Polyhydroxyalkanoates: opening doors for a sustainable 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. Non-toxic and biodegradable polymers synthesized by bacteria have desirable attributes for tissue engineering and drug delivery applications. Polyhydroxyalkanoates (PHAs) are linear polyesters, produced within microbe cells to store energy and carbon. They can be synthesized from over 150 molecular precursors — a diversity that can generate petroleum-free plastics with a range of physical properties. Xian Jun Loh from A*STAR in Singapore and co-workers review efforts to improve the economics and poor mechanical stability of PHAs by two techniques. Blending PHAs with other biopolymers, such as starches or cellulose, can reduce manufacturing costs while tweaking characteristics such as melting points and fracture toughness. Alternatively, PHAs can be chemically modified by grafting or copolymerizing them with natural polymers. Such synthetic approaches are critical for tuning blood compatibility in implantable, PHA-based devices. PHAs are natural biodegradable polyesters synthesized by microorganisms. However, several disadvantages such as their poor mechanical properties and limited functionalities limit their competition with traditional synthetic plastics or their application as ideal biomaterials. To circumvent these drawbacks, PHAs need to be modified to ensure improved performance in specific applications. 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 are summarized. The functionalization of PHAs by block copolymerization and graft copolymerization is described. The expanded utilization of the modified PHAs as (bio)engineering materials is addressed.