Analytical prediction of hydrolysis behavior of tricalcium phosphate/poly-L-lactic acid composites in simulated body environment

Abstract

Bioactive ceramics/poly-L-lactic acid (PLLA) composites have been expected as a material for bone fracture fixations which have more biocompatibility than monolithic PLLA. In this study, monolithic PLLA and β-tricalcium phosphate (β-TCP)/PLLA composites containing three different β-TCP contents (5, 10, 15 wt%) were prepared by injection molding and hydrolysis behavior in simulated body environment was characterized. The specimens were immersed in phosphate buffered solution to measure water absorption and molecular weight of the specimen. Water absorption in monolithic PLLA increased with increasing immersion time up to 14 days, and then saturated, whereas water absorption in composites increased with increasing immersion time up to 168 days. The composites with higher β-TCP content showed larger water absorption. Degradation of number averaged molecular weight for the composites became faster with β-TCP content at the same immersion time. Number averaged molecular weight of 15 wt% composites decreased from 60,000 to 39,000 after 24 weeks immersion. Two layers and three layers models were proposed to predict water absorption and number average molecular weight variation, respectively. To predict hydrolysis behavior of bioactive ceramics/PLLA composites more precisely, effect of water diffusion was considered in the proposed models. Predictions based on the present models were in good agreement with experimental results and the effectiveness of the models was confirmed.