Effect of Surrounding Chemical Environment on Adsorption and Accumulation of Serum Protein onto Octacalcium Phosphate Crystals

Abstract

Octacalcium phosphate (OCP; Ca₈(HPO₄)₂(PO₄)₄·5H₂O) is a precursor of hydroxyapatite (HA; Ca₁₀(PO₄)₆(OH)₂). OCP is allowed to convert into HA (Ca-deficient HA) through a hydrolysis reaction in vivo and in vitro, because OCP and HA are metastable and stable phase under the physiological condition, respectively. Dissolution-reprecipitation reaction and ion diffusion-crystallization in hydrated layer are considered the mechanisms of the hydrolysis reaction. We have reported that chemical environment regulated by the hydrolysis of OCP stimulates osteoblastic and osteoclastic differentiation resulting in showing higher osteoconductivity and biodegradability of this material in various animal bone defect models. Based on these results, the possibility applying OCP as a bone substitute has been examined. Adsorption of serum proteins also controls the activities of the cells on the surface of biomaterials. Previous in vivo and in vitro studies indicate that accumulation of serum proteins onto OCP surface is involved in the bone formation by osteoblasts. However, it is still unclear about how surrounding chemical environment regulated by the OCP affects the behavior of serum protein adsorption onto OCP crystals. In this review article, the bioactivities of OCP related with its physiochemical properties including the protein adsorption will be explained.