Structural and antibacterial activity of hydroxyapatite and fluorohydroxyapatite co-substituted with zirconium–cerium ions

The effect of zirconium (Zr) and cerium (Ce) ions co-substituted in hydroxyapatite (HA) and fluorohydroxyapatite (FHA), by sol–gel method, is reported in this technical article. Addition of Zr4+ and Ce3+ ions into HA and FHA reportedly transforms t-ZrO2 (tetragonal) to m-ZrO2 (monoclinic) phases resulting in HA/CSZ (Ce-stabilized zirconia) composites which improves the toughness of the materials widely used in biomedical applications. Samples with compositions 5Zr/5Ce-HA, 5Zr/5Ce-FHA, 40Zr/XCe-FHA (where X = 5, 10 and 20 mol% of Ce ions) were prepared and calcined at 800 °C. Incorporation of Ce ion stabilizes the zirconia, and fluorine ion improves thermal stability. Crystallite size, crystallinity and presence of m-ZrO2 and t-ZrO2 phases were analysed by XRD. The FTIR spectrum confirmed the presence of Zr–O stretching band. SEM reveals agglomerated spherical particles of 50–300 nm size, and ionic doping on HA was analysed through EDAX. The TG/DSC curves confirmed the formation of m-ZrO2 and t-ZrO2 phases and thermal stability of the samples. Higher concentrations of Zr and Ce ions in FHA resulted in reduction in crystallite size. The antibacterial activities of the samples were evaluated against the micro-organisms, Staphylococcus aureus and Escherichia coli exhibiting a inhibition zone diameter as 42 and 37 mm, respectively, for 40Zr/20Ce-FHA.