Growth and differentiation factors: role in bone induction and potential application in craniofacial surgery.

Repair of craniofacial bone often requires autogenous or allogeneic bone. Natural materials deliver bone-inducing substances to wound beds and provide scaffolding for osteoconduction, but not without risk of morbidity. We are developing a synthetic material consisting of proteins which stimulate bone repair encased within a moldable, biodegradable delivery system. The stages of bone induction include chemoattraction of stem cells, proliferation and differentiation of these cells to competent chondrocytes and osteoblasts, angiogenesis, mineralization, and remodeling. Bovine osteogenin induces bone formation in soft tissue in rats, and accelerates bone repair in cranial defects. The protein has been purified and partially sequenced. Growth factors may augment the inductive effects of osteogenin by attracting preosteoblasts, accelerating their proliferation, and stimulating angiogenesis. A composite material of osteogenin and growth factors released from a biodegradable delivery system in a time-dependent fashion is proposed to decrease the necessity for autogenous and allogeneic bone implants.