Ta-containing TiO2 films with Ta contents of 5%, 20%, 33% （mole fraction） were sol-gel coated on the surface roughened Ti6AI4V alloy by dip coating method for biomedical applications. The Ta-TiO2 films on 1.5 mol/L NaOH-HCI pretreated substrate are adherent, but there are cracks for the sample with 33% Ta. X-ray photoelectron spectroscopy results show that Ti and Ta exist as TiP2 and Ta205 in the film, and A1 element is not detectable. X-ray diffraction and Raman scattering analyses reveal that the addition of Ta decreases crystallization of the films. Potentiodynamic polarization test in a Ca-free Hank＇s balanced solution demonstrates that the coating samples markedly improve the corrosion resistance compared with the polished sample. The addition of Ta impedes UV light-induced hydrophilic conversion of the coating samples. The sample with 20% Ta has enough film integrity and hydrophilic conversion rate, and is expected to possess good biological properties.
Titania films with nano-sized pores were prepared on the NaOH？HCl pretreated NiTi alloy substrate by sol？gel method.A crack-free film is obtained for the sample with a dense inner layer and a porous outside layer（sample TC1＋1）.The X-ray diffraction shows that the titania films are composed of anatase,and a little Ni4Ti3 phase in the heat treated substrate is also detected.The X-ray photoelectron spectroscopy results indicate that the titania film completely covered the NiTi substrate for sample TC1＋1.The sample TC1＋1 is hydrophilic with a contact angle about 20°,and UV illumination treatment for 15 min further decreases the contact angle to（9.2±3.2）°.The potentiodynamic polarization test in 0.9% NaCl solution reveals a better corrosion resistance of sample TC1＋1 than the polished NiTi sample.
The surface of NiTi alloy was roughened by NaOH-HC1 treatment, and the Ta-containing TiO2 films were coated on the pretreated NiTi alloy by the sol-gel method. Thermal analyses indicate that the evaporation temperature of the organics decreases with the addition of tantalum ethoxide in the TiO2 sol, but the crystallization temperature of anatase increases. The NaOH-HC1 pre- treatment improves the film integrity, but cracks still form in the films at high Ta contents （_〉20 %, molar ratio） owing to the increasing film thickness. X-ray diffraction （XRD） confirms that the addition of Ta suppresses the crystalli- zation of anatase. X-ray photoelectron spectroscopy （XPS） reveals that Ta exists as Ta2Os in the film. With the increase of Ta content, the hydrophilic conversion of the films under UV illumination is impeded, but their corrosion resistance in 0.9 % NaC1 solution increases, tested by the potentiodynamic polarization. The coating samples have acceptable hemolysis ratios for biomaterials （〈5）. The introduction of Ta improves the anti-aggregating function of the TiO2 film in the platelet adhesion test.
Bing-Hui DongFeng WuZafer AlajmiChen ZhangTao FuYuan Ge
