Corrosion resistance and biocompatibility of Ti–Ta alloys for biomedical applications

Abstract

Corrosion resistance, wear resistance and biocompatibility of the studied Ti–Ta alloys with Ta contents of 10, 30 and 70 mass% together with the currently used metallic biomaterials pure titanium (Ti) and Ti–6Al–4V extra low interstitial (ELI) alloy were investigated for biomedical applications. Corrosion resistance was measured by an anodic polarization test using an automatic potentiostat in 5% HCl solution at 310 K. Wear resistance was evaluated using a pin-on-disk type friction wear test system with a load of 4.9 N at 310 K in a simulated body fluid (Ringer's solution), and biocompatibility was judged by evaluating the cyto-toxicity through MTT assay. The passive behaviors are observed for all the studied Ti–Ta alloys, and the TiO₂ passive films strengthened by the more stable Ta₂O₅ passive films result in improved corrosion resistance of the studied Ti–Ta alloys with increasing Ta content. All the studied Ti–Ta alloys are non-cytotoxic like pure Ti. The crystal structure shows little influence on the corrosion resistance and cyto-toxicity of the studied Ti–Ta alloys. The experimental results conform the expected excellent corrosion resistance and biocompatibility of the studied Ti–Ta alloys, which are better than or similar to those of pure Ti or Ti–6Al–4V ELI alloy used as standard biomaterials, suggesting their promising potential for biomedical applications.

Introduction

Metallic biomaterials, including stainless steels, Co–Cr-based alloys, Ti and its alloys are the most widely used biomaterials especially for orthopedic implants even in highly loaded areas such as the stem of artificial joints, and hence are required to possess some special mechanical, physical, chemical or biological properties such as high strength and a Young's modulus close to that of a human bone which are indispensable to bear various biofunctions. Recently, Ti and its alloys have become one of the most attractive biomaterials due to their better corrosion resistance, biocompatibility, greater specific strength and much lower elastic modulus than the other metallic biomaterials [1].

The previous investigations [2], [3] indicate that the Ti–Ta alloys are expected to become promising candidates for biomedical applications due to their better mechanical biocompatibility than pure Ti and Ti–6Al–4V alloy used as standard biomaterials, i.e. their lower moduli and higher strength-to-modulus ratios than those of the above currently used implant materials. However, an excellent corrosion resistance preventing any degradation of metallic biomaterials in the body fluids and biocompatibility indicating no toxicity and allergic reactions inside a living creature are crucial prerequisites for biomedical applications. The superior corrosion resistance and biocompatibility of pure Ti and pure Ta have been extensively evaluated and recognized by many researchers [4], [5], [6], [7], [8], [9], [10]; however, both the alloys and their components should be individually tested for the above properties for safety in biomedical applications [10]. Although the previous studies show that the corrosion resistance of Ti–40% and 50% Ta alloys in the simulated biological solution surpasses that of Ti–6Al–4V ELI alloy [11], and that there is no difference in biocompatibility between Ti–5% Ta alloy and pure Ti [12], to date, the corrosion resistance and biocompatibility of Ti–Ta alloys have not yet been studied systematically.

The aim of this study is to investigate the corrosion resistance and biocompatibility of typical Ti–Ta alloys with Ta contents of 10, 30 and 70 mass% for biomedical applications. For comparative purpose, the same measurements were also performed on pure Ti and Ti–6Al–4V ELI alloy which was annealed at 1023 K for 3.6 ks to remove any residual stress.