Improved electrode stimulation stability of Utah arrays*

The Utah electrode array (UEA) is a promising microelectrode technology with potential applications to assist patients with sensory loss, spinal cord injuries, and limb loss serving as neural prosthetics and brain-computer interfaces. Performance lifetime of microelectrodes, particularly when used for stimulation, remains one of the challenges for their clinical translation. This study characterizes the stimulation stability of an optimized iridium oxide (IrOx) research metallization for the UEA in comparison to the Blackrock standard practice metallization. The stimulation stability (Stim-Stab) protocol used electrochemical characterization and either 106 or 4 × 106 pulses at 2,100 µA (420 nC/ph) with longitudinal voltage transient measurements and physical characterization to quantify electrode lifetime. Approximately 50% of electrodes using the Blackrock standard practice process electrical failed during 106 pulses, whereas no electrical failures were observed from 4 × 106 pulses for the research metallization. Backscattered scanning electron microscopy (BSEM) determined that all electrodes with electrical failures during Stim-Stab testing had complete loss of metallization. Of electrodes with good electrical outcomes from Stim-Stab testing 80% and 50% of those had notable metallization damage for BRM and research metallization, respectively. These results suggest that the research metallization makes important steps for improving electrode metallization lifetime of Utah arrays. Additionally, the Stim-Stab method provides valuable feedback for engineering improved electrode metallization.