Bacterial polyhydroxyalkanoates-eco-friendly next generation plastic: Production, biocompatibility, biodegradation, physical properties and applications

Abstract

Polyhydroxyalkanoates (PHAs) are intracellular aliphatic polyesters synthesized as energy reserves, in the form of water-insoluble, nano-sized discrete and optically dense granules in cytoplasm by a diverse bacteria and some archae under conditions of limiting nutrients in the presence of excess carbon source. Bacteria synthesize different PHAs from coenzyme A thioesters of respective hydroxyalkanoic acid, and degrade intracellularly for reuse and extracellularly in natural environments by other microorganisms. In vivo, PHAs exist as amorphous mobile liquid and water-insoluble inclusions but in vitro, exhibit material and mechanical properties, ranging from stiff and brittle crystalline to elastomeric and molding, similar to petrochemical thermoplastics. Further, they are hydrophobic, isotactic, biocompatible and exhibit piezoelectric properties. But as commodity plastics their applications are limited by high production cost, low yield, in vivo degradation, complexity of technology and difficulty of extraction. Therefore, to replace the conventional plastic with PHAs, it is prerequisite to standardize the PHA production systems.

Antibacterial PHAs coating for titanium implants

“…There has been an increasing interest in the use of natural materials as drug delivery vehicles due to their appealing properties. The natural origin, biodegradability, and biocompatibility of PHAs make them suitable for a variety of applications in the health industry [10,25,26]. Particularly because of their property of biodegradation, PHAs were studied as a matrix for the antibiotic and as a controlled drug delivery system.…”

Enhanced production of poly(3-hydroxybutyrate) in recombinant Escherichia coli and EDTA–microwave-assisted cell lysis for polymer recovery

“…But their wide spread application as commodity plastics is hampered mainly by high cost of production and extraction from bacterial biomass (Muhammadi et al 2015). To circumvent this, several alternative approaches including the use of cheap substrates and hyper producing bacterial strains are being tested (Khanna and Srivastava 2005; Madison and Huisman 1999).…”

Biodegradable Polyhydroxyalkanoates by Stereoselective Copolymerization of Racemic Diolides: Stereocontrol and Polyolefin‐Like Properties

“…In this context, polyhydroxyalkanoates (PHAs), a unique class of biorenewable aliphatic polyesters that are biodegradable in ambient environments, have shown great potential as a replacement for petroleum‐based plastics. Natural PHAs, produced by bacteria and other living microorganisms from biorenewable resources, are purely isotactic polymers containing a chiral site in each repeat unit, and their thermal and mechanical properties span a wide range depending on the length of the pendant group on the β‐carbon atom, making them attractive for a wide range of applications . Among them, bacterial poly[( R )‐3‐hydroxybutyrate], P[( R )‐3HB], with a methyl group as the side‐chain, is highly crystalline with a melting temperature ( T m ) of 170–180 °C, showing comparable thermal and mechanical properties (especially tensile strength) to those of isotactic polypropylene ( it ‐PP).…”