Effect of etching on the composition and structure of anodic spark deposition films on titanium

Anodic spark deposition is particularly spread as coating treatment of titanium in biomedical applications, as it allows to improve both durability and biocompatibility of titanium and its alloys. This work proposes an analysis of different surface treatments on titanium, where surface etching in HF prior to anodizing and final alkali etching of the anodic oxide are chosen as possible methods to alter surface roughness, crystal structure and chemical composition. Anodizing was performed at two different voltages to produce different morphologies and crystal phases. Larger and more regular porosity was obtained at higher voltages, together with the formation of sodium titanates. While the HF pre-treatment only affected surface roughness but not surface chemistry, the NaOH post treatment promoted the formation of Na2TiO3 especially on high voltage formed oxides. This was identified as the cause for a larger presence of radical species, which modify surface bioactivity and is responsible for a bacteriostatic effect of the treatments reported in previous biological studies. [Display omitted] •The role of etching and alkali treatment on anodic titanium oxides is analyzed.•At higher anodizing voltages TiO2 pores get larger and more regular, and titanates are formed.•Alkali treatment creates wrinkles and cracks and promotes Na2TiO3 formation.•Titanates promote disorder, increasing radical species formation, enhancing bioactivity.