Efficacy Assessment of Newly-designed Filtering Facemasks during the SARS-CoV-2 Pandemic

The SARS-CoV-2 pandemic resulted in shortages of production and test capacity of FFP2respirators. Such facemasks are required to be worn by healthcare professionals when performing aerosol-generating procedures on COVID-19 patients. In response to the high demand and short supply, we designed three models of facemasks that are suitable for local production. As these facemasks should meet the requirements of an FFP2-certified facemask, the newly-designed facemasks were tested on the filtration efficiency of the filter material, inward leakage, and breathing resistance with custom-made experimental setups. In these tests, the facemasks were benchmarked against a commercial FFP2 facemask. The filtration efficiency of the facemask’s filter material was also tested with coronavirus-loaded aerosols under physiologically relevant conditions. This multidisciplinary effort resulted in the design and production of facemasks that meet the FFP2 requirements, and which can be produced at local production facilities.


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facemask and subsequently, the number of environmental particles was counted after fixing a 91 facemask on the particle chamber (# particlesmask) and averaged over three one-minute 92 measurements. For each of the five particle size ranges, the filter capacity was calculated 93 according to the following formula: NaCl particle penetration test. For the NaCl particle penetration test a PVC-tube system 98 was constructed with a 90º bend, going from a vertical to a horizontal direction (the design and 99 instructions to build are online available at https://projectmask.nl/testing/filter-material-100 penetration/build/). The vertical part of the tube system was connected with an Atomizer 101 Aerosol Generator ATM 226, and the distal end of the horizontal part contained a PMMA tube 102 with a sample holder in which a facemask was fixed in an airtight manner (Fig. S1, 2). The 103 aerosol generator produced NaCl particles from a 2% NaCl solution, resulting in a particle 104 concentration of 2.5 -3.5 x 10 4 particles / cm 3 in the tube system. The number of NaCl particles 105 that passed through the facemask's filter material was counted by a TSI PortaCount Pro 8030 106 particle counter, which detects particles in a 0.02 ->1 µm size range and generated an air 107 velocity of 0.1 m sec -1 through the filter material of the facemasks. The number of particles that 108 passed through the filter material was analysed with TSI FitPro + software. 109 The fittest. The fittest was performed to determine the leakage of particles around the 110 edges of the facemasks. First, a probe was placed in the facemask by which it was connected to 111 the PortaCount particle counter. To obtain representative results, each facemask was tested by

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polymerase (RdRp). The primers and probe for the EAV internal control were also added and

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The size of the virus particle is estimated to be 0.1 µm, but to which extend transmission takes 190 places via aerosols (< 5 µm droplets) or larger respiratory droplets (> 5 µm) remains to be 191 determined. When the FFP2-certified facemask was placed on the particle chamber, 99.4 -192 99.9% of the environmental particles of between 0.3 -10.0 µm was filtered (Fig. 1a). Two

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The masks were therefore also challenged with non-neutralized polydisperse NaCl-  (Fig 1b). The Reinier-0.1 and -1.0 facemasks filtered respectively 98.9±0.42% and 99.3±0.36% 208 of the NaCl particles. This is significantly more than observed for the dry environmental three layers of melt-blown polypropylene filters and showed the highest NaCl-particle filtration

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efficiency of 99.83±0.12% (Fig. 1b). This model also performed best in the environmental 215 particle filtration test (Fig 1a). 216 The submicron-sized environmental particles were filtered less efficiently by the newly-217 designed facemasks than the NaCl particles, which might be explained by the higher air velocity 218 during the environmental particle filtration test. It has been well described in literature that an   Table 1). As our facemasks were tested by only three different persons, not the

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average, but maximal observed inwards leakage was taken as a measure for the fit of a facemask 241 ( Table 2), thus defining a worst-case scenario. The FFP2-certified facemasks showed a 242 maximal inward leakage of 0.5% (Table 2)

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were passed through a tube over 0.9 m distance, 99% of the particles were <5.0 µm in size (Fig.   267 2). Particles smaller than 5.0 µm are generally defined as aerosols that can be easily inhaled 268 (Heyder et al., 1980). The three types of facemask were tested in two separate sessions, which 269 resulted in two independent datasets (Fig. 3) In the no mask-control, MHV was sampled in 270 absence of a facemask in the sample holder to determine the maximum amount of virus that 271 could be recovered from the air. This resulted in virus recovery of 4.09 ± 0.21 log PFU ml -1 in 272 the first, and 5.89 ± 0.21 log PFU ml -1 in the second session (Fig. 3a, c ), indicating that the  (Fig. 3b). When this type of facemask was used in the second 280 session, the infectious virus and viral RNA recovery decreased by respectively 3.1-and 3.5-281 logs on average, which corresponds to 99.92 and 99.96% filtration efficiency (Fig. 3d). The

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Reinier-0.1 facemasks reduced the recovery rates of infectious virus and RNA copies on 283 average by 2.1 and 2.8-logs respectively compared to the no mask-control (Fig. 3a). This 284 corresponds with the filtration efficiencies of 99.2 and 99.9% (Fig. 3b) (Fig. 3c, d). The RNA copy nr to PFU-289 ratio with and without facemask are similar within each experiment, indicating that the mask's 290 filter material does not inactivate the virus upon passage.

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The virus filtration efficiency of the facemasks was determined at a continuous air velocity of 292 0.42 m sec -1 , which is significantly higher than during the NaCl particle penetration test, that conditions is needed to assess the protective capacity of the new facemasks.