Characterization of a Calcium Phosphate-Based Matrix for rhBMP-2

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-β (TGF-β) superfamily of proteins that have crucial roles in growth and regeneration of skeletal tissues. In particular, recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to induce new bone formation by differentiation of mesenchymal progenitor cells into osteoblasts (1 ). BMPs act locally, and thus for a clinically beneficial outcome, a carrier matrix is required to retain therapeutic levels of BMP at the repair site (2 ,3 ). The potent osteoinductive ability of BMP-2 has been demonstrated in numerous preclinical (4 –9 ) and clinical studies (10 –14 ). Recent data from clinical trials have reported success in the areas of open fracture repair (10 ,14 ), interbody spinal fusion (11 ), and maxillofacial reconstruction (12 ,13 ) using rhBMP-2 delivered in an absorbable collagen sponge (ACS). Because rhBMP-2/ACS requires implantation, there is a continuing need for an easily injectable carrier to deliver rhBMP-2 percutaneously to closed fractures. Here, we outline characterization of a calcium phosphate (CaP)-based injectable carrier as a delivery matrix for rhBMP-2.