Electrochemical, Microstructural and Mechanical Investigations of H2O2-Driven Degradation of Ti6Al4V

Abstract

Titanium and its alloys consitute one of the main classes of materials utilized as non-biodegradable implants in the human body. The corrosion resistance of titanium is mainly due to the presence of a thin, compact and passive layer on its surface. However, this layer degrades in the presence of reactive oxygen species, such as oxygen peroxide (H2O2) [1,2]. This leads to the device degradation and the release of its constituents in the surrounding tissues, which may bring about serious health issues (peri-implantitis, osteolysis, neurotoxicity...) [3]. H2O2 is produced by the immune system during inflammatory episodes by specific enzymes, such as NADPH oxidase and superoxide dismutase [4]. It is also utilized by surgeons at high concentrations (ca. 1 M) during peri-implant tissue disinfection. Ti6Al4V (titanium grade 5, an α + β alloy) is a popular implant material because of its excellent mechanical properties. However, in recent years, Ti6Al4V with equiaxed α grains (and β phase located at the grain boundaries) was reported to undergo a significant degradation by H2O2 characterized by the growth of a thick oxide layer on the α grains and the development of porosity and cracks in the β phase [1]. Ti6Al4V could be susceptible to stress corrosion cracking (SCC) under mechanical load due to the β phase dissolution in H2O2-containing physiological solutions (Figure 1). However, no clear link has been established yet between the corrosive environment, the mechanical load and the microstructure of the Ti6Al4V alloy.This contribution will report about the influence of H2O2 concentration on the in vitro corrosion of Ti6Al4V simulating inflammation conditions (low concentration) as well as disinfection procedures (high concentrations). Results on the electrochemical behavior (monitored by impedance spectroscopy), the degraded microstructure (obtained with focused ion beam scanning electron microscopy and transmission electron microscopy) and the impact of the H2O2-driven degradation on the mechanical properties of the alloy will be presented and discussed.Acknowledgements:The authors gratefully acknowledge the financial support of the French National Research Agency (grant agreement ANR-22-CE93-0007-02) and that of the Swiss National Science Foundation (grant agreement 200021L_213161).