Evaluation of polylactic acid homopolymers as carriers for bone morphogenetic protein.

Polylactic acid (PLA) homopolymers with molecular weights of 105,000; 21,000; 3300; 650; and 160d (PLA105000, PLA21000, PLA3300, PLA650, and PLA160, respectively) were prepared and evaluated as carriers for bone morphogenetic protein (BMP). Composites consisting of 4 mg of water-soluble, semipurified BMP and 100 mg of one of the PLA homopolymers were implanted into the dorsal muscles of mice. PLA105000/BMP, PLA21000/BMP, PLA3300/BMP, and PLA160/BMP composites failed to induce new bone formation; PLA105000, PLA21000, and PLA3300 elicited foreign-body reactions or chronic inflammation (or both), and PLA160 produced tissue necrosis. PLA650/BMP composites induced cartilage formation within one week and induced bone with hematopoietic marrow at three weeks postimplantation. PLA650/BMP composites were completely absorbed and replaced by new bone. The results suggest that within this group of PLA homopolymers, PLA650 may be the only type suitable for use as a BMP carrier.