Sodium and silver ionic competition for conjugated octacalcium phosphate sites in weak basic solutions

Abstract

Octacalcium phosphate (OCP) has attracted the interest of researchers looking for new biomaterials due to its excellent biocompatibility and high formability. Furthermore, it was an attraction for medical combination products that ions and molecule doping ability of OCP, which originated its distinct crystal structure. Then, as an antibacterial bone substitute, Ag-substituted OCP (OCP-Ag) was a candidate of a centerpiece. However, for OCP-Ag block fabrication, drawback Ag contents of OCP-Ag blocks were significantly reduced compared to OCP-Ag powder when they were fabricated in the same Ag concentration solutions. It was still unclear the role of Na, an important matter for OCP block structure fabrication, in Ag substitution into OCP unit lattice. Thus, in this study, we analyzed the Na and Ag substitution process into OCP during OCP fabrication in the presence of Na and Ag solutions. Both cations improved the OCP’s layer structure, even though both ions co-exist. As the concentration of Na in the solutions increased, Ag contents of samples decreased until threshold values were achieved. According to the ionic species analysis, both PO₄ ion complexes of Na and Ag showed no tendency toward other cation concentrations. Spectroscopic investigation showed that both ions were substituted in the conjugated site of P5 PO₄, resulting in a competition of Ag and Na substitution into the same.