key: cord-0825427-l5i6w96j authors: Monzamodeth, R.S.; Román-Roldán, N.I.; Hernández-Morales, B.; Puente, I.; Flores, O.; Castillo, F.; Campillo, B. title: The feasibility of masks and face shields designed by 3D printing makers; some considerations of their use against the COVID-19 date: 2021-12-31 journal: Mater Today Proc DOI: 10.1016/j.matpr.2021.12.503 sha: 5baee9728c21e2ac3e3325a7c74be415a2d8fb55 doc_id: 825427 cord_uid: l5i6w96j The use of mask and face shield has been established as one of the main preventive measures for the control of COVID 19 spread. In Mexico, as well as in other regions of the world, 3D printing has been employed for the design and production of masks and face shields as personal protective equipment (PPE). These models have been fabricated mainly by the makers, industries, and university communities; therefore, it is necessary to analyze the feasibility of the 3D printed PPE to understand its advantages and limitations. In this work, some characteristics of masks and face shields fabricated by additive manufacturing were studied to explore their viability as protection against flow fluids similar to human sneeze. In the present paper, the PPE was designed, and 3D printed utilizing three types of polylactic acid (PLA) as base material. The morphology and the surface elemental analyses of sectioned samples were analyzed by scanning electron microscopy (SEM) and energy dispersion x-ray spectroscopy (EDS). Showing spacing between printed layers, porous areas, and dispersed copper particles. On the other hand, a computational fluid dynamics (CFD) simulation was carried out, the results demonstrated the importance of using PPE for protection of a possible exposure to a “contaminated” aerosol and human sneeze. Based on the abovementioned results, it is possible to consider the commercial PLA as suitable material for the manufacturing of PPE due to its capability to be disinfected employing isopropanol, ethanol, or commercial disinfectants. The COVID 19 disease has affected a large part of the countries of the world, to the point that on March 2020 was classified by the world health organization (WHO) as a pandemic. The serious complications associated with the disease include pneumonia, mainly in adults; the population that is at higher risk is composed of those who suffer chronic diseases such as diabetes, hypertension, and obesity [1, 2] . Because the spread of COVID 19 can occur from direct contact with surfaces and through particles in the air, a prompt response was necessary to counteract the pandemic [1] [2] [3] [4] . This added to the complexity of identifying asymptomatic and pre-asymptomatic persons through large-scale tests [2] . Consequently, the new disease has caused a worldwide shortage of personal protective equipment (PPE) [1, [2] [3] [4] [5] [6] [7] [8] [9] , mainly for healthcare professionals. Several work teams around the world have developed PPE using additive manufacturing technology, having significant contributions in the fabrication of masks, face shields, swabs for PCR analysis, ventilators, door holders, respiratory valves, among other components for medical applications [2] [3] [4] [5] [6] [7] [8] . The advantage that 3D printing has shown for supporting healthcare professionals is based on its capability to manufacture prototypes and functional equipment in a very short time. The global industrial, university and "makers" community has shared several open-source designs [1, [2] [3] [4] [5] [6] [7] [8] . The most employed material for 3D printing is polylactic acid (PLA), which is a low-cost, commercially available, and relatively biodegradable polymer. It has been implemented for various applications such as engineering, medical, recreational areas, among others [10] [11] [12] [13] [14] . PLA has adequate mechanical properties to develop prototypes or components that do not required high strength demand. Furthermore, considering some important features of PLA for continuous use, such as filtering, cleaning, and low allergenic skin response, it can be employed for medical purposes. The viability of PLA to produce masks and face shields has been reported, it is not permeable to sub-microscopic particles; in addition, it can be commonly disinfected using ethanol, isopropanol, or commercial disinfectants [1, 4] . In the present work, masks and face shields were design and manufactured by 3D printing, introducing modifications to the original mask design and its performance. Besides, morphology analysis and an elemental mapping were carried out by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS), respectively. On the other hand, a model was computed utilizing computational fluids dynamics (CFD) to demonstrate the importance of using face shields and masks. Throughout this hard current situation, this research team has supported nearby clinics with PPE and by communicating the correct use of 3D printed equipment, as well as its limitations. A general process of the present work that includes the design and manufacture of the masks and face shields, the material characterization and fluid flow simulation by CFD is shown in Figure 1 . Starting with the CAD design of the masks and face shields followed by the 3D printing, using three different PLA types. Subsequently, samples were sectioned from the manufactured PPE to analyze the surface morphology of the PLA by SEM, as well as its elemental constituents by EDS. The masks and face shields were designed by CAD software, the "STereoLithography" (STL) formats were obtained and finally G-code was developed employing open-source software. The manufacturing of the 3D printing designs was performed with low-cost commercially available 3D printer equipment and three different types of PLA were used: PLA-Copper, PLA-Wood and PLA-Standard; the 3D printing parameters are shown in Table 1 Regarding the breathing valve of the mask, it was cancelled due to several world recommended suggestions. However, the "threaded plug" (TP) designed was preserved and instead commercially available copper membranes (CM) and conventional filters (CF) were placed in the resulting space, as shown in Figure 3 . Copper can provide additional protection to the filters because eliminate pathogenic organisms such as coronavirus [16] in less time compared with other materials including steels, cloth, and plastics [17] [18] [19] [20] . The geometric model was imported and generated in ANSYS DesignModeler with a compatible extension. An enclosure was generated to cover and simulate the external conditions which assist to define the boundary conditions (see Figure 4a ). The dimensions of the mask structure considered two main values, one in front-structure contact with 150 mm long and the other structure-acetate with 208 mm long, both having a thickness of 10 mm and separated by 40 mm between themselves. Furthermore, the mask has a width of 147 mm, a length of 197 mm and a thickness of 1 mm. Meshing is a fundamental part of the simulation process to solve the Navier-Stokes equations which model fluid dynamics. The geometric model (domain) was divided into elements, creating an unstructured mesh. According to the shape of the geometrical model described above, the type of element that best adapts to the mask was the tetrahedron. The mesh was fabricated with ANSYS Mesh tools, applying an element size refinement of 0.004 m to meet mesh quality requirements. The resulting mesh is comprised of 6.5 million elements with a bias mesh metric of 2.6831e-09 minimum and 0.9712 maximum, which meets minimum mesh quality requirements. These values reduce computation time and provide adequate results. The computed systems were head-mask (HM), head-face shield (HF) and headmask-face shield (HMF). Mesh details are presented in Figure 4b . The geometric model contained the mask and face shield placed on a human head. In this study, boundary conditions previously described in the literature [21] [22] [23] [24] were applied. The flow direction of ambient air (at constant temperature) is perpendicular to the mask. In this case study, it was considered a frontal exposure of the model to a human sneeze with a velocity of 10m/s, also, a hypothetical uniform distribution of the fluid. The conditions are shown schematically in Figure 5 and the actual values are listed in Table 2 . It was assumed that the inlet air velocity is equally distributed throughout the area. The mathematical model was based in equations considering 3D, steady state, incompressible fluid, isothermal conditions, and laminar flow; the average speed of a human sneeze [21] [22] [23] [24] was also incorporated in the boundary conditions. Thus, fluid flow can be modeled by the momentum conservation and the mass conservation equations, Eq.1 and Eq.2, respectively: Where : fluid density; : fluid velocity; : static pressure; : gravitational body force; : dynamic viscosity of fluid [25] . Mask samples were taken to perform morphological analysis of the different printed materials and to observe the structure of the material after it was manufactured. EDS elemental mapping was carried out to observe possible copper particles, the equipment used was a SEM JEOL, 5900 LV coupled with an Inca Oxford EDS detector. The masks and face shields were fabricated implementing the manufacturing parameters as mentioned in the CAD design and 3D printing section. The printed designs are shown in Figure 6a and 6b; these were used for their subsequent SEM-EDS characterization. The manufactured items were molded using human face models (see Figure 6c ); this process was carried out using hot air at ~60 °C as a constant temperature. (1) Velocity inlet Velocity outlet Enclosure As mentioned in the CFD model section, a simulation was performed to demonstrate the efficiency of masks and face shields against the flow caused by a human sneeze. Although the model had many assumptions (isothermal, steady state, and laminar flow conditions) it is considered to be useful in demonstrating the effectiveness offered by this type of protection (in general, not necessarily 3D printed PPE). In Figures 7a, 7b and 7c the HM, HF and HMF systems are presented. The zone in red represents fluid flow without significant interaction with the solids (keeping its speed constant). The other colors represent the interaction of the air with the solids; it is possible to observe that the mask fulfills its protective function with respect to the mouth and nose; however, the eyes are exposed to the potentially contaminated fluid. Figures 7b and 7c show the wide protection of the face shield, it is possible to suggest its use at crowded places. The protection provided by the face shield is more efficient because it covers the entire face. In Figure 7d a bottom view of the face shield is shown; fluid flow can be seen surrounding the model. Finally, in Figure 7e two fluid flow planes are shown in an isometric view, demonstrating the extensive protection provided by the modified design. The former results suggest that the use of the PLA-Copper mask added with filters with copper membranes could be considered as a good protection against the frontal fluid of a human sneeze. However, due to the behavior of the fluid, it may be possible that viruses and bacteria get trapped in the filters and nearby regions. The mask designed could provide a better protection due to the use of copper, decreasing the active time of the virus due to the inhibit action of copper [16] . In this case, the SARS-CoV-2 that managed to get trapped in the copper membranes and PLA-Copper regions could be inactivated in less time than the home-made masks or those made with common materials [17] [18] [19] [20] . The main idea of the preceding inhibition is illustrated in Figure 8 , it is evident that this a hypothesis of the great advantage of using membranes and PLA added with copper. The SEM analyses for different printed materials are shown in Figure 9 ; it can be observed the internal structure of the printed designs, showing the separation between printed layers, porous areas, and dispersed particles in the three PLA materials (indicated with arrows). In the case of PLA-Copper (see Figures 9a and 9d) , a uniform printed product is observed, that is, the spacing between layers has good quality interlayer which helps to avoid porosity. In Figures 9b and 9e corresponds to the PLA-Wood, this material appears to contain porosity on its surface and lower quality of spacing and surface finish compared with the PLA-Copper. Finally, PLA-Standard material is shown in Figures 9c and 9f , it has a greater spacing between layers than the others printed materials which represents a decrease in interlayer quality. Despite the layers spacing, the filtering capacity can be more efficient than home-made fabric masks since these contain a wide pore distribution [26] . Since the PLA is composed by (C3H4O2)n it was expected that the EDS analysis show the carbon and oxygen elements. In addition to the above mentioned, small concentrations of other elements were expected because the PLA-Copper and PLA-Wood materials were also used. In Figure 10a the EDS analysis corresponding to PLA-Copper shows the copper concentration. The amount of copper detected was low; however, it is very helpful against SARS-CoV-2 since it can inhibit the virus in less time compared to materials such as steels, polymers, cloth, among others [16] [17] [18] [19] . On the other hand, in Figures 10b and 10c the mappings corresponding to PLA-Wood and PLA-Standard are presented. In both cases, silicon particles are observed, this may be due to contamination during handling of the manufacturing surface or the presence of dust. The present work shows the viability of 3D printed mask and face shields for daily use as a means of protection against the spread of COVID 19. Several published works reported various types of masks and face shields as immediate response to the current emergency [2] [3] [4] [5] [6] [7] [8] . Some of the reports mention advantages that are mentioned below. The implementation of this type of masks and face shields can be mass produce with the possible versatile manufacture of customized PPE [1] [2] [3] [4] [5] [6] [7] [8] . The ease of being 3D printing by engineers and non-expertise in the area is an advantage this type of technology [10] [11] [12] [13] [14] , also, their low cost in relation to their long lifetime. Additionally, the possibility of 3D printed masks to be cleaned using simple methods such as the application of isopropanol [1, 4] . It is important to mention some characteristics and projections on the mask, these mainly lie in its ability to be reusable, and it can be use intensively through daily application of disinfectants. Also, the use of PLA-Copper as base material and filters with copper membranes can offer additional protection to the user as this element is capable to inactive the virus in less time than conventional mask-making materials [16] [17] [18] [19] [20] . However, a disadvantage considered lies in the 3D printing time of each PPE, which makes the mass production of PPE impossible. In addition, the effect of long-time exposure of the material to human skin must be carefully analyzed. In general, the current pandemic due to COVID 19 is still a delicate issue due to the new strains of the virus that have been reported in several countries and because of the need for daily work in many sectors of the world population. In México, ~3.9 million confirmed cases, ~2.3 million people recovered and unfortunately ~284 thousand deaths have been reported up to 10/17/2021 (see Figure 11 ) [27] . The employ of 3D printed personal protective equipment has been widely discussed by several authors, agreeing that the use of masks and face shields is essential to reduce the virus spread [1] [2] [3] [4] [5] [6] [7] [8] . Also, some other works suggest supply medical grade masks for the general population due to their greater filtering efficiency. Recently, the United Kingdom's prime minister reported a new variant found in London, which may be associated with higher mortality. Therefore, health safety measures should not be lowered since this virus can mutate and be more contagious or deadly [28] . In this work, the use of masks and face shields is always recommended outside the home since it is the second-best protection, being confinement the first one. Regarding the masks and face shields reported in this work, several PPE have been donated to healthcare professionals and to the general population (see Figure 12 ). The recommendations for using the 3D printed personal protective equipment lie in its use combined with masks of different filters such as KN95, constant sanitization and filter change. The feasibility of the use of masks and face shields for personal protective equipment (PPE) against COVID 19 was studied. Masks were designed based in the NanoHack Copper3D initiative, modifying the design, cancelling the breathing valve, and placing additional filters with copper membranes. In addition, face shields were also manufactured to complement the PPE. Morphology and elemental analyses by SEM/EDS were carried out, it was confirmed the presence of copper in the PLA-Copper. On the other hand, the CFD model computed, considering air flowing at a human sneeze speed, was able to demonstrate the protection provided by the 3D printed PPE. It was possible to contribute to the medical community functional masks and face shields, whose main advantage is the use of copper either in the base materials and in the filters. Furthermore, the use of PLA-Copper and copper-added membranes represent a boost for the inhibition of the virus. The proposed design can be considered similar in operation with the basic designs reported by various authors; however, the advantage lies in the use of copper as a base material a b a and added to an extra compartment, the latter replace the common valve. These characteristics are very important for medical personnel who are in direct contact with asymptomatic, pre-asymptomatic and confirmed COVID 19 patients. Review on 3D printing: Fight against COVID-19 Epidemiology of COVID-19 in Mexico, symptomatic profiles and presymptomatic people COVID-19 and the role of 3D printing in medicine. 3D Printing in Medicine Polylactic acid as a suitable material for 3D printing of protective masks in times of COVID-19 pandemic Impact of 3D printed medical equipment on the management of the Covid19 pandemic 3D Printing to Support the Shortage in Personal Protective Equipment Caused by COVID-19 Pandemic 3D printing for development of medical equipment amidst coronavirus (COVID-19) pandemic-review and advancements 3D printing of face shields to meet the immediate need for PPE in an anesthesiology department during the COVID-19 pandemic Filtration Efficiency, Effectiveness, and Availability of N95 Face Masks for COVID-19 Prevention On the Tensile Behaviour of Bio-Sourced 3D-Printed Structures from a Microstructural Perspective Dispersion and Reinforcing Potential of Carboxymethylated Nanofibrillated Cellulose Powders Modified with 1-Hexanol in Extruded Poly(Lactic Acid) (PLA) Composites Rapid prototyping of continuous carbon fiber reinforced polylacticacid composites by 3D printing The role of 3D printing and open design on adoption of socially sustainable supply chain innovation A global sustainability perspective on 3D printing technologies EPA officially says copper surfaces help fight COVID-19. Advanced materials & processes Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1 Nanotechnology as an Alternative to Reduce the Spread of COVID-19 Future antiviral surfaces: Lessons from COVID-19 pandemic The use of copper to help prevent transmission of SARS coronavirus and influenza viruses. A general review The flow physics of COVID-19 An experimental framework to capture the flow dynamics of droplets expelled by a sneeze Numerical modelling of the distribution of virus carrying saliva droplets during sneeze and cough A New Methodology for Studying Dynamics of Aerosol Particles in Sneeze and Cough Using a Digital High-Vision, High-Speed Video System and Vector Analyses User's Guide, Fluent Inc Performance of fabrics for home-made masks against the spread of COVID-19 through droplets: A quantitative mechanistic study CSSEGISandData/COVID-19 Covid-19: What new variants are emerging and how are they being investigated? ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The feasibility of masks and face shields designed by 3D printing makers; some considerations of their use against the COVID-19  Masks and face shields for personal protective equipment (PPE) against COVID 19 was manufactured using 3D printing.  It was possible to simulate the protection provided by the PPE against flow fluids employing CFD.  Despite the layers spacing observed in the SEM analysis, the filtering capacity of the 3D printed PPE can be more efficient than home-made fabric masks since the later contain a wide pore distribution.  Copper concentration was detected by employing energy dispersive spectroscopy in the PLA-Copper, utilized for the masks and face shields fabrication.  The copper detected is very helpful against SARS-CoV-2 since it can destroy the virus in less time compared to materials such as steels, polymers, cloth, among others.