Increased osteoblast functions on undoped and yttrium-doped nanocrystalline hydroxyapatite coatings on titanium

In order to improve orthopedic implant performance, the objective of this in vitro study was to synthesize nanocrystalline hydroxyapatite (HA) powders to coat titanium. HA was synthesized through a wet chemical process. The precipitated powders were either sintered at 1100 °C for 1 h in order to produce UltraCap HA (or microcrystalline size HA) or were treated hydrothermally at 200 °C for 20 h to produce nanocrystalline HA. Some of the UltraCap and nanocrystalline HA powders were doped with yttrium (Y) since previous studies demonstrated that Y-doped HA in bulk improved osteoblast (or bone-forming cell) function over undoped HA. The original HA particles were characterized using X-ray diffraction (XRD), inductively coupled plasma–atomic emission spectroscopy (ICP–AES), BET, a laser particle size analyzer, and scanning electron microscopy (SEM). These powders were then deposited onto titanium by a novel room-temperature process, called IonTite™. The properties of the resulting HA-coatings on titanium were compared to respective properties of the original HA powders. The results showed that the chemical and physical properties of the original HA powders were retained when coated on titanium by IonTite™, as determined by XRD, SEM, and atomic force microscopy (AFM) analysis. More importantly, results showed increased osteoblast adhesion on the nanocrystalline HA IonTite™ coatings compared to traditionally used plasma-sprayed HA coatings. Results also demonstrated greater amounts of calcium deposition by osteoblasts cultured on Y-doped nanocrystalline HA coatings compared to either UltraCap IonTite™ coatings or plasma-sprayed HA coatings. These results encourage further studies on nanocrystalline IonTite™ HA coatings on titanium for improved orthopedic applications.