Anodic thin films on titanium used as masks for surface micropatterning of biomedical devices

Abstract

Ceramic oxide films like TiO 2 are used on medical implants to improve biocompatibility and corrosion behavior. Along with the chemical composition, the topography of implants with surface features in the tens of microns range is known to promote osteointegration. In this work, the prospective of anodically grown TiO 2 thin films as mask material for subsequent electrochemical micro/nanopatterning of medical implant surfaces sensitized by He-ion beam and YAG-laser irradiation is investigated. Electrochemical impedance spectroscopy was used to characterize resistance and capacitance of oxide films anodized under various conditions. The resistance obtained by fitting to an appropriate equivalent circuit was compared to the film stability in electrochemical pitting experiments. Film thickness, composition and microstructure were analyzed by glow discharge optical emission spectroscopy (GDOES), X-ray photoelectron spectroscopy, scanning and transmission electron microscopy and Raman spectroscopy. An increasing film resistance of the porous part of the oxide was found to correlate to increasing pitting resistance. GDOES revealed a low carbon and sulfur concentration in the film as well as an accumulation of hydrogen at the oxide/metal interface. Based on the performance in pitting tests, suitable anatase TiO 2 films were used for laser micropatterning, and thinner mainly amorphous films were used for He-ion beam micropatterning experiments. YAG-laser treatment led to preferential dissolution of the irradiated sites during the subsequent etching step. Both preferential and reduced dissolution was observed in case of He-ion implantation. Potential physico-chemical mechanisms for observed micropatterning effects are discussed.