Scaling Effects on the Electrochemical Stimulation Performance of Au, Pt, and PEDOT:PSS Electrocorticography Arrays

Abstract

The efficacy of electrical brain stimulation in combatting neurodegenerative diseases and initiating function is expected to be significantly enhanced with the development of smaller scale microstimulation electrodes and refined stimulation protocols. These benefits cannot be realized without a thorough understanding of scaling effects on electrochemical charge injection charac teristics. This study fabricates and characterizes the electrochemical stimu lation capabilities of Au, Pt, poly(3,4ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS/Au), and PEDOT:PSS/Pt electrode arrays in the 20-2000 µm diameter range. This study observes substantial enhancement in charge injection capacity up to 9.5× for PEDOT:PSS microelectrodes com pared to metal ones, and 88% lower required power for injecting the same charge density. These significant benefits are strongest for electrode dia meters below 200 µm. Detailed quantitative analyses are provided, enabling optimization of charge injection capacity with potential bias and symmetric and asymmetric pulse width engineering for all diameters. These systematic analyses inform the optimal design for acute and potentially chronic implants in regards to safety and clinically effective stimulation protocols, ensure the longevity of the electrodes below critical electrochemical limits of stimulation, and demonstrate that the material choice and pulse design can lead to more energy efficiency stimulation protocols that are of critical importance for fully implanted devices.

A Platform to Study the Effects of Electrical Stimulation on Immune Cell Activation During Wound Healing

“…The platform consisted of a polyvinyl alcohol (PVA) sponge which was implanted subcutaneously at the wound site. [22,23] As prior meta-studies [6,8,11] show that there is ongoing debate over the types of ES parameters necessary for wound treatment, the magnitude and frequency of ES waveforms were varied here to examine their effects on immune cells in mice wound models. [15][16][17][18] Using subcutaneous implants of PVA sponges, we are able to establish data in animal models that can be measured in a laboratory setting.…”

“…The finer patterning capability of the inkjet printing process allows for rapid prototyping and fabrication of high-density arrays. [22,23] As shown in Figure our ES studies comparing the effects of applied current amplitudes and frequencies, as shown in the table of Figure 1C. We used hydrogel phantoms to create areas of low and high impedance and measured the impedance magnitude and phase angle between pairs of neighboring electrodes.…”

“…2019, 3,1900106 Both screen-printed and inkjet-printed electrodes were covered with a conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to provide a stable, biocompatible interface, [20,[36][37][38][39] to further lower the impedance at the electrode-skin interface, and to provide a greater charge injection capacity for ES than metal surfaces. [22,23] As shown in Figure S2, Supporting Information, the electrodes without PEDOT:PSS coated on the ends exhibited a reduction in current supplied over time, reducing from 300 µA to less than 10 µA current after 40 min, while the PEDOT:PSS-coated electrodes maintained the current magnitude for the full 1 h stimulation time. The electrode arrays with PEDOT:PSS were then used in Adv.…”

“…[19] The additively printed [20,21] ES electrodes used in this study were flexible with enhanced adhesion to skin, allowed precise control over stimulation locations, and were optimized for improved charge injection capacity. [22,23] As prior meta-studies [6,8,11] show that there is ongoing debate over the types of ES parameters necessary for wound treatment, the magnitude and frequency of ES waveforms were varied here to examine their effects on immune cells in mice wound models.To assess the effects of ES, the cells captured in the PVA sponge were analyzed via flow cytometry, which enabled highthroughput measurement of cell populations and intra-cellular protein levels at the single cell level. [24] The multi-parametric flow cytometry analysis allowed us to isolate signals from specific sub-populations of cells, to rapidly distinguish different cell types in particular immune cells and investigate cell-typespecific signal transduction pathways.Wound healing is a complex process involving diverse changes in multiple cell types where the application of electric fields has been shown to accelerate wound closure.…”

“…[19] The additively printed [20,21] ES electrodes used in this study were flexible with enhanced adhesion to skin, allowed precise control over stimulation locations, and were optimized for improved charge injection capacity. [22,23] As prior meta-studies [6,8,11] show that there is ongoing debate over the types of ES parameters necessary for wound treatment, the magnitude and frequency of ES waveforms were varied here to examine their effects on immune cells in mice wound models.…”