Coatings of Low-Temperature Calcium Phosphates on Hydroxyapatite Ceramic

This work is aimed at developing homogeneous, uniformly distributed fine-crystalline coatings based on triclinic octacalcium phosphate pentahydrate (OCP, Ca8H2(PO4)6⋅5H2O) on the surface of ceramic substrates made of hydroxyapatite (HA, Ca10(PO4)6(OH)2). The process of the crystalline layer of low-temperature calcium phosphates consists in a partial dissolution and recrystallization of surface layers of ceramic substrates through the intermediate phase of dicalcium phosphate dihydrate (DCPD, CaHPO4⋅2H2O). A buffer solution having an increased concentration of $${{{\text{H}}}_{{\text{2}}}}{\text{PO}}_{4}^{ + }$$ and $${\text{HPO}}_{4}^{{2 + }}$$ anions and containing Ca2+ ions is proposed for surface modification. When creating the crystalline coating, the buffer solution partly dissolves the surface layers, and the coating with the required phase composition and morphology is formed upon reaching the necessary concentration of Ca2+ ions on the solution–ceramic interface. To obtain a uniform coating, Ca2+ ions are gradually added to the buffer solution. The conditions of the beginning of the dissolution of calcium phosphate ceramic substrates and the thermodynamic conditions of the formation of uniform OCP-based coatings are established.