Evaluation of hydroxylapatite/poly(L-lactide) composites: mechanical behavior.

By mixing hydroxylapatite (HA) into L(-)-dilactide monomer, prior to polymerization to poly(L-lactide) (PLLA), hydroxylapatite filled poly(L-lactide) composites were obtained. This study reports about the mechanical properties of these composites compared with unfilled PLLA. It was concluded that a 30 wt% HA/PLLA composite has better compressive and tensile strengths, higher stiffness and Vickers hardness number than unfilled PLLA (Mv: 125-150,000). Gas sterilization (ethylene oxide) affects molecular weight and flexural strength significantly. Implantation studies revealed loss of 50% of initial flexural strength within 3 weeks, and a faster decline of flexural strength was observed in phosphate buffered saline than in the subcutis of goats. From a mechanical point of view storage at -20 degrees C proved to be a safe method. In its current state HA/PLLA composites can not be used as implant materials that have to resist major forces. However, such composites might be useful in non-loadbearing applications in orthopedic or maxillofacial surgery.