The Morphostructural, Compositional, and Electrochemical Characterization of Electrodeposited Nanolayers on a New Ti-15Ta-5Zr Alloy

A porous, homogeneous, phosphorous-enriched oxide nanolayer was realized on the new Ti-15Ta-5Zr alloy surface by the anodic galvanostatic electrodeposition in phosphoric acid solution. This nanolayer contains TiO2, ZrO2 oxides, tantalum suboxides, and PO43- ions incorporated in the time of the electrodeposition process and has a thickness of 15.5 nm (X-ray photoelectron spectroscopy data). Atomic force microscopy determined a homogeneous roughness. Scanning electron microscopy evinced a porous microstructure that can stimulate the growth of the bone tissue into pores. The presence of the PO43- anions promotes the electrostatic bonds between the nanolayer and different species from the biofluid, namely, osteoinduction. The anodic oxidation nanolayer improved all electrochemical and corrosion parameters conferring superior protection to the substrate by its higher resistance to the ion migration. Impedance spectra showed that the electrodeposited nanolayer is formed by an inner, dense, barrier layer and an outer porous layer. The nanolayer thickened in time, namely, is bioactive. The oxidized nanolayer is able to protect the alloy from ion release, to assure long-term corrosion resistance, to minimize adverse reactions, to increase alloy bioactivity, to stimulate cell growth, and to favor osseointegration

Bucureºti) ♦ 61♦ Nr

A new Materials used as permanent implants must possess corrosion resistance, biocompatibility, vitality and elasticity. Titanium base materials partly realize these conditions. Titanium and its Ti-6Al-4V alloy were frequently used in orthopaedic applications. But, it was proved that vanadium is a toxic material both as element and as oxide V 2 O 5 [1]. Now, new titanium base alloys without vanadium are developed Several metallic elements can be used as β stabilizer for titanium alloys: Fe, V, Ta, Nb, Mo, Ni, Cr, etc.; α stabilizer can be: Al, O and Zr Protective oxides on the alloy surface are in contact with human cells and fluids and by friction, wear and corrosion can release their component ions in surrounding tissues. Therefore, is very important to analyse the biocompatibility of the individual elements There is a number of alloys used for biomedical applications such as: Ti-15Mo-5Zr-3Al [13][14] In recent times it was proved that the following titanium base alloys may be used as implants: Ti-15Zr-4Nb-4Ta A new Romanian, cheaper alloy that contains only nontoxic elements Ti-10Zr-5Ta-5Nb was obtained. Anticorrosive resistance of this new alloy was studied in simulated physiological fluids, Ringer solution, in extreme functional conditions, namely acidic, neutral and alkaline pH. Acidic pH appears after surgery (because the hydrogen ions concentration increases in the traumatic tissues) and by the hydrolysis in time of the protective oxides [30, * email: [email protected] Experimental part Ti-10Zr-5Ta-5Nb alloy was obtained by vacuum melting. An electron beam furnace type EMO 80, with an installed power of 80 kW was used. The alloy synthesis was performed in two steps under vacuum, consisting in melting and re-melting both with cooling stages inside furnace. The chemical composition, in weight % was: Zr -9.12; Nb -4.09; Ta -4.16; Fe -0.036; O 2 -0.195; N 2 -0.004; H 2 -0.0016; Ti -up to the balance. The electrodes were grinded with emery paper and aluminium paste to mirror surface, fixed in a SternMakrides mount system, rinsed with distilled water, degreased in boiling benzene and dried. All measurements were carried out in Ringer solution of pH = 2.33 (obtained by HCl addition), pH = 7.1 (normal pH) and pH = 9.12 (obtained by KOH addition). Solution composition as (g/L) is: NaCl -6.8; KCl -0.4; CaCl 2 -0.2; MgSO 4 .7H 2 O -0.2048; NaH 2 PO 4 .H 2 O -0.1438; NaHCO 3 -1.1; glucose -1. Temperature was 37 0 ± 1 0 C and was constantly maintained by a thermostated bath for shortterm experiments and by a drying oven for long-term experiments. An electrochemical glass cell with three electrodes provided with a central inlet for the electrode assembly, a cylindrical platinum grid counter electrode, a Luggin probe connected with a saturated calomel electrode (SCE) was used. The electrochemical techniques of potentiodynamic and linear polarization were used. Cyclic potentiodynamic measurements were applied starting from -0.5 V to +4.0 V (versus SCE) using a scan rate of 10 mV/s. Voltalab 80 equipment with a VoltaMaster 4 software was used for data processing. From the voltammograms, the main electrochemical parameters were determined: E corrcorrosion potential, like the zero current potential; E ppassivation potential; E cp -complete passivation potential; ΔE p -passive potential range; i p -passive current density. If the reverse curve of cyclic voltammogram presents lower current densities than the current densities from the direct curve it results that the studied material has a passive, stable behaviour. If the reverse curve shows the highe

Corrosion resistance improvement of titanium base alloys

The corrosion resistance of the new Ti-6Al-4V-1Zr alloy in comparison with ternary Ti-6Al-4V alloy in Ringer-Brown solution and artificial Carter-Brugirard saliva of different pH values was studied. In Ringer-Brown solution, the new alloy presented an improvement of all electrochemical parameters due to the alloying with Zr; also, impedance spectra revealed better protective properties of its passive layer. In Carter-Brugirard artificial saliva, an increase of the passive film thickness was proved. Fluoride ions had a slight negative influence on the corrosion and ion release rates, without to affect the very good stability of the new Ti-6Al-4V-1Zr alloy

Surface Characterization, Corrosion Resistance and in Vitro Biocompatibility of a New Ti‐Hf‐Mo‐Sn Alloy

A new superelastic Ti‐23Hf‐3Mo‐4Sn biomedical alloy displaying a particularly large recovery strain was synthesized and characterized in this study. Its native passive film is very thick (18 nm) and contains very protective TiO2, Ti2O3, HfO2, MoO2, and SnO2 oxides (XPS analysis). This alloy revealed nobler electrochemical behavior, more favorable values of the corrosion parameters and open circuit potentials in simulated body fluid in comparison with commercially pure titanium (CP‐Ti) and Ti‐6Al‐4V alloy taken as reference biomaterials in this study. This is due to the favorable influence of the alloying elements Hf, Sn, Mo, which enhance the protective properties of the native passive film on alloy surface. Impedance spectra showed a passive film with two layers, an inner, capacitive, barrier, dense layer and an outer, less insulating, porous layer that confer both high corrosion resistance and bioactivity to the alloy. In vitro tests were carried out in order to evaluate the response of Human Umbilical Vein Endothelial Cells (HUVECs) to Ti‐23Hf‐3Mo‐4Sn alloy in terms of cell viability, cell proliferation, phenotypic marker expression and nitric oxide release. The results indicate a similar level of cytocompatibility with HUVEC cells cultured on Ti‐23Hf‐3Mo‐4Sn substrate and those cultured on the conventional CP‐Ti and Ti‐6Al‐4V metallic materials

Biological Behaviour and Enhanced Anticorrosive Performance of the Nitrided Superelastic Ti-23Nb-0.7Ta-2Zr-0.5N Alloy

International audienceThe influence of gas nitriding surface treatment on the superelastic Ti-23Nb-0.7Ta-2Zr-0.5N alloy was evaluated. A thorough characterization of bare and nitrided Ti-based alloy and pure Ti was performed in terms of surface film composition and morphology, electrochemical behaviour, and short term osteoblast response. XPS analysis showed that the nitriding treatment strongly influenced the composition (nitrides and oxynitrides) and surface properties both of the substrate and of the bulk alloy. SEM images revealed that the nitrided surface appears as a similar dotted pattern caused by the formation of N-rich domains coexisting with less nitrided domains, while before treatment only topographical features could be observed. All the electrochemical results confirmed the high chemical stability of the nitride and oxynitride coating and the superiority of the applied treatment. The values of the corrosion parameters ascertained the excellent corrosion resistance of the coated alloy in the real functional conditions from the human body. Cell culture experiments with MG63 osteoblasts demonstrated that the studied biomaterials do not elicit any toxic effects and support cell adhesion and enhanced cell proliferation. Altogether, these data indicate that the nitrided Ti-23Nb-0.7Ta-2Zr-0.5N alloy is the most suitable substrate for application in bone implantolog

Enhancement of the biocompatibility by surface nitriding of a low-modulus titanium alloy for dental implant applications

International audienceTo enhance their longevity, dental implants must be highly biocompatible and must have a low elastic modulus close to that of the bone. They must also possess a high superficial hardness and a high corrosion resistance. For these reasons, a recently developed low-modulus Ti-27Nb alloy with nontoxic elements was treated by gas nitriding at high temperature in this study. A very thin nitrided layer of 0.5 μm in thickness followed by an enriched nitrogen zone was observed. Consequently, a very high hardness evaluated at about 1800 HV was obtained in surface, which represents an increase of 4-5 times the hardness of the non-nitrided alloy. This superficial hardness was experimentally observed to decrease up to 800 nm in depth from the surface to the core. The low modulus of Ti-27Nb (evaluated at 55 GPa, which is twice lower than the commercially pure titanium) was not affected by the surface nitriding treatment. A better corrosion resistance was observed and a significant decrease in ion release rates for the nitrided alloy (ion release of 1.41 ng/cm compared to the 163.58 ng/cm obtained for the commercially pure titanium at pH = 7.48 in artificial Carter-Brugirard saliva). The cytocompatibility was not compromised and the cell viability performed on human osteoblasts, fibroblastic cells, and epithelial cells was enhanced on the nitrided surface in comparison with the non-nitrided surface. These combined properties make the nitrided Ti-27Nb alloy a good candidate for dental implant applications