Sol-Gel Derived Nanocrystalline Fluoridated Hydroxyapatite Powders and Nanostructured Coatings for Tissue Engineering Applications

Nanocrystalline fluoridated hydroxyapatite (FHA) powders and coatings with a chemical composition of Ca₁₀(PO₄)₆OH_2–x F _x (where x values were selected equal to 0.0 ,0.5, 1.0, 1.5, and 2.0) were prepared through a modified simple sol-gel technique in comparison with conventional alkoxide-based sol-gel route. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), fourier transform infrared (FTIR) spectroscopy, pF-meter with a fluorine-sensitive electrode, and inductively coupled plasma–optical emission spectroscopy (ICP-OES) analysis techniques were employed in order to evaluate phase composition, particle size distribution, morphology, functional groups, fluorine content, and purity of prepared FHA nanopowders, respectively. SEM analysis was used to study the surface morphology and cross section of the FHA coatings, deposited on 316L stainless steel substrate. Results indicated that single-phase and homogeneous FHA nanopowders with carbonate peaks in the FTIR spectrum were synthesized through the modified sol-gel technique. TEM analysis revealed that fluorapatite (FA) powder was composed of nanosized particles, ~25 nm in size, with polyhedron shape and straight corners. In the modified sol-gel technique, polymerization and gelation kinetic of the sol were significantly improved without any need to use additives or pH control. Uniform, dense, well-adhered, and compacted FHA coatings were formed on the 316L stainless steel substrate after 24 hours of aging.