Gel casting of resorbable polymers. 2. In-vitro degradation of bone graft substitutes.

Gel cast microporous materials produced from: slow resorbing, poly(L-lactide); fast resorbing, 50:50 poly(DL lactide coglycolide); and blends of these polymers have been characterized by weight loss, compression testing and thermal analysis after immersion in phosphate buffered saline (37 degrees C, pH 7.4) for times up to 6 months. Increasing weight loss and reduction in compressive properties with immersion time were measured. Blending reduces the rate of weight loss and material shrinkage relative to the copolymer. Thermal analysis of degraded samples revealed evidence of reorganization of the crystalline phase in poly(L-lactide) and a crystalline component in the 50:50 copolymer, estimated at 5-7% of the original material content, which is probably responsible for gel formation. Thermograms of the blend are effectively a superposition of thermograms of the individual components. Gel casting shows potential for varying the resorption rate, form stability and compressive properties of micro/macroporous bone graft substitutes.