Synthesis, Properties, and Antibacterial Activity of Zinc-Substituted Hydroxyapatite

Hydroxyapatite (HA) and zinc-substituted hydroxyapatite (ZnHA) have been prepared via precipitation from solution. The lattice parameters of ZnHA (а, b = 9.41766 Å, с = 6.88048 Å) are about 0.001 Å smaller than those of HA (а, b = 9.41866 Å, с = 6.88158 Å). The change in the lattice parameters of the ZnHA studied confirms partial Zn²⁺ substitution for Ca²⁺ in the crystal lattice of hydroxyapatite. IR spectra indicated the presence of functional groups (OH^– and \({\text{PO}}_{4}^{{3 - }}\) ) in the composition of HA. According to scanning electron microscopy data, the particle size of the ZnHA powder prepared via precipitation followed by heat treatment at 900°C is 200–400 nm. Energy dispersive X-ray microanalysis was used to determine the Ca/P and (Ca + Zn)/P ratios in HA and ZnHA: 1.68 and 1.66, respectively. The solubility of ZnHA in physiological saline was found to be twice that of HA, suggesting good ZnHA resorption in the human body. Tests of disk-shaped samples in SBF solution demonstrated active formation of a new calcium phosphate layer as a result of chemisorption of Ca²⁺, Mg²⁺, \({\text{HPO}}_{4}^{{2 - }}\) , \({\text{PO}}_{4}^{{3 - }}\) , and OH^– ions from solution. ZnHA exhibits activity for both gram positive (Bacillus cereus and Staphylococcus aureus) and gram negative (Escherichia coli and Acinetobacter calcoaceticus) microorganisms.