Vanadium ionic species from degradation of Ti-6Al-4V metallic implants: In vitro cytotoxicity and speciation evaluation

Abstract

Among the metallic materials used in biomedical industry, the most common choice for orthopedics and dental implants is titanium (Ti) and its alloys, mainly due to their superior corrosion and tribocorrosion resistance and biocompatibility. Under different conditions in vivo, such as different pH levels, composition of body fluid and mechanical loads, metallic materials may suffer from degradation, resulting in the release of undesired wear particles and ions. In particular, the Ti-6Al-4V system represents almost half of the production of Ti as a biomaterial and many concerns have been raised about titanium, aluminum and vanadium ions releasing. This work evaluates the cytotoxic effects of vanadium ionic species generated from Ti-6Al-4V surfaces regarding mouse pre-osteoblasts and fibroblasts. In our cell viability tests, we noticed a significant decrease in the fibroblasts' cell viability with vanadium concentrations (23 μM) close to those previously reported to be observed in vivo in patients with poor functioning of their medical devices based on Ti-6Al-4V (30 μM). Speciation modelling was carried-out, for the first time, to this system. Results of the modelling reveal that vanadates(V), namely H₂VO₄^- and HVO₄^2-, are the main species present in cell culture media. Otherwise, in synovial fluids of individuals with poorly functioning implants, wherein the concentration of vanadium may go up to ca. 30 μM, the tentative theoretical speciation data indicates a high occurrence probability for V^V- and V^IV-species bound to albumin and hyaluronic acid. In conclusion, even though relatively low concentrations of vanadium may be released from Ti-6Al-4V implants in vivo, the continuous contact with peri-implant cells for long periods of time may represent a potentially hazardous situation.

Keywords: Cytotoxicity; Ionic speciation; Oxidovanadium(IV); Ti-6Al-4V; Tribocorrosion; Vanadate(V).