Abstract
The COVID-19 pandemic has led to widespread shortages of N95 respirators and other personal protective equipment (PPE). An effective, reusable, locally-manufactured respirator can mitigate this problem. We describe the development, manufacture, and preliminary testing of an open-hardware-licensed device, the "simple silicone mask" (SSM). A multidisciplinary team developed a reusable silicone half facepiece respirator over 9 prototype iterations. The manufacturing process consisted of 3D printing and silicone casting. Prototypes were assessed for comfort and breathability. Filtration was assessed by user seal checks and quantitative fit-testing according to CSA Z94.4-18. The respirator originally included a cartridge for holding filter material; this was modified to connect to standard heat-moisture exchange (HME) filters (N95 or greater) after the cartridge showed poor filtration performance due to flow acceleration around the filter edges, which was exacerbated by high filter resistance. All 8 HME-based iterations provided an adequate seal by user seal checks and achieved a pass rate of 87.5% (N = 8) on quantitative testing, with all failures occurring in the first iteration. The overall median fit-factor was 1662 (100 = pass). Estimated unit cost for a production run of 1000 using distributed manufacturing techniques is CAD $15 in materials and 20 minutes of labor. Small-scale manufacturing of an effective, reusable N95 respirator during a pandemic is feasible and cost-effective. Required quantities of reusables are more predictable and less vulnerable to supply chain disruption than disposables. With further evaluation, such devices may be an alternative to disposable respirators during public health emergencies. The respirator described above is an investigational device and requires further evaluation and regulatory requirements before clinical deployment. The authors and affiliates do not endorse the use of this device at present.
Highlights
The COVID-19 pandemic has led to widespread shortages of N95 respirators and other personal protective equipment (PPE)
The respirator originally included a cartridge for holding filter material; this was modified to connect to standard heat-moisture exchange (HME) filters (N95 or greater) after the cartridge showed poor filtration performance due to flow acceleration around the filter edges, which was exacerbated by high filter resistance
All 8 HME-based iterations provided an adequate seal by user seal checks and achieved a pass rate of 87.5% (N = 8) on quantitative testing, with all failures occurring in the first iteration
Summary
A multidisciplinary team developed a reusable silicone half facepiece respirator over 9 prototype iterations. Our design process began with the “Stop-Gap Face Mask (SFM)” (Fig 1) an open-source licensed design by Chris Richburg available through the National Institutes of Health’s 3D Print Exchange (https://3dprint.nih.gov/discover/3dpx-013429). This mask consists of a rigid 3D-printable body with a built-in cartridge frame designs to hold flat sheets of filter material. Samples were tested at a flow of 30 +/- 4 L/min using 2% sodium chloride solution in distilled water (NaCl), according to US Government 42 Code of Federal Regulations (CFR) Part 84 Test for RPD [11, 12] This regulation on respiratory protection equipment is informed by the research and guidance by the National Institute for Occupational Safety and Health (NIOSH). Particle count (count / cm3) and resistance (kPa) around mask and filter seal were measured
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