In vitro biodegradation of poly(beta-hydroxybutyrate-hydroxyvalerate) microspheres exposed to Hanks' buffer, newborn calf serum, pancreatin and synthetic gastric juice.

Spherical BSA loaded microporous matrix type microspheres composed of P(HB-HV) blended with 20% PCL II and fabricated using 0/W emulsification with solvent evaporation have been incubated in Hanks' buffer, pH 7.4; newborn calf serum; 1.5% pancreatin and synthetic gastric juice over 30 days and their percentage weight loss (PWL) and changes in ultrastructural morphology monitored by gravimetry and SEM respectively. The greatest percentage weight loss was observed after incubation in newborn calf serum and decreased in the order newborn calf serum > pancreatin > synthetic gastric juice > Hanks' buffer. Only incubation in synthetic gastric juice and Hanks' buffer produced a significant increase in PWL with increasing theoretical percentage loading. Incubation in Hanks' buffer produced limited surface erosion leading to an increase in micropore diameter and the coalescence of micropores to from surface pits. With pancreatin, surface erosion led to the disappearance of surface micropores and a reduction in microsphere diameter. Subsequent fracturing of the microsphere surface facilitated the breakup of the matrix. In synthetic gastric juice there was little surface erosion and surface flaking and bulk erosion were responsible for the breakup of the matrix. In newborn calf serum, spherical shape was maintained despite a reduction in microsphere diameter. Bulk erosion in the form of large macroporous pits extending deep into the matrix gave the microspheres a hollow appearance. The enhanced biodegradation in NCS and significant surface erosion in pancreatin was assumed to be due to the effects of exogenous enzyme activity in addition to simple ester hydrolysis.