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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Polyhydroxyalkanoates (PHAs) are excellent candidate biomaterials due to their exceptional biodegradability and biocompatibility. However, PHAs need to have tunable hydrophilicity, chemical functionalities, and appropriate hydrolytic stability to expand their therapeutic applications towards more advanced areas. In this Tutorial Review, we present the most recent progress in the synthetic strategies of PHA-based water soluble polymers, including the functionalisation of PHAs with polar functional groups and the block/graft copolymerization of PHAs with hydrophilic components in various polymeric architectures. These chemically modified water soluble PHAs have significant impact on materials engineering and show great value in the fulfilment of smart biomaterials in emerging areas. The applications of water soluble PHAs in controlled drug release, cancer therapy, DNA/siRNA delivery and tissue engineering in new aspects are discussed. In addition, water soluble PHA monomer production will be briefly introduced, with emphasis on its bio-significance in medical physiology and the therapeutic effect in the treatment of diseases.

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Polylactide (PLA) has been receiving significant attention in biopolymer research due to its excellent biodegradability, biocompatibility and sustainability. The mass production of PLA from renewable agricultural resources has delved this green material as a top alternative to replace the petroleum-based conventional polymers. However, the inherent weaknesses of PLA in its raw state such as brittleness, low heat distortion temperature and recrystallization rate, as well as the inadequate crystallization ability and degree after fast processing have limited the competitive edge of PLA over traditional synthetic plastics in industrial use or for biomedical applications. Being different from other types of biodegradable polymers, the diverse isomeric forms of PLA have provided great opportunities for thermal and mechanical enhancement through stereocomplexation formation. In this review, we present the most recent development in thermal and mechanical enhancement of PLA via stereocomplexation of PLA in different polymeric systems, including enantiomeric PLA homopolymers, PLA-based block and graft copolymers, as well as enantiomeric PLA materials having unique architectures such as cyclic, star, dendritic and comb-shaped. Insightful discussion on the influence of crystal structure and intermolecular interactions between PLLA and PDLA in the different polymeric systems on the enhanced performance of the resultant materials are provided. The enhanced PLA with diverse functions oriented toward engineering materials and their biosignificance in different areas are also covered in this review.

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