Abstract

The development and use of novel materials is one of the main tasks of industrial, biomedical, and environmentally safe technologies. Polyhydroxyalkanoates (PHAs) - biodegradable biocompatible polyesters of microbial origin - are among the most promising materials, which can be used in various areas. The authors' collection of highly productive strains and original technologies were used to synthesize a family of PHA heteropolymers composed of such monomer units as 3-hydroxybutyrate (3HB), 4-hydroxybutyrate (4HB), 3-hydroxyvalerate (3HV), and 3-hydroxyhexanoate (3HHx). The purpose of this study was to investigate kinetic and production parameters of PHA producing bacterial strains of Cupriavidus genus, their ability to synthesize PHA terpolymers, and physicochemical properties of PHA heteropolymers. NMR, differential scanning calorimetry, chromatography-mass spectrometry, gel permeation chromatography, and X-ray structure analysis were used. Optimization of a number of parameters of bacterial cultures (cell concentration in the inoculum, physiological activity of the inoculum, determined by the initial intracellular polymer content, and concentration of carbohydrates in the culture medium during cultivation) provided cell concentrations and PHA yields reaching 110 g/L and 80%, respectively, under two-stage batch culture conditions. Addition of precursor substrates (valerate, hexanoate, propionate, γ-butyrolactone) to the culture medium enabled synthesis of PHA terpolymers, P(3HB/3HV/4HB) and P(3HB/3HV/3HHx), with different composition and different molar fractions of monomers. PHA terpolymers obtained were used to prepare films, whose physicochemical and physical-mechanical properties were investigated. The properties of PHA terpolymers were significantly different from those of the P3HB homopolymer: they had much lower degrees of crystallinity and lower melting points and thermal decomposition temperatures, with the difference between these temperatures remaining practically unchanged. Films prepared from all PHA terpolymers had higher mechanical strength and elasticity than P3HB films. In spite of dissimilar surface structures, all films prepared from PHA terpolymers facilitated attachment and proliferation of mouse fibroblast NIH 3T3 cells more effectively than polystyrene and the highly crystalline P3HB. Thus, we have developed a fundamental approach to the production of PHAs with different composition, with tailored physical and mechanical properties.