key: cord-0286214-48ivod8a
authors: Bayan, Sayan; Adhikari, Aniruddha; Pal, Uttam; Ghosh, Ria; Mondal, Susmita; Darbar, Soumendra; Saha-Dasgupta, Tanusri; Ray, Samit Kumar; Pal, Samir Kumar
title: Development of Tribo-Electroceutical Fabrics for Potential Application in Self-sanitizing Personal Protective Equipment (PPE)
date: 2021-02-24
journal: bioRxiv
DOI: 10.1101/2021.02.23.432624
sha: 81af33915cd0cb596c97b97c49121434a9a16dc3
doc_id: 286214
cord_uid: 48ivod8a

Attachment of microbial bodies including coronavirus on the surface of personal protective equipment (PPE) is found to be potential threat of spreading infection. Here, we report the development of a novel tribo-electroceutical fabric (TECF) consisting of commonly available materials namely Nylon, and Silicone Rubber (SR) for the fabrication of protective gloves on Nitrile platform, as a model wearable PPE. A small triboelectric device (2 cm × 2 cm) consisting of SR and Nylon on Nitrile can generate more than 20 volt transient or 41 µW output power, which is capable of charging a capacitor up to 65 V in only ∼50 sec. The novelty of the present work relies on the TECF led anti-microbial activity through the generation of an electric current in saline water. The fabrication of TECF based functional prototype gloves can generate hypochlorite ions through the formation of electrolysed water upon rubbing them with saline water. Further a computational modelling has been employed to reveal the optimum structure and mechanistic pathway of anti-microbial hypochlorite generation. Detailed anti-microbial assays have been performed to establish effectiveness of such TECF based gloves to reduce the risk from life threatening pathogen spreading. The present work provides the rationale to consider the studied TECF, or other material with comparable properties, as material of choice for the development of self-sanitizing PPE in the fight against microbial infections including COVID-19.

The respiratory diseases such as COVID-19 can spread from the virus-laden respiratory droplets emerging out from the coughing or sneezing of any infected person. 1 In practice, health workers are continuously exposed to such life threatening biological agents and can become potential carriers of the diseases. To minimize the life risk of the health workers the use of Personal Protective Equipments (PPEs) in the form of gowns, face masks, gloves, goggles, face shields etc. are highly recommended. 2 The proper use of PPEs is considered as a common precautionary measure to reduce the risk of contamination from blood or other body fluids of patients. However, during the COVID-19 pandemic, the whole world has experienced an unprecedented challenge in PPE supply for active patients as well as health workers. [3] [4] [5] Consequently it has been realized that the long duration use of PPEs has led to the adverse effect due to the negligence of hand hygiene practices and recycling following the disease protocols in regular intervals. For disinfection and reuse of PPEs a number of routes such as exposure to heat (autoclave), ultraviolet ray-C, alcohol, washers etc. have been recommended. 5 However, most of these methods are time consuming and face affordability issues by economically weaker sections of the society. So, the development of self sanitizing PPEs can be a novel and alternate solution for the all sections of the society including the health workers.

The contact electrification process (also known as tribo-electrification) has attracted the attention of medical research community for healthcare application. [6] [7] [8] The triboelectrification involving the phenomena of tribology with subsequent charge transfer/exchange has led to the development of energy harvesting devices called triboelectric nanogenerators (TENG). [9] [10] [11] [12] [13] In this context, a TENG can be exploited as a health monitoring sensor as well as power generator, where the electrical signals in response to a stimuli originating from human body are able to power up energy storage devices that can operate the sensor. 6, [14] [15] [16] [17] [18] For example, activities like muscular motion or abdominal respiration, where the body displacement is significant, can be easily detected by TENG 7, 8 and can power the sensing systems to detect heart beat, body temperature, and lactate concentration etc. [14] [15] [16] The potential applicability of TENG in antibacterial wearable systems has also been reported. [19] [20] [21] The fabrication of self-powered filter by combining TENG and photocatalysis technique has been found to be efficient to protect from harmful organic vapour pollutants, which are believed to be the cause of diseases like asthma and chronic bronchitis. 19 On the other hand, antibacterial composite film-based TENG has been demonstrated to be useful to protect athlete's foot from fungal infection effectively. 20 Excellent antibacterial activity along with capability of removing fine particle (PM2.5) by the virtue of cellulose fiber based TENG has also been reported. 21 Here, we first report the development of a tribo-electroceutical fabric (TECF) for the fabrication of personal protective equipment like protective gloves, as a representative wearable PPE against deadly viruses in a situation like COVID 19 pandemic. We demonstrate the tribo-electroceutical fabric (TECF) based gloves deploying the virtue of contact electrification using commonly available materials like nylon, teflon or silicone rubber (SR). The TECF based on nylon or SR, act as contacting materials on nitrile platform, a common material for hand gloves, and can generate electrical power. The developed TECF based gloves when rubbed in presence of saline water produce hypochlorous acid or hypochlorite ions, which lead to their self-sanitization while using for a longer duration. The production of the hypochlorite ions has been characterized in vitro through a redox dye degradation as well as colorimetric test. In addition, theoretical modelling has been performed to establish the concept of electrolysis and the consequent formation of hypochlorous acid. Finally, the efficacy of the TECF has been revealed by demonstrating the sterilizing effect through killing a vast majority of Pseudomonous auregionosa bacteria, which has similarities with SARS CoV-2 virus. The present investigation suggests that TECF based gloves can effectively reduce the chance of contamination from microorganisms that are spread by direct or indirect contact through a self-sanitization process, making them attractive to prevent further spread of the diseases from an otherwise uninfected personnel.

1. Development of triboelectric materials: Nylon layer, one of the tribo-eletroceutical surfaces in the present work, was prepared using commercially available nylon beads (~ 0.04 gm), which were mixed in ~ 10 ml acetone solution and stirred at ~ 400 rpm for 15 min by maintaining a temperature of 50 o C. The resulting viscous solution was drop casted on commercial nitrile gloves and was allowed to dry in a hot air oven. Silicon rubber (SR) layer, acting as the counter tribo-material, was prepared from liquid SR and a catalyst (e.g. dibutyl tin dilaurate), which were mixed in 13:1 ratio and casted on nitrile gloves. The desired prototype of nylon and SR coated nitrile gloves were obtained upon curing the samples in a hot air oven at ~ 70 o C.

For investigating the triboelectric characteristics, approximately 2 cm x 2 cm nylon and SR coated nitrile sheets were attached to the adhesive aluminium tape. An adhesive aluminium foil was used to make the back contact of the triboelectric layers. An indigenously developed system with two wooden slabs separated by four springs at the corners was deployed to measure the triboelectric characteristics under tapping conditions. The triboelectric layers were attached to the two inner faces of the system so that the layers could come in contact with each other under pressed condition. Further for sliding/rubbing mode, the triboelectric layers were fixed to a polyethylene terephthalate (PET) platform with a spacer such that the horizontal movement can be executed.

The electrical properties of the nanogenerators were studied using a digital oscilloscope (Scientific) and Keithley 2450 source meter. Optical absorbance was recorded using an UV-Visible spectrophotometer (Jasco) at room temperature.

For dye degradation experiment, the TECF based gloves were submerged in methylene blue solution (4.5 M) in normal saline (0.9% NaCl) condition. The system was continuously rubbed and the absorbance was measured from aliquots collected from the sample at 5 min The bacteria cells after treatment with TECF, were stained with DAPI and PI. The DAPI can stain all cells while the PI can only stain the living cells, and thus the red/blue ratio was obtained to assess the survivality of E. coli.

The fabricated TECF was simulated using the electrostatic module of the COMSOL Multiphysics simulator. The potential difference (U) was obtained by solving the equation: U = σ∆d/ε0, where σ is the surface charges density; ε0 is the vacuum permittivity and ∆d represents the gap distance between the two tribo-materials with electrodes. 22 In the simulations, a charge density of −10 nC/m 2 was assumed on the SR layer surface. The bottom electrode was taken as a reference in the simulation and was grounded for the purpose. 23, 24 The secondary current distribution through the electrolyte is simulated using the electrochemistry module of COMSOL. Electrolyte in between the two triboelectric materials can be modeled as an electrolysis cell with an anode and a cathode. Chlorine/chloride reduction (Eeq,Cl) potential of +1.23V was applied to the anode where the chlorine gas evolution takes place. Water/hydrogen reduction potential (Eeq,H) of -0.828V was applied to the cathode where reduction of water to hydrogen takes place releasing also hydroxide ions. Therefore, the thermodynamically equilibrium cell potential becomes, Eeq,cell = Eeq,Cl-Eeq,H = +2.058V. However, at this potential, reaction does not take place due to some kinetic loss.

The chloride oxidation reaction at anode is very fast (reversible reaction) and departs very little from the equilibrium potential. On the other hand, hydrogen evolution reaction is inherently slow (irreversible reaction and the cathode material not being a perfect catalyst results in a kinetic limitation) and requires a potential, Epol, significantly greater in magnitude than the equilibrium potential (Eeq,cell) to achieve a reasonable current density to make up for the kinetic losses and drive the reaction. This potential is called the overpotential and the electrode is said to be polarized. Here, the cell is polarized to +10V vs the cell equilibrium to drive the reaction. Thus, the overall cell potential or the electrode to electrode potential becomes Ecell = Eeq,cell + Epol = +12.058V. Common Butler-Volmer equation 25 was used to parameterize the slow hydrogen evolution reaction at cathode with an exchange current density of 1mA/m 2 on the reacting surfaces. Electrolyte conductivity of the free electrolyte is defined as 5 S/m. A stationary study was performed to describe the steady state current in the system.

Quantum chemical study of Cl2 splitting and HOCl formation was carried out with B3LYP exchange correlation functional 26 and 6-31g(d) basis set on all atoms as implemented in Gaussian 16 software. 27 Bond distance between two chlorine atoms was perturbed to obtain the potential energy diagram in presence of explicit water molecules.

Structure and sequence of the cell surface adhesion lectin protein lecA of Pseudomonous auregionosa was obtained from Protein Data Bank (PDB ID: 4YWA). Structure and sequence of the receptor binding domain (RBD) of SARS-CoV-2 was also obtained from the PDB (ID: 6LZG). Sequence alignment was performed using Clustal Omega web server. 28 Similar amino acids in the binding sites of the two proteins were mapped using PyMOL molecular graphics software.

Initially the triboelectrical output of the TECF pairs has been investigated using a indigenously built spring based experimental arrangement. Figure 1(a) shows the schematic representation of the experimental set-up used for measuring the electrical output of triboelectric devices. The mechanical pressing and releasing actions of the spring based system lead to the contact and separation states of two layers. Initially, the triboelectrification has been investigated in three TECF pairs: nitrile-nylon, teflon-nylon and SRnylon. The active materials have been chosen based on their affinity towards positive and negative charges following triboelectric series. As shown in Figure 1 With an aim to deploy the TECF in wearable kits, the performance of the two triboelectric materials has been checked upon rubbing/sliding action. The output voltage under different rubbing arrangements of the contact layers are presented in Figure S4(a,b) , while the charging profile of a capacitor under rubbing actions with different frequencies is shown in Figure S4 (c). Next, to generate a short circuit current between the tribo-layers, the contactseparation experiments have been performed in sliding mode with an intermediate medium between the layers. The results of the sliding experiments in presence of deionized (DI) water and sodium chloride (NaCl) electrolyte solution are presented in Figure 1(d) . In contrast to air medium, the voltage developed across the capacitor is quite low when the sliding experiments are carried out in presence of DI water and NaCl solution. In both situations, there is a signature of saturation. It indicates that the liquid medium present within the two dielectrics, experiences two opposite type of charges at the two liquid/dielectric interfaces and thus allows substantial electron flow leading to a situation of internal short circuit condition.

However, owing to the finite resistance of water or electrolyte solution, the potential doesn't drop to zero and thus a saturated value of voltage is maintained across the capacitor.

To visualize the contact electrification process in the presence of varying medium (dielectric) between the tribo-layers, finite element simulation has been carried out using COMSOL Multiphysics software. Figure 2(a,b) shows the potential distribution between the two electrodes in air medium with a varying separation of 1.00 and 10.0 mm. It is observed that a maximum potential difference of ~ 18 V can be achieved when the electrode separation reaches 10 mm. This is because, as the two layers are separated, mechanical work has to be done against the electric field and thus results in the increase in potential difference between the top and bottom electrodes. On the other hand, the potential distribution becomes negligible, under the same condition for the two triboelectric materials when the intervening medium is replaced from air to water or an electrolyte solution (Figure 2(c) ). These calculated results are in agreement with our observed experimental results, with the output voltage diminishing when the contact electrification experiment is performed in presence of water or electrolyte medium, as shown in Figure 1(d) . It is expected that the internal short circuit leads to the electrolysis of the electrolyte solution, where the oxidation of chloride to chlorine takes place at the anode. On the other hand, the reduction of water into hydrogen gas takes place at the cathode along with the release of hydroxide ion. The solution of the secondary current distribution calculation (Figure 2(d) ) represents the electrolyte potential in the cell and reveals a higher electrolyte potential in the anode side of the cell. The arrow plot indicates the direction of the current flowing from anode to cathode. Electrolyte to electrode potential difference at the cathode is 1.72 V, which corresponds to the kinetic loss of the potential drop. Owing to this kinetic loss in the system, a large over-potential is required to drive the reaction. Nevertheless, the evolution of the circulating current in TECF is quite attractive for achieving self-sanitation effect, which will be discussed later.

The TECF has been successfully introduced in a functional prototype of personal protective equipment in the form of hand gloves. In this context commercial nitrile gloves have been modified by coating nylon and SR dots, as shown in the photograph presented in Figure 3 (a).

The brighter and larger dots (size ~ 0.8-2.0 cm 2 ) represent SR, while the lighter ones correspond to nylon (size ~ 03-0.5 cm 2 ). With such a design, the rubbing or tapping of the two hands generate triboelectric charges. Further the coating of the gloves in a dotted fashion allows the triboelectric charge generation even using a single hand, when the fingers and palm of the user come in contact with each other. Particularly the design presented in Figure   S5 is useful for single hand operation. Figure 3 Figure 3 (c) shows the absorption spectra of the MB dye before and after rubbing with TECF based gloves. In the absorption spectra of virgin MB (rubbing time zero), a prominent peak at ~ 662 nm and the shoulder at ~ 621 nm indicates the absorption due to monomer and dimer, respectively. 30 It is noticed that the rubbing for a longer duration leads to the lowering of the absorption peak of MB indicating the degrading tendency of the dye. The degradation percentage has been extracted from the residual MB % as calculated from the absorbance values considering the relation:

where Abs represents the absorption at a particular wavelength. As observed in Figure 3 products are produced as compared to direct electrolysis process. 31 In this case, it is expected that the active chlorine in the form of hypochlorous acid or hypochlorite ions act as the oxidizing agent to degrade MB dye. The dye degradation experiment has been further confirmed with nylon and teflon layers as presented in Figure S6 (a,b) . Apart from the gradual lowering of the MB absorption peak, the development of an absorption peak of leucomethylene blue (at ~ 268 nm) confirms the degradation of the MB solution ( Figure S6 (c)). In order to ensure the role of the short circuit current, similar experiment has been performed with teflon-teflon contact system. In this case, the signature of leucomethylene blue related peak is absent in the absorption spectra, as shown in Figure S6 The absorbance spectrum of the obtained pinkish solution (Figure 4(b) ) shows the presence of a doublet peak with maxima at ~ 511 and 551 nm, which is in accordance of the absorption peak of Würster dye. 32 The reduction of the Würster dye using a ferrous reducing agent via titrimetric method has led to the reappearance of the initial colourless solution. The disappearance of the doublet peak in the absorbance spectrum (Figure 4(b) ) indicates the regaining of the initial form of DPD. Additionally, such titrimetric analysis indicates the presence of ~ 5 ppm of HOCl in the salt solution subjected to 5 min slow rubbing with TECF based gloves. It is worth to mention that the concentration of HOCl produced in this process is not harmful to human being even if it comes in direct contact with the skin. 33 Next, to understand the formation of HOCl with TECF based gloves, the ongoing electrolysis process has been revisited. During the electrolysis, water takes up electrons to produce hydrogen gas and hydroxyl ions (OH -) at the cathode following equation (1) . The OHor Cl -, present in the saline water gets attracted to the anode. At the anode, Clreleases an electron to form chloride radicals (Cl) and the combination of two Cl forms chlorine gas (Cl2), as in equation (2). Such Cl2 gas upon splitting from the Cl-Cl bond, can combine with water to form HOCl following equation ( For demonstrating the antibacterial activity P. auregionosa has been investigated owing to its similar amino acids in the binding sites of the proteins as that of SARS-CoV-2 virus. As can be seen in Figure 5 (a-c), there is significant similarities in the amino acid sequence in lecA of P. aeruginosa lectin and spike RBD of SARS-CoV-2. In order to evaluate antibacterial efficacy of the developed TECF based gloves, the plate count method has been deployed. It is evident from the plate count assay (Figure 6(a,b) ) that in TECF based gloves, the bacterial growth is ~69% lower compared to control (p<0.001) and ~64% lower compared to control TECF (nylon-nylon) based system (p<0.001). Thus it is quite evident that TECF based gloves can hinder the growth of P. auregionosa through their anti-microbial activity and hence can also be expected to be effective for viruses like CoV-2. In a similar fashion, the anti-microbial activity of the TECF based gloves has been examined for E. coli. The effectiveness of TECF can be realized from the perturbed growth of the bacteria as can be observed in the plate count assay (Figure 6(c,d) ). Furthermore, in order to evaluate inhibition kinetics of the nanobiocomposites under dynamic condition as a function of time, submerged culture or growth kinetics method is adopted. Figure 6 (e) clearly shows that the growth of E.

coli subjected to the TECF is significantly retarded. The growth rate is ~6 times lower in case of TECF compared to both usual control and TECF control ( 

We report on the fabrication of tribo-electroceutical fabric (TECF) based hand gloves with self sanitization ability. The triboelectric charges from Silicone Rubber (SR)-Nylon pair has been deployed to activate the self sanitization process. The power generation ability of the SR-Nylon pair has been understood upon investigating the contact electrification process. 

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