Cobalt-substituted hydroxyapatite as a potential basis of biomaterials: synthesis, crystal-chemistry properties and antibacterial activity

This paper presents the results of the synthesis of solid solutions of cobalt-substituted hydroxyapatite of the composition Ca10-xCox(PO4)6(OH)2 by the solid-phase and solution method. The formation of only the composition of Ca9.5Co0.5(PO4)6(OH)2 has been reliably established, whereas an increase in the cobalt content, as well as an increase in the temperature of synthesis and calcination of the samples prepared in solution, leads to the formation of stable mixtures of calcium and cobalt phosphates. The crystal structure has been refined for Ca9.5Co0.5(PO4)6(OH)2 (a = 9.4121(28) Å, c = 6.8762(20) Å, V = 527.54(35) Å3; R-Bragg = 2.455%) under the assumption of cobalt localization at position 6h, which is confirmed by the similarity of structural parameters (average bond lengths in polyhedra) to previously published data. The powder obtained consists of hexagonal half-prisms devoted to two fractions (5–7 μm and 15–20 μm). Thermal expansion of the apatite under study is similar to that of other calcium phosphate apatites and characterized by isotropic expansion (αa/αc ≈ 1). The bactericidal activity of the substance obtained in relation to E. coli culture has been experimentally established.