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Rafael Cui ACSNANO 2020.Pdf This article is made available via the ACS COVID-19 subset for unrestricted RESEARCH re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic. Article www.acsnano.org Decontamination of SARS-CoV‑2 and Other RNA Viruses from N95 Level Meltblown Polypropylene Fabric Using Heat under Different Humidities # # Rafael K. Campos, Jing Jin, Grace H. Rafael, Mervin Zhao, Lei Liao, Graham Simmons, Steven Chu, Scott C. Weaver,* Wah Chiu,* and Yi Cui* Cite This: https://dx.doi.org/10.1021/acsnano.0c06565 Read Online ACCESS Metrics & More Article Recommendations *sı Supporting Information ABSTRACT: In March of 2020, the World Health Organ- ization declared a pandemic of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The pandemic led to a shortage of N95-grade filtering facepiece respirators (FFRs), especially surgical-grade N95 FFRs for protection of healthcare profes- sionals against airborne transmission of SARS-CoV-2. We and others have previously reported promising decontamination methods that may be applied to the recycling and reuse of FFRs. In this study we tested disinfection of three viruses, including SARS-CoV-2, dried on a piece of meltblown fabric, the principal component responsible for filtering of fine particles in N95- level FFRs, under a range of temperatures (60−95 °C) at ambient or 100% relative humidity (RH) in conjunction with filtration efficiency testing. We found that heat treatments of 75 °C for 30 min or 85 °C for 20 min at 100% RH resulted in efficient decontamination from the fabric of SARS-CoV-2, human coronavirus NL63 (HCoV-NL63), and another enveloped RNA virus, chikungunya virus vaccine strain 181/25 (CHIKV-181/25), without lowering the meltblown fabric’s filtration efficiency. KEYWORDS: COVID-19, SARS-CoV-2, coronavirus, humidity, N95, decontamination, aerosol he coronavirus disease 2019 (COVID-19) has affected particles9 by medical workers or other professionals at high risk Downloaded via STANFORD UNIV on October 1, 2020 at 17:12:46 (UTC). millions of people globally and caused far-reaching of infection by SARS-CoV-2. Recent systemic studies impacts on public health and on the global economy.1 demonstrate that facial coverings, including FFRs and masks, T 10 The etiologic agent, severe acute respiratory syndrome may reduce COVID-19 spread by 85% and are a highly 5 See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. coronavirus 2 (SARS-CoV-2), a member of the family important mitigation measure. FFRs of N95 or other highly Coronaviridae, genus Betacoronavirus, subgenus Sarbecovirus, filtering grade (e.g., FFP2, KN95, DS/DL2, and KF94) are able emerged in 2019. Its transmission is thought to take place to filter 75 nm particles (median diameter) with >95% through droplets and subsequently formed aerosols, generated efficiency, which should provide sufficient protection against ∼ when infected people sneeze, cough, speak, sing, and even SARS-CoV-2, which measures 120 nm or larger in aerosol − 11 breathe, or by contact between people or through fomites.2 5 particles containing the virus. Data from influenza virus research revealed that aerosols The SARS-CoV-2 pandemic has led to shortages of personal generated by people can be classified into coarse (>5 μm) or protective equipment (PPE), including N95-grade FFRs fi μ (especially surgical-grade N95 FFRs among healthcare work- ne (<5 m) particles, and while coarse particles settle within ff 1h,fine particles can remain suspended in the air for long ers). To mitigate this issue, di erent methods were proposed periods of time when in poorly ventilated indoor environ- − ments;6 8 in the case of SARS-CoV-2, it can remain infectious Received: August 5, 2020 in fine particle aerosols for at least 16 h.8 The virus particles Accepted: September 21, 2020 contained in these aerosols can be inhaled to infect cells of the Published: September 21, 2020 upper or lower respiratory tracts.6,7 The use of particulate filtering facepiece respirators (FFRs) is a form of personal protection that can minimize the inhalation of small airborne © XXXX American Chemical Society https://dx.doi.org/10.1021/acsnano.0c06565 A ACS Nano XXXX, XXX, XXX−XXX ACS Nano www.acsnano.org Article to decontaminate these face masks and allow for safe − reutilization: heat,12 15 ultraviolet (UV) irradiation,12,16 steam,17 ozone,18 vaporized hydrogen peroxide (VHP),19 chemical disinfectants,12 and autoclaving.20 Although some of these methods show promise, most can lead to a reduction in the meltblown’s filtration efficiency or alteration in the physical fit of the FFR,12,16 making them potentially unsafe for repeated usage. In addition, the proposed decontamination methods that may not alter the physical properties of the FFR (filtration efficiency and fit) have varying levels of efficacy. For example, Figure 1. Scanning electron microscope (SEM) images of mild UV irradiation, which is an accessible and promising meltblown fabric before and after aerosol loading. Images of one piece of meltblown fabric (A) before and after loading with aerosol method for FFR decontamination when used within certain containing NaCl particles for 1 min (B) or 10 min (C). Particles dosages, may have poor penetration when many layers of trapped in the fabric can be observed in B and C. material are present. This raises the concern that the virus may be protected from inactivation if it penetrates deep into the fi 21 test the particle adsorption of the meltblown bers, we used layers of the FFR. On the other hand, decontamination using sodium chloride (NaCl) solution as an aerosol source (0.26 ° moderate heat (<100 C) has emerged as one of the most μm mass median diameter, 0.075 μm count median diameter) promising methods to decontaminate FFRs during the and loaded the NaCl aerosol onto the meltblown fabric. SEM COVID-19 pandemic because it causes little damage to the 12,22 images showed clear NaCl particles adsorbed onto the FFR and can be done in high throughput. While there is meltblown fibers (Figure 1B and C). evidence that viruses can show considerable resistance to dry fi 23,24 As the primary ltering material for small particles in FFRs, heat after being dried on surfaces, detailed data are not meltblown fabric was used to give a worst-case scenario for consistently available for all viral families. For example, one how the filtration efficiency changes as respirators are treated fl study found that when in uenza virus was dried on a stainless- under various temperatures and humidities. Thus, if the ff steel surface, heating was more e ective at reducing viral meltblown fabric is observed to be unaffected by the treatment, 24 fl infectivity when the humidity was high. Heating in uenza it is not expected that all of an FFR’s filtration properties ° virus at 60 C for 15 min at 25% relative humidity (RH) would be affected. However, if the meltblown fabric’s filtration resulted in a decrease of 1 log10-fold in viral titers, whereas the properties are changed, this does not necessarily indicate that same heating process at 50% RH reduced viral titers by a factor ’ fi ff 24 all of an FFR s ltration properties would be a ected, as the of 4 log10-fold. Although SARS-CoV-2 has been shown to be full respirator has other supporting materials and is made up of ffi 25 e ciently inactivated by heat in solution, a comparison of multilayers, which can make it more robust. As there are inactivation by dry or moist heat when the virus is dried on multiple brands of FFRs with different meltblown fabrics and surfaces has not been carried out, although one study found basis weights, some may be more robust than others. that stability of SARS-CoV-2 is lower in high humidity at Evaluating the meltblown fabric alone, particularly a single ≤ ° 26 common environmental temperatures ( 38 C). layer, can give an indication of worst-case conditions. In To further address the relationship between humidity and addition, we only considered how the meltblown’s filtration virus susceptibility to heat inactivation, we tested heat efficiency would change, but as FFRs also require proper inactivation protocols using three positive strand enveloped fitting, it is possible that treatment conditions can alter the fit RNA viruses: SARS-CoV-2, human coronavirus NL63 (HCoV- of FFRs. The data currently show that with respect to heat NL63), and chikungunya virus, vaccine strain 181/25 decontamination, it is unlikely to alter the fit of FFRs.27 (CHIKV-181/25). We tested infectivity of virus samples We used a meltblown fabric of 20 g/m2 with initial efficiency dried on meltblown fabric, before subjecting the samples to a around 95% (details given in the Methods section) to simulate − ° − treatment of temperatures (60 95 C) at either ambient (40 how the filtration efficiency would change after application of 60% RH) or 100% RH. heat for multiple treatment cycles. We first performed filtration efficiency testing after heat treatment of the meltblown fabrics RESULTS under low humidity conditions (≤30%) to determine the FFRs of N95 or equivalent grade are usually composed of upper limit of applicable heat. We observed no change in the many layers of polypropylene nonwoven fabrics. Among the filtration efficiency after treatment from 75 to 100 °C, with up most important layers for its protective functionality is one to 20 treatment cycles hovering around 95% filtration produced by the meltblown process (i.e., meltblown nonwoven efficiency. However, we observed that heating at 125 °C led fabric), in which high velocity air blows a molten polymer, to a sharp drop in the filtration efficiency at the fifth cycle, forming filaments that extend in different orientations and leading to a filtration efficiency of around 90%.
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