A laboratory-based study examining the properties of silk fabric to evaluate its potential as a protective barrier for personal protective equipment and as a functional material for face coverings during the COVID-19 pandemic.

Adam F Parlin,Samuel M Stratton,Patrick A Guerra,Theresa M Culley,Noreen J Hickok

doi:10.1371/journal.pone.0239531

Abstract

The worldwide shortage of single-use N95 respirators and surgical masks due to the COVID-19 pandemic has forced many health care personnel to use their existing equipment for as long as possible. In many cases, workers cover respirators with available masks in an attempt to extend their effectiveness against the virus. Due to low mask supplies, many people instead are using face coverings improvised from common fabrics. Our goal was to determine what fabrics would be most effective in both practices. Under laboratory conditions, we examined the hydrophobicity of fabrics (cotton, polyester, silk), as measured by their resistance to the penetration of small and aerosolized water droplets, an important transmission avenue for the virus causing COVID-19. We also examined the breathability of these fabrics and their ability to maintain hydrophobicity despite undergoing repeated cleaning. Laboratory-based tests were conducted when fabrics were fashioned as an overlaying barrier for respirators and when constructed as face coverings. When used as material in these two situations, silk was more effective at impeding the penetration and absorption of droplets due to its greater hydrophobicity relative to other tested fabrics. We found that silk face coverings repelled droplets in spray tests as well as disposable single-use surgical masks, and silk face coverings have the added advantage over masks such that they can be sterilized for immediate reuse. We show that silk is a hydrophobic barrier to droplets, can be more breathable than other fabrics that trap humidity, and are re-useable via cleaning. We suggest that silk can serve as an effective material for making hydrophobic barriers that protect respirators, and silk can now be tested under clinical conditions to verify its efficacy for this function. Although respirators are still the most appropriate form of protection, silk face coverings possess properties that make them capable of repelling droplets.

Highlights

Personal protective equipment (PPE), N95 respirators and surgical masks, are vital to protect against viral transmission during the current COVID-19 pandemic, yet global shortages of these items will likely continue in many locations for the foreseeable future
Respirators and masks used by health care providers (HCP) and essential workers (EW) form part of the critical armament against COVID-19, a significant drawback of PPE are that they are purposed for only single use
The hydrophobicity of silk fabric is further enhanced when used in multiple layers, which when combined, are still thinner than most cotton materials and standard PPE such as surgical masks

Summary

Introduction

Personal protective equipment (PPE), N95 respirators and surgical masks, are vital to protect against viral transmission during the current COVID-19 pandemic, yet global shortages of these items will likely continue in many locations for the foreseeable future. To prolong the life of respirators, many HCPs have adopted the clinical practice of wearing multiple pieces of PPE simultaneously, e.g., a mask on top of a respirator [2,3,4] This strategy is unsustainable as layering masks over respirators can negatively impact the wearer psychologically (e.g., increased and prolonged thermal discomfort while working due to the extra layer) and physiologically (e.g., further strain on breathing due to increased thickness) [2,3,4]. HCPs and EWs remain vulnerable as they have resorted to using (and reusing) less efficient masks on their own when respirators are unavailable, leaving them at greater risk to viral transmission

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