The effect of cathodic voltage-controlled electrical stimulation of titanium on the surrounding microenvironment pH: An experimental and computational study

Cathodic voltage-controlled electrical stimulation (CVCES) is being explored for the treatment and prevention of orthopedic implant associated infections. However, the precise mechanism of the antimicrobial action of CVCES is not fully understood. Here, we present a combined experimental and computational study evaluating the spatial and temporal evolution of pH in a saline electrolyte near a titanium electrode in response to CVCES magnitudes of -1.0 V, -1.5 V, and -1.8 V vs Ag/AgCl. Scanning electrochemical microscopy was used to make spatially resolved measurements of pH with potentiometric microelectrodes. COMSOL Multiphysics was utilized to construct a computational model to predict the effects of the CVCES on the surrounding microenvironment. The outcomes showed that an alkalization of the microenvironment occurs that is voltage-dependent, with application of greater cathodic potentials resulting in greater alkaline pH shifts. The pH displayed a rapid, logarithmic-like increase over time at a distance of 10 µ from the polarized titanium surface. The pH increase was more sluggish at a distance of 5 mm from the titanium surface, due to the longer diffusion length for the reduction reaction products that are responsible for the alkalization. The computational methods developed herein show sufficiently good agreement with the experimental results to warrant further development as a tool to help guide the development of antimicrobial electrochemical treatment methodologies.