Fabrication of dicarboxylic-acid-substituted octacalcium phosphate blocks via cementing

Octacalcium phosphate (OCP) blocks with substituted dicarboxylic acid are attractive materials for new bio-ceramics because the substituted dicarboxylic acid enhances and regulates the biocompatibility of OCP. Therefore, OCP blocks can be model materials for biological bones and new medical combination products. However, dicarboxylic-acid-substituted OCP blocks are difficult to fabricate using conventional OCP fabrication methods such as dissolution-precipitation and simple precipitation methods because the counter cations in buffer solutions strongly inhibit dicarboxylic acid substitution into the OCP unit lattice. This study proposes a pure OCP-block fabrication method based on the cement setting of CaCO3, H3PO4, and dicarboxylic acid, which inserts dicarboxylic acid into the OCP matrix. OCP blocks with various dicarboxylic-acid substituents (succinate, thiomalate, and citrate) were obtained after optimizing the amount of CaCO3 in the mixtures. The mechanical strength of the dicarboxylic-acid-substituted OCP blocks significantly exceeded that of unsubstituted OCP.