Osteoconductivity of synthetic octacalcium phosphate (OCP) was found first by its implantation in subperiosteal region of mouse calvaria. New bone appeared on OCP earlier than other calcium phosphate materials, such as synthetic stoichiometric hydroxyapatite (HA), while OCP was converted to apatite structure in situ. Osteoblastic differentiation of mouse bone marrow stromal cells and formation of osteoclasts from mouse bone marrow cells in the presence of osteoblasts were enhanced if they were inoculated on OCP surfaces. It is becoming clear that the stimulatory capacity of OCP is enhanced during a process of OCP hydrolysis into HA at physiological conditions that induces physicochemical reaction around the OCP crystals. The stoichiometry and the microstructure of OCP crystals, which could be determined by the preparation conditions, control its osteoconductivity. Combining OCP with natural polymers, such as collagen, gelatin, alginate and hyaluronic acids, through mixing or co-precipitation processes, improves not only the handling property of OCP but also the bone regenerative capacity as bone substitute materials.
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