Purchase this article with an account.
Guenther Zeck, Ramona Samba, Thoralf Herrmann; Comparison of the electrical stimulation performance of PEDOT-CNT and iridium oxide electrodes. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):757.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Stimulating microelectrodes must be able to stimulate retinal neurons using low voltage to avoid electrochemical surface reactions and using low charge to avoid tissue damage. Here we address these two challenges by comparing two different microelectrode materials - the conductive polymer composite comprising poly-3,4-ethylenedioxythiophene and carbon nanotubes (PEDOT-CNT) and iridium oxide (IrOx) - at activating spikes in retinal ganglion cells through stimulation of retinal interneurons. Stimulation efficacy of the microelectrodes was analyzed by comparing voltage, current and transferred charge at stimulation threshold.<br />
Ex vivo retinas from adult, female Sprague-Dawley rats were interfaced ganglion-cell side down on microelectrode arrays comprising either iridium oxide or PEDOT-CNT coated gold electrodes. Cathodal constant-voltage pulses (duration: 0.1 - 1ms) were applied to a ring-like stimulation electrode configuration. The stimulus-induced ganglion cell spiking was recorded by an additional electrode located in the center. Threshold voltage was determined as the pulse amplitude required to evoke network-mediated ganglion cell spiking in a defined post stimulus time window (10 - 20 milliseconds) in 50% of identical stimulus repetitions. For each of the two electrode materials nine experiments were compared with respect to threshold voltage, transferred charge at threshold, maximum current and the residual current at the end of the pulse.<br />
The two materials exhibit a similar charge injection capacity of 11 mC/cm2 as inferred from cyclic voltammetry. However, the threshold voltages for stimulus durations of 0.5 ms and 1 ms were significantly lower using PEDOT-CNT coated electrodes compared to IrOx electrodes (p<0.05, n= 9 experiments for each condition). Threshold voltages for shorter stimulus durations (0.1 ms and 0.2 ms respectively) did not different significantly for the two materials. A preliminary evaluation (n=5) of the maximal charge injected during the pulse (0.5 ms and 1 ms) suggests a smaller value for PEDOT-CNT electrodes as compared to IrOx.
In retinal implants, PEDOT-CNT coated electrodes may allow for smaller electrodes, stimulation in a safe voltage regime and lower energy consumption. The presented framework can be easily extended to estimate stimulation efficacy of different electrode materials.<br />
This PDF is available to Subscribers Only