In vitro degradation behavior of β-calcium metaphosphate whiskers/poly L-lactide composite

The strength, molecular weight and morphology of β-calcium metaphosphate whiskers/poly L-lactide composites (β-CMP_W/PLLA) for internal fixation of bone fractures were measured after degradation in the simulated body fluid. The results indicate that the compress strength of the composites can maintain in 8 weeks. The strength of 25wt% β-CMP_W/75wt% PLLA maintains at 103 MPa in 20 weeks, and the strength of 45wt% β-CMP_W/55wt% PLLA drops to approximately 88% of the initial value in 12 weeks. The scanning electron microscope (SEM) images show that PLLA disappears increasingly and a few pores are formed on the rods surface of the samples. The pH value of the simulated body fluid can keep stabilization during degradation. Gel permeation chromatography(GPC) patterns show that the molecular weight of PLLA significantly decreases with the immersion time. The number-average molecular weight is about 200000 and the weight-average drops 32% after degradation for 20 weeks.