Tailoring the surface properties of Ti6Al4V by controlled chemical oxidation

Many efforts have been made to promote cell activity at the surface of implants, mainly by modifying their topography and physicochemical properties. Here we demonstrate the feasibility of creating Ti6Al4V surfaces having both a microtexture and a nanotexture, and show that their properties can be tailored by controlling the length of exposure to a mixture of H2SO4 and H2O2. Scanning electron microscopy (SEM), combined with energy-dispersive X-ray spectroscopy (EDX), indicated that beta-phase grains, which surround larger alpha-phase grains, are etched more rapidly, resulting in a surface composed of microscale cavities with alpha-grain boundaries. Furthermore, high-resolution SEM and atomic force microscopy (AFM) revealed the presence on the surfaces of both alpha- and beta-phase grains of a network of nanopits with mean diameters ranging between 13 and 21 nm. The grain surface roughness increases from about 4 nm on untreated samples to about 12 nm after 4h of treatment. AFM analysis showed that the depth of microscale cavities can be varied in the 10-180 nm range by controlling the extent of chemical etching. Fourier transform infrared spectroscopy (FT-IR), combined with ellipsometry, established that the etching generated an oxide layer with a thickness in the range 15-45 nm. The resulting new surfaces selectively promote the growth of osteoblasts while inhibiting that of fibroblasts, making them promising tools for regulating the activities of cells in biological environments.