In Vitro and In Vivo Evaluation of PEDOT Microelectrodes for Neural Stimulation and Recording

Abstract

Cortical neural prostheses require chronically implanted small-area microelectrode arrays that simultaneously record and stimulate neural activity. It is necessary to develop new materials with low interface impedance and large charge transfer capacity for this application and we explore the use of conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) for the same. We subjected PEDOT coated electrodes to voltage cycling between -0.6 and 0.8 V, 24 h continuous biphasic stimulation at 3 mC/cm² and accelerated aging for four weeks. Characterization was performed using cyclic voltammetry, electrochemical impedance spectroscopy, and voltage transient measurements. We found that PEDOT coated electrodes showed a charge injection limit 15 times higher than Platinum Iridium (PtIr) electrodes and electroplated Iridium Oxide (IrOx) electrodes when using constant current stimulation at zero voltage bias. In vivo chronic testing of microelectrode arrays implanted in rat cortex revealed that PEDOT coated electrodes show higher signal-to-noise recordings and superior charge injection compared to PtIr electrodes.

Bioelectronic neural pixel: Chemical stimulation and electrical sensing at the same site

“…These results show that a single-cell-scale electrode has the ability to both record and chemically stimulate, demonstrating the local effects of therapeutic treatment, and opening a range of opportunities in basic neuroscience as well as medical technology development. one order of magnitude lower than bare Au, Pt, and Ir electrodes of similar dimensions at 1 kHz), with the low impedance being attributed partly to the high porosity, giving an increased electrochemical surface area (12)(13)(14). Additionally, with their mixed electronic and ionic conductivity and the soft mechanical properties that match those of the neural tissue, conducting polymers are ideally suited to obtain high signal-to-noise ratio recordings at the neural interface (15,16).…”

State-of-the-art MEMS and microsystem tools for brain research

“…Over the last decade, conductive polymers, particularly poly(3,4-ethylenedioxythiophene) (PEDOT), have received much attention, outperforming thin-film metals in the first several weeks of use before biofouling and the foreign body response presumably reduce performance 142,143 . PEDOT has excellent charge injection capacity 144 and one of the lowest site impedances per unit area of any material. The two most common dopant molecules for PEDOT are polystyrene sulfonate (PSS) and, more recently, carbon nanotubes (CNT) 143 .…”

Electrochemical Evaluation of Geometrical Effect and Three-dimensionalized Effect of Iridium Oxide Electrodes Used for Retinal Stimulation

“…One promising approach is to utilize capacitive electrodes (4)(5)(6) that improve electrode performance by increasing the real surface area obtained by a micro/nano-scale surface morphology. The introduction of reactive electrodes such as oxides (7)(8)(9) and organic polymers (10) has also been investigated. Our focus has been on achieving high-performance iridium oxide (IrOx) materials by optimizing the fabrication process and fundamental electrochemical properties.…”