In vitro and in silico evaluation of hydrogen embrittlement of cathodically stimulated titanium

Cathodic Voltage Controlled Electrical Stimulation (CVCES) is a novel electrochemical technique that has been previously shown to prevent and eradicate bacterial infections on the surface of orthopedic implants. Application of cathodic voltage to the metallic implants leads to production of hydrogen on the implants’ surface. The introduction, and subsequent diffusion and adsorption of hydrogen within the metal surface can lead to hydrogen embrittlement. In this work we employed both experimental and computational methods to study hydrogen production and its possible embrittlement on the surface of Titanium - 6 % Aluminum - 4 % Vanadium (Ti64) working sample upon application of −1.8 V v/s Ag/AgCl. A total of 8 Ti64 hydrogen embrittlement bars, 4 with a sleeve around the central notch and 4 without any sleeve, were subject to the cathodic stimulation for 24 hours. The samples were then mechanically evaluated according to ASTM F519 hydrogen embrittlement test. None of the 8 samples showed any signs of mechanical failure, and thereby hydrogen embrittlement upon application of CVCES. The elimination of risk associated with CVCES could pave the way towards clinical translation of the technique. COMSOL Multiphysics was used to design computational models to simulate hydrogen production and distribution on the surface of Ti64 and in its vicinity upon application of −1.8 V for 1 hour for both with- and without-sleeve cases. The models predicted a rapid increase in hydrogen concentration in the microenvironment of the polarized titanium surface. Henry's Law solubility calculations showed instantaneous hydrogen bubble formations at these predicted concentrations, which was consistent with the experimental observations.