Effect of the Ionic Radius of Alkali Metal Ions on Octacalcium Phosphate Formation via Different Substitution Modes

Octacalcium phosphate (OCP), a layered calcium phosphate compound, is an attractive material for new medical combination products, which are hybrid materials consisting of both drugs and biomaterials that have shown excellent therapy scores. OCP is fabricated primarily from soluble calcium salt via an aqueous-mediated hydrolysis process. The coexisting cations are likely to be incorporated into the OCP unit lattice during this process and affect the development of the OCP crystal structure and its thermodynamic stability. However, the key parameters of the coexisting cations, such as the ionic radii and charge number, that affect OCP formation are still unclear. In this study, we focused on the ionic radius of each monovalent ion of alkali metal ions (Li+, Na+, K+, Rb+, and Cs+) for OCP incorporation and formation in a CaHPO4·2H2O (DCPD)-(NH4)2HPO4 system with alkali metal salts. There was little incorporation of Li into the OCP unit lattice at low concentrations, whereas Li was incorporated into the OCP ...