In vivo microstimulation stability of electrodeposited platinum-iridium on carbon fiber electrodes

Carbon fiber electrodes (CF) have proven effective at recording neural activity at single cell resolution. CF elicit a minimal foreign body reaction due to their small size, thus the longevity of recording is extended vs. traditional electrodes. However, microstimulation with carbon fibers is not possible chronically, due to the limited ability of carbon to transfer stimulus charge without degradation. Electrodeposited platinum iridium alloy (PtIr) has been applied to carbon to enable microstimulation. Studies to date have shown durability of PtIr in vitro. Here, we show that PtIr is robust to electrical stimulation in vivo. CF electrode arrays were implanted in rat visual cortex. After a 4 week recovery period, we stimulated for 7 hours (50 Hz, 0.2 ms biphasic pulses, up to 12 nC/phase, up to 1.3 mC/cm²/phase). 12 CF electrodes were tested. We measured electrical impedance, charge storage capacity, and electrode voltage before and after pulsing to assess the PtIr stability. Analysis of the measured data shows typical changes in impedance (decrease with pulsing), no change in charge storage capacity, and stability of electrode voltage. These results support the use of PtIr for long-term intracortical microstimulation.Clinical Relevance- Intracortical microstimulation with CF can provide precise activation of brain and peripherals nerves. Implantable devices using CF can treat neurological disorders.