| The biological properties of titanium implant depend on its surface oxid film. Because of the bioinert natural oxide film, titanium is generally bioactivated by modifying oxide film. In this paper, in order to prevent metal ions dissociating into body fluid and improve the biocompatibility of pure titanium implant, the surface of pure titanium specimen was modified by a novel compound method of pre-anodic oxidation and then micro-arc oxidation (MAO). The surface morphology, components and structure of the coatings were analyzed by scanning electron microscope (SEM) and X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The biological performance of the modified materials was investigated in vitro by immersion in the simulated body fluid (SBF) and the osteoblast culture.In the first instance titanium surface was oxidized by pre-anodic oxidation, the better technologic parameters were determined. That is, pre-anodic oxidation voltage is 50V, the oxidized time 10min and electrolyte H3PO4. In the SEM it showed that an oxide film with a pore size of 1um was formed on the outer titanium surface, more compact than that of the oxide surface prepared by micro-arc oxide method, and a dense oxide film is formed in the inner titanium surface. This oxide film can prevent metal ions dissociating effectively, which is beneficial to preparing the compound structure of big hole oxide layer - pinhole oxide layer - the titanium substrate. In the XRD patterns crystal TiO2 was not observed. The reason might be that the temperature is not high enough to make it become crystal in the anodic oxidation .with the low voltage.By regulating the electrolyte components in MAO calcium (Ca) and phosphorus (P) elements were introduced in the oxide film. Therefore, three compound oxidefilms were prepared, including containing Ca, containing P and containing both Ca and P respectively. The existence of Ca or P in the oxide coatings was confirmed by Energy Dispersive X-ray (EDX) analysis. XRD analyses indicated that the oxide coatings containing Ca and containing Ca-P were made up of anatase and rutile, but the film containing P had no rutile. The SEM photographs showed that the coatings were porous, and the pore size was 5um (Ca-P sample), 3um (Ca sample) and lum (P sample) respectively. Contact angle test indicated that surface energy of all three samples was larger than that of the pure titanium. The surface energy of Ca-P sample is the largest, and that of the Ca sample is the least.The titanium surface bioactivity was characterized by the biomimetic mineralization and osteoblast culture test. When the Ca sample and Ca-P sample were immersed in the 1.5SBF for a period, a hydroxyapatite (HA) coating formed on the surface. According to Sherrer equation, the crystal size in the HA coating is about 43nm, In the existence of bovine serum albumin (BSA) in the 1.5SBF, BSA could accelerate the growth of the HA and its crystal size reduced to 13nm more or less. The osteoblast culture test on the three samples showed that the sample surface treated by compound oxidation could improve cell adhesion, proliferation and polarization comparing with the pure titanium. The Ca-P sample is more beneficial to the cell adhesion and proliferation than other two samples. Thus, better bioactive oxide films could be fabricated by this compound oxidation technology... |
