Electrodeposited PEDOT:BF₄ Coatings Improve Impedance of Chronic Neural Stimulating Probes In Vivo

Abstract

require low-impedance at the electrodetissue interface to maintain efficient charge injection during stimulation. [4] The impedance of the electrode sites of neural probes steadily increases with time during implantation due to the immune system's response to the insertion of the probes into tissue. [5] Conducting polymers have been widely explored as coatings for stimulating neural probes to reduce the impedance at the electrode-tissue interface. [6,7] Among conducting polymers, poly(3,4ethylenedioxythiophene) (PEDOT) has significantly contributed to improving the electrical stability of neural probes due to its high conductivity, electrochemical stability under chronic exposure to biological environments, and compliant mechanical properties which provide a softer interface between brain tissue and stiff probes. [8][9][10] The stability of PEDOT coatings on the electrode sites of neural probes is critical for ensuring the long-term functionality of the neural device. [11] One major mode of PEDOT coating failure is through coating delamination or cracking. [12][13][14][15] The coating must be able to survive mechanical stresses, swelling, and electrode corrosion in order to be considered for use in clinical applications. [16] Substantial improvements in PEDOT stability have been achieved through tuning the polymerization parameters, accurately selecting dopants and solvents used for polymerization, and incorporating additives into the PEDOT film. [10,[17][18][19][20] Chronic stability of PEDOT-based recording neural electrodes has been extensively studied and reviewed. [8,19,[21][22][23][24][25][26][27][28][29] Studies of PEDOT coating stability under stimulation have been recently reviewed. [7,16,17] In one study, electropolymerized PEDOT, containing carbon nanotubes, on Pt microelectrodes was monitored over 3 months of soaking in phosphate buffered saline (PBS) with and without stimulation, and were reported to have stable impedance. [30] An in vivo study stimulated the Au electrode sites of a neural probe coated with PEDOT and carbon nanotubes for 1 h a day for 10 days (20 mA, 200 Hz). PEDOT demonstrated similar impedance values to Au electrode sites at the end of the study. [31] On the other hand, PEDOT doped with tetrafluoroborate (PEDOT:BF 4 ) electropolymerized on platinum iridium (PtIr) neural probes was implanted for 15 days, stimulated daily for 90 min (20 mA, 130 Hz) while monitoring the impedance. At the end of the implantation period, Resulting from its many unique properties, such as mechanical compliancy, electrochemical stability, and high conductivity, the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is a promising material for improving the stimulation efficiency of neural microelectrodes. The long-term electrochemical stability of penetrating PEDOT-coated electrodes undergoing high-frequency stimulation is not extensively studied in vivo and the inflammatory response of the brain to PEDOT-coated stimulating neural probes is not well understood. In this work, electropolymerized PE...

Advances in Electrode Materials for Scalp, Forehead, and Ear EEG: A Mini-Review

“…To address this issue, we believe that materials based on conducting polymers that can conform to the shape of the ear can provide better contact between the electrode and the skin. Conductive polymer electrodes have shown promising results in improving signal quality and reducing noise, making them a potential solution for enhancing ear-EEG technology. − These electrodes can offer some advantages over traditional metallic electrodes, such as improved comfort (due to their flexibility) and versatility (can be easily integrated into various form factors and devices). Additionally, they can potentially offer reduced motion artifacts due to their flexibility and improved adherence to the skin, which helps reduce the impact of motion artifacts on EEG signal recordings, making them suitable for applications in which users are in motion.…”

Electrical stimulation for therapeutic approach

“…This can be achieved by designing the materials for the electrode or by modifications on the surface of the electrode. [74][75][76][77][78] Second, the reference electrode is a non-current-carrying electrode, which is used to form a voltage transient between the active electrodes. Therefore, when using a pulsed potential bias for electrical stimulation, a reference electrode is required against the active electrode.…”

“… 68 As it is directly related to the injecting of charges into the target tissues, studies on active electrodes mainly focus on the modifications on the electrode's electrical properties to lower the impedance or to enhance the CIC. This can be achieved by designing the materials for the electrode or by modifications on the surface of the electrode 74–78 . Second, the reference electrode is a non‐current‐carrying electrode, which is used to form a voltage transient between the active electrodes.…”

Bioelectronic Applications of Intrinsically Conductive Polymers

“…ICPs have been studied as the neural interfaces because of mechanical matching and low contact impedance to neurons. [77] For example, Hagler et al deposited PEDOT:BF 4 on PtIr neural microelectrodes and used them to monitor the electrophysiological signals of a rat over 2 months. [77] The PEDTO:BF 4 layer lowered the impedance of the neural interface.…”

“…[77] For example, Hagler et al deposited PEDOT:BF 4 on PtIr neural microelectrodes and used them to monitor the electrophysiological signals of a rat over 2 months. [77] The PEDTO:BF 4 layer lowered the impedance of the neural interface. However, the presence of rigid metals still inevitably led to immunoreaction.…”