aThe influence of phosphate (and its concentration) on the electrochemical properties of anodic porous oxide films formed on titanium surfaces in fluoride containing electrolyte was investigated by performing electrochemical measurements [potentiodynamic/potentiostatic polarization, open circuit potential (OCP), and capacitance measurements] for a titanium/oxide film/solution interface system in SBF solution. In previous work we demonstrated, that during anodizing titanium and titaniumbased implant materials in 2 M phosphoric acid solution the highly bioactive phosphate gel-like layer can be formed over compact titania which can significantly stimulate apatite formation. In the present work, we report that anodizing titanium in the same solution with the addition of fluorides leads to formation of titanium oxide nanotubes rich in both phosphates and fluorides which makes the method highly suitable for additional promoting of apatite deposition into titania nanotubes. To study the effect of phosphates concentration, layers of titania nanotubes were produced in electrolytes of different phosphoric acid concentration. Their behavior as the future coatings on titanium for biomaterial applications was characterized by capacitance tests in simulated body fluids and by Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) observations. Judging on the results of XPS analysis, the competition between fluorides and phosphates is observed during anodizing, and the higher concentration of the latter is responsible for higher bioactivity of nanotubes formed in 2M H 3 PO 4 + 0.4% wt hydrofluoric acid (HF).

The formation of nanotube oxide layers on Ti6Al7Nb alloy in H 3 PO 4 acid solutions containing fluoride ions is presented here. Among several parameters influencing the quality of nanotubes formed anodically such as potential, time of anodizing, fluoride ions concentration and scan rate of polarization, in particular, the last two seem to be the most responsible for the structure and morphology of nanotubes. The effect of fluoride ions concentration on the morphology of nanotubes on the two-phase (α + β) Ti6Al7Nb implant alloy, has been evaluated in our work. The formation of nanotubes was performed by polarizing the Ti6Al7Nb alloy samples in 1 M H 3 PO 4 containing 0.2%, 0.3% and 0.4% wt. Hydrofluoric acid (HF) to 20 V using scan rate 500 mV/s and then holding them at that potential for further 2 h in the same electrolyte. Nanotubes of diameter ranging from 50 to 80 nm, with thicker walls over β-phase grains than over α-phase grains, were obtained. During the formation process, which includes two stages-the first, potentiodynamic and the second, potentiostatic (20 V)-different electrochemical behavior was observed in electrolytes of various fluoride concentration. The clear relationship between the highest currents and the biggest diameter of nanotubes for 0.3% wt. HF containing electrolyte observed during the first stage of anodizing is explained with regard to electrochemical characteristics of alloying elements and transport of electrolyte anions in oxide layers.

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One of the major research interests of nanomedicine is the designing of harmless and biocompatible medical devices. To improve the features of Ti surface, TiO2 based nanotube (TNT) films (50 nm diameter) achieved by anodic oxidation and thermal treatment were grown on titanium and on Ti6Al4V and Ti6Al7Nb alloys. Their in vitro toxicity and biocompatibility were investigated using G292 osteoblast cell line. The LDH release after 24 and 48 h of exposure demonstrated that TNT layers were not cytotoxic. The cell growth on TNT films deposited on titanium and Ti6Al4V was significantly increased compared with Ti6Al7Nb. F-actin staining showed a better organized actin cytoskeleton in osteoblasts grown on these two samples, which provide the best conditions for osteoblast attachment and spreading. Analysis of GSH distribution revealed a higher nuclear level in the samples with TNTs compared with Ti plate without nanotubes, indicating an active proliferation. Thus, nuclear glutathione levels can be used as a useful biomarker for biocompatibility assessment. Our results suggest that the substrate for TNTs can have a significant impact on cell morphology and fate. In conclusion, the TNT/Ti and TNT/Ti6Al4V were toxicity-free and can provide a proper nanostructure for a positive cell response.