Resorption of Ca_{3– x}M_2x(PO₄)₂ (M = Na, K) Calcium Phosphate Bioceramics in Model Solutions

The resorbability of bioceramics in the Ca₃(PO₄)₂–CaNaPO₄–CaKPO₄ system is evaluated in an approach involving thermodynamic assessment of solubility and investigation of the dissolution kinetics in model media, in particular in citric acid solutions. Thermodynamic calculation indicates high solubility of the Ca₅Na₂(PO₄)₄, α-CaМPO₄, β-CaKPO₄, and β-СаK_0.6Na_0.4PO₄ phases. Investigation of the dissolution kinetics of ceramics has made it possible to identify two distinct types of behavior of resorbable materials in weakly acidic solutions: with fast resorption kinetics in the case of the phases based on nagelschmidtite solid solutions and α-CaМPO₄ disordered high-temperature solid solutions, and with a nearly constant, relatively low dissolution rate and a high solubility limit in the case of β-СaK_{1– x}Na_x-based phases.