Fabrication of Dicarboxylic-Acid- and Silica-Substituted Octacalcium Phosphate Blocks with Stronger Mechanical Strength

Abstract

Octacalcium phosphate (OCP) is an attractive base material to combine into components developed for medical purposes, especially those used in bone replacement procedures, not only because of its excellent biocompatibility but also because of its ability to intercalate with multiple types of molecular layers such as silica, dicarboxylic acid, and various cations. On the other hand, there are no examples of simultaneous substituting for several different compounds on OCPs. Therefore, in this study, the physical and mechanical strength (DTS: diametral tensile strength) of OCPs substituted with both silica and dicarboxylic acids (thiomalate: SH-malate) were evaluated. By optimizing the amount of SH-malate, we were able to prepare a block consisting of OCPs with both silica and SH-malate supported in the interlayer. The composition of the OCP-based compound comprising this block was Ca8Na1.07H6.33(PO4)4.44(SiO4)1.32(SH-malate)2.40·nH2O. Interestingly, the low mechanical strength, a drawback of silica-substituted OCP blocks, could be improved by dicarboxylic acid substituting. The dicarboxylic acid addition increased the mechanical strength of silica-substituted OCP blocks, and the acid successfully incorporated into the interlayer, even with the presence of silica. These results are expected to advance the creation of better silica-substituted OCPs and improved bone replacement materials.