Osteoinductive biomaterials for medical implantation

The search for the ideal implant material continues since presently available implants all have significant drawbacks. This paper reviews three studies that we recently completed with bone-inducing implants. Long-term clinical follow-up of 75 allogeneic demineralized bone implants showed an average degree of resorption of 49%. Implants used for dorsal nasal augmentation showed an average degree of resorption of 50.7%, increasing to 82.5% after a 24-month follow-up. The efficacy of demineralized bone implants is dependent on many factors including site of implantation, method of preparation, etc. Transforming growth factor-beta 1 (TGF-beta 1) is a regulator of bone formation. We combined recombinant TGF-beta 1 with demineralized bone powder in a rabbit facial augmentation model. At 6 weeks, there was evidence of increased bone formation in the implants containing TGF-beta 1. Even though TGF-beta 1 can increase bone formation in demineralized bone implants, the overall bone-inducing activity in these implants seems to be suboptimal. Osteoinductive factor extract (OFE) is a partially purified bone factor preparation that has been shown to form bone when implanted into rats. Using a collagen/ceramic carrier, we implanted OFE into a rabbit facial augmentation model. At 21 d, histomorphometry revealed numerous osteoblasts and bone formation in the OFE implants. The bone-inducing activity of many partially purified osteoinductive preparations such as OFE is probably due to Bone Morphogenetic Protein-2A (BMP-2A), which has been shown to induce bone formation in its recombinant form. Recombinant DNA methodology provides the technology necessary to produce these molecules in their homogeneous form, permitting evaluation of bone-inducing activity in a preparation free of contaminants. Finally, the ideal carrier must be devised to permit safe and effective delivery of recombinant bone-inducing factors.