STIMULATION OF BONE HEALING BY TRANSFORMING GROWTH-FACTOR-BETA-1 RELEASED FROM POLYMERIC OR CERAMIC IMPLANTS

The ability of transforming growth factor-beta1 (TGF-beta1) to stimulate bone healing was evaluated in a rat critical calvarial defect model. Both a low dose and a high dose of TGF-beta1 were incorporated into two different types of implants: one made from a composite of poly(lactic-co-glycolic acid) (PLPG) (50:50) and demineralized bone matrix (DBM), and the other from calcium sulfate (CaSO4). Scanning electron microscopy showed that the CaSO4 implants were more porous than the PLPG/DBM samples. Both types of implants released biologically active TGF-beta1, for over 300 h in vitro. The samples were implanted in a 9-mm diameter rat calvarial defect for 6 weeks along with contralateral control implants containing no TGF-beta1. Microradiography and histological analysis were used to assess the bone healing in the defects. Microradiography revealed that the greatest amount of calcified bone (67.5%) was present in the CaSO4 implants containing a high dose of TGF-beta1 while minimal new bone formation occurred in the PLPG/DBM implants. Histologically, the PLPG/DBM implants exhibited an inflammatory response with little mineralization or bone formation. The defects containing the PLPG/DBM implants consisted of a connective tissue stroma with large void spaces. Giant cells and numerous polymorphonuclear leukocytes were present throughout the implants. In contrast, the CaSO4 implants had only a few inflammatory cells and the presence of mineralization and true bone was a more consistent feature. These preliminary studies show that TGF-beta1 is capable of inducing new bone formation. Furthermore, the materials used to deliver the growth factor can play a significant role in the bone healing process. (C) 1994 John Wiley & Sons, Inc.