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Abstract
Polyhydroxyalkanoates (PHAs) are biopolyesters that accumulate as intracellular inclusion bodies in a wide variety of bacteria. The most studied member of the PHA family, Polyhydroxybutyrate (PHB), is an FDA approved biomaterial used in biomedical applications. While PHB has the advantages of biocompatibility and biodegradability, its brittle nature and relative high manufacturing costs limit its application. Consequently a number of studies have investigated strategies to support is application. Blending with other FDA approved polymers can be used to improve the material properties, biodegradability and biocompatibility of PHB as well as reduce resin costs. This study examined the influence of blending PHB with another FDA approved polymer, Poly(ethylene glycol) (PEG), and ‘bioPEGylation’.
Blending PHB with various loadings of PEG106 (DEG) and PEG2000 produced natural-synthetic composite films with significant reductions in crystallinity, from 70 ± 3.23 to 37 ± 2.11 % and hydrophobicity from 90.32 ± 1.72 to 60.01 ± 2.95 °. Blending with PEGs also permitted the manipulation of the physiochemical and material properties, including tensile strength (18.74 ± 1.48 to 22.11 ± 1.45 MPa), extension at break (2.49 ± 1.01 to 8.32 ± 1.06 %), fold number (28 ± 2 to 36 ± 2), water uptake (2.62 ± 0.34 to 9.86 ± 1.37 %) and porosity (58.00 ± 3.01 to 65.50 ± 3.55 %). Hydrophilic PEG was readily released from the composites when incubated in phosphate buffered saline under a physiological condition, resulting in a two-stage degradation profile. Blending the hydrophobic PHB with hydrophilic PEG also supported the attachment and proliferation of olfactory ensheathing cells (OECs). Cell Cycle analysis determined that OECs cultivated on the PHB/PEG composites exhibited greater viability and cell health than those cultivated on PHB films. Similar changes were also determined for PEG composites with a copolymer of poly(hydroxybutyrate-co-hydroxyvalerate) (P(HB-co-HV)).
PHB and its bioPEGylated hybrid were successfully synthesised through bioprocessing using Cupriavidus necator. The PHB-b-DEG hybrid possessed a lower crystallinity (49 ± 3.65 %) and molecular weight (146 k) than PHB, 62 ± 4.67 % and 1143 k respectively. Similar to PHB/PEG composites, the hybrid exhibited significantly improved physiochemical, material and biological properties, while avoiding the initial PEG loss during degradation. Genes for the expression of neurite inhibitory proteins, Nogo and PirB in OECs cultivated on films of PHB and its hybrid were down-regulated confirming the promotion of cell proliferation. The data suggests that control of PEG composition in PHB based biomaterials supports their design of biomedical devices.