Production, structure and biocompatible properties of oxide nanotubes on Ti13Nb13Zr alloy for medical applications

This work deals with production and characterization of the oxide nanotubes on the biomedical Ti13Nb13Zr alloy. Anodic oxidation of this new type of vanadium-free titanium alloy was carried out in 1 M ethylene glycol electrolyte with the addition of 4 wt% NH₄F under voltage-time conditions of 50 V for 80 min at room temperature. The results of FE-SEM, TEM, EDS, GIXD and XPS investigations confirmed the possibility of formation of the single-walled nanotubes on the bi-phase (α + β) alloy under study. An amorphous character of the obtained nanotubes was ascertained. The morphological parameters such as the length (~ 10 μm), outer (362 nm) and internal (218 nm) diameter of the nanotube, were determined. The formed nanotubes were composed of oxides of the alloying elements derived from TiO₂, Nb₂O₅, ZrO₂, and ZrO_x. Spontaneous passivation of the as-received Ti13Nb13Zr alloy in the normal saline solution at 37 °C, was revealed by open-circuit potential measurements. The interface impedance of Ti13Nb13Zr electrode | oxide layer | normal saline solution, was determined by approximation of the experimental EIS data using the equivalent electrical circuit of modified Randle's cell. Potentiodynamic studies have shown no initiation of pitting corrosion up to 9.5 V vs. SCE. The proposed surface modification method has been shown to eliminate the hemolysis of the alloy and to decrease slightly its corrosion resistance due to the porous structure of the formed nanotubes. These results give a new insight into improvement of the ability of the Ti13Nb13Zr implant alloy to osseointegration in a biological milieu.