; Miranda et al. 2016) , injectable thermosensitive chitosan/β-glycerophosphate/hydroxyapatite hydrogels , chitosanbased risedronate/zinc-hydroxyapatite intrapocket dental films (Khajuria et al. 2018) , asymmetric chitosan/tripolyphosphate cross-linked membranes , porous chitosan/collagen scaffolds (Yang et al. 2012b ), mucoadhesive electrospun chitosan and thiolated chitosan nanofibers (Samprasit et al. 2015) , chitosan-coated titanium surfaces (Campos et al. 2015) , chitosan modified glass ionomer restoratives (Petri et al. 2007 ), chitosan-intercalated montmorillonite/poly(vinyl alcohol) nanofibers (Ghasemi Hamidabadi et al. 2017) , and polyhydroxybutyrate/chitosan/ nano-bioglass nanofiber scaffolds (Hashemi-Beni et al. 2018) .

In one of the first studies that used growth factors to promote dental pulp stem cell differentiation, porous chitosan/collagen scaffolds prepared by freeze-drying were used and loaded with a plasmid vector encoding the human BMP-7 gene (Yang et al. 2012b ). The stem cells grown in this scaffold were successfully transfected by the plasmid vector, which led to the formation of BMP-7 triggering odontoblastic differentiation as indicated by the activation of specific marker genes encoding steocalcin, bone sialoprotein, dentin sialophosphoprotein, and dentin matrix protein 1. The chitosan/collagen scaffolds with stem cells were subcutaneously implanted into the back of BALB/c mice. After 4 weeks, the material was explanted and evaluated by immunohistochemistry. In the gene-activated scaffold group, there were still transfected cells detectable showing the upregulated gene expression when compared to pure scaffold groups.

Cutaneous wound healing is a complex process in which the skin repairs itself. The process is divided into different stages, which include blood clotting (hemostasis), inflammation, cell migration and proliferation, and tissue remodeling (maturation). The wound healing process may be delayed or completely fail leading to non-healing chronic wounds, which are frequently found in patients with diabetes, venous or arterial diseases, infections, and age-related metabolic deficiencies. Bedsore and burns behave differently, as the healing process is complicated by coagulation, necrosis, and infections. Small, non-severe wounds may be treated with chitosancontaining ointments (Kweon et al. 2003) , topical gels (Alsarra 2009) , and/or wound dressings (Jayakumar et al. 2011) . For instance, Kang et al. (2016) reported the synthesis of silver chloride nanoparticles stabilized with chitosan oligomer for an ointment that was tested on burn wound healing in a rat model. Burn wound healing of rats treated with this ointment was superior to rats treated with pure Vaseline or chitosan ointments. More severe wounds may require removal of necrotic tissue and surgical wound closure using suturing techniques. If the defects are too large to be covered in this way, autologous avascular mesh grafts, microvascular flap grafts, mikroskin grafts, and/or cultured epithelial grafts are transplanted to the wound site (Chua et al. 2016) . However, surgical intervention is only possible up to a critical size. To cover large-sized skin defects, artificial grafts produced by tissue engineering techniques are required. This type of wound dressings must protect from infections, absorb excess exudates, and facilitate oxygen and nutrient exchange. In addition, the material must be nontoxic, non-allergenic, non-adherent, and biocompatible.

Chitosan-based materials are a good choice for wound dressings, as they fullfil most of the criteria mentioned above, and they are known to promote wound healing by activating platelets when getting into contact with blood (Periayah et al. 2013) . Moreover, chitosan-based scaffolds can be loaded with growth factors to facilitate skin repair by promoting cell adhesion and proliferation (Lu et al. 2016) . Several in vitro, preclinical and clinical studies actually demonstrated that chitosan-based hydrogels films, powders, and dressings, as well as artificial skins, accelerate wound healing and reepithelialization (Patrulea et al. 2015) . However, the precise mechanism of action in promoting wound healing is still under debate. Next to chitosan-mediated immunomodulation, the type of functionalization contributes to wound healing.

Chitosan-based scaffolds used to promote wound healing comprise hydrogels, films, micro-and nanoparticles, nanocomposite materials, and micelles, and many biocompatible chitosan derivatives have been tested including N-carboxybutyl chitosan (Dias et al. 2010 ), hydroxybutyl chitosan (Hu et al. 2018 , fluorinated methacrylamide chitosan (Wijekoon et al. 2013; Patil et al. 2016; Akula et al. 2017) , and chitosan/polyvinyl alcohol materials (Charernsriwilaiwat et al. 2014; Wang et al. 2016b ).

In addition, numerous chitosan hybrid materials have been synthesized for wound healing, which comprise chitosan or carboxymethyl chitosan/gelatin hydrogels Patel et al. 2018) , chitosan/heparin/poly(γ-glutamic acid) composite hydrogels , chitosan-hyaluronan composite sponge scaffolds (Sanad and Abdel-Bar 2017; Tamer et al. 2018 ), heparin-chitosan complexes (Kratz et al. 1997 Kweon et al. 2003) , chitosan-fibrin nanocomposites (Vedakumari et al. 2015) , polyvinyl alcohol/chitosan/fibroin-blended sponges (Yeo et al. 2000) , polyvinyl alcohol/starch/chitosan hydrogels with nano zinc oxide (Baghaie et al. 2017) , poly(caprolactone)/chitosan/poly(vinyl alcohol) nanofibrous sponges (Gholipour-Kanani et al. 2014) , chitosan/poly(ethylene glycol)-tyramine hydrogels (Lih et al. 2012) , chitosan-alginate polyelectrolyte complexes (Wang et al. 2002; Hong et al. 2008; Caetano et al. 2015; Kong et al. 2016) , porous keratin/chitosan scaffolds without and with zinc oxide (Tan et al. 2015; Zhai et al. 2018) , nanotitanium oxide/chitosan complexes (Peng et al. 2008) , chitosan/collagen hydrogels and sponges (Wang et al. 2008a; Cui et al. 2011; Ti et al. 2015) , chitosan green tea polyphenol complexes (Qin et al. 2010 (Qin et al. , 2013 , dextran hydrogels loaded with chitosan microparticles (Ribeiro et al. 2013) , chitosan/polycaprolactone scaffolds Zhou et al. 2017b) , chitosan oleate ionic micelles (Dellera et al. 2014) , castor oil polymeric films reinforced with chitosan/zinc oxide nanoparticles (Diez-Pascual and Diez-Vicente 2015), sponge-like nano-silver/zinc oxide-loaded chitosan composites , gellan gum-chitosan hydrogels (Shukla et al. 2016) , chitosan-silica hybrid dressing materials (Park et al. 2017 ), chitosan/bentonite or tourmaline nanocomposites (Devi and Dutta 2017; Zou et al. 2017) , chitosan/ gelatin/chondroitin-4-sulfate films with and without zinc oxide (Cahu et al. 2017) , chitosan/polyvinylpyrrolidone/cellulose nanowhiskers nanocomposites (Hasan et al. 2017) , α-tocopherol-loaded chitosan oleate nanoemulsions (Bonferoni et al. 2018) , chitosan-based liposome formulations (Mengoni et al. 2017) , and electrospun chitosan/polyethylene oxide/fibrinogen biocomposites (Yuan et al. 2018) .

Topical application of anti-inflammatory and antioxidant curcumin, which is a component of many curry powders, has been shown to promote wound healing, significantly preventing oxidative damage in tissues (Gopinath et al. 2004 ). Chitosan-alginate sponges have been used to deliver curcumin for dermal wound healing in rat. Loading curcumin onto the chitosan sponge enhanced the therapeutic healing effect when compared to other carriers like cotton gauze. Similarly, injectable nanocomposite hydrogels composed of curcumin, N,O-carboxymethyl chitosan, and oxidized alginate possess many characteristics that promote wound healing including exudate absorption and immobilization and activation of growth factors. Nano-curcumin, which is released slowly from the hydrogel in a sustained manner, evidently stimulates fibroblast proliferation, angiogenesis, and collagen production, supporting the healing process when tested in a mice model (Li et al. 2012b) . Wound dressings made of chitosan/poly-γ-glutamic acid/pluronic/curcumin nanoparticles also promoted collagen formation and tissue regeneration (Lin et al. 2017) , and collagen-alginate scaffolds impregnated with curcumin-loaded chitosan nanoparticles proved promising in the treatment of various pathological manifestations of diabetic wounds (Karri et al. 2016) . Most recently, Zhao et al. (2018) prepared a thermosensitive chitosan/β-glycerophosphate hydrogel loaded with β-cyclodextrin-curcumin and demonstrated improved healing of infected cutaneous wounds in rats, which may be due to the combination of antioxidative, antimicrobial, and anti-NF-κB signaling effects.

As silver has been demonstrated to have potent antimicrobial activities with no reports on bacterial resistances, several laboratories prepared chitosan wound dressings impregnated with silver to prevent wound infections and promote wound healing (Graham 2005) . Indeed, a wound dressing composed of nano-silver and chitosan improved wound healing in rats better than a silver sulfadiazine dressing, which led to unwanted higher silver levels in the blood than the chitosan-silver dressing (Lu et al. 2008) . In another study, Abdelgawad et al. (2014) combined silver nanoparticles that were embedded in chitosan with polyvinyl alcohol to produce antimicrobial nanofibrous material for wound dressing. The material with the highest chitosan-silver nanoparticle content was tested against E. coli and showed significant antibacterial activity. A combined antibacterial/tissue regeneration response triggered by functional chitosan-silver nanocomposites was also reported for thermal burns (Luna-Hernandez et al. 2017) . To increase antibacterial activity wound dressings, several groups combined chitosan-silver-based materials with sulfadiazine, a sulfonamide antibiotic. Topical administration of chitosan-based hydrogels containing silver sulfadiazine improved burn and wound healing capacities in different studies (Nascimento et al. 2009; Chakavala et al. 2012; Aguzzi et al. 2014; Lee et al. 2014; El-Feky et al. 2017a) . Besides inhibiting Gram-negative bacteria such as E. coli, chitosan-based dressings carrying silver sulfadiazine also inhibited the growth of Gram-positive bacteria as well as fungi such as C. albicans on an infected wound (El-Feky et al. 2017b) .

Several studies reported that wound healing is accelerated when chitosan hydrogels are combined with adipose-derived or mesenchymal stem cells. Altman et al. (2009) grew human adipose-derived stem cells onto a chitosan/silk fibroin scaffolds and used it in a cutaneous wound healing model. They found that this regimen significantly enhanced wound healing, increasing micro-vascularization and differentiation into epidermal epithelial cells. In another study, an artificial dermis was fabricated by culturing human adipose-derived stem cells on a poly (L-glutamic acid)/chitosan scaffold (Shen et al. 2013b) . Notably, the seeded stem cells maintained their capability to proliferate, produce extracellular matrix, and secrete cytokines including transforming growth factor β1 and vascular endothelial growth factor. The artificial dermis was used to cover wounds that have been generated before in streptozotocin-induced diabetic mice. The artificial dermis significantly accelerated wound closure and healing in diabetic mice. Tong et al. (2016) used a different stem cell-based strategy to generate a skin substitute promoting wound healing. They manufactured a collagen-chitosan sponge scaffold to culture bone marrow-derived stem cells, which were pre-treated by hypoxia to induce the expression of pro-angiogenic cytokines. When the skin substitute was used to treat wounds generated in diabetic rats with hindlimb ischemia, wound healing was enhanced in comparison to scaffold-only controls or skin substitutes that were generated with normoxic stem cells.

A novel strategy for wound healing involving exosomes was reported recently. Exosomes are small secretory membrane vesicles that are involved in cell-to-cell communication. Stem cell-derived exosomes can improve wound healing and promote skin regeneration by stimulating cell proliferation and migration, angiogenesis, and reepithelization and modulating immune responses (Phinney and Pittenger 2017) . Based on these observations, Shi et al. (2017b) isolated exosomes derived from gingival mesenchymal stem cells and encapsulated them in chitosan/silk hydrogel sponge. The combination of the exosomes and hydrogel was effective in promoting skin wound healing in a diabetic rat model by inducing reepithelialization, vascularization, and neuronalization paralleled by the remodeling of the extracellular matrix.

Corneal damage can be the result of different diseases and injuries and may lead to a reduction or even loss of vision. Currently, the only therapy to cure vision loss after irreversible corneal damage is a surgical procedure where the cornea is replaced by donated corneal tissue. Frequently, the entire cornea is replaced in a surgical intervention called penetrating keratoplasty. As there is a shortage of corneal donors and there is a certain risk associated with the surgery and graft rejection, new types of corneal replacements are examined including materials containing chitosan. Actually, topical application of chitosan or chitosan/N-acetylcysteine to the eye is known to enhance corneal epithelial proliferation and migration during the wound healing in rabbits (Fischak et al. 2017) . This process appears to involve the activation of the extracellular signal-regulated kinases (ERK) pathway (Cui et al. 2017) . Another study evaluated the effects on corneal epithelium regeneration by combination of exogenous recombinant human serum-derived factor-1α (rhSDF-1α) with a thermosensitive chitosan/gelatin hydrogel and analyzed the underlying mechanism (Tang et al. 2017) . Conducting in vitro experiments, the team showed that rhSDF-1α enhanced stem cell proliferation, chemotaxis, and migration, as well as the expression of related genes in limbal epithelial and mesenchymal stem cells (LESCs and MSCs). In vivo experiment using an alkali burn-injury rat model further revealed enhanced corneal epithelium regeneration and increased local expression of growth factors known to be essential for corneal epithelium repair. The underlying mechanism by which rhSDF-1α released from the chitosan/gelatin hydrogel stimulates corneal regeneration may involve activation of C-X-C chemokine receptor type 4 (CXCR4) expressing cells (LESCs and MSCs) and chemotactic attraction of these cells to the sites of lesion via the binding of rhSDF-1α to the CXCR4 receptor. Chen et al. (2005) had considered a tissue-engineering scaffold made of collagen, chitosan, and hyaluronic acid as a potential replacement for corneal tissue. To study cytocompatibility in vitro, they cultured rabbit limbal corneal epithelial cells, corneal endothelial cells, and keratocytes on the polymer complexes and demonstrated that the corneal cells were able to attach, migrate, and proliferate. To evaluate biocompatibility in vivo, they implanted the polymer complex into the corneal stroma of rabbit eyes and inspected ocular reactions. Overall, the polymer complexes exhibited transparency and good biocompatibility, as they were degraded and absorbed within the corneal tissue while maintaining transparency. In another study, poly(ethylene glycol)-stabilized carbodiimide-cross-linked collagen-chitosan hydrogels were tested for biocompatibility and host-graft integration. For this purpose, Rafat et al. (2008) performed in vitro and in vivo studies demonstrating excellent biocompatibility when analyzing human corneal cells, dorsal root ganglia from chick embryos, or subcutaneous implants. The hydrogel scaffold was also studied as corneal substitute by implanting it into the cornea of pig eyes and monitoring them for 12 months. The substitute was seamlessly integrated into the cornea with regeneration of host corneal epithelium, stroma, and nerves. Liang et al. (2011) prepared a blend membrane composed of hydroxyethyl-chitosan, gelatin, and chondroitin sulfate. The membrane exhibited good transparency, ion and glucose permeability, and cytocompatibility for corneal endothelial cells, which formed a monolayer on the membrane in cell culture. In vivo animal experiments revealed that the membranes were characterized by biodegradability and a good histocompatibility suggesting that the membranes may be employed as carriers for corneal endothelial cell transplantation. Similar results were obtained for chitosan/ polycaprolactone, chitosan/poly(ethylene glycol), silk fibroin/chitosan, carboxymethyl chitosan/gelatin/hyaluronic acid, as well as hydroxyethyl-chitosan blend membranes, which were tested as potential scaffolds and carriers for bovine, ovine, and rabbit corneal endothelial cells, respectively Guan et al. 2013; Ozcelik et al. 2013; Liang et al. 2014; Xu et al. 2018) .

Using an allogeneic rabbit model of stromal destruction caused by bacterial keratitis, Chou et al. (2018) tested the hypothesis that intra-stromal injection of keratocyte spheroids manufactured on chitosan coatings has higher therapeutic efficacies than eye drop instillations or isolated cell injections. The results of clinical observations and histological studies performed 2 weeks after the surgical intervention showed that, in comparison to a treatment relying only on antibiotics, intrastromal grafting of keratocytes provides additional benefits due to improved preservation of cellular phenotypes, secretion of collagen matrix, and retention of the graft.

In a stem cell therapeutic approach published by Chien et al. (2012) , human corneal fibroblasts (keratocytes) were reprogrammed into human-induced pluripotent stem cells (iPSC) using a feeder cell-free culturing system. To increase iPSC delivery and engraftment, the researchers generated an injectable thermogelling carboxymethyl-hexanoyl chitosan nanogel with seeded iPSCs and showed that viability and pluripotent properties of the reprogrammed iPSCs were maintained in the hydrogel system. They further demonstrated that the reprogrammed iPSCs grown on the hydrogel could be used to enhance corneal wound healing efficiently. This strategy opens the possibility for a personalized therapy for human corneal damage when iPSCs are reprogrammed from cells derived from corneal surgical residues.

The plethora of favorable characteristics of chitosan outlined in this chapter prompted many researchers around the world to employ chitosan-based materials also in the reconstruction of peripheral nerves to improve healing of nerve damage caused by accidents or diseases. Although therapeutic interventions to peripheral nerve repair have yielded some progress during the past years, a full recovery of nerve function is usually not achieved. Current therapies mostly rely on microsurgical techniques, which either try to directly establish a tension-free connection between the ends of severed nerves (epineural, fascicular, and grouped fascicular repair) or bridge larger nerve defects by autologous grafts (cable grafts, trunk grafts, and vascularized nerve grafts) (Matsuyama et al. 2000; Houschyar et al. 2016 ). The various neurosurgical techniques used to connect nerve ends are challenging, and the therapeutic results are frequently not satisfactory. Many studies have provided evidence that various types of conduits, such as veins, pseudo-sheaths, and bioabsorbable tubes, are helpful in bridging shorter gaps by promoting nerve regeneration. After bridging nerve gaps with hollow conduits, the lumen between the nerve ends becomes filled with fibrin, and macrophages and other cells are attracted, which create a favorable microenvironment for vascularization and neuronalization.

Chitosan-based conduits have been extensively analyzed for this purpose. An early electrophysiological and histological study on nerve regeneration using rat sciatic nerve defects demonstrated that pure chitosan/collagen conduits were superior in bridging 1 cm nerve defects to that of control groups (Wei et al. 2003) . The chitosan/collagen film was found to be degraded about 3 months after the surgery. In a methodologically similar study, Wang et al. (2005) generated an artificial nerve graft composed of a chitosan conduit and tested them to bridge a 3 cm dog sciatic nerve defect. In contrast to the previous study, the conduit was filled with longitudinally arranged filaments of polyglcyolic acid. The team found that the sciatic nerve trunk was successfully reconstructed in dogs treated with the chitosan/polyglycolic acid graft with reinnervation of the target skeletal muscle. In a case report on a 55-year-old man with a 3 cm median nerve defect in the distal forearm, implantation of chitosan/polyglycolic acid graft promoted nerve regeneration and functional reconstruction, so that the patient was able after 36 months to fully use the injured hand during daily activities . Other chitosan-based conduits have been successfully used to guide and promote nerve generation in various in vitro and in vivo models. These materials include chitosan/gelatin and chitosan/poly(L-lysine) polyelectrolyte-based scaffolds (Martin-Lopez et al. 2012) , chitosan-gold nanocomposites (Lin et al. 2008) , chitosan/polylactic acid films (Xie et al. 2008) , chitosan/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nanofibers (Biazar and Heidari Keshel 2014) , porous chitosan-poly(p-dioxanone)/silk fibroin copolymers (Wu et al. 2015) , poly(D,L-lactide-co-glycolide) sleeves with multifilament chitosan yarn or a microcrystalline chitosan sponge core (Wlaszczuk et al. 2016) , chitosan/ hyaluronic acid hybrid materials (Li et al. 2018a) , porous chitosan-γ-glycidoxypropyltrimethoxysilane hybrid membranes (Shirosaki et al. 2014) , hydroxyapatite-coated tendon chitosan tubes with adsorbed laminin peptides (Itoh et al. 2003) , and hyaluronic acid doped-poly(3,4-ethylenedioxythiophene) nanoparticles in a chitosan/gelatin matrix ). An evident upgrade of chitosan-based conduits is lumenal loading with neurotrophic factors such as nerve growth factor (NGF), ciliary neurotrophic factor (CNF), or brain-derived neurotrophic factor (BDNF), which are all secreted by Schwann cells that support growth of neuronal cells (Houschyar et al. 2016 ). In addition, fibroblast growth factor (FGF), glial growth factor (GGF), and vascular endothelial growth factor (VEGF) were reported to have positive effects on nerve regeneration. Yang et al. (2011) immobilized NGF on genipin-cross-linked chitosan and tested the material for cytotoxicity using primary cultured Schwann cells and for neuronal differentiation of PC12 cells in response to NGF release. Subsequently, Wang et al. (2012a) demonstrated that genipin-cross-linked chitosan conduits loaded with NGF can be successfully used to bridge 1-cm-long sciatic nerve defects in rats as revealed by electrophysiological assessment, behavioral analysis, and histological examination 24 weeks after the surgery. Similar results were obtained, when NGF-containing microspheres were implanted into chitosan conduits to repair a 1 cm defect of the facial nerve in rabbits . In another NGF-based approach, Chao et al. (2016) combined an autologous vein conduit with a chitosan-β-glycerophosphate-NGF hydrogel. The researchers surgically reconstructed a 5-mm-long defect of a rat facial nerve with an autologous vein and then injected the chitosan-β-glycerophosphate-NGF hydrogel into the lumen of the conduit. Facial nerve regeneration was as efficient as in control groups, which were transplanted with an autologous nerve, but significantly better than in control groups where the vein conduit was injected with NGF only. Shen et al. (2010) used a polylactic/polyglycolic acid chitosan nerve conduit loaded with CNF to repair larger canine tibial nerve defects in crossbred dogs and evaluated nerve regeneration by general inspection, electrophysiological, immunological, and histological analyses 3 months after the surgery. Nerve regeneration was significantly improved in animals that were treated with CNF-loaded polylactic/ polyglycolic acid chitosan conduits when compared to groups treated with the polylactic/polyglycolic acid chitosan conduits. The results were similar to controls groups that were treated with autologous nerve grafts, suggesting that the artificial nerve conduit is a promising alternative for bridging nerve defects.

Furthermore, Zhao et al. (2014) hypothesized that tacrolismus-loaded chitosan enhances peripheral nerve regeneration through modulation of the expression profiles of neurotrophic factors. To test this hypothesis, they loaded tacrolismus onto chitosan conduits and examined nerve regeneration of sciatic nerve injury in a rat model. They found significant regeneration of sciatic nerves with normal morphology but higher density of myelinated nerve fibers in rats treated with tacrolismusloaded chitosan. The underlying mechanism seems to involve BDNF signaling, because nerve regeneration was paralleled by an increased expression of BDNF and its corresponding receptor (TrkB) in the motor neurons in the spinal cord.

The membrane-bound cell adhesion molecule L1 is known to promote neurite growth and prevent neuronal apoptosis, a function which can be mimicked by a recombinant chimeric version of this molecule called L1-Fc (Roonprapunt et al. 2003) . Loading L1-Fc to an artificial chitosan/polyglycolic acid conduit, Xu et al. (2004) studied guided regeneration of rat optic nerves. They found that the implanted chitosan/polyglycolic acid conduit was degraded and absorbed. When L1-Fc loaded conduits were implanted to bridge a defect caused by surgical intervention, axonal regeneration and remyelination were significantly improved when compared to control groups that were treated with conduits lacking L1-Fc.

Nerve regeneration can be additionally promoted using chitosan-based scaffolds as conduits seeded with stem cells that express neurotrophic factors and can differentiate into nerve cells. Zheng and Cui (2010) tested chitosan conduits of such kind combined with rat bone marrow mesenchymal stem cells to evaluate their potential for the reconstruction of 8-mm-long rat sciatic nerve defects. They demonstrated that the combination of chitosan and mesenchymal stem cells alone was sufficient to improve nerve regeneration and functional recovery. Moreover, some of the mesenchymal stem cells were found to have differentiated into neural stem cells. Similar results were obtained when injured rat sciatic nerves were treated in this way, and the nerve repair was monitored electrophysiologically and histomorphologically (Moattari et al. 2018) or by noninvasive magnetic resonance neurographic imaging (Liao et al. 2012 ). In addition, chitosan-coated poly-3-hydroxybutyrate conduits combined with human bone marrow mesenchymal stem cells were recently shown to be efficient in promoting nerve regeneration in this rat model of sciatic nerve injury (Ozer et al. 2018) . Improved nerve regeneration was also reported for chitosan/poly(lactic-co-glycolic acid) scaffolds seeded with autologous bone marrow mesenchymal stem cells to treat injuries of dog sciatic nerves and rhesus monkey median nerves (Xue et al. 2012; . In another approach, Zhu et al. (2015) used chitosan conduits filled with bone marrow mesenchymal stem cells and evaluated nerve regeneration and neuronal survival when injured lumbosacral nerves were bridged with this material. They found that this treatment enhanced sacral nerve regeneration and motor function 6 and 12 weeks after the surgery. Moreover, the mesenchymal stem cells prevented cell death of motor neurons in the anterior horn of the spinal cord, thereby improving the motor function in rats treated with the mesenchymal stem cell-seeded chitosan conduit. Finally, a clinical study performed with 14 patients suggests that defects in chronic spinal cord injury can be successfully bridged with peripheral nerve grafts combined with a chitosan-laminin scaffold and co-transplanted bone marrow-derived mesenchymal stem cells, which enhanced recovery (Amr et al. 2014) .

Using chitosan/silk fibroin scaffolds grafts seeded with adipose-derived stem cells, Wei et al. (2011) examined regeneration of surgically injured rat sciatic nerves. Implantation of this conduit significantly improved axonal regeneration and functional recovery in comparison to control groups. The positive effect was partially attributed to the differentiation of adipose-derived stem cells into Schwann cells, which additionally secrete neurotrophic factors and prevent apoptosis. Nie et al. (2014) investigated axonal regeneration and remyelination using a chitosan/gelatin-based conduit combined with TGF-β1 and Schwann cells. For this purpose, they bridged a 10-mm defect of a rat sciatic nerve and examined nerve regeneration based on functional recovery, electrophysiological measurements, retrograde labeling, and immunohistochemical analysis. The obtained data indicate satisfactory functional recovery of the injured sciatic nerve. Meyer et al. (2016) filled chitosan (5% degree of acetylation) conduits with a gel containing hyaluronic acid and laminin (NVR-gel) and added genetically modified neonatal rat Schwann cells as cellular delivery system for neurotrophic factors. Testing the chitosan conduits in the rat sciatic nerve model revealed that the chitosan conduit, which only is filled with the NVR-gel, was insufficient to promote nerve regeneration in contrast to autologous nerve grafts. Notably, delivery of FGF by seeded Schwann cells genetically modified to overexpress this factor improved nerve regeneration significantly. Unexpectedly, Schwann cells expressing GDNF did not show positive effects in this experimental setup. Recently, Zhu et al. (2017) used skin-derived precursor Schwann cells to seed chitosan/silk scaffolds for bridging a 10-mm-long rat sciatic nerve gap. The artificial graft exhibited significant promoting effects on peripheral nerve repair and hence constitutes an alternative to other stem cell-based approach promoting nerve regeneration.

Numerous studies reported favorable effects of chitosan-based materials for a wide range of applications. Doubtless, the controlled and targeted delivery of drugs to specific tissues has a great potential in biomedicine, and first clinical trials with chitosan-based drug carrier systems revealed promising results for the therapy of a variety of diseases including diabetes and cancer and also mainly because adverse side effects are reduced. The antimicrobial activity of chitosan and its derivatives is particularly important when the polymer is used for textile fabrication, food packaging, wound dressings, and tissue engineering. However, the underlying mechanism of antimicrobial activity is not fully understood. One prominent explanation is the assumed interaction of chitosan's positively charged amine groups with the negatively charged surface of bacteria and fungi, which might impair the movement of ions across membranes and hence disrupt cellular integrity. Although the proposed mechanisms seem plausible, there is a clear lack of experimental data that would provide evidence at a molecular level reminding us to continue basic research on the mode of actions. The studies conducted so far indicate that the antimicrobial activity of pure chitosan is not sufficient to prevent microbial infections completely in vivo. However, chitosan and its derivatives can be combined with other antimicrobial compounds including essential oils (Krausz et al. 2015) , polyphenols (Madureira et al. 2015) , tretinoin (Ridolfi et al. 2012) , metal ions (Sanpui et al. 2008; Tran et al. 2010) , lysozyme , or antibodies (Jamil et al. 2016) , to prevent bacterial of fungal infections. Thus, chitosan appears to be an ideal adjuvant polymer for design and production of new materials exhibiting intrinsic antimicrobial properties for a large variety of potential applications in the chemical, pharmaceutical, food, and textile industry. Similarly, the observed immunestimulatory effects of chitosan need further investigation, as there may be a certain risk to develop allergic or even anaphylactic reactions after oral ingestion (Kato et al. 2005) . However, it has to be noted that overall the beneficial characteristics exceed possible side effects due to some allergic potential. Finally, the antitumor activity of chitosan also needs to be analyzed in more detail. Recently, Li et al. (2018b) provided some evidence indicating that chitosan activates dendritic cells, which subsequently secrete pro-inflammatory cytokines and thereby enhance immune surveillance by natural killer cells. Accordingly, the antitumor effects of chitosan can be enhanced by specifically targeting dendritic cells by attaching mannose to the surface of chitosan nanoparticles (Shi et al. 2017a) . Different pattern recognition receptors that are expressed on the surface of dendritic cells are potential receptors for chitosan. This includes Toll-like receptors, C-type lectin receptors, and other molecules, which are known to recognize specific molecular patterns, particularly those associated with pathogens. However, currently it is not known how dendritic cells recognize chitosan. In summary, it has to be noted that chitosan is a highly promising material for a variety of applications in industry and medicine. While chitosan-based materials have been commercially launched as packaging and coating material in food industry, as an ingredient in cosmetics, and as ion exchanger in water treatment and are approved for human dietary use and wound dressing, their commercial applications in medicine as drug delivery systems or scaffold for tissue engineering are pending. Nevertheless, there are clinical phase 2/3 trials, and depending on their outcome, some products may reach first approval by the health authorities in near future. 

Grafting of aniline derivatives onto chitosan and their applications for removal of reactive dyes from industrial effluents

Nano chitosan-NPK fertilizer enhances the growth and productivity of wheat plants grown in sandy soil

Antimicrobial wound dressing nanofiber mats from multicomponent (chitosan/silver-NPs/polyvinyl alcohol) systems

Impedimetic immunosensor for the label-free and direct detection of botulinum neurotoxin serotype A using Au nanoparticles/graphene-chitosan composite

In vitro cartilage construct generation from silk fibroin-chitosan porous scaffold and umbilical cord blood derived human mesenchymal stem cells in dynamic culture condition

Solid state characterisation of silver sulfadiazine loaded on montmorillonite/chitosan nanocomposite for wound healing

Chitosan microparticles as oral delivery system for tetanus toxoid

Characterisation of composite films fabricated from collagen/chitosan and collagen/soy protein isolate for food packaging applications

Preparation and characterization of a nanoparticles modified chitosan sensor and its application for the determination of heavy metals from different aqueous media

Chitosan as biomaterial in drug delivery and tissue engineering

Chitosan application for active bio-based films production and potential in the food industry: review

Functionalized graphene oxidepolypyrrole-chitosan (fGO-PPy-CS) modified screen-printed electrodes for non-enzymatic hydrogen peroxide detection

Fluorinated methacrylamide chitosan hydrogels enhance cellular wound healing processes

Synthesis and characterization of chitosan and silver loaded chitosan nanoparticles for bioactive polyester

Double layer coatings: a new technique for maintaining physico-chemical characteristics and antioxidant properties of dragon fruit during storage

Exploring antibacterial activity and hydrolytic stability of resin dental composite restorative materials containing chitosan

Active pseudo-multilayered films from polycaprolactone and starch based matrix for food-packaging applications

Coating electrospun chitosan nanofibers with polyelectrolyte multilayers using the polysaccharides heparin and N,N,N-trimethyl chitosan

The development of non-enzymatic glucose biosensors based on electrochemically prepared polypyrrole-chitosantitanium dioxide nanocomposite films

Chitosan-zinc oxide nanoparticle composite coating for active food packaging applications

Chitosan topical gel formulation in the management of burn wounds

IFATS collection: Human adipose-derived stem cells seeded on a silk fibroin-chitosan scaffold enhance wound repair in a murine soft tissue injury model

Chitosan/polyester-based scaffolds for cartilage tissue engineering: assessment of extracellular matrix formation

A short review on presence of pharmaceuticals in water bodies and the potential of chitosan and chitosan derivatives for elimination of pharmaceuticals

A sensor for simultaneous determination of dopamine and morphine in biological samples using a multi-walled carbon nanotube/chitosan composite modified glassy carbon electrode

Selective simultaneous determination of paracetamol and uric acid using a glassy carbon electrode modified with multiwalled carbon nanotube/ chitosan composite

Preparation and characterization of SDF-1alpha-chitosan-dextran sulfate nanoparticles

Wound healing properties of PVA/starch/chitosan hydrogel membranes with nano Zinc oxide as antibacterial wound dressing material

The effect of active ingredient-containing chitosan/ polycaprolactone nonwoven mat on wound healing: in vitro and in vivo studies

Chitosan/nano-hydroxyapatite/nano-zirconium dioxide scaffolds with miR-590-5p for bone regeneration

Chitosan: A potential biopolymer for wound management

Ocular application of chitosan

Smart and fragrant garment via surface modification of cotton fabric with cinnamon oil/stimuli responsive PNIPAAm/chitosan nano hydrogels

pH responsive N-succinyl chitosan/Poly (acrylamide-co-acrylic acid) hydrogels and in vitro release of 5-fluorouracil

Induction of systemic resistance to Fusarium crown and root-rot in tomato plants by seed treatment with chitosan

Structure and interactions in covalently and ionically crosslinked chitosan hydrogels for biomedical applications

Chitosan treatment of wheat seeds induces resistance to Fusarium graminearum and improves seed quality

Supermacroprous chitosan-agarose-gelatin cryogels: in vitro characterization and in vivo assessment for cartilage tissue engineering

Development of chitosan-crosslinked nanofibrous PHBV guide for repair of nerve defects

Chitosan beads immobilized manganese peroxidase catalytic potential for detoxification and decolorization of textile effluent

Carbon fiber embedded chitosan/ PVA composites for decontamination of endocrine disruptor bisphenol-A from water

Removal of hexavalent chromium from wastewater using a new composite chitosan biosorbent

Alpha tocopherol loaded chitosan oleate nanoemulsions for wound healing. Evaluation on cell lines and ex vivo human biopsies, and stabilization in spray dried Trojan microparticles

Alginate coated chitosan nanoparticles are an effective subcutaneous adjuvant for hepatitis B surface antigen

CD44 Interaction with Tiam1 promotes Rac1 signaling and hyaluronic acid-mediated breast tumor cell migration

Antimicrobial activity of lactoferrin against foodborne pathogenic bacteria incorporated into edible chitosan film

Complexation of copper(II) with chitosan nanogels: toward control of microbial growth

Trans-resveratrol loaded chitosan nanoparticles modified with biotin and avidin to target hepatic carcinoma

Chitosan but not chitin activates the inflammasome by a mechanism dependent upon phagocytosis

Spectrum and mechanisms of inflammasome activation by chitosan

Chitosan-alginate membranes accelerate wound healing

Evaluation of chitosan-based films containing gelatin, chondroitin 4-sulfate and ZnO for wound healing

Preparation and characterization of homogeneous chitosan-polylactic acid/hydroxyapatite nanocomposite for bone tissue engineering and evaluation of its mechanical properties

Acidic pH resistance of grafted chitosan on dental implant

Chitosan nanoparticles functionalized with β-cyclodextrin: a promising carrier for botanical pesticides

Fabrication of chitosan/graphene oxide polymer nanofiber and its biocompatibility for cartilage tissue engineering

Mucoadhesive and thermogelling systems for vaginal drug delivery

Flame retardant multilayered coatings on acrylic fabrics prepared by one-step deposition of chitosan/montmorillonite complexes

The vaccine adjuvant chitosan promotes cellular immunity via DNA sensor cGAS-STING-dependent induction of Type I interferons

Chitosan in nasal delivery systems for therapeutic drugs

Preparation of a milk spoilage indicator adsorbed to a modified polypropylene film as an attempt to build a smart packaging

A strategy to employ polymerised riboflavin in the development of electrochemical biosensors

Antimicrobial controlled release systems for the knitted cotton fabrics based on natural substances

Development and in vivo evaluation of silver sulfadiazine loaded hydrogel consisting polyvinyl alcohol and chitosan for severe burns

Effect of visco-elastic silk-chitosan microcomposite scaffolds on matrix deposition and biomechanical functionality for cartilage tissue engineering

Comparison of adjuvant efficacy of chitosan and aluminum hydroxide for intraperitoneally administered inactivated influenza H5N1 vaccine

Facilitation of facial nerve regeneration using chitosan-beta-glycerophosphate-nerve growth factor hydrogel

Electrospun chitosan/ polyvinyl alcohol nanofibre mats for wound healing

Development of chitosan nanocapsules for the controlled release of hexaconazole

Study on biocompatibility of complexes of collagen-chitosan-sodium hyaluronate and cornea

In vitro proliferation and osteogenic differentiation of human dental pulp stem cells in injectable thermo-sensitive chitosan/betaglycerophosphate/hydroxyapatite hydrogel

Quaternized carboxymethyl chitosan/organic montmorillonite nanocomposite as a novel cosmetic ingredient against skin aging

Preparation and characterization of antimicrobial cotton fabrics via N-halamine chitosan derivative/poly(2-acrylamide-2-methylpropane sulfonic acid sodium salt) self-assembled composite films

Composite chitosan/ nano-hydroxyapatite scaffolds induce osteocalcin production by osteoblasts in vitro and support bone formation in vivo

Corneal repair by human corneal keratocyte-reprogrammed iPSCs and amphiphatic carboxymethyl-hexanoyl chitosan hydrogel

Covalently conjugated transforming growth factor-beta1 in modular chitosan hydrogels for the effective treatment of articular cartilage defects

Chitosan as an immunomodulating adjuvant on T-cells and antigen-presenting cells in Herpes Simplex virus type 1 infection

Bioengineered keratocyte spheroids fabricated on chitosan coatings enhance tissue repair in a rabbit corneal stromal defect model

Cu-chitosan nanoparticle boost defense responses and plant growth in maize

Assessment of Cu-chitosan nanoparticles for its antibacterial activity against Pseudomonas syringae pv. Glycinea

Skin tissue engineering advances in severe burns: review and therapeutic applications

Photostabilization of an entomopathogenic fungus using composite clay matrices

Sodium hyaluronate/ chitosan polyelectrolyte complex scaffolds for dental pulp regeneration: synthesis and characterization

A preliminary study of the incorporation of NPK fertilizer into chitosan nanoparticles

Controlled release matrices and micro/nanoparticles of chitosan with antimicrobial potential: development of new strategies for microbial control in agriculture

Highly sensitive lactate biosensor by engineering chitosan/ PVI-Os/CNT/LOD network nanocomposite

Development of chitosancollagen hydrogel incorporated with lysostaphin (CCHL) burn dressing with anti-methicillinresistant Staphylococcus aureus and promotion wound healing properties

Chitosan promoted the corneal epithelial wound healing via activation of erk pathway

Biocompatible electrochemiluminescent biosensor for choline based on enzyme/titanate nanotubes/chitosan composite modified electrode

PVA-chitosan composite hydrogel versus alginate beads as a potential mesenchymal stem cell carrier for the treatment of focal cartilage defects

Chitosan nanoparticles: a new vehicle for the improvement of the delivery of drugs to the ocular surface. Application to cyclosporine A

The effect of a PEG versus a chitosan coating on the interaction of drug colloidal carriers with the ocular mucosa

Local controlled release of VEGF and PDGF from a combined brushitechitosan system enhances bone regeneration

Removal of cationic dyes from aqueous solutions using Nbenzyl-O-carboxymethylchitosan magnetic nanoparticles

An overview of chitin or chitosan/nano ceramic composite scaffolds for bone tissue engineering

Development of chitosan oleate ionic micelles loaded with silver sulfadiazine to be associated with platelet lysate for application in wound healing

Dendronized chitosan derivative as a biocompatible gene delivery carrier

Hollow chitosan-silica nanospheres as pH-sensitive targeted delivery carriers in breast cancer therapy

A silk fibroin/chitosan scaffold in combination with bone marrow-derived mesenchymal stem cells to repair cartilage defects in the rabbit knee

Novel electrochemical xanthine biosensor based on chitosan-polypyrrole-gold nanoparticles hybrid bio-nanocomposite platform

Preparation and characterization of chitosan-bentonite nanocomposite films for wound healing application

Chitosan: antimicrobial activity, interactions with food components and applicability as a coating on fruit and vegetables

Mucoadhesive microspheres for gastroretentive delivery of acyclovir: in vitro and in vivo evaluation

Antibacterial activity of hybrid chitosan-cupric oxide nanoparticles on cotton fabric

Supercritical solvent impregnation of natural bioactive compounds in N-carboxybutyl chitosan membranes for the development of topical wound healing applications

Ocular drug delivery by liposome-chitosan nanoparticle complexes (LCS-NP)

Wound healing bionanocomposites based on castor oil polymeric films reinforced with chitosan-modified ZnO nanoparticles

In vitro cytocompatibility evaluation of chitosan/graphene oxide 3D scaffold composites designed for bone tissue engineering

Sorption of Cu (II) ions on chitosan-Zeolite x composites: impact of gelling and drying conditions

Oligogalacturonides and chitosan activate plant defensive genes through the octadecanoid pathway

Characterizations of blend gels of carboxymethylated polysaccharides and their use for the controlled release of herbicide

Construction and characterization of a chitosan-immobilized-enzyme and beta-cyclodextrin-included-ferrocene-based electrochemical biosensor for H2O2 detection

Application of chitosan based coating in fruit and vegetable preservation: a review

Supramolecular composite materials from cellulose, chitosan and cyclodextrin: facile preparation and their selective inclusion complex formation with endocrine disruptors

Chitin and chitosan: Chemistry, properties and applications

The impact of the codelivery of drug-siRNA by trimethyl chitosan nanoparticles on the efficacy of chemotherapy for metastatic breast cancer cell line (MDA-MB-231)

Evaluation of released malathion and spinosad from chitosan/alginate/gelatin capsules against Culex pipiens larvae

Chitosan in plant protection

Alginate coated chitosan nanogel for the controlled topical delivery of Silver sulfadiazine

Using chitosan nanoparticles as drug carriers for the development of a silver sulfadiazine wound dressing

Chitosan and sodium alginate-based bioadhesive vaginal tablets

Eco-friendly finishing agent for cotton fabrics to improve flame retardant and antibacterial properties

Chitosan microparticles for sustaining the topical delivery of minoxidil sulphate

Kinetics of hexavalent chromium removal from water by chitosan-Fe0 nanoparticles

Assessment of antibacterial and antioxidant properties of chitosan edible films incorporated with maqui berry (Aristotelia chilensis)

Chitosan/gelatin scaffolds support bone regeneration

Gene delivery using chitosan, trimethyl chitosan or polyethylenglycol-graft-trimethyl chitosan block copolymers: establishment of structure-activity relationships in vitro

Chitosan-intercalated montmorillonite/poly(vinyl alcohol) nanofibers as a platform to guide neuronlike differentiation of human dental pulp stem cells

Chitosan as an adjuvant for poliovaccine

Tissue engineered poly(caprolactone)-chitosan-poly (vinyl alcohol) nanofibrous scaffolds for burn and cutting wound healing

Innovative gold-free carbon nanotube/ chitosan-based competitive immunosensor for determination of HIV-related p24 capsid protein in serum

Removal of the heavy metal ion chromiuim (VI) using Chitosan and Alginate nanocomposites

Chitosan microparticles incorporating a hydrophilic sunscreen agent

Use of synovium-derived stromal cells and chitosan/collagen type I scaffolds for cartilage tissue engineering

Dermal wound healing processes with curcumin incorporated collagen films

The role of silver in wound healing

Thermoplastic blends of chitosan: A method for the preparation of high thermally stable blends with polyesters

Endocrine disruptors compounds, pharmaceuticals and personal care products in urban wastewater: implications for agricultural reuse and their removal by adsorption process

Chitosan/ tripolyphosphate nanoparticles loaded with paraquat herbicide: an environmentally safer alternative for weed control

Surgical repair of a 30 mm long human median nerve defect in the distal forearm by implantation of a chitosan-PGA nerve guidance conduit

Use of a silk fibroinchitosan scaffold to construct a tissue-engineered corneal stroma

The synthesis and antioxidant activity of the Schiff bases of chitosan and carboxymethyl chitosan

Antibacterial chitosan coating on nano-hydroxyapatite/polyamide66 porous bone scaffold for drug delivery

Influence of radiation crosslinked carboxymethyl-chitosan/gelatin hydrogel on cutaneous wound healing

Development of a novel reagentless, screenprinted amperometric biosensor based on glutamate dehydrogenase and NAD(+), integrated with multi-walled carbon nanotubes for the determination of glutamate in food and clinical applications

Characterization of chitosan/TiO 2 cano-powder modified glass-ionomer cement for restorative dental applications

Loading of chitosannano metal oxide hybrids onto cotton/polyester fabrics to impart permanent and effective multifunctions

Kaempferol loaded lecithin/chitosan nanoparticles: preparation, characterization, and their potential applications as a sustainable antifungal agent

Chitosan and its use as a pharmaceutical excipient

Nasal drug delivery-possibilities, problems and solutions

Biomimetic three-dimensional nanocrystalline hydroxyapatite and magnetically synthesized single-walled carbon nanotube chitosan nanocomposite for bone regeneration

Chitosan hydrogel as a drug delivery carrier to control angiogenesis

In vitro properties of a chitosan-bonded hydroxyapatite bone-filling paste

Hydroxyapatite-coated tendon chitosan tubes with adsorbed laminin peptides facilitate nerve regeneration in vivo

Active naringin-chitosan films: impact of UV irradiation

Curcumin-loaded chitosan/ carboxymethyl starch/montmorillonite bio-nanocomposite for reduction of dental bacterial biofilm formation

Beg AM (2010) Design and development of ligand-appended polysaccharidic nanoparticles for the delivery of oxaliplatin in colorectal cancer

Cefazolin loaded chitosan nanoparticles to cure multi drug resistant Gram-negative pathogens

Development of a carbon nanotubes paste electrode modified with crosslinked chitosan for cadmium (II) and mercury(II) determination

Chitosan microencapsulation of various essential oils to enhance the functional properties of cotton fabric

Biomaterials based on chitin and chitosan in wound dressing applications

Chitosan coatings to control release and target tissues for therapeutic delivery

Controlled release of Bordetella bronchiseptica dermonecrotoxin (BBD) vaccine from BBD-loaded chitosan microspheres in vitro

In vitro evaluation of chitosan/poly(lactic acidglycolic acid) sintered microsphere scaffolds for bone tissue engineering

Novel chitosan derivative nanoparticles enhance the immunogenicity of a DNA vaccine encoding hepatitis B virus core antigen in mice

Removal of methyl orange from aqueous solutions by magnetic maghemite/chitosan nanocomposite films: Adsorption kinetics and equilibrium

Synthesis of novel biocompatible composite Fe 3 O 4 /ZrO 2 /chitosan and its application for dye removal

Biomimetic spiral-cylindrical scaffold based on hybrid chitosan/cellulose/nano-hydroxyapatite membrane for bone regeneration

Microintumescent mechanism of flame-retardant water-based chitosan-ammonium polyphosphate multilayer nanocoating on cotton fabric

Utilization of carboxymethyl chitosan in cosmetics

In vivo evaluation of porous hydroxyapatite/chitosan-alginate composite scaffolds for bone tissue engineering

Glutaraldehyde cross-linked magnetic chitosan nanocomposites: Reduction precipitation synthesis, characterization, and application for removal of hazardous textile dyes

Amphiphilic chitosan derivatives as carrier agents for rotenone

Antimicrobial silver chloride nanoparticles stabilized with chitosan oligomer for the healing of burns

Curcumin loaded chitosan nanoparticles impregnated into collagen-alginate scaffolds for diabetic wound healing

Chitosan nanoparticle based delivery systems for sustainable agriculture

A future perspective in crop protection: chitosan and its oligosaccharides

A case of anaphylaxis caused by the health food chitosan

Synthesis and characterization of a novel chitosan/montmorillonite/hydroxyapatite nanocomposite for bone tissue engineering

Microwave-induced biomimetic approach for hydroxyapatite coatings of chitosan scaffolds

Biodegradation, biodistribution and toxicity of chitosan

Effect of locally administered novel biodegradable chitosan based risedronate/zinc-hydroxyapatite intra-pocket dental film on alveolar bone density in rat model of periodontitis

A green approach to constructing multilayered nanocoating for flame retardant treatment of polyamide 66 fabric from chitosan and sodium alginate

Cartilage regeneration by novel polyethylene oxide/chitin/chitosan scaffolds

Incorporation of chitosan in biomimetic gelatin/ chondroitin-6-sulfate/hyaluronan cryogel for cartilage tissue engineering

Preparation of water-soluble chitosan/heparin complex and its application as wound healing accelerator

Recent modifications of chitosan for adsorption applications: a critical and systematic review

Environmental friendly technology for the removal of pharmaceutical contaminants from wastewaters using modified chitosan adsorbents

Removal of dorzolamide from biomedical wastewaters with adsorption onto graphite oxide/poly(acrylic acid) grafted chitosan nanocomposite

Anti-tumor immune response of folate-conjugated chitosan nanoparticles containing the IP-10 gene in mice with hepatocellular carcinoma

Polyelectrolyte complexes via desalting mixtures of hyaluronic acid and chitosan-Physicochemical study and structural analysis

Effect of fiber length and blending method on the tensile properties of ring spun chitosan-cotton blend yarns

A pilot intervention with chitosan/cotton knitted jersey fabric to provide comfort for epidermolysis bullosa patients

Chitosan modified poly(L-lactide) microspheres as cell microcarriers for cartilage tissue engineering

Characterization and antimicrobial analysis of chitosan-based films

Chitin, chitinases and chitinase-like proteins in allergic inflammation and tissue remodeling

Preparation of multiwalled carbon nanotube-chitosan-alcohol dehydrogenase nanobiocomposite for amperometric detection of ethanol

Chitin regulation of immune responses: an old molecule with new roles

Chitosonic((R)) acid as a novel cosmetic ingredient: evaluation of its antimicrobial, antioxidant and hydration activities

Chitosan/polyurethane blended fiber sheets containing silver sulfadiazine for use as an antimicrobial wound dressing

Oxygen plasma treatment on 3D-printed chitosan/ gelatin/hydroxyapatite scaffolds for bone tissue engineering

Water-based chitosan/melamine polyphosphate multilayer nanocoating that extinguishes fire on polyester-cotton fabric

Chitosan-alginate as scaffolding material for cartilage tissue engineering

Chitosan-alginate hybrid scaffolds for bone tissue engineering

Controlled release and retarded leaching of pesticides by encapsulating in carboxymethyl chitosan/bentonite composite gel

In situ injectable nano-composite hydrogel composed of curcumin, N,O-carboxymethyl chitosan and oxidized alginate for wound healing application

Antibacterial mechanism of chitosan and its applications in protection of plant from bacterial disease

Chitin, chitosan, and glycated chitosan regulate immune responses: the novel adjuvants for cancer vaccine

Chitosan grafted with phosphorylcholine and macrocyclic polyamine as an effective gene delivery vector: Preparation, characterization and in vitro transfection

Preparation, characterization, and insecticidal activity of avermectin-grafted-carboxymethyl chitosan

Preparation and adsorption properties of magnetic chitosan composite adsorbent for Cu 2+ removal

Chitosan conduit combined with hyaluronic acid prevent sciatic nerve scar in a rat model of peripheral nerve crush injury

The natural product chitosan enhances the anti-tumor activity of natural killer cells by activating dendritic cells

Fabrication and characters of a corneal endothelial cells scaffold based on chitosan

Tissue-engineered membrane based on chitosan for repair of mechanically damaged corneal epithelium

Peripheral nerve repair: monitoring by using gadofluorine M-enhanced MR imaging with chitosan nerve conduits with cultured mesenchymal stem cells in rat model of neurotmesis

Preparation, bioactivity and mechanism of nano-hydroxyapatite/sodium alginate/chitosan bone repair material

Chitooligosaccharides and their biological activities: a comprehensive review

Films based on neutralized chitosan citrate as innovative composition for cosmetic application

Rapidly curable chitosan-PEG hydrogels as tissue adhesives for hemostasis and wound healing

Development of Ca-alginate-chitosan microcapsules for encapsulation and controlled release of imidacloprid to control dengue outbreaks

Preparation, characterization and biological test of 3D-scaffolds based on chitosan, fibroin and hydroxyapatite for bone tissue engineering

Sciatic nerve repair by microgrooved nerve conduits made of chitosan-gold nanocomposites

Sensitive amperometric immunosensor for alphafetoprotein based on carbon nanotube/gold nanoparticle doped chitosan film

Enhancing catalytic performance of laccase via immobilization on chitosan/CeO2 microspheres

Development of chitosan/poly-gamma-glutamic acid/pluronic/ curcumin nanoparticles in chitosan dressings for wound regeneration

Differentiation potential of mesenchymal stem cells from equine bone marrow cultured on hyaluronic acid-chitosan polyelectrolyte multilayer biofilm

Recent advances in chitosan and its derivatives as adsorbents for removal of pollutants from water and wastewater

The direct electron transfer of glucose oxidase and glucose biosensor based on carbon nanotubes/chitosan matrix

Integrin α(v)β(3)-targeted cancer therapy

Ultrasensitive amperometric immunosensor for the determination of carcinoembryonic antigen based on a porous chitosan and gold nanoparticles functionalized interface

Amperometric biosensors based on alumina nanoparticles-chitosan-horseradish peroxidase nanobiocomposites for the determination of phenolic compounds

Chitosan conduits combined with nerve growth factor microspheres repair facial nerve defects

Conjugating influenza a (H1N1) antigen to N-trimethylaminoethylmethacrylate chitosan nanoparticles improves the immunogenicity of the antigen after nasal administration

Effect of collagen peptidescarboxymethyl chitosan microspheres on ultraviolet induced damages

A novel reusable nanocomposite adsorbent, xanthated Fe 3 O 4 -chitosan grafted onto graphene oxide, for removing Cu(II) from aqueous solutions

The efficient removal of Cu(II) from aqueous solutions by Fe 3 O 4 @hexadecyl trimethoxysilane@chitosan composites

Preparation and biological properties of a novel composite scaffold of nano-hydroxyapatite/chitosan/carboxymethyl cellulose for bone tissue engineering

Chitosan coated textiles may improve atopic dermatitis severity by modulating skin staphylococcal profile: a randomized controlled trial

Silver ions release from antibacterial chitosan films containing in situ generated silver nanoparticles

Chitosan nanoparticles on the improvement of thermal, barrier, and mechanical properties of high-and low-methyl pectin films

Biological evaluation (in vitro and in vivo) of bilayered collagenous coated (nano electrospun and solid wall) chitosan membrane for periodontal guided bone regeneration

Preparation and characterization of chitosan-natural nano hydroxyapatite-fucoidan nanocomposites for bone tissue engineering

Construction, application and biosafety of silver nanocrystalline chitosan wound dressing

Preparation of quaternary ammonium salt of chitosan nanoparticles and their textile properties on Antheraea pernyi silk modification

Healing of skin wounds with a chitosan-gelatin sponge loaded with tannins and platelet-rich plasma

Enhanced antibacterial and wound healing activities of microporous chitosan-Ag/ZnO composite dressing

High-activity chitosan/nano hydroxyapatite/zoledronic acid scaffolds for simultaneous tumor inhibition, bone repair and infection eradication

Combined antibacterial/tissue regeneration response in thermal burns promoted by functional chitosan/silver nanocomposites

Fabrication and characterization of kidney bean (Phaseolus vulgaris L.) protein isolate-chitosan composite films at acidic pH

Chitosan and oligochitosan enhance the resistance of peach fruit to brown rot

Guided bone regeneration with tripolyphosphate cross-linked asymmetric chitosan membrane

Interleukin/chitosan (JY) adjuvant enhances the mucosal immunity of human papillomavirus 16 L1 virus-like particles in mice

Current state on the development of nanoparticles for use against bacterial gastrointestinal pathogens. Focus on chitosan nanoparticles loaded with phenolic compounds

Development of gelatin-chitosan-hydroxyapatite based bioactive bone scaffold with controlled pore size and mechanical strength

Chitosan effects on plant systems

Trimethyl chitosan nanoparticles encapsulated protective antigen protects the mice against anthrax

Chitosan, gelatin and poly (L-lysine) polyelectrolyte-based scaffolds and films for neural tissue engineering

Development of a multilayered antimicrobial edible coating for shelf-life extension of fresh-cut cantaloupe (Cucumis melo L.) stored at 4 C

Influence of α-tocopherol on physicochemical properties of chitosan-based films

A non-enzymatic nanomagnetic electro-immunosensor for determination of Aflatoxin B-1 as a model antigen

Chitosan nanoparticles for targeting and sustaining minoxidil sulphate delivery to hair follicles

A new concept for macromolecular therapeutics in cancer chemotherapy: mechanism of tumoritropic accumulation of proteins and the antitumor agent smancs

Peripheral nerve repair and grafting techniques: a review

N,N-dicarboxymethyl chitosan as delivery agent for bone morphogenetic protein in the repair of articular cartilage

A mucosal vaccine against diphtheria: formulation of cross reacting material (CRM(197)) of diphtheria toxin with chitosan enhances local and systemic antibody and Th2 responses following nasal delivery

Fattakhova AN (2014) determination of antidepressants using monoamine oxidase amperometric biosensors based on screen-printed graphite electrodes modified with multi-walled carbon nanotubes

Preparation and characterization of potassium nitrate controlledrelease fertilizers based on chitosan and xanthan layered tablets

Poly(Nisopropylacrylamide) hydrogel/chitosan scaffold hybrid for three-dimensional stem cell culture and cartilage tissue engineering

Determination of chlorophenol in environmental samples using a voltammetric biosensor based on hybrid nanocomposite

A composite scaffold of MSC affinity peptide-modified demineralized bone matrix particles and chitosan hydrogel for cartilage regeneration

A Chitosanbased liposome formulation enhances the in vitro wound healing efficacy of substance P. Neuropeptide 9

Peripheral nerve regeneration through hydrogel-enriched chitosan conduits containing engineered Schwann cells for drug delivery

A chitosanhyaluronic acid hydrogel scaffold for periodontal tissue engineering

Tumour targeted delivery of encapsulated dextrandoxorubicin conjugate using chitosan nanoparticles as carrier

Chitosan-film associated with mesenchymal stem cells enhanced regeneration of peripheral nerves: a rat sciatic nerve model

Antimicrobial and physicochemical properties of chitosanÀHPMC-based films

Amperometric glucose biosensor utilizing FAD-dependent glucose dehydrogenase immobilized on nanocomposite electrode

The vaccine adjuvant alum inhibits IL-12 by promoting PI3 kinase signaling while chitosan does not inhibit IL-12 and enhances Th1 and Th17 responses

Osteoconduction exerted by methylpyrrolidinone chitosan used in dental surgery

Osteoconductive properties of methylpyrrolidinone chitosan in an animal model

Chitosan, hyaluronan and chondroitin sulfate in tissue engineering for cartilage regeneration: a review

Pyrazole-based compounds in chitosan liposomal emulsion for antimicrobial cotton fabrics

Protein growth factors loaded highly porous chitosan scaffold: a comparison of bone healing properties

Evaluation of chitosan gel with 1% silver sulfadiazine as an alternative for burn wound treatment in rats

Plasma-assisted preparation of high-performance chitosan nanofibers/gauze composite bandages

Chitosan/poly(epsilon-caprolactone) blend scaffolds for cartilage repair

Antioxidant effects of chitin, chitosan, and their derivatives

Photoprotection for deltamethrin using chitosancoated beeswax solid lipid nanoparticles

Preparation of magnetic composite based on zinc oxide nanoparticles and chitosan as a photocatalyst for removal of reactive blue 198

A high photo-catalytic activity of magnetic composite based on chitosan and manganese-doped zinc oxide nanoparticles for removal of dyeing wastewater

GABAB receptor ligand-directed trimethyl chitosan/tripolyphosphate nanoparticles and their pMDI formulation for survivin siRNA pulmonary delivery

Axonal regeneration and remyelination evaluation of chitosan/gelatin-based nerve guide combined with transforming growth factor-beta1 and Schwann cells

Novel recyclable adsorbent for the removal of copper (II) and lead(II) from aqueous solution

Applications of chitosan for improvement of quality and shelf life of foods: a review

A comparative study of gelatin and starch-based nano-composite films modified by nano-cellulose and chitosan for food packaging applications

Multilayer-coated NPK compound fertilizer hydrogel with controlled nutrient release and water absorbency

Degradation of fully water-soluble, partially N-acetylated chitosans with lysozyme

Novel hydroxyapatite/chitosan bilayered scaffold for osteochondral tissueengineering applications: Scaffold design and its performance when seeded with goat bone marrow stromal cells

Chitosan/gelatin/platelet gel enriched by a combination of hydroxyapatite and beta-tricalcium phosphate in healing of a radial bone defect model in rat

Spray dried inhalable ciprofloxacin powder with improved aerosolisation and antimicrobial activity

HER2 amplification ratios by fluorescence in situ hybridization and correlation with immunohistochemistry in a cohort of 6556 breast cancer tissues

Ultrathin chitosanpoly(ethylene glycol) hydrogel films for corneal tissue engineering

Regenerative potential of chitosan-coated poly-3-hydroxybutyrate conduits seeded with mesenchymal stem cells in a rat sciatic nerve injury model

Nanoamphiphilic chitosan dispersed poly(lactic acid) bionanocomposite films with improved thermal, mechanical, and gas barrier properties

Biophysicochemical evaluation of chitosanhydroxyapatite-marine sponge collagen composite for bone tissue engineering

Human exposure to wastewater-derived pharmaceuticals in fresh produce: a randomized controlled trial focusing on carbamazepine

New drug delivery systems based on chitosan

Controlled release of plateletderived growth factor-BB from chondroitin sulfate-chitosan sponge for guided bone regeneration

Platelet derived growth factor releasing chitosan sponge for periodontal bone regeneration

The accelerating effect of chitosan-silica hybrid dressing materials on the early phase of wound healing

Preparation and optimization of chitosan-gelatin films for sustained delivery of lupeol for wound healing

Fluorinated methacrylamide chitosan hydrogels enhance collagen synthesis in wound healing through increased oxygen availability

Chitosan as a starting material for wound healing applications

Chitosan-mediated stimulation of macrophage function

Composite nano-titanium oxide-chitosan artificial skin exhibits strong wound-healing effect-an approach with anti-inflammatory and bactericidal kinetics

Nanoporous magnetic cellulose-chitosan composite microspheres: preparation, characterization, and application for Cu(II) adsorption

Chitosan-montmorillonite biocomposite as an adsorbent for copper (II) cations from aqueous solutions

Chitosan-starch beads prepared by ionotropic gelation as potential matrices for controlled release of fertilizers

In vitro capacity of different grades of chitosan derivatives to induce platelet adhesion and aggregation

Cotton filter fabrics functionalization by chitosan UV-grafting for removal of dyes

Antimicrobial chitosan finish of cotton and silk fabrics by UV-curing with 2-hydroxy-2-methylphenylpropane-1-one

Sonochemical coating of textiles with hybrid ZnO/chitosan antimicrobial nanoparticles

Preliminary study on chitosan modified glass ionomer restoratives

Concise review: msc-derived exosomes for cell-free therapy

Chitosan derivatives for gene transfer: effect of phosphorylcholine and diethylaminoethyl grafts on the in vitro transfection efficiency

Immunoadjuvant potential of cross-linked dextran microspheres mixed with chitosan nanospheres encapsulated with tetanus toxoid

Layer-by-layer electrostatic deposition of edible coating on fresh cut melon model: anticipated and unexpected effects of alginate-chitosan combination

Effects of a composite chitosan-gelatin edible coating on postharvest quality and storability of red bell peppers

Chitosan-based nanoparticles for tumor-targeted drug delivery

Chitosan/beta-1,3-glucan/hydroxyapatite bone scaffold enhances osteogenic differentiation through TNF-alpha-mediated mechanism

Evaluation of the potential of chitosan/beta-1,3-glucan/hydroxyapatite material as a scaffold for living bone graft production in vitro by comparison of ADSC and BMDSC behaviour on its surface

Chitosan-modified smectite clay and study on adsorptiondesorption of urea

Electrospinning of chitosan-based solutions for tissue engineering and regenerative medicine

In vivo antitumor activity of chitosan nanoparticles

Chitosan/poly(vinyl alcohol) hydrogel combined with Ad-hTGF-beta1 transfected mesenchymal stem cells to repair rabbit articular cartilage defects

Chitosan green tea polyphenol complex as a released control compound for wound healing

The antioxidant property of chitosan green tea polyphenols complex induces transglutaminase activation in wound healing

A label-free amperometric immunosensor based on biocompatible conductive redox chitosan-ferrocene/gold nanoparticles matrix

A nitrite biosensor based on co-immobilization of nitrite reductase and viologen-modified chitosan on a glassy carbon electrode

Chitosan and its antimicrobial potential-a critical literature survey

Chitosan as antimicrobial agent: applications and mode of action

Doxorubicin hydrochloride -Loaded electrospun chitosan/cobalt ferrite/titanium oxide nanofibers for hyperthermic tumor cell treatment and controlled drug release

PEG-stabilized carbodiimide crosslinked collagen-chitosan hydrogels for corneal tissue engineering

Dendritic cell targeted chitosan nanoparticles for nasal DNA immunization against SARS CoV nucleocapsid protein

Hyaluronidase enzyme core-5-fluorouracilloaded chitosan-PEG-gelatin polymer nanocomposites as targeted and controlled drug delivery vehicles

Studies on an anti-aging formulation prepared using Aloe vera blended collagen and chitosan

Removal of copper(II) using chitin/chitosan nano-hydroxyapatite composite

Octadecanoid signaling component "burst" in rice (Oryza sativa L.) seedling leaves upon wounding by cut and treatment with fungal elicitor chitosan

Adsorption of cadmium (II) and copper (II) ions from aqueous solution using chitosan composite

A novel chitosan-tussah silk fibroin/ nano-hydroxyapatite composite bone scaffold platform with tunable mechanical strength in a wide range

Evaluation of durability to laundering of triclosan and chitosan on a textile substrate

Dermatan sulfate/chitosan polyelectrolyte complex with potential application in the treatment and diagnosis of vascular disease

Role of chitosan on some physical properties and the urea controlled release of the silk fibroin/gelatin hydrogel

Fabrication of ZnO incorporated chitosan nanocomposites for enhanced functional properties of cellulosic fabric

Effective nasal influenza vaccine delivery using chitosan

Application of magnetic chitosan composites for the removal of toxic metal and dyes from aqueous solutions

Development and characterization of an LDPE/chitosan composite antimicrobial film for chilled fish storage

Nanocomposites based on chitosan/ silver/clay for durable multi-functional properties of cotton fabrics

Synthesis of chitosan incorporated neem seed extract (Azadirachta indica) for medical textiles

Dextran-based hydrogel containing chitosan microparticles loaded with growth factors to be used in wound healing

Potential of low molecular mass chitosan as a DNA delivery system: biocompatibility, body distribution and ability to complex and protect DNA

Chitosan-solid lipid nanoparticles as carriers for topical delivery of tretinoin

Soluble cell adhesion molecule L1-Fc promotes locomotor recovery in rats after spinal cord injury

Enhancement of nitrogen release properties of urea-kaolinite fertilizer with chitosan binder

Amelogenin-chitosan matrix for human enamel regrowth: effects of viscosity and supersaturation degree

Vitamin-mediated targeting as a potential mechanism to increase drug uptake by tumours

Application of a biopolymer chitosan-poly (propylene)imine dendrimer hybrid as an antimicrobial agent on the wool fabrics

Cu-chitosan nanoparticle mediated sustainable approach to enhance seedling growth in maize by mobilizing reserved food

Potential prospects of chitosan derivative trimethyl chitosan chloride (TMC) as a polymeric absorption enhancer: synthesis, characterization and applications

Scintigraphic verification of adherence of a chitosan formulation to the human oesophagus

Preparation of poly (chitosan-acrylamide) flocculant using gamma radiation for adsorption of Cu(II) and Ni(II) ions

A review on chitosan-based adsorptive membranes

Mucoadhesive electrospun chitosan-based nanofibre mats for dental caries prevention

Chitosan-hyaluronic acid composite sponge scaffold enriched with Andrographolide-loaded lipid nanoparticles for enhanced wound healing

Buccal penetration enhancement properties of N-trimethyl chitosan: Influence of quaternization degree on absorption of a high molecular weight molecule

The antibacterial properties of a novel chitosan-Ag-nanoparticle composite

Synthesis and characterization of zinc oxide-neem oilchitosan bionanocomposite for food packaging application

Efficiency of chitosan-algal biomass composite microbeads at heavy metal removal

Microfungal spores (Ustilago maydis and U. digitariae) immobilised chitosan microcapsules for heavy metal removal

Chitosan as a suitable nanocarrier material for anti-Alzheimer drug delivery

Intranasal chitosan-DNA vaccines that protect across influenza virus subtypes

Preparation and characterization of cotton fabrics with antimicrobial properties through the application of chitosan/silver-zeolite film

In vivo evaluation of chitosan as an adjuvant in subcutaneous vaccine formulations

Diphtheria toxoid and N-trimethyl chitosan layer-by-layer coated pH-sensitive microneedles induce potent immune responses upon dermal vaccination in mice

Perfusion conditioning of hydroxyapatite-chitosan-gelatin scaffolds for bone tissue regeneration from human mesenchymal stem cells

Evaluation of chitosan based vaginal bioadhesive gel formulations for antifungal drugs

Nano-hydroxyapatite/beta-CD/chitosan nanocomposite for potential applications in bone tissue engineering

Enhanced antibacterial efficacy of silver nanoparticles immobilized in a chitosan nanocarrier

A novel squid pen chitosan/hydroxyapatite/beta-tricalcium phosphate composite for bone tissue engineering

Ciliary neurotrophic factor-coated polylactic-polyglycolic acid chitosan nerve conduit promotes peripheral nerve regeneration in canine tibial nerve defect repair

cRGD-functionalized polymeric magnetic nanoparticles as a dual-drug delivery system for safe targeted cancer therapy

Accelerated healing of diabetic wound using artificial dermis constructed with adipose stem cells and poly (L-glutamic acid)/chitosan scaffold

Hydrodynamic delivery of chitosan-folate-DNA nanoparticles in rats with adjuvant-induced arthritis

Enhanced antitumor immunity by targeting dendritic cells with tumor cell lysate-loaded chitosan nanoparticles vaccine

GMSC-derived exosomes combined with a chitosan/silk hydrogel sponge accelerates wound healing in a diabetic rat skin defect model

pH response of human dental plaque to chewing gum supplemented with low molecular chitosan

Alveolar macrophage priming by intravenous administration of chitin particles, polymers of N-acetyl-D-glucosamine, in mice

Chitin particle-induced cell-mediated immunity is inhibited by soluble mannan: mannose receptor-mediated phagocytosis initiates IL-12 production

Challenges for nerve repair using chitosan-siloxane hybrid porous scaffolds

High-performance glucose biosensor based on chitosan-glucose oxidase immobilized polypyrrole/Nafion/functionalized multi-walled carbon nanotubes bio-nanohybrid film

Fabrication of Apigenin loaded gellan gum-chitosan hydrogels (GGCH-HGs) for effective diabetic wound healing

Silicone doped chitosan-acrylamide coencapsulated urea fertilizer: an approach to controlled release fertilizers

Paraquat-loaded alginate/chitosan nanoparticles: preparation, characterization and soil sorption studies

Novel genipin-cross-linked chitosan/silk fibroin sponges for cartilage engineering strategies

Degrading endocrine disrupting chemicals from wastewater by TiO 2 photocatalysis: a review

Graphene oxide-chitosan nanocomposite based electrochemical DNA biosensor for detection of typhoid

Sustainable fragrance cum antimicrobial finishing on cotton: indigenous essential oil

Preparation and characterization of collagen/chitosan/hyaluronic acid thin films for application in hair care

Chitosan-based microparticles for immobilization of TiO 2 nanoparticles and their application for photodegradation of textile dyes

Chitosan: a promising safe and immune-enhancing adjuvant for intranasal vaccines

Odontogenic differentiation potential of human dental pulp cells cultured on a calciumaluminate enriched chitosan-collagen scaffold

Chitosan-silica hybrid nanosorbents for oil removal from water

Oral hepatitis B vaccine: chitosan or glucan based delivery systems for efficient HBsAg immunization following subcutaneous priming

A nanotechnological approach to biosensors sensitivity improvement: application to organophosphorus pesticides determination

Embedment of silver into temperatureand pH-responsive microgel for the development of smart textiles with simultaneous moisture management and controlled antimicrobial activities

Heavy-metal ion sensors using chitosan-capped gold nanoparticles

Promotion of angiogenesis by sustained release of rhGM-CSF from heparinized collagen/chitosan scaffolds

An amperometric immunosensor based on multi-walled carbon nanotubes-thionine-chitosan nanocomposite film for chlorpyrifos detection

Antimicrobial and mechanical properties of beta-cyclodextrin inclusion with essential oils in chitosan films

The mucosal and systemic immune responses elicited by a chitosan-adjuvanted intranasal influenza H5N1 vaccine

Antioxidant edible films based on chitosan and starch containing polyphenols from thyme extracts

MitoQ loaded chitosan-hyaluronan composite membranes for wound healing

Gelatin/chitosan/hyaluronan ternary complex scaffold containing basic fibroblast growth factor for cartilage tissue engineering

Fabrication and evaluation of porous keratin/chitosan (KCS) scaffolds for effectively accelerating wound healing

A facile fabrication of multifunctional knit polyester fabric based on chitosan and polyaniline polymer nanocomposite

Thermosensitive chitosan-based hydrogels releasing stromal cell derived factor-1 alpha recruit MSC for corneal epithelium regeneration

Evaluation of immunostimulatory effects of N-(2-hydroxy) propyl-3-trimethylammonium chitosan chloride for improving live attenuated hepatitis a virus vaccine efficacy

N-(2-hydroxy) propyl-3-trimethylammonium chitosan chloride: An immune-enhancing adjuvant for hepatitis E virus recombinant polypeptide vaccine in mice

electrospun chitosan-gelatin biopolymer composite nanofibers for horseradish peroxidase immobilization in a hydrogen peroxide biosensor

Three-layered membranes of collagen/ hydroxyapatite and chitosan for guided bone regeneration

Cross-linked chitosan microspheres: preparation and evaluation as a matrix for the controlled release of pharmaceuticals

Oral drug absorption enhancement by chitosan and its derivatives

Controlled release of thymosin beta 4 using a collagen-chitosan sponge scaffold augments cutaneous wound healing and increases angiogenesis in diabetic rats with hindlimb ischemia

Ultraviolet protection cotton fabric achieved via layer-by-layer self-assembly of graphene oxide and chitosan

The use of single walled carbon nanotubes dispersed in a chitosan matrix for preparation of a galactose biosensor

Immunological aspects of chitin and chitin derivatives administered to animals

Hypoxia pretreatment of bone marrow-derived mesenchymal stem cells seeded in a collagen-chitosan sponge scaffold promotes skin wound healing in diabetic rats with hindlimb ischemia

Pure chitosan microfibres for biomedical applications

Bactericidal effect of iron oxide nanoparticles on Staphylococcus aureus

Graphite oxide/chitosan composite for reactive dye removal

A novel nanoparticle formulation for sustained paclitaxel delivery

Immobilization of lactate dehydrogenase within multiwalled carbon nanotube-chitos anhanocompo site for application to lactate biosensors

Amperometric cholesterol biosensors based on carbon nanotube-chitosan-platinum-cholesterol oxidase nanobiocomposite

Antitumor efficacy of doxorubicin released from crosslinked nanoparticulate chondroitin sulfate/chitosan polyelectrolyte complexes

Poly(poly(ethylene glycol) methyl ether methacrylate) grafted chitosan for dye removal from water

Trimethylated chitosan as polymeric absorption enhancer for improved peroral delivery of peptide drugs

Targeted delivery of doxorubicin to breast cancer cells by magnetic LHRH chitosan bioconjugated nanoparticles

Chitosan porous 3D scaffolds embedded with resolvin D1 to improve in vivo bone healing

Chitosan-induced programmed cell death in plants

Chitosan-based vaccine adjuvants: incomplete characterization complicates preclinical and clinical evaluation

Chitosan-fibrin nanocomposites as drug delivering and wound healing materials

Impact of chitosan-beeswax edible coatings on the quality of fresh strawberries (Fragaria ananassa cv Camarosa) under commercial storage conditions

Chitosan composites for bone tissue engineering-an overview

Chitosan-amylopectin/hydroxyapatite and chitosan-chondroitin sulphate/hydroxyapatite composite scaffolds for bone tissue engineering

Preparation and characterization of chitosancarbon nanotube scaffolds for bone tissue engineering

Optimization and evaluation of silk fibroin-chitosan freeze-dried porous scaffolds for cartilage tissue engineering application

Adsorption of dyes and heavy metal ions by chitosan composites: a review

Antioxidant activity of high molecular weight chitosan and N,Oquaternized chitosans

Chitosan-based biosorbents: Modification and application for biosorption of heavy metals and radionuclides

Chitosan-poly(vinyl alcohol)/attapulgite nanocomposites for copper (II) ions removal: pH dependence and adsorption mechanisms

Chitosan-alginate PEC membrane as a wound dressing: assessment of incisional wound healing

Chitosan/Prussian blue-based biosensors

Dog sciatic nerve regeneration across a 30-mm defect bridged by a chitosan/PGA artificial nerve graft

Acceleration of diabetic wound healing with chitosan-crosslinked collagen sponge containing recombinant human acidic fibroblast growth factor in healing-impaired STZ diabetic rats

Synthesis and characterization of collagen-chitosan-hydroxyapatite artificial bone matrix

Synthesis and evaluation of collagenchitosan-hydroxyapatite nanocomposites for bone grafting

Synergistic antimicrobial activities of natural essential oils with chitosan films

Repairing rat sciatic nerve injury by a nerve-growth-factor-loaded, chitosan-based nerve conduit

Novel chitosan-polycaprolactone blends as potential scaffold and carrier for corneal endothelial transplantation

Kinetics and functional effectiveness of nisin loaded antimicrobial packaging film based on chitosan/poly(vinyl alcohol)

Thermosensitive behavior and antibacterial activity of cotton fabric modified with a chitosan-poly(n-isopropylacrylamide) interpenetrating polymer network hydrogel

Development of chitosan/poly(vinyl alcohol) electrospun nanofibers for infection related wound healing

Chitosan and β-cyclodextrinepichlorohydrin polymer composite film as a plant healthcare material for carbendazimcontrolled release to protect rape against Sclerotinia sclerotiorum (Lib.) de Bary

Hyaluronic acid doped-poly(3,4-ethylenedioxythiophene)/chitosan/gelatin (PEDOT-HA/Cs/Gel) porous conductive scaffold for nerve regeneration

Emerging chitosan-based films for food packaging applications

Bridging peripheral nerve defect with chitosan-collagen film

Chitosan/silk fibroin-based tissue-engineered graft seeded with adipose-derived stem cells enhances nerve regeneration in a rat model

Application of a biosensor for monitoring of ethanol

Chitosan nanoparticles act as an adjuvant to promote both Th1 and Th2 immune responses induced by ovalbumin in mice

Thiolated chitosans: useful excipients for oral drug delivery

Differentiation of dental pulp stem cells into chondrocytes upon culture on porous chitosan-xanthan scaffolds in the presence of kartogenin

Fluorinated methacrylamide chitosan hydrogel systems as adaptable oxygen carriers for wound healing

Methods of gene delivery

Poly(D, L-lactide-co-glycolide) tubes with multifilament chitosan yarn or chitosan sponge core in nerve regeneration

Environmentally-friendly RF plasma treatment of Thai silk fabrics with chitosan for durable antibacterial property

The mechanical properties and osteoconductivity of hydroxyapatite bone scaffolds with multi-scale porosity

Preparation and properties of chitosan-coated NPK compound fertilizer with controlled-release and water-retention

Amperometric glucose biosensor based on layer-by-layer assembly of multilayer films composed of chitosan, gold nanoparticles and glucose oxidase modified Pt electrode

Mechanical properties and permeability of porous chitosan-poly(p-dioxanone)/silk fibroin conduits used for peripheral nerve repair

Removal of Cu(II) ions from aqueous water by l-arginine modifying magnetic chitosan

Integration of lysozyme into chitosan nanoparticles for improving antibacterial activity

Tissue engineering of cartilage with the use of chitosan-gelatin complex scaffolds

Gemcitabine conjugated chitosan and double antibodies (Abc-GC-gemcitabine nanoparticles) enhanced cytoplasmic uptake of gemcitabine and inhibit proliferation and metastasis in human SW1990 pancreatic cancer cells

Antibacterial hybrid materials fabricated by nanocoating of microfibril bundles of cellulose substance with titania/chitosan/silvernanoparticle composite films

Sub-micron-sized polyethylenimine-modified polystyrene/Fe3O4/chitosan magnetic composites for the efficient and recyclable adsorption of Cu(II) ions

Antioxidant activity of water-soluble chitosan derivatives

In vitro and in vivo evaluation of a biodegradable chitosan-PLA composite peripheral nerve guide conduit material

Synthesis and adsorption behavior of magnetic microspheres based on chitosan/organic rectorite for low-concentration heavy metal removal

Chitosan antimicrobial and eliciting properties for pest control in agriculture: a review

Chitosan-based coating with antimicrobial agents: preparation, property, mechanism, and application effectiveness on fruits and vegetables international

Optic nerve regeneration in polyglycolic acid-chitosan conduits coated with recombinant L1-Fc

Selective recognition of 5-hydroxytryptamine and dopamine on a multi-walled carbon nanotube-chitosan hybrid filmmodified microelectrode array

Durable antibacterial cotton modified by silver nanoparticles and chitosan derivative binder

Antibacterial property and biocompatibility of Chitosan/Poly(vinyl alcohol)/ZnO (CS/PVA/ZnO) beads as an efficient adsorbent for Cu (II) removal from aqueous solution

Electrochemical DNA biosensor based on graphene oxide-chitosan hybrid nanocomposites for detection of Escherichia coli O157:H7

The graphene oxide and chitosan biopolymer loads TiO 2 for antibacterial and preservative research

Carboxymethyl chitosan/ gelatin/hyaluronic acid blended-membranes as epithelia transplanting scaffold for corneal wound healing

Joint use of a chitosan/PLGA scaffold and MSCs to bridge an extra large gap in dog sciatic nerve

Induction of phytoalexin formation in suspension-cultured rice cells by N-acetyl-chitooligosaccharides

Removal of various cationic dyes from aqueous solutions using a kind of fully biodegradable magnetic composite microsphere

Mechanochemical modification of kaolin surfaces for immobilization and delivery of pesticides in alginate-chitosan composite beads

A practical glucose biosensor based on Fe 3 O 4 nanoparticles and chitosan/nafion composite film

Preparation and application of nanochitosan to finishing treatment with anti-microbial and anti-shrinking properties

Nerve conduits based on immobilization of nerve growth factor onto modified chitosan by using genipin as a crosslinking agent

A novel tyrosinase biosensor based on chitosancarbon-coated nickel nanocomposite film

Chitosan/collagen scaffold containing bone morphogenetic protein-7 DNA supports dental pulp stem cell differentiation in vitro and in vivo

Preparation and controllable release of chitosan/vanillin microcapsules and their application to cotton fabric

Release of doxorubicin by a folate-grafted, chitosan-coated magnetic nanoparticle

pH-responsive mesoporous ZSM-5 zeolites/ chitosan core-shell nanodisks loaded with doxorubicin against osteosarcoma

Avidin targeting of intraperitoneal tumor xenografts

Preparation, characterization, and cytotoxicity of various chitosan nanoparticles

Preventative vaccine-loaded mannosylated chitosan nanoparticles intended for nasal mucosal delivery enhance immune responses and potent tumor immunity

Application of silk fibroin/chitosan/nanohydroxyapatite composite scaffold in the repair of rabbit radial bone defect

Antioxidant properties of chitosan from crab shells

The effects of Pva/chitosan/fibroin (PCF)-blended spongy sheets on wound healing in rats

Effects of tumor microenvironments on targeted delivery of glycol chitosan nanoparticles

Enhanced wettability and moisture retention of cotton fabrics coated with selfsuspended chitosan derivative

Targeted delivery of doxorubicin-utilizing chitosan nanoparticles surface-functionalized with anti-Her2 trastuzumab

Chitosan nanocomposite films based on Ag-NP and Au-NP biosynthesis by Bacillus subtilis as packaging materials

Enhancement of Egyptian soft white cheese shelf life using a novel chitosan/carboxymethyl cellulose/zinc oxide bionanocomposite film

Self-assembled high-strength hydroxyapatite/ graphene oxide/chitosan composite hydrogel for bone tissue engineering

Chitosan films and coatings containing essential oils: The antioxidant and antimicrobial activity, and application in food systems

Development of Electrospun chitosan-polyethylene oxide/fibrinogen biocomposite for potential wound healing applications

Antimicrobial lysozyme-chitosan coatings affect functional properties and shelf life of chicken eggs during storage

Administration of growth factors for bone regeneration

Chitosan solution enhances both humoral and cell-mediated immune responses to subcutaneous vaccination

Intravesical immunotherapy of superficial bladder cancer with chitosan/ interleukin-12

Intratumoral immunotherapy of established solid tumors with chitosan/IL-12

Incorporation of heparin-binding proteins into preformed dextran sulfate-chitosan nanoparticles

Modification of wool fabric using prepared chitosan-cyanuric chloride hybrid

Cu(II) removal enhancement from aqueous solutions using ion-imprinted membrane technique

Preparation and application of a novel environmentally friendly organic seed coating for rice

Application of bioactive coatings based on chitosan for soybean seed protection international

Keratin-chitosan/n-ZnO nanocomposite hydrogel for antimicrobial treatment of burn wound healing: characterization and biomedical application

Amperometric Ethanol biosensors based on chitosan-NAD(+)-alcohol dehydrogenase films

Carbon nanotube-chitosan system for electrochemical sensing based on dehydrogenase enzymes

Oligochitosan induces programmed cell death in tobacco suspension cells

Repair of an articular cartilage defect using adipose-derived stem cells loaded on a polyelectrolyte complex scaffold based on poly(l-glutamic acid) and chitosan

Expression of gamma-aminobutyric acid receptors on neoplastic growth and prediction of prognosis in non-small cell lung cancer

Sorption of carbamazepine from water by magnetic molecularly imprinted polymers based on chitosan-Fe 3 O 4

Removal of selected pharmaceuticals from aqueous solution using magnetic chitosan: sorption behavior and mechanism

In-situ birth of MSCs multicellular spheroids in poly (L-glutamic acid)/chitosan scaffold for hyaline-like cartilage regeneration

Biocomposite scaffolds for bone regeneration: role of chitosan and hydroxyapatite within poly-3-hydroxybutyrate-co-3-hydroxyvalerate on mechanical properties and in vitro evaluation

Multifunctional glucose biosensors from Fe3O4 nanoparticles modified chitosan/graphene nanocomposites

Adsorption of pharmaceuticals on chitosan-based magnetic composite particles with core-brush topology

Preparation of chitosan-TiO 2 composite film with efficient antimicrobial activities under visible light for food packaging applications

A composite hydrogel of chitosan/ heparin/poly (gamma-glutamic acid) loaded with superoxide dismutase for wound healing

Experimental study on chitosan mediated insulinlike growth factor gene transfection repairing injured articular cartilage in rabbits

FK506-loaded chitosan conduit promotes the regeneration of injured sciatic nerves in the rat through the upregulation of brain-derived neurotrophic factor and TrkB

Efficacy of thermosensitive chitosan/betaglycerophosphate hydrogel loaded with beta-cyclodextrin-curcumin for the treatment of cutaneous wound infection in rats

Use of chitosan conduit combined with bone marrow mesenchymal stem cells for promoting peripheral nerve regeneration

Nanoparticles based on the complex of chitosan and polyaspartic acid sodium salt: preparation, characterization and the use for 5-fluorouracil delivery

Receptor mediated gene delivery by folate conjugated N-trimethyl chitosan in vitro

Exploring advantages/disadvantages and improvements in overcoming gene delivery barriers of amino acid modified trimethylated chitosan

Surface molecularly imprinted polymer of chitosan grafted poly(methyl methacrylate) for 5-fluorouracil and controlled release

Development of hybrid-type modified chitosan derivative nanoparticles for the intracellular delivery of midkine-siRNA in hepatocellular carcinoma cells

Adsorption of acid dyes from aqueous solutions by the ethylenediamine-modified magnetic chitosan nanoparticles

Comparative study of porous hydroxyapatite/chitosan and whitlockite/chitosan scaffolds for bone regeneration in calvarial defects

Functional poly (epsilon-caprolactone)/chitosan dressings with nitric oxide-releasing property improve wound healing

Preparation, characterization, adsorption kinetics and thermodynamics of novel magnetic chitosan enwrapping nanosized γ-Fe2O3 and multi-walled carbon nanotubes with enhanced adsorption properties for methyl orange

Repair and regeneration of lumbosacral nerve defects in rats with chitosan conduits containing bone marrow mesenchymal stem cells

Skin derived precursor Schwann cell-generated acellular matrix modified chitosan/silk scaffolds for bridging rat sciatic nerve gap

Adsorption of three selected pharmaceuticals and personal care products (PPCPs) onto MIL-101(Cr)/natural polymer composite beads

Application of bioactive coatings based on chitosan for artichoke seed protection

In vitro and in vivo evaluation of the chitosan/Tur composite film for wound healing applications

Chitosan induces Ca 2+ -mediated programmed cell death in soybean cells

Acknowledgment The authors are grateful to Subbaratnam Muthukrishnan for critically reading the manuscript.

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