Properties of PHA bi-, ter-, and quarter-polymers containing 4-hydroxybutyrate monomer units

The present study investigates physicochemical, mechanical, and biological properties of polyhydroxyalkanoate (PHA) copolymers containing 4-hydroxybutyrate (4HB) synthesized in Cupriavidus eutrophus B10646 culture. In poly(3-hydroxybutyrate/4-hydroxybutyrate) [P(3HB/4HB)] bipolymers, 4HB varied between 10.4 and 75.0 mol%; in poly(3-hydroxybutyrate/3-hydroxyvalerate/4-hydroxybutyrate) terpolymers, 4HB constituted 28.7-55.6 mol%; and in poly(3-hydroxybutyrate/3-hydroxyvalerate/4-hydroxybutyrate/3-hydroxyhexanoate) quaterpolymers, 4HB varied between 9.3 and 13.3 mol%. The degree of crystallinity of P(3HB/4HB) copolymers decreased consistently with an increase in 4HB content, reaching 38%. The incorporation of 3-hydroxyvalerate and 3-hydroxyhexanoate into copolymers enhanced that effect. The effect of 4HB monomer units on temperature properties of copolymers was exhibited as lowering of the melting temperature and crystallization temperature, which improved the processing-related properties of the copolymers. All copolymers containing 4HB showed enhanced elongation at break compared to poly(3-hydroxybutyrate). Polymer films prepared from PHAs with different chemical composition had similar microstructure and porosity and had no toxic effect on mouse fibroblast NIH 3 T3 cells, proving their high biocompatibility.