Electrodeposited Platinum Iridium Enables Microstimulation With Carbon Fiber Electrodes

Abstract

Ultrasmall microelectrode arrays have the potential to improve the spatial resolution of microstimulation. Carbon fiber (CF) microelectrodes with cross-sections of less than 8 μm have been demonstrated to penetrate cortical tissue and evoke minimal scarring in chronic implant tests. In this study, we investigate the stability and performance of neural stimulation electrodes comprised of electrodeposited platinum-iridium (PtIr) on carbon fibers. We conducted pulse testing and characterized charge injection in vitro and recorded voltage transients in vitro and in vivo. Standard electrochemical measurements (impedance spectroscopy and cyclic voltammetry) and visual inspection (scanning electron microscopy) were used to assess changes due to pulsing. Similar to other studies, the application of pulses caused a decrease in impedance and a reduction in voltage transients, but analysis of the impedance data suggests that these changes are due to surface modification and not permanent changes to the electrode. Comparison of scanning electron microscope images before and after pulse testing confirmed electrode stability.

Full-field, conformal epiretinal electrode array using hydrogel and polymer hybrid technology

“…5 b). A percentage of 59% for Pt and 41% of Ir was measured on one electrode, comparable with previous results 43 . SEM was done after electrodeposition but prior to hydrogel coating.…”

“…Electrical performance of the FFA was significantly improved by Pt/Ir electrodeposition and most of this improvement was maintained despite coating the electrodes with hydrogel. We found that contaminations from SEM and residual PDMS caused a variation of both impedance and CSC C of the naïve electrodes, but electrodeposition effectively cleaned the electrode surface and improved the electrical properties of the electrodes due to the properties of the Pt/Ir alloy 43 . After electrodeposition, the standard deviation of the impedance at 1 kHz was reduced to 5.53%.…”

“…The EIS data were fitted into an equivalent circuit model 43 to further analyze the electrical properties of electrodes. The circuit model consisted of the following components: (1) series resistance Ru, which reflected the geometric surface area of the electrode and the resistivity of the conducting path to the counter electrode, (2) a constant phase element with admittance (Y0)and exponent (α), which reflected the electrochemical surface area and the porosity or roughness of the electrode surface and (3) a parasitic capacitance, C, which reflected instrumentation artifact caused by coupling between connecting lines.…”

“…As described in prior work 43 , the plating solution was prepared with 0.2 g/L Na 3 IrCl 6 H 2 O and 0.186 g/L Na 2 PtCl 6 H 2 O in 0.1 M of nitric acid (HNO 3 ). The solution was boiled until the color turned reddish, and then was cooled down to 45 °C.…”

Profiling neurons surrounding subcellular-scale carbon fiber electrode tracts enables modeling recorded signals

“…Carbon fibers were then plasma ashed in a Glen 1000P Plasma Cleaner (Glen Technologies Inc., Fremont, CA). Fiber tips were functionalized in one of two ways: 1) electrodeposition by dipping carbon fibers in a solution of 0.01 M 3,4-ethylenedioxythiophene (483028, MilliporeSigma, Darmstadt, Germany) and 0.1 M sodium p-toluenesulfonate (152536, MilliporeSigma) and applying 600 pA/channel using a PGSTAT12 potentiostat (EcoChemie, Utrecht, Netherlands) to coat the tips with PEDOT:pTS 25,61 (N=3 arrays) or 2) electrodeposition of Platinum Iridium (PtIr) with a Gamry 600+ potentiostat (Gamry Instruments, Warminster, PA) (N=2 arrays) using previously published methods 89 .Silver ground and reference wires (AGT05100, World Precision Instruments, Sarasota, FL) were soldered to the PCB, completing assembly. For one electrode, a support tine was broken off prior to implant as a sham channel for a separate study (for rat #1).…”