Surface characteristics and bioactivity of oxide films formed by anodic spark oxidation on titanium in different electrolytes

Porous oxide films were fabricated on commercially pure titanium (CP-Ti) using an anodic spark oxidation technique with different electrolytes, 1 M H2SO4, 1 M H3PO4, and 1 M CH3COOH. The micro-morphology, surface roughness, and crystalline structure were evaluated by scanning electron microscopy, profilometry, and X-ray diffraction, respectively. The chemical composition and binding state of the specimen groups were evaluated by X-ray photoelectron spectroscopy (XPS). TiO2 films were observed on the specimens anodized in the acetic acid and sulfuric acid electrolytes. However, a TiP2O7 film was mainly observed on the specimen anodized in the phosphoric acid electrolyte. The dominant Ti4+ peaks for all sample groups and the additional Ti3+ peaks for the groups anodized in the acetic and phosphoric acid electrolytes were detected by high-resolution XPS. The effects of the surface characteristics of the specimens on the bioactivity were examined using an immersion test in a minimum essential medium (MEM) solution. There was a higher level of calcium formed on the anodized specimens than on the as-received titanium while there was no significant difference in the calcium content between the anodized specimen groups. Fourier transform infrared spectroscopy showed a different content of chemical function groups in the deposits formed in MEM according to the type of electrolyte used. These results were attributed to the different surface chemical states of the oxide films.