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.

Polyhydroxyalkanoates (PHAs) comprise a group of natural biodegradable polyesters that are synthesized by microorganisms. However, several disadvantages limit their competition with traditional synthetic plastics or their application as ideal biomaterials. These disadvantages include their poor mechanical properties, high production cost, limited functionalities, incompatibility with conventional thermal processing techniques and susceptibility to thermal degradation. To circumvent these drawbacks, PHAs need to be modified to ensure improved performance in specific applications. In this review, well-established modification methods of PHAs are summarized and discussed. The improved properties of PHA that blends with natural raw materials or other biodegradable polymers, including starch, cellulose derivatives, lignin, poly(lactic acid), polycaprolactone and different PHA-type blends, are summarized. The functionalization of PHAs by chemical modification is described with respect to two important synthesis approaches: block copolymerization and graft copolymerization. The expanded utilization of the modified PHAs as engineering materials and the biomedical significance in different areas are also addressed.

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