A microstructural study on the alkali-treated titanium subjected to induction heating

Alkali-treated titanium and its alloys (with or without heat treatment) have been paid more attention in the biomaterial field for the formation of a nanoporous layer that can induce apatite deposition and improve bone-implant integration. In this work, a hierarchical micro-nano structure was fabricated by alkali treatment and subsequent induction heating at different temperatures. The surface morphology, phase composition, microstructure, and elemental binding state were investigated using scanning electron microscopy (SEM), X-ray diffractometer (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. As the induction heating temperature increases, the porous structure of the outmost sodium titanate layer is maintained with increased anatase TiO2 and decreased wetting angle from 21.8° to 11.8°. At a relatively high temperature (700 °C), the composite layer is composed of a porous sodium titanate layer with a thickness of around 1 μm and a titanium oxide layer of about 2 μm thickness with nanopores. Importantly, the amorphous structure with the oxygen vacancy that exists on the sample surface is conducive to apatite deposition. The assessment of the in-vitro bioactivity performed in 1.5 simulated body fluid shows that the ability to induce apatite deposition increases with the increasing induction heating temperature from 500 to 700 °C. These results are helpful to understand the microstructure of the alkali and induction heating treated titanium that may be responsible for its bioactivity.