Influence of proteins in octacalcium phosphate synthesis for the development of biomimetic synthetic bone substitutes

Gelatin and collagen, known as natural proteins, have been used as additives to improve clinical usability and efficacy of synthetic bone substitutes. In particular, a method of adding natural proteins while synthesizing calcium phosphate minerals has been used to implement a composition similar to natural bone. In this study, octacalcium phosphate (OCP), a raw material for synthetic bone substitutes, was synthesized in a natural protein solution, and the effect of the added protein on the characteristics of OCP crystals was evaluated. OCP powders were prepared by the hydration of dicalcium phosphate dihydrate (DCPD) (CaHPO₄.H₂O) in a protein solution via a heterogeneous crystallization route. The properties of the synthesized OCP crystals were investigated to examine how they were influenced by the protein solution. Collagen and gelatin, used as protein molecules, expanded the a-axis lattice parameter (100) of OCP crystals by 3.1 % and 1.5 %, respectively, which is thought to be due to their incorporation into the hydration layer together with water molecules during OCP synthesis. In addition, the size of OCP crystals became smaller than that of OCP crystals synthesized in distilled water, which is thought to be due to the encapsulation oradsorption of OCP crystals by the added proteins. The incorporation or adsorption/encapsulation effects of proteins on OCP crystals varied depending on the type of protein. Gelatin showed greater changes than collagen in the crystal structure, particle shape, and thermal and hydrolytic stability of OCP powder due to protein incorporation into the hydration layer or adsorption on the surface of OCP crystal.