Semi-interpenetrating networks of bacterial poly(3-hydroxybutyrate) with net-poly(ethylene glycol)

Semi-interpenetrating network (IPN) hydrogels based on bacterial poly(3-hydroxybutyrate) (PHB) and net-poly(ethylene glycol) (net-PEG) were prepared by the UV irradiation technique. The swelling and thermal behavior of the hydrogels, as well as their mechanical properties were studied by means of swelling tests, differential scanning calorimetry and tensile experiments. Net-PEG-based hydrogels all show higher equilibrium water contents (EWCs), while a remarkably decreased EWC is observed for the hydrogel containing 75% PHB. The thermal behavior of PHB in the semi-IPNs is not greatly affected by hydrogel composition. However, the crystallinity of PEG segments is noticeably decreased by crosslinking and would further drop with increasing amount of PHB. Incorporation of semi-IPN structure with PHB could significantly improve the mechanical properties of hydrogels when compared with that of pure net-PEG. The PHB/net-PEG (50/50) semi-IPN2, ranking as that possessing the best mechanical properties in the wet state, is expected to be useful as a biomedical material.