Growth factors in bone

Bone contains several growth factors, including bone morphogenetic proteins (BMPs), transforming growth factor beta (TGF-beta), insulin-like growth fa ctors I and II (IGF-I and IGF-II), platelet derived growth factor (PDGF) an d basic and acidic fibroblast growth factor (bFGF and aFGF). Spatial and te mporal variations in the expression and secretion of the various growth fac tors have been demonstrated in osteoblastic cultures and in various experim ental and clinical in vivo models including fracture healing in humans. Loc al application of various growth factors influences proliferation, differen tiation and protein synthesis in osteoblastic cultures and bone formation i n different animal models, including experimental fractures and skeletal de fects. The BMPs are the only growth factors known to provoke bone formation heterotopically by making undifferentiated mesenchymal cells differentiate into osteoblasts (osteoinduction). BMPs and other growth factors, soon to become commercially available for clinical use, need a delivery system for their sustained release, as the factors are otherwise rapidly absorbed. Som e existing systems inhibit bone formation by inducing chronic inflammation or physically by unresorbed carrier obstructing bone formation. New deliver y systems are being investigated.