Inside Cover

Abstract

Access to sterile personal protective equipment, in particular for filtered face respirators is critical in the current pandemic for front line healthcare workers. Extended use may be required during supply shortages or due to economic considerations. UVC sterilization can be a cost‐effective technique capable of high throughput. The suitability of various N95 respirator designs for UV mediated reuse were evaluated based on the materials utilized. (Background image: with permission from Prescientx. Virus image: Sophia Lilge. Further details can be found in the article by Lothar Lilge, Angelica Manalac, Madrigal Weersink, Fynn Schwiegelshohn, Tanner Young‐Schultz, Abdallatif Satti Abdalrhman, Chengjin Wang, Aldrich Ngan, Frank X. Gu, Vaughn Betz, Ron Hofmann (https://onlinelibrary.wiley.com/doi/10.1002/jbio.202000232).

Modeling the efficiency of UV at 254 nm for disinfecting the different layers within N95 respirators

“…The eight FFRs used in this simulation study are 3 M models 1805, 9105s 1860, 8110s, 8210, 1870+, 9210 and Moldex model 1512. The optical properties of each of the three layers of the FFRs at 254 nm were obtained from the study by Lilge et al [ 6 ]. In brief, the previous work calculated the optical properties of fabric layers at four wavelengths between 250 and 300 nm, based on the transmission and reflection spectra of the fabric layer materials and assumed refractive indices based on the refractive index of fabric fibers and average densities of fabrics.…”

“…For depth profiles, only fluence rate data from the central 10‐cm‐diameter disc of the FFR disc were used to avoid any simulations boundary effects. More details can be found in the study by Lilge et al [ 6 ]. Simulations were executed with micron‐sized tetrahedral voxels, and then, the photon weight per voxel volume was converted into fluence‐rate values, which resulted in rounding error causing noise; hence, a boxcar smoothing algorithm was applied.…”

“…A gap in the research to date on UV 254 treatment for N95 FFR decontamination is the potential for viruses to penetrate the FFR such that its material may partially shield the pathogens from UV exposure. Most N95 FFRs contain three main layers of polymeric fabrics (such as polypropylene and polyester) and cellulose nonwoven fabrics [ 4 , 5 , 6 ]. Generally, the inner and outer layers provide form, stability, comfort, water resistance and large particle filtration.…”

“…The filtration (middle) layer acts as the principal trapping media for submicron particles. The filtration layer comprises polypropylene microfibers with a diameter in the range from ~1 to 10 μm arranged as a three‐dimensional network [ 4 , 5 , 6 ]. Considering the small fiber diameters, the void space within this layer is usually vast.…”

“…While exploring the ability of UV to inactivate viruses embedded within the depths of an FFR would ideally involve empirical testing, such work is highly challenging and time‐consuming. In the meantime, this article describes mathematical modeling to predict the ability of UV 254 to penetrate different N95 FFRs to inactivate embedded SARS‐CoV‐2 virus on a mesoscopic length scale based on the optical properties of the material layers of eight common FFRs recently reported by Lilge et al [ 6 ]. While such model predictions based on assumptions are no replacement for experiments, the results can guide decontamination practices in the absence of better empirical data as the world tries to cope with the COVID‐19 pandemic under very challenging circumstances.…”