Biosynthesis and characterization of polyhydroxyalkanoate containing 5-hydroxyvalerate units: Effects of 5HV units on biodegradability, cytotoxicity, mechanical and thermal properties

This study describes the biosynthesis of polyhydroxyalkanoate (PHA) containing 5-hydroxyvalerate (5HV) units. Monomer units like 5HV, with variation in length of the backbone segment of the repeat unit, are known to more greatly impact mechanical properties of polymers. Introduction of 5HV units was also aimed at enhancing biodegradability of the material, as it had been found previously that a homopolymer of 5HV could be degraded by lipase. The produced poly[(R)-3-hydroxybutyrate-co-3-hydroxypropionate-co-5-hydroxyvalerate]s [P(3HB-co-3HP-co-5HV)s] with 5HV content ranging from 1 to 32 mol% by the choice of strain, type and concentration of carbon substrate, exhibited low melting temperature (Tm), reduced crystallinity and elastomeric behavior. Enzymatic degradation test confirmed the role of 5HV unit in enabling lipase-mediated degradation of P(3HB-co-3HP-co-5HV)s, as poly[(R)-3-hydroxybutyrate] and poly[(R)-3-hydroxypropionate] films were not hydrolyzed by porcine pancreas lipase. Additionally, viability assay of human mesenchymal stem cells revealed that the P(3HB-co-3HP-co-5HV) films were less cytotoxic and supported cell proliferation, highlighting the potential of P(3HB-co-3HP-co-5HV)s as biomaterials.