Subthreshold Electrical Stimulation for Controlling Protein-Mediated Impedance Increases in Platinum Cochlear Electrode

Objective: This study evaluated subthreshold biphasic stimulation pulses as a strategy to stabilize electrode impedance via control of protein adsorption. Following implantation, cochlear electrodes undergo impedance fluctuations thought to be caused by protein adsorption and/or inflammatory responses. Impedance increases can impact device power consumption, safe charge injection limits, and long-term stability of electrodes. Methods: Protein-mediated changes in polarization impedance (Zp) were measured by voltage transient responses to biphasic current pulses and electrochemical impedance spectroscopy, with and without protein solutions. Four subthreshold stimulation regimes were studied to assess their effects on protein adsorption and impedance; (1) symmetric charge-balanced pulses delivered continuously, (2) at 10% duty cycle, (3) at 1% duty cycle, and (4) an asymmetric charge balanced pulse delivered continuously with a cathodic phase twice as long as the anodic phase. Results: The Zp of electrodes incubated in protein solutions without stimulation for 2 h increased by between ~28% and ~55%. Subthreshold stimulation reduced the rate at which impedance increased following exposure to all protein solutions. Decreases in Zp were dependent on the type of protein solution and the stimulation regime. Subthreshold stimulation pulses were more effective when delivered continuously compared to 1% and 10% duty cycles. Conclusion: These results support the potential of subthreshold stimulation pulses to mitigate protein-mediated increase in impedance. Significance: This research highlights the potential of clinically translatable stimulation pulses to mitigate perilymph protein adsorption on cochlear electrodes, a key phenomenon precursor of the inflammatory response.