PHA, the Greenest Plastic So Far: Advancing Microbial Synthesis, Recovery, and Sustainable Applications for Circularity.

The global proliferation of nonbiodegradable petrochemical plastics presents severe environmental, health, and economic challenges, underscoring the urgent need for sustainable alternatives. Polyhydroxyalkanoates (PHAs), a family of biobased and biodegradable polyesters, offer a promising solution with their environmental compatibility, versatility, and ability to mimic conventional plastics. This review explores PHA production, encompassing microbial biosynthesis, metabolic pathways, and innovative extraction methods to optimize production and material properties. Genetic and metabolic engineering advances address cost and scalability barriers, and novel feedstock utilization. Innovations in copolymerization, blending, and nanocomposites have expanded PHA applications across packaging, agriculture, and biomedical fields. The evolution of smart and functionalized PHAs for high-value sectors such as regenerative medicine, drug delivery, and smart packaging further demonstrates their expanded potential beyond conventional bioplastics. Emphasis is placed on integrating PHAs into circular economy models by leveraging waste-derived feedstocks, emerging microbial strategies, including mixed microbial cultures (MMCs), halophilic systems, and aquaculture-integrated production, offer scalable and resilient routes for cost-effective, sustainable PHA biosynthesis. Despite their potential, PHAs remain hindered by challenges involving high production costs, inconsistent mechanical properties, and environmental trade-offs in downstream processing. PHAs are sustainable bioplastics that align competently with Green Chemistry principles, though improvements in energy efficiency and catalytic optimization are required for broader commercial applications. The review highlights novel recovery techniques aligned with a green bioeconomy, including green solvents, supercritical fluid extraction, enzymatic, mealworm, and other biorecovery methods. Integration with circular economy frameworks through waste valorization, biobased feedstocks, and zero-waste biorefinery models further enhances the sustainability of PHA production. Future research must optimize extraction methods, address microplastic risks, and expand into high-value markets. PHAs represent one of the most environmentally promising bioplastics to date due to their complete biodegradability, non-persistent microplastics, and lower emissions, with advancements in production further enhancing their viability. By advancing PHA technologies and fostering interdisciplinary collaboration, PHAs can accelerate the transition to a circular bioeconomy, offering a unique combination of full biodegradability, material tunability, and circular design that positions them as frontrunners in the transition away from fossil-based plastics.