Scaling Effects on the Electrochemical Stimulation Performance of Au, Pt, and PEDOT:PSS Electrocorticography Arrays

The efficacy of electrical brain stimulation in combatting neurodegenerative diseases and initiating function is expected to be significantly enhanced with the development of smaller scale microstimulation electrodes and refined stimulation protocols. These benefits cannot be realized without a thorough understanding of scaling effects on electrochemical charge injection charac­ teristics. This study fabricates and characterizes the electrochemical stimu­ lation capabilities of Au, Pt, poly(3,4­ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS/Au), and PEDOT:PSS/Pt electrode arrays in the 20–2000 μm diameter range. This study observes substantial enhancement in charge injection capacity up to 9.5× for PEDOT:PSS microelectrodes com­ pared to metal ones, and 88% lower required power for injecting the same charge density. These significant benefits are strongest for electrode dia­ meters below 200 μm. Detailed quantitative analyses are provided, enabling optimization of charge injection capacity with potential bias and symmetric and asymmetric pulse width engineering for all diameters. These systematic analyses inform the optimal design for acute and potentially chronic implants in regards to safety and clinically effective stimulation protocols, ensure the longevity of the electrodes below critical electrochemical limits of stimulation, and demonstrate that the material choice and pulse design can lead to more energy efficiency stimulation protocols that are of critical importance for fully implanted devices.