Degradation behavior of composite pins made of tricalcium phosphate and poly(L,DL-lactide).

Combining a bioactive ceramic with a resorbable polymer may improve the biocompatibility and the osseointegration of degradable fracture fixation devices. This study reports on the mechanical properties and degradation behavior of two composite pins made of poly(L,DL-lactide) and 10 and 30% beta-tricalcium phosphate (TCP), respectively. The pins were compared to a pin made of 100% poly(L,DL-lactide). The failure force, bending strength, and molecular weight were determined during in vitro degradation at 37 degrees C up to 78 weeks. The blending with 10 or 30% beta-TCP decreased the initial mechanical properties and led to an accelerated degradation rate. The pins with 30% TCP lost half of their strength after 16 weeks, i.e. faster than the unmodified pin (40 weeks). The pins with 10% TCP, however, showed a decreased initial strength (128+/-9 MPa) compared to the unmodified pin (152+/-9 MPa) but very similar degradation characteristics. The drop of the molecular weight was not significantly different between the three types of pins. It was concluded that the mechanical requirements for a pin for the fixation of small bony fragments with improved biocompatibility were fulfilled by the composite pin with 10% TCP but not by the pin with 30% TCP.