Synthesis and characterization of zinc and fluorine co-substituted hydroxyapatite for bone and dental applications

Ionic substituted hydroxyapatites are widely used in bone tissue engineering applications. The present research is aimed at the synthesis of zinc and fluorine co-substituted hydroxyapatite (ZnFHA10, Ca9.0Zn1.0(PO4)6(OH)F) using a sol–gel method. This research investigates the effect of zinc and fluorine co-substitution on the structure of synthesized hydroxyapatite. The as-synthesized nanopowder was heat-treated in the temperature range 800 °C–1200 °C. The physicochemical properties were investigated using X-ray fluorescence spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy and transmission electron microscopy. The thermal stability of nanopowder was assessed by the thermogravimetric analysis. Bioactive behavior was evaluated by studying the variation in pH of simulated body fluid on immersion of nanopowders. Peaks of zinc and fluorine in the XRF spectra confirmed the substitution of ions. TEM images of as-synthesized and calcined nanopowders showed rod-like and spherical morphology. X-ray diffraction pattern of as-synthesized nanopowder showed the formation of nanoparticles of low crystallinity. On calcination, the crystallinity and crystallite size increased and the biphasic mixture of hydroxyapatite and tricalcium phosphate was formed. Spectra obtained from Fourier-transform infrared spectroscopy showed the presence of OH…F…OH group, depicting the presence of fluorine in hydroxyapatite. FTIR spectra of nanopowders obtained after immersion in simulated body fluid and change in pH values on immersion of nanopowders in simulated body fluid confirmed the bioactive behavior of nanopowders. The study revealed that the substitution of ions in hydroxyapatite could significantly increase the bioactivity and bioresorbability of hydroxyapatite, thus finding a wide range of clinical applications in orthopedics and dentistry.