ICMCTF2018 Session D1-1: Surface Coatings and Surface Modifications in Biological Environments

TNZT alloys with compositions of Ti-35Nb-7Zr-5Ta are materials that are more biocompatible than the more widely used Ti-6Al-4V alloy since each of its constituent elements is biocompatible. In addition, it has the lowest Young’s modulus of all the titanium-based alloys created so far (50-60 GPa). This property allows for a greater transfer of functional loads, which ultimately leads to bone growth stimulation. TNZT alloys were produced by arc melting of pure elements and were forged into rods. Oxide nano-scaffolds were grown on TNZT using the hydrothermal method to investgate the potential of these nanostructured surfaces to improve osseointegration. The alloys with and without nano-scaffolds were characterized using top-view and cross-sectional scanning electron microscopy equipped with an energy dispersive x-ray spetrometer to investigate the structure, morphology and chemistry of the resulting nanostructures. Finally, the formation of hydroxyapatitite on the modified surfaces was investigated upon immersion in simulated body fluid (SBF).

This work is about the formation of crystalline nanotubes of titanium oxide at the surface of the Ti-6Al-4V alloy and the evaluation of their effect on the cellular proliferation. The formation of nanotubes was performed by the anodic oxidation technique. The work potential was established in 60 V. The anodizing process was performed at times of 10, 20, 30, 40 50 and 60 min, in order to evaluate the effect of treatment time on the characteristics of the nanotubes and thus, on the cellular proliferation. A mixture of ethylene glycol, water and ammonium fluoride was used as electrolytic fluid. Scanning electron microscopy (SEM) and X ray diffraction (XRD) were applied to determine the morphology and the crystalline nature of the nanotubes. SEM examination showed a well-defined matrix of nanotubes of titanium oxide with crystalline structure and diameter in the range of 60 to 80 nm. The XRD patterns showed more and more defined picks as the treatment time was increased. The results also revealed a clear influence of the treatment time on the structure of the titanium oxide nanotubes, especially on the adherence to the substrate, where the best adherence was observed with 60 min of treatment. The cellular assays showed that the cells attach to the nanotubes and proliferated.

Recently, thin film metallic glasses (TFMGs) have drawn lots of attention from researchers due to their potential applications in the biomedical fields. In this work, a series of Zr-based and Fe-based TFMGs were prepared by a pulsed DC and RF magnetron co-sputtering system. TFMGs were deposited on 316L stainless steel and P-type (100) Si wafers. For the Zr-based and Fe-based TFMG, Nb and Ti elements were added, respectively. The amorphous structures of coatings were determined by a glancing angle X-ray diffractometer. The surface and cross sectional morphologies of thin films were examined by a scanning electron microscopy (SEM). The surface roughness of thin films was explored by an atomic force microscopy (AFM). A nanoindenter, HRC-DB adhesion test were used to evaluate the hardness and adhesion properties of thin films, respectively. The bio-corrosion properties were tested by an electrochemical polarization measurements. The biocompatibility of TFMGs was examined using MG63 cell and the MTS assay. Effects of Nb and Ti addition on the corrosion resistance and biocompatibility behavior of TFMGs were discussed.

β-type titanium alloys have been proposed to replace the Ti–6Al–4V alloy due to the V and Al toxicity for long term use. Such β alloys with Nb, Mo, Zr, Sn or Ta additions are considered nontoxic, presenting lower elastic modulus than other conventional biomaterials. However, the tribological behavior of Ti and its alloys are unsatisfactory, featured by high wear rates and friction coefficients that limit applications in the biomedical area. Surface treatments can be employed to improve the surface properties while maintaining the bulk properties. Nanotubes can be produced through anodization, composed of oxides with elements from the substrate, such as TiO₂. Structure and morphology of nanotubes grown on Ti and its alloys can improve the surface biocompatibility, wettability and corrosion resistance as compared to untreated materials. However, there are few studies on the tribological properties of these films. The purpose of this study was to investigate the friction coefficient and wear rate of nanotubes grown on Ti-35Nb alloy, using a linear reciprocating tribometer. Results were compared with Ti and polished Ti-35Nb alloy. Hardness and elastic modulus of the substrates were measured through instrumented indentation. The produced coatings were also characterized by X-ray diffraction, scanning electron microscopy and metallographic analysis with optical microscopy. Nanotube layers were grown in an electrolyte containing 1 M H₃PO4 + 0.8 wt.% NH₄F, at 20 V for 160 minutes. The nanotubes were annealed at 530 ºC for 3 h. The Ti-35Nb alloy comprises α and β phases. The Ti-35Nb alloy presented higher hardness (3.7 GPa) and lower elastic modulus (96 GPa) than the pure Ti, a consequence of the β phase-containing microstructure. The nanotubes exhibited random diameters and approximately 2 μm thick. The crystal structure of the nanotube layers was a mixture of TiO₂ and Nb₂O₅ oxides. Friction coefficient of the nanotube layers was in the 1.0-1.1 range, lower than that of the polished Ti-35Nb (1.3) and the Ti surfaces. Likewise, wear rate of these coatings was (0.06 ± 0.01).10^-3 mm³/N.m, which was much lower than the value obtained for Ti-35Nb alloy [(1.66 ± 0.13).10^-3 mm³/N.m]. The wear mechanisms were adhesive and abrasive on Ti and Ti-35Nb alloy. However, the surface coated by the nanotube layers disclosed nor adhesive neither abrasive characteristics, in contrast to the reference surfaces. The low wear rates suggested a good adhesion between layer and substrate.