Effect of carbonate substitution on physicochemical and biological properties of silver containing hydroxyapatites

Ag⁺-substituted hydroxyapatites (Ag-HAs) and Ag⁺/CO₃^2--co-substituted hydroxyapatites (Ag-CHAs) with two different concentrations of silver ions were synthesized by the standard precipitation method. For comparison, pure hydroxyapatite (HA) and carbonated hydroxyapatite (CHA) were synthesized using the same method. The obtained powders were examined by various physicochemical methods, such PXRD, TEM, FTIR and ssNMR. Elemental analysis was provided by WD-XRF and ICP-MS methods. The strains of Staphylococcus aureus and Escherichia coli were used to evaluate the antibacterial activity of the materials. The study demonstrates that the substituted samples are homogenous and poorly crystalline. Introducing carbonates into the crystal structure significantly affects the physicochemical properties of the silver containing hydroxyapatite, i.e., crystallinity, lattice parameters, crystal size and morphology or content of structural hydroxyl groups. Carbonate substitution leads to a significant increase in the contribution of the hydrated surface layer. Ag-CHA nanocrystals with an enhanced hydrated surface layer and higher solubility demonstrate an admirable antibacterial effect.