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Face Off: 3D-Printed Masks as a Cost-Effective and Reusable Alternative to N95 Respirators: A Feasibility Study

      Abstract

      Background

      One of the best methods for protection against respiratory diseases is the use of an N95 mask. Supply shortages have demonstrated a significant need for effective alternatives to N95 masks. Benefits of 3D-printed respirators over N95s include reduced cost and ease of production, widespread availability, reusability/sterilizability, and customizability. 3D-printed mask designs have been downloaded thousands of times; however, there is little to no data on the efficacy of these potential alternatives.

      Methods

      Three of the most popular 3D-printed respirator designs were modified to allow for the Occupational Safety and Health Administration (OSHA) quantitative fit testing that disperses saline into the ambient air and determines concentrations within the mask during multiple trials. Five volunteers conducted standardized fit tests of these masks, as well as an N95 and a KN95, and the results were compared.

      Results

      One of the 3D-printed respirators, low poly COVID-19 face mask respirator (mask 2), achieved a fit factor greater than 100 in every trial, representing sufficient fit according to OSHA protocols. The N95 mask achieved a sufficient fit in 60% of the trials, and none of the remaining masks provided a suitable fit factor reliably according to the OSHA fit test. Further trials showed no change in fit factor when different 3D-printable plastics are used or when a widely available high efficiency particulate air (HEPA) filter was used.

      Conclusion

      3D-printed respirators provide a possible alternative to N95 masks to protect against respiratory pathogens such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Fit testing results demonstrate that certain 3D-printed mask designs may exceed the fit of N95 masks.

      Keywords

      Clinical Significance
      • Low poly coronavirus disease 2019 (COVID-19) face mask respirator achieved a fit factor greater than 100 in every trial.
      • 3D-printed respirators are preferrable over N95 masks in terms of cost of production, widespread availability, and reusability.
      • 3D-printed respirators may present a viable alternative to N95 masks, especially given supply shortages.

      Introduction

      The N95 filtering facepiece respirator (N95 respirator or N95 mask) was first patented in 1995 by Taiwanese American Peter Tsai.

      U.S. Embassy in Georgia. Meet the U.S. scientist who invented the N95 mask filter. Available at: https://ge.usembassy.gov/meet-the-u-s-scientist-who-invented-the-n95-mask-filter. Accessed November 20, 2021.

      This mechanical filter respirator, approved by National Institute for Occupational Safety and Health (NIOSH), was designed to filter 95% of particulates (but not gases or vapors). Its efficacy is dependent on appropriate user usage and mask size and fit to ensure adequate seal, thus requiring regulated, yearly medical evaluations and fit testing.

      U.S. National Institute for Occupational Safety and Health. Ancillary respirator information. Available at: https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part/respsource3fittest.html. Accessed November 20, 2021.

      Although originally designed for industry use, the N95 respirator is more effective than surgical masks in protecting the wearer from environmental pathogens.
      • Bałazy A
      • Toivola M
      • Adhikari A
      • Sivasubramani SK
      • Reponen T
      • Grinshpun SA.
      Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks?.
      Thus, it has been approved by the US Centers for Disease Control and Prevention (CDC) to be used by health care workers to protect against clinical respiratory illnesses, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), coronavirus disease 2019 (COVID-19), severe acute respiratory syndrome (SARS), and Mycobacterium tuberculosis.

      U.S. Centers for Disease Control and Prevention (CDC). 2007 Guideline for isolation precautions: preventing transmission of infectious agents in healthcare settings. Available at: https://www.cdc.gov/infectioncontrol/pdf/guidelines/isolation-guidelines-H.pdf. Accessed November 20, 2021.

      The novel, zoonotic COVID-19 is a clinical respiratory illness resulting in unprecedented demand for rapid public health developments in diagnostics, treatments, and prevention. With the initial rise of the pandemic, containment efforts became focused on disease isolation and prevention by using personal protective equipment (PPE). One of the most visible and politicized challenges has been the shortage of and rationing of PPE.
      • Mahmood SU
      • Crimbly F
      • Khan S
      • Choudry E
      • Mehwish S.
      Strategies for rational use of personal protective equipment (PPE) among healthcare providers during the COVID-19 crisis.
      N95 masks are highly effective at filtering viral particles and are used by health care workers who may be in direct contact with patients with COVID-19.

      U.S. Embassy in Georgia. Meet the U.S. scientist who invented the N95 mask filter. Available at: https://ge.usembassy.gov/meet-the-u-s-scientist-who-invented-the-n95-mask-filter. Accessed November 20, 2021.

      Outside of the hospital setting, many people may desire the increased protection afforded by N95 masks, especially those most susceptible to increased morbidity and mortality from the virus, such as the elderly and the immunocompromised.
      • Liu K
      • Chen Y
      • Lin R
      • Han K.
      Clinical features of COVID-19 in elderly patients: a comparison with young and middle-aged patients.
      However, the CDC has stated explicitly that the general public should not use N95 masks to protect against COVID-19 to preserve the limited supply for health care workers and first responders.

      U.S. Centers for Disease Control and Prevention (CDC). Stockpiled N95 Respirators Q/A. Available at: https://www.cdc.gov/coronavirus/2019-ncov/hcp/respirator-use-faq.html. Accessed November 20, 2021.

      These supply concerns have resulted in rationing policies, and some hospitals provide only 1 N95 respirator to be used for up to 1 week, despite a filter life of roughly 8 hours.
      • Radonovich LJ
      • Cheng J
      • Shenal BV
      • Hodgson M
      • Bender BS
      Respirator tolerance in health care workers.
      Additionally, N95s have been shown to reliably fail fit testing after 5 dons and doffs.
      • Cassorla L.
      Decontamination and reuse of N95 filtering facepiece respirators: where do we stand?.
      Due to the scarcity of N95s, an increasing number of individuals are wearing surgical masks in place of N95 masks. The research on the efficacy of surgical masks in reduction of SARS-CoV-2 infection rates is inconclusive; the only clinical, randomized control trial to-date did not show a statistically significant decrease in infection rates due to surgical mask use.
      • Bundgaard H
      • Bundgaard JS
      • Raaschou-Pedersen DET
      • et al.
      Effectiveness of adding a mask recommendation to other public health measures to prevent SARS-CoV-2 infection in Danish mask wearers: a randomized control trial.
      Therefore, there is a global need for accessible alternatives to N95 respirators. Although many alternatives have been proposed, such as modified scuba masks, production and supply chain must be considered for accessibility.
      • Gierthmuehlen M
      • Kuhlenkoetter B
      • Parpaley Y
      • Gierthmuehlen S
      • Köhler D
      • Dellweg D
      Evaluation and discussion of handmade face-masks and commercial diving-equipment as personal protection in pandemic scenarios.
      In recent years, 3D printing has become an affordable and attainable method of manufacturing for professionals and laypersons.
      • Xun H
      • Clarke S
      • Baker N
      • et al.
      Method, material, and machine: a review for the surgeon using three-dimensional printing for accelerated device production.
      Entry-level printers are available for less than $200, and countless resources are available to help users get started. There are numerous respirator designs to choose from, and they can be 3D-printed in several hours from a variety of materials. The most widely available and affordable material is polylactic acid (PLA), conveniently also one of the easiest materials to print with because of its bed adhesion and minimal hardware requirements. PLA comes in a wide range of colors that can be used to personalize the masks, potentially increasing desirability, boosting morale, and minimizing unintentional exchanging and cross-contamination of masks between users. Additional benefits of 3D-printed masks are inexpensive production and reusability (the mask can be sanitized, and the filters can be replaced).
      • Belhouideg S.
      Impact of 3D printed medical equipment on the management of the COVID-19 pandemic.
      There are even transparent versions of PLA, thus increasing visualization of the mouth, which reduces visual barriers to communication for the hearing impaired or language acquisition in children.
      • Kratzee IM
      • Rosenbaum ME
      • Cox C
      • Odilla DW
      • Kapadia MR.
      Effect of clear vs standard covered masks on communication with patients during surgical clinic encounters: a randomized clinical trial.
      Despite the promises of 3D-printed masks, they have not been well studied due to their novelty. Therefore, possible proposed disadvantages include carbon dioxide accumulation (due to increased respiratory dead space), insufficient protection, or lack of full face (including eye) protection.
      Standard assessment of respirator effectiveness has 2 components: fit testing and particle penetration quantification. The name N95 refers to >95% filtration of airborne particles less than 0.3 μm but is dependent on adequate fit to the user. A fit test, such as the Occupational Safety and Health Administration (OSHA) N95 fit test, involves a modified mask with a hose attachment that measures particles inside of the mask. Saline is aerosolized into the ambient air, and the number of particles inside of the mask are measured. Trials are replicated and repeated with the participant engaged in different activities, such as talking or shaking their head.
      • Crutchfield CD
      • Fairbank EO
      • Greenstein SL.
      Effect of test exercises and mask donning on measured respirator fit.
      The fit factor (score from 0 to 200+) is then calculated, representing efficacy of the mask in preventing particle entry. A fit factor score of 100 or higher is required for N95 masks to be considered appropriately protective.

      U.S. Centers for Disease Control and Prevention (CDC). NIOSH-approved filtering facepiece respirators. Available at:https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part/default.html. Accessed November 20, 2021.

      This is the first investigation to fit-test 3 popular 3D-printed masks on a diversity of face shapes, as compared to conventional N95 and KN95 masks. The aim is to rule out inadequate 3D-printed mask designs; although fit testing does not guarantee a respirator is viable (rule in), the lack of a proper fit indicates the respirator is likely not protective (rule out). We hypothesize that 3D-printed respirators may be a suitable alternative to N95 masks. Furthermore, we hope to inform health care providers and the general public about the importance of mask fit and comparable masks for different facial measurements.

      Materials and Methods

      This was a human subjects study approved by the institutional review board. Popular 3D-printing design repositories such as Thingiverse

      Thingiverse. Items 4240948, 4256244, and 4225667. Available at: www.thingiverse.com. Accessed on December 3, 2020.

      and MyMiniFactory

      Myminifactory. Available at: https://www.myminifactory.com/search/?query=respirators. Accessed December 3, 2020.

      were searched with terms such as “respirator” and “COVID.” Inclusion criteria includes greater than 1,000 downloads. Exclusion criteria includes gross air leakage on visual observation postproduction, greater than 4 pieces due to challenges in assembly, extensive postprocessing requirements, need of non-3D-printed components for respiratory mechanism, and personalized designs not contributing to filtration functionality. Three masks were found to meet the listed criteria (Table 1). The designs were modified using basic Boolean operators and plane-cut operations using TinkerCad (Autodesk) and Meshmixer (Autodesk) to allow an N95 to be used as the filter. The designs were then imported into Ultimaker Cura (Ultimaker) and were sliced according to the recommended settings. The sliced gcode files were run on an Ender 3 Pro 3D printer, modified with a BLTouch auto-leveling sensor and Marlin custom firmware, using PLA filament (PLA 1.75 mm, Overture) with print parameters: 214°C nozzle temperature, 0.12-mm layer height (resolution), 60°C bed temperature, infill 10%. Elastic bands 6 mm wide were tied to each mask, and clasps were 3D-printed to hold the bands in place.
      Table 13D Printed Masks
      MaskMaterialDesignPriceTime to Print
      Mask 1PLA 1.75 mmCOVID mask respirator$28 h
      Mask 2Printed with both PLA 1.75 mm and TPULow poly COVID-19 face mask respirator$24 h
      Mask 3PLA 1.75 mmCOVID-19 respirator$29 h
      COVID = coronavirus disease; PLA = polylactic acid; TPU = thermoplastic polyurethane.
      This chart depicts the material, design, prices, and time to print of the three masks we chose to 3D print.
      One mask was also printed with thermoplastic polyurethane (TPU) (TPU 1.75 mm, Priline). All 3D model files used in this experiment are available for download (Figure 1).
      Figure 1
      Figure 1Mask configurations tested. Top row, left to right: N95 1860S, N95 46727, and KN95. Bottom row, left to right: mask 1; low poly COVID-19 face mask respirator, and mask 3. The K95 and mask 3 pictured include the attachment hose used for fit testing. COVID = coronavirus disease.
      A recruitment flyer was emailed to medical students and undergraduate premedical students at a single institution, ∼300 students. Five responding volunteers did not possess any contraindications to testing, such as chronic pulmonary disease. Other exclusion criteria included active respiratory disease, recent COVID-19 infection, and pregnancy. Inclusion criteria was ability to provide informed consent, mental capacity to don and doff masks independently, and age > 18. The volunteers all signed consent documents and had facial measurements taken by an examiner. Face length was measured from the bridge of the nose to the chin, and face width was measured from the tip of the nose to the top of the ear. All volunteers were instructed to be clean-shaven for testing. Fit testing was performed using a particle counter (TSI PortaCount Pro+; TSI Incorporated) and a particle generator (TSI Model 826 Particle Generator; TSI Incorporated) (Figure 2).
      Figure 2
      Figure 2The particle counter and particle generator used for the fit testing.
      A fit test involved 4 trials simulating daily activities/movements that is the standard testing conditions per OSHA protocols:

      Occupational Health and Safety Administration. Fit testing procedures. Available at: https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=9780&p_table=STANDARDS. Accessed on December 3, 2020.

      1) leaning forward for 50 seconds, 2) speaking for 30 seconds, 3) moving one's head from side to side for 30 seconds, and 4) moving one's head up and down for 30 seconds (Figure 3). The fit factor (ffx) for each trial x was calculated automatically by measuring the area under the curve of particles measured inside the respirator.
      • Xun H
      • He W
      • Chen J
      • Sylvester S
      • Lerman SF
      • Caffrey J.
      Characterization and comparison of the utilization of Facebook groups between public medical professionals and technical communities to facilitate idea sharing and crowdsourcing during the COVID-19 pandemic: cross-sectional observational study.
      The overall fit factor was calculated by the particle counter based on the formula:
      OverallFitFactor=41ff1+1ff2+1ff3+1ff4


      Figure 3
      Figure 3Volunteers undergoing fit tests: This image depicts a volunteer testing an 1870 N95.
      Fit testing to commercially available N95 masks were performed following standard OSHA protocol.

      Occupational Health and Safety Administration. Fit testing procedures. Available at: https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=9780&p_table=STANDARDS. Accessed on December 3, 2020.

      This included: 1) Volunteers performed a standard fit test using commercially available 1860S N95 masks (N95 1860S, 3M); 2) Retesting individuals who failed initial fit tests was performed with an alternative N95 (46727 Fluidshield, O&M Halyard Inc.) (Figure 4).
      Figure 4
      Figure 4The image depicts an experimenter demonstrating proper wearing of test Mask 3 for fit test analysis utilizing an N95 as a filter.
      Fit testing was then performed to compare KN95 efficacy to standard N95 following the same procedure. Each 3D-printed mask was fitted to the participant using heat molding; the mask was heated with a hair dryer until the plastic was malleable, and the volunteers then pressed the mask against their faces using their thumbs and index fingers to apply gentle pressure, focusing on the nose, to mold the mask to their faces. This step could alternatively be performed by submerging the mask in warm water. Due to availability and ease of use, the hair dryer method was performed. An N95 with the hose attachment was then screwed into the filter portion of the mask, and a fit test was performed. In 1 volunteer, numerous additional studies were done, such as testing a mask with a different type of plastic, different filters, and measuring end tidal carbon dioxide at rest using a capnograph (Smith CapnoCheck II, Smiths Medical).

      Results

      The following is data for 5 volunteers using 3D-printed masks made from PLA and using an N95 as a filter are shown in Table 2.
      Table 2Volunteer Characteristics
      VolunteerGenderFace Width (cm)Face Length (cm)Height (cm)Weight (kg)BMIRace
      1M18.515N/AN/AN/ACaucasian
      2F17.512.5N/AN/AN/ACaucasian
      3M17141887521.2Caucasian
      4M16.5151837522.4Caucasian
      5F17.514N/AN/AN/AHispanic
      BMI = body mass index.
      The only mask to pass the OSHA N95 fit test for every volunteer was the low poly COVID-19 face mask respirator (mask 2) (Figure 5A). In 2 of the volunteers, the standard 1860S N95 did not pass the fit test and the 46727 model N95 was needed. Additional testing in 1 volunteer demonstrated that the fit factor was unchanged when mask 2 was printed in TPU as opposed to PLA. Fit factor was unchanged when a high efficiency particulate air (HEPA) filter with 95% filtration at 0.3 μm (HEPA triboelectric filter media face mask replacement inserts; Snaptotes) or a NIOSH-approved N95 replacement filter (Envo mask N95 disposable filter, Sleepnet Corporation) were used as the filter for mask 2. When the KN95 was used as the filter for mask 2, the fit factor was insufficient and comparable to that of a standard surgical mask (Figure 5B). We also measured the end-tidal carbon dioxide (CO2) over 10 minutes using each of the 3D-printed masks as well as monitoring oxygen saturation (SpO2) levels (Figure 6).
      Figure 5
      Figure 5(A) Individual fit factor results. Scores greater than 200 are reported as 200+. (B) Fit factor results per mask. Scores greater than 200 (200+) were calculated as 200. A cutoff value of 100 is used to determine adequate fit, seen on graph as dotted line. Values significantly different compared to N95 is denoted with *P < .01.
      Figure 6
      Figure 6End-tidal CO2 measured over 10 minutes. End-tidal CO2 was measured for 10 minutes on the three 3D-printed masks and increased a maximum of 2 mm Hg during testing. SpO2 remained unchanged at 10 minutes for all 3 masks. All values remained within the physiologic range. CO2 = carbon dioxide; SpO2 = oxygen saturation.

      Discussion

      The COVID-19 pandemic has emphasized the need for inexpensive, easy-to-produce, high-quality filtration devices to protect against respiratory illnesses. Supply shortages of the N95 masks have led to the CDC suggesting alternative masks for everyday public use, while reserving N95 masks for health care workers. In this study, we propose that 3D-printed face masks are a feasible alternative to N95 masks and provide advantages during public shortages of N95s. Therefore, we investigated the fit and filtration efficiency of multiple open-sourced 3D-printed mask designs as compared to N95s and provide recommendations for the development of 3D-printed N95 alternatives.
      Our primary results indicate that the ability of 3D-printed masks to meet OSHA N95 filtration standards is dependent on mask design and fit to individual faces. Summarized in Figure 5B, we found that mask 2 demonstrated equivocal fit and filtration compared with N95s (141.3 ± 43.37 vs 175.6 ± 39.39, P = .226). Mask 2 passed OSHA N95 fit testing standard in all volunteers when used with NIOSH-approved filter materials. This is likely due to the shape of the mask, which conforms to the face of the individual and, thus, is a more universal fit. On the other hand, masks 1 and 3 performed significantly worse, possibly due to being composed of more pieces, thus requiring more assembly, resulting in increased points of failed seals. Masks 1 and 3 are composed of 4 and 3 components, respectively, whereas mask 2 is composed of only 2 pieces. Therefore, mask 2 could be a feasible alternative to N95 in layperson populations at high risk for complications of COVID-19, who may desire the enhanced protection provided by N95 masks but do not have access to them.
      • Noghee D
      • Tomassoni AJ.
      COVID-19 and the N95 respirator shortage: closing the gap.
      The production of 3D-printed masks is more available and affordable for laypersons, thus reserving medical grade N95s for frontline workers. On average, the 3D-printed masks cost $2 and took 7 hours per mask to produce. Specifically, the recommended mask 2 using a HEPA filter with 95% efficiency at 0.3 μm was produced for less than $2 and can be printed in only 4 hours. This is compared to N95s, which can range from $2 to $20 per mask. The COVID-19 pandemic has uniquely crowdsourced supply and demand, including networking of 3D maker groups to request aid.
      • Xun H
      • He W
      • Chen J
      • Sylvester S
      • Lerman SF
      • Caffrey J.
      Characterization and comparison of the utilization of Facebook groups between public medical professionals and technical communities to facilitate idea sharing and crowdsourcing during the COVID-19 pandemic: cross-sectional observational study.
      This influential space of 3D makers during the COVID-19 pandemic is recognized by the Food and Drug Administration and is actively being studied in partnership with America Makes.

      Food and Drug Administration. 3D printing in FDA's rapid response to COVID-19. Available at: https://www.fda.gov/emergency-preparedness-and-response/coronavirus-disease-2019-covid-19/3d-printing-fdas-rapid-response-covid-19. Accessed on November 20, 2021.

      The ability to tap into individual makers or maker spaces has enormous potential to fill supply chain gaps due to the additive manufacturing process allowing for on-demand solutions and supply chain independent of traditional manufacturers.
      • Choong YYC
      • Tan HW
      • Patel DC
      • et al.
      The global rise of 3D printing during the COVID-19 pandemic.
      3D-printed respirators provide several improvements over N95s, such as reusability. N95 filters only last 8 hours, at which point the entire mask must be discarded. Additionally, research has shown that N95 mask fit factors consistently drop to insufficient levels after 5 donnings and doffings. With a more rigid framework, 3D-printed masks theoretically may not have these shortcomings. With 3D-printed masks, the filter can easily be removed, the mask can be sanitized, and a new filter can be installed. Even if an N95 mask is available but another filter is not, cutting the mask and using it as a filter for a 3D-printed respirator can quadruple the benefit of the mask. Finally, 3D printers are capable of printing in a variety of different materials. Further research may assess the performance of other common 3D-printing materials, such as acrylonitrile butadiene styrene (ABS) or nylon. Different materials will vary in levels of durability, comfort, weight, cost, ease-of-printing, and so on.
      Our second finding was that the KN95 had a poor fit in all volunteers, and the fit factor of other masks dropped substantially when the KN95 was used as the filter. This likely indicates a lack of filtration and fit in these masks that make them more comparable to surgical masks than N95 masks. The false sense of security while wearing a KN95 can mislead the wearer. Thus, the public should not only be educated on the importance of face coverings but also the efficiency of each kind.

      Limitations

      This study is not without limitations. First, the sample size of 3D-printed masks and number of individuals fit-tested are small. Our tested population of 3 masks and 5 participants by no means scratches the surface of the large number of open-sourced mask designs or the diversity of facial features and dimensions. Nevertheless, as the first third-party study to perform standardized fit-testing of these masks compared to N95, the proof-of-concept provides grounds for future investigations and developments.
      Future work includes iterative design and testing of mask designs to 1) more efficiently filter particles, 2) provide more uniform efficiency across a diversity of face shapes, 3) minimize production parts, time, and materials used, and 4) educate the 3D-printing maker space on appropriate mask designs for adequate protection. This includes designing 3D-printed face masks customized to an individual's facial architecture, thereby increasing the fit factor more and ensuring a tight seal. 3D scanning can be used to design such personalized masks. Future mask designs should emphasize reducing the number of components required to minimize the chance of leak, reduce material, and assembly time.

      Conclusion

      Three of the most popular 3D-printed respirator designs were modified for compatibility with an OSHA N95 fit test, and results were compared with N95 and KN95 masks. Additionally, end-tidal CO2 and pulse oximetry were measured and indicated adequate safety for all masks. One of the 3D-printed masks passed the fit test for all volunteers, even when a standard N95 did not. Mask 2, combined with an approved filter, provides a cheap, easily producible, customizable, and reusable respirator that may rival N95 masks in their ability to defend against SARS-CoV-2 and other respiratory pathogens.

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      2. U.S. National Institute for Occupational Safety and Health. Ancillary respirator information. Available at: https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part/respsource3fittest.html. Accessed November 20, 2021.

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        • Chen J
        • Sylvester S
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        Characterization and comparison of the utilization of Facebook groups between public medical professionals and technical communities to facilitate idea sharing and crowdsourcing during the COVID-19 pandemic: cross-sectional observational study.
        JMIR. 2021; 5: e22983
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        • Choong YYC
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