The influence of microstructure on the corrosion behavior of platinum used for cochlea implant electrodes

Cochlear implants (CIs) have revolutionized the treatment of profound hearing loss, yet their long-term durability remains a challenge due to potential corrosion-induced degradation of the platinum electrodes of the CI. This study examines the corrosion behavior of platinum wires under accelerated test conditions, and compares the results with corrosion patterns observed in explanted CI electrodes from patients after almost 1 year and 26 years. Accelerated corrosion tests with frequencies from 1 to 5 kHz were validated as predictive tools for long-term performance, as the surface morphologies of stimulated platinum wires exhibit notable similarities to those of explanted electrodes. The as-drawn wires analyzed in this study exhibit up to 50 % more corrosion attack than annealed ones. Additionally, the impact of grain orientation on corrosion is examined by testing platinum single crystals with different electrochemical methods. For this purpose, single crystals with the orientation [111], [110] and [100] were analyzed. The research highlights the importance of annealing platinum and minimizing plastic deformation during electrode assembly to enhance electrode durability. Corrosion was found to primarily occur at grain boundaries, with grain orientation showing minimal influence. These findings suggest that engineering grain boundary characteristics could significantly improve the corrosion resistance of polycrystalline electrodes, offering a promising pathway to enhance the longevity of CIs.