Hydroxyapatite coating on titanium surface with titania nanotube layer and its bond strength to substrate

A vertically aligned titania nanotube layer on titanium surface was prepared by electrochemical anodic oxidation in an F--containing electrolyte, followed by annealing at 450 A degrees C. Bioactive hydroxyapatite (HA) coatings on as anodized titania nanotube layer were obtained by a biomimetic method without other surface treatment. The morphology, crystal structure, and components of the titania nanotube layer and bioactive coatings were examined by scanning electron microscopy, thin film X-ray diffraction, and Fourier transform infrared spectroscopy. The bond strength between the HA coatings and substrates was tested using a mechanical tester. The diameter of the titania nanotubes was about 100 nm, the wall thickness about 19 nm and the height about 1 mu m. HA rapidly deposited on the as anodized nanotube surface after immersion in a biomineral solution only for 1 day. The HA coatings were carbonated apatite and composed of a number of column-like crystals with nanometer size. Tensile test shows that the bond strength between the HA coating and the nanotube layer was larger than 15.3 MPa.