STUDY ON HYDROLYTIC DEGRADATION OF POLY (p-DIOXANONE) WITH HIGH MOLECULAR WEIGHT IN VITRO

As there was no report on the degradation properties of poly (p-dioxanone) (PPDO) with molecular weight above 2.0 x 10(5) and most studies on PPDO were carried out using monofilament suture of poly (p-dioxanone) as model in previous reports, so it was interesting to study the behavior of PPDO with higher molecular in other solid form, such as plates and bars. The in vitro hydrolytic degradation of high molecular weight poly-(p-dioxanone), (M = 2.8 x 10(5)) was studied by the changes of weight retention, water absorption, pH value, intrinsic viscosity, tensile strength, break elongation, thermal properties, crystalline structure and the morphology of PPDO bars in phosphate buffered saline (PBS) (pH 7.44) at 37 degrees C for 8 weeks. During 8 weeks degradation in PBS, the PPDO samples exhibit obvious changes in their morphology, thermal properties, mechanical properties and degradation behaviors. It was found that the weight loss and water absorption increased slightly, at the same time pH almost maintained original value while the significant decrease of molecular weight was observed. The surface micrographs of PPDO samples showed that microcracks grew with the hydrolytic degradation. The glass transition temperature (T-g) of samples decreased notably, while the degree of crystallinity (D-c) increased and the original crystalline structure substantially remained. The samples lost their tensile strengths and breaking elongation almost completely after 6 weeks of degradation. The results suggested that the PPDO bars with high molecular weight exhibited much smaller degradation rate in vitro hydrolytic degradation.