Strain rate dependency of mechanical properties of TCP/PLLA composites after immersion in simulated body environments

In order to clarify strain rate dependency of mechanical properties of β-tricalcium phosphate (TCP)/poly(l-lactic acid) (PLLA) composites after immersion in simulated body environment, tensile tests at various loading rate were conducted on the TCP/PLLA specimens with and without immersion. TCP contents in the composite were 5, 10 and 15 wt%. Phosphate buffered solution was selected as simulated body environment and immersion periods were 8, 16 and 24 weeks. Young's modulus and tensile strength increased with increasing strain rates. However, the strain rate dependencies decreased with immersion. Swelling and cracks around TCP agglomerations were observed in the cross-section of 15 wt% specimen after 24 weeks immersion. From the fracture surface observation, voids existed only in the ductile fracture surface of the specimen without immersion, whereas they existed in both ductile and brittle surface of the specimen with immersion. These results indicated that diffused water through the interfaces between TCP and PLLA hydrolyzed and weakened the interfaces and/or matrix near the interfaces.