key: cord-0308104-v49j2a5x authors: Fraenkl, M.; Krbal, M.; Houdek, J.; Zmrhalova, Z. O.; Prokes, B.; Hejda, P.; Slang, S.; Prikryl, J.; Ondracek, J.; Makes, O.; Kostyk, J.; Nasadil, P.; Malcik, P.; Zdimal, V.; Vlcek, M. title: High-Quality and Easy-to-Regenerate Personal Filter date: 2021-12-21 journal: nan DOI: 10.1101/2021.12.16.21267766 sha: ea6641f696a002f9bfaedf3aa84c5418a632bea6 doc_id: 308104 cord_uid: v49j2a5x Proper respiratory tract protection is the key factor to limiting the rate of COVID-19 spread and providing a safe environment for health care workers. Traditional N95 (FFP2) respirators are not easy to regenerate and thus create certain financial and ecological burdens; moreover, their quality may vary significantly. A solution that would overcome these disadvantages is desirable. In this study a commercially available knit polyester fleece fabric was selected as the filter material, and a total of 25 filters of different areas and thicknesses were prepared. Then, the size-resolved filtration efficiency (40-400 nm) and pressure drop were evaluated at a volumetric flow rate of 95 L/min. We showed the excellent synergistic effect of expanding the filtration area and increasing the number of filtering layers on the filtration efficiency; a filter cartridge with 8 layers of knit polyester fabric with a surface area of 900 cm2 and sized 25 x 14 x 8 cm achieved filtration efficiencies of 98 % at 95 L/min and 99.5 % at 30 L/min. The assembled filter kit consists of a filter cartridge (14 Pa) carried in a small backpack connected to a half mask with a total pressure drop of 84 Pa at 95 L/min. In addition, it is reusable, and the filter material can be regenerated at least ten times by simple methods, such as boiling. We have demonstrated a novel approach for creating high-quality and easy-to-breathe-through respiratory protective equipment that reduces operating costs and is a green solution because it is easy to regenerate. desirable. In this study a commercially available knit polyester fleece fabric was selected as the 23 filter material, and a total of 25 filters of different areas and thicknesses were prepared. Then, is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.16.21267766 doi: medRxiv preprint 4 at the same time achieves very good filtration efficiency as well as low respiratory resistance 80 and is easy to regenerate. Such a solution will reduce the amount of waste produced and make In the present study, two common materials were tested as filtering materials: (1) single-faced 94 jersey knit fabric, double-sided fleece, 100% polyester (PES), with a thickness of 2.3 mm and 95 mass per unit area of 163 g.m -2 , and (2) knit fabric, 100% cotton, with a thickness of 0.6 mm 96 and area density 152 g.m -2 (Table S1 and Figure S1 ). Both materials were washed once at is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.16.21267766 doi: medRxiv preprint mask size 10 × 15 cm (150 cm 2 ), and the filter thickness was increased by increasing the 104 number of PES fabric layers ( Figure S2 ). The size-resolved filtration efficiency of the prepared filters was evaluated in the range of 106 40-400 nm with a scanning mobility particle sizer (SMPS) (3936L 75, TSI, USA). The In the present study, we propose two mutually supportive approaches that can increase the is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. However, particle penetration, rather than filtration efficiency, better describes the ability of 166 the filter to protect the respiratory system. As shown in Figure 2B , the number of particles out 167 of 1,000 that pass through the filter significantly differentiates between the quality of filters 168 with very similar filtration efficiency. For instance, it is obvious from Figure 2B The filtration efficiency is affected by the size of the airborne particles, with a typical curve 174 spanning particle sizes up to 400 nm, as shown for filter size 6 with 8 PES layers in Figure 2C is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. In this study, we compared PES and cotton fabrics, both knit, with similar fiber diameters 191 and similar area densities (Table S1 ). Unlike the cotton fabric, the PES fabric had an 192 additional fleece finish. As shown in Figure 2E , the particle penetration through the PES is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint Using the results in Figure 2 , we designed a filter cartridge composed of commonly available 212 materials that is an inexpensive and easy-to-prepare alternative to commercial respirators. The 213 supporting core of the filter cartridge was made on a 3D printer in the shape of a cuboid frame 214 (21 × 14 × 4 cm), which alternatively can be replaced with a wooden or cardboard frame with 215 an opening on one side for the insertion of a rubber hose. The frame is further wrapped 8 times with the PES fabric to obtain a filter area of 900 cm 2 . The protruding PES fabric is firmly tightened with a twine at both ends to prevent ambient air 218 from entering through these ends of the filter. For wearability, the filter prepared in this way 219 is subsequently inserted into a small backpack that has two suction openings with a diameter is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.16.21267766 doi: medRxiv preprint 11 and oxygenated air. A detailed step-by-step assembly of the filter unit and a cross-sectional 225 illustration of the filled backpack are shown in Figure 3 and in the Supplement. Shown are all parts of the filter kit and its gradual assembly, including a demonstration of how it is to 230 be worn (manikin). The purpose of the blue porous material is to allow air to access the filter cartridge; 231 . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. Figure 2C and Figure S7 . is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint In the present work, we describe an RPE constructed from commonly available materials with 266 a high filtration efficiency that meets the strict requirement for FFP2 (N95) respirators. [22] 267 A the size of a single virus particle (virion) has been estimated to be in the range of 60- Figure 2C ). Note that the certified filter outperforms most of the 43 tested 284 FFP2, N95 and KN95 class respirators, as published in recent studies [8, 9] (see Figure S9 ). is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.16.21267766 doi: medRxiv preprint filter size and particle diameters, the minimum filtration efficiency can reach 99.9 %, with a 287 pressure drop of 29 Pa at a volumetric flow rate of 95 L/min (see Figures S10 and S11). We showed that fabric surface treatment can have a decisive influence on the filtration 296 properties. In our study, we examined knit fabrics made of cotton and PES with similar 297 parameters except that the PES fabric had a fleece finish that increased the total thickness of 298 one layer approximately 3-fold ( Figure S1 ) while significantly increasing the active area for 299 potential capture of hazardous particles. As shown in Figure 2E , particle penetration through is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.16.21267766 doi: medRxiv preprint filtration properties after first boiling or washing at 95 °C is due to a combination of an 312 increase in the density of the fabric due to shrinkage by 4 % while maintaining the structure of 313 the fleece treatment and possibly removing chemicals (fabric softener and oil) that remain 314 inside the PES fabric after its industrial production. Therefore, we recommend as a first step 315 before the assembly of the filter cartridge to boil the PES fabric to improve and unify its Table 1 . We did not perform the fit testing on human subjects in the study, however standard is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint full face mask). Moreover, unlike the nanofiber membrane in the P3 filter, the PES material is 342 less prone to clogging due to the larger pore size and thickness of the filter material. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.16.21267766 doi: medRxiv preprint estimated at 56 EUR (retail price). The prices of individual components can be seen in Figure 351 S14. We identified that the fleece treatment of the fabric has a positive effect on its filtration Because it can be easily regenerated, our proposed solution has the potential to reduce the 361 environmental impact and simplify access to high-quality respiratory protective devices for 362 health care workers, especially in low-and middle-income countries or in crisis situations. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.16.21267766 doi: medRxiv preprint Airborne Transmission of COVID-19: Aerosol Dispersion Lung Deposition, and Virus-Receptor Interactions Effectiveness of Mask Wearing to Control Community Spread of 381 SARS-CoV-2 An evidence review of face masks 383 against COVID-19 Transmission of COVID-19 385 virus by droplets and aerosols: A critical review on the unresolved dichotomy Breathing Is Enough: For the Spread of Influenza Virus and SARS-CoV-2 388 by Breathing only Indoor Air Changes and Potential Implications for SARS-CoV-391 Navigating the Covid-393 Pandemic by Caring for Our Health Care Workforce as They Care for Our Patients. 394 NEJM Catal How Effective Is the Filtration of 'KN95' Filtering 396 Facepiece Respirators During the COVID-19 Pandemic? Ann Work Expo Heal Qualitative Knowledge of Filtering Facepiece is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted Facepiece Respirator (N95 Respirator) Reprocessing: A Systematic Review Exploring options for reprocessing of N95 Filtering 404 Facepiece Respirators ( N95-FFRs ) amidst COVID-19 pandemic : A systematic 405 review 3M. 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Viruses . 2020 Inactivation of coronaviruses by heat is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted COVID-19 431 and the dearth of health workers Managing COVID-19 in Low-and Middle-Income 434 Aerosol technology: properties, behaviour, and measurement of airborne 436 particles Science 3M. Comparison of FFP2 , KN95 , and N95 Filtering Facepiece Respi rator A Novel Coronavirus from 440 Patients with Pneumonia in China Respiratory virus shedding in exhaled breath and efficacy of face masks Transmission risk of 446 infectious droplets in physical spreading process at different times: A review Advice on the use of masks in the context of COVID-19 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprintThe copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.16.21267766 doi: medRxiv preprint