Preparation Of TiO₂ Nanotube Layers On Titanium And Their Biological Properties

In the air, the natural oxide film on the surface of pure titanium is bioinert. Surface modifications are generally used to bioactivate tiutnaium. In this paper, in order to improve the bioactivity of pure titanium implant, titanium dioxide (TiO₂) nanotube layers on titanium surfaces were prepared by electrochemistry anodic oxidation for commercial pure titanium. Then, the TiO₂ nanotube layers were treated by precalcification and with low concentrationed alkali. The biological performance of the modified materials was investigated in vitro by immersion in the simulated body fluid (SBF) and the osteoblast culture.The TiO₂ nanotube layers distributed continuously and aligned closely at the direction perpendicular to titanium surfaces. The formation of TiO₂ nanotube layers was influenced by several parameters including voltage, concentration of hydrofluoric acid (HF), oxidation time, pH value. In a certain range of voltage, different voltages resulted in the TiO₂ nanotubes with different diameters. The concentration of HF played an important role at formation of nanotube structure. Oxidation time was a crucial factor for tube length. The analysis showed that anodic oxidation TiO₂ was amorphous and could transform into anatase after annealed. The feature of TiO₂ nanotube layers was not destroyed after annealing. The calculation based on measurement of contact angles indicated the titanium surface with TiO₂ nanotube layers had higher surface energy compared to untreated titanium.After the TiO₂ nanotube layers were pre-calcified and treated with low concentration alkali respectively, hydroxyapatite (HA) could spontanously deposite onto the surface. However, HA difficultly deposited on the surface of non-treated TiO₂ nanotube layers. In immersion, the calcium carbonate formed by pre-calcification could partially dissolve, resulting in the increase of Ca²⁺ and PO₄^3- concentrations in the solution nearby the surfaces. Thus HA began to nucleate and grow gradually on the surfaces. After treatment with low concentration alkali, HA deposition on the nanotube surface should be related to the change of element distribution and charge on the surface.In SBF with high ions concentration (3×SBF), HA rapidly deposited onto the surfaces of TiO₂ nanotube layers without bioactive treatment. 3×SBF had much higher Ca²⁺ and PO₄^3- concentrations and enchanced the supersaturation of solution. Therefore, HA could deposit onto the surface of TiO₂ nanotube layers in short time. The bonding strength between the coating and TiO₂ nanotube layers was higher than 15.3MPa. The titanium with nanostructural surface had high surface energy and could offer more nucleation point of HA. As the results, the strength was improved obviously.The osteoblast culture test on three samples showed that the TiO₂ nanotube layers obviously promoted cell adhesion and proliferation. The HA coating on TiO₂ nanotube layers was also benificial to cell adhesion and proliferation. The surface energy, distribution of elements and surface charge could be major factors which effected on cell behaviour. Thus, TiO₂ nanotube layers and the HA coating had better bioactivity and biocompatibility.