Evolution of octacalcium phosphate biomaterials

In this chapter the major findings and advances in octacalcium phosphate (OCP) biomaterials were summarized through discussion of factors for selection of biomaterials used in bone tissue repair and the fundamental properties of these biomaterials, particularly in terms of enhancing bone regeneration and clinical applications. The first hypothesis was that biominerals such as OCP, which is presumed to be a precursor to bone apatite crystals, could be actively involved in physiological intramembranous bone development. As such, introduction of synthetic OCP in active biomineralization sites could facilitate additional new bone formation for bone tissue derived from the OCP-like phase. The first experiment to test this hypothesis produced the finding that synthetic OCP placed onto mouse calvaria can be converted to the apatitic phase and induce the early appearance of new bone tissue more readily than other calcium phosphate materials including amorphous calcium phosphate (ACP) or nonsintered hydroxyapatite (HA) materials. Subsequent studies found that OCP induces physicochemical reactions during the hydrolysis of OCP to Ca-deficient HA and enhances osteoblastic differentiation and formation of osteoclasts from bone marrow cells. OCP-based materials have been critical in the development of successful clinical applications that promote bone augmentation.