A technical review of face mask wearing in preventing respiratory COVID-19 transmission

Abstract

Since the outbreak of the COVID-19 pandemic, most countries have recommended their citizens to adopt social distance, hand hygiene, and face mask wearing. However, wearing face masks has not been well adopted by many citizens. While the reasons are complex, there is a general perception that the evidence to support face mask wearing is lacking, especially for the general public in a community setting. Face mask wearing can block or filter airborne virus-carrying particles through the working of colloid and interface science. This paper assesses current knowledge behind the design and functioning of face masks by reviewing the selection of materials, mask specifications, relevant laboratory tests, and respiratory virus transmission trials, with an overview of future development of reusable masks for the general public. This review highlights the effectiveness of face mask wearing in the prevention of COVID-19 infection.

Keywords: Aerosols; Airborne colloids; Fabric; Face masks; Fibers; Filtering; Porous materials; Viral particles.

Graphical abstract

Figure 1

Structure and composition of materials in different layers of a standard medical face mask and illustrations of key features from four commercial face masks. (a) Schematic assignment of the function of the respective layers in a medical face mask: a combination of a physical barrier and electrostatic absorption against droplets, viruses, bacteria, and aerosols, containing viruses/bacteria. (b) Typical materials used in respective layers. (c) 3D Morphologies of (i) spunbonded nonwoven fabrics and (ii) melt-blown nonwoven fabrics; (iii) 3D structure of a knitted fabric and (iv) schematic of a wet padding process. (d) Comparison of four representative commercial face masks. (i) UNIQLO AIRism face mask consisting of three functional layers, sunscreen layer, particle filtration layer, and skin-friendly layer; (ii) Graphene-coated mask surface is of excellent self-cleaning and photothermal properties; (iii) Bioinspired spider web-like mask filling ZIF-8 around the nanofibers; (iv) Thermal-management nanofiber-based face mask coating with Ag thin layer. Inset pictures in Figure 1d are reprinted from Ref. [53, 61, 67] with permissions from American Chemical Society and Elsevier.

Figure 2

Antimicrobial/bacterial filtration mechanisms of different mask types and their corresponding antimicrobial agents. (a) Virus/bacterial filtration via a physical barrier and electrostatic absorption in cloth and surgical masks. Antimicrobial/antiviral action via masks modified with (b) silver-nanoparticle coating, (c) graphene layer with photothermal effects, and (d) cationic surfactants/polymers, and amphiphilic polymers [73, 74, 75]. (e) The chemical structure of some commonly used antimicrobial agents: graphene, quaternary ammonium compounds, silver nanoparticles, cationic and amphiphilic polymers (from top to bottom). The last picture in Figure 2e are reprinted from Ref. [73] with permission from Elsevier.