Face Masks in the New COVID-19 Normal: Materials, Testing, and Perspectives

Abstract

The increasing prevalence of infectious diseases in recent decades has posed a serious threat to public health. Routes of transmission differ, but the respiratory droplet or airborne route has the greatest potential to disrupt social intercourse, while being amenable to prevention by the humble face mask. Different types of masks give different levels of protection to the user. The ongoing COVID-19 pandemic has even resulted in a global shortage of face masks and the raw materials that go into them, driving individuals to self-produce masks from household items. At the same time, research has been accelerated towards improving the quality and performance of face masks, e.g., by introducing properties such as antimicrobial activity and superhydrophobicity. This review will cover mask-wearing from the public health perspective, the technical details of commercial and home-made masks, and recent advances in mask engineering, disinfection, and materials and discuss the sustainability of mask-wearing and mask production into the future.

Figure 1

Relative size chart of common airborne contaminants and pathogens.

Figure 2

Simulated future (cumulative) death tolls for Washington state, using either a fixed (top panels) or variable (bottom panels) transmission rate, β, and nine different permutations of general public mask coverage and effectiveness. The y-axes are scaled differently in the top and bottom panels. Reproduced with permission from Ref. [18]. Copyright 2020, Elsevier B.V. on behalf of KeAi Communications Co., Ltd.

Figure 3

Illustration showing the function of each individual layers of a 3-ply surgical mask.

Figure 4

Schematic illustration of spunbond and melt-blown process. Republished with permission from Ref. [59]. Copyright 2015, Butterworth-Heinemann.

Figure 5

Schematic illustration of air manifold in melt-blown process. Republished with permission from Ref. [61]. Copyright 2014, Woodhead Publishing Limited.

Figure 6

Air flows through a channel with different sizes.

Figure 7

Design of the setup for evaluating BFE and VFE of mask materials using a six-stage Andersen sampler.

Figure 8

(a) Photos showing examples of simple cloth masks. Reproduced with permission from Ref. [91]. Copyright 2019, Neupane et al., PeerJ. (b) Schematic showing the pattern for a homemade mask. Reproduced with permission from Ref. [92]. Copyright 2020, Springer Nature.

Figure 9

A new design of homemade cloth masks from common fabric materials. Reproduced with permission from Ref. [95]. Copyright 2020, the American Chemical Society.

Figure 10

(a) Schematic showing the fabrication of nylon-6/PAN nanofibre/net membranes by electrospinning/netting technology. (b) Schematic showing an electret filter consists of PE/PP nanofibre as the matrix and magnesium stearate as the charge enhancer. (c) Schematic image of the filtration mechanism of the filter with R-TENG. (d) Structure and photo of a self-powered electrostatic adsorption face mask with R-TENG. Reprinted with permission from Ref. [126], copyright 2015, Macmillan Publishers Limited; Ref. [139], copyright 2015, The Royal Society of Chemistry; and Ref. [–142], copyright 2017–2019, American Chemical Society.

Figure 11

(a) Proposed capture mechanism of the MOF-based filter for air pollutants. Inset is the SEM image of the surface of the MOF/polymer composite fibre. (b) MOF filters based on various flexible substrates produced by a roll-to-roll hot-pressing method. (c–e) SEM images of the ZIF-8@plastic mesh achieved after seven layer-by-layer coating cycles. Reprinted with permission from Ref. [159] and Ref. [156]. Copyright 2016 and 2017, the American Chemical Society and WILEY-VCH.

Figure 12

Schematic representation of MOF-based filter (MOFilter) for integrated air cleaning. Reproduced with permission from Ref. [196]. Copyright 2019, Springer Nature.