Dicarboxylate-substituted octacalcium phosphates for hydrogel filling and resorbable ceramics fabrication

The main features of the synthesis of carboxylate-substituted analogs of octacalcium phosphate Ca8(HPO4)2(PO4)4·5H2O (OCP) by hydrolysis of brushite (CaHPO4·2H2O) and tricalcium phosphate α-Са3(РО4)2 (α-TCP) in buffer solutions based on the salts of succinic, adipic, and citric acids were summarized. The synthesis of succinate-substituted (Suc@OCP) and adipinate-substituted (Adi@OCP) OCPs gives the powders with Ca8(HPO4)2 – xАx(PO4)4·zH2O (А = Suc, Аdi) composition. Thermolysis of substituted OCPs results in a mixture of β-Са3(РО4)2 (β-TCP) and hydroxyapatite Са10(РО4)6(ОН)2 (HAp). Thermolysis features include the absence of an apatite-like decomposition product of pure OCP and higher decomposition temperatures compared to the pure OCP. Suc@OCP and Adi@OCP powders were used for the filling of hydrogels based on polyethylene glycol diacrylate (PEGDA) for the creation of a deformable composite implant by a stereolithographic 3D printing method, and fabrication of biphasic TCP/HAp ceramics.