Electron transfer processes occurring on platinum neural stimulating electrodes: calculated charge-storage capacities are inaccessible during applied stimulation

Abstract

Objective Neural prostheses employing platinum electrodes are often constrained by a charge/charge-density parameter known as the Shannon limit. In examining the relationship between charge injection and observed tissue damage, the electrochemistry at the electrode-tissue interface should be considered. The charge-storage capacity (CSC) is often used as a predictor of how much charge an electrode can inject during stimulation, but calculating charge from a steady-state i-E curve (cyclic voltammogram) over the water window misrepresents how electrodes operate during stimulation. We aim to gain insight into why CSC predictions from classic i-E curves overestimate the amount of charge that can be injected during neural stimulation pulsing. Approach In this study, we use a standard electrochemical technique to investigate how platinum electrochemistry depends on the potentials accessed by the electrode and on the electrolyte composition. Main Results The experiments indicate: 1) platinum electrodes must be subjected to a “cleaning” procedure in order to expose the maximum number of surface platinum sites for hydrogen adsorption; 2) the “cleaned” platinum surface will likely revert to an obstructed condition under typical neural stimulation conditions; 3) irreversible oxygen reduction may occur under neural stimulation conditions, so the consequences of this reaction should be considered; and 4) the presence of the chloride ion (Cl−) or proteins (bovine serum albumin) inhibits oxide formation and alters H adsorption. Significance These observations help explain why traditional CSC calculations overestimate the charge that can be injected during neural stimulation. The results underscore how careful electrochemical examination of the electrode-electrolyte interface can result in more accurate expectations of electrode performance during applied stimulation.

Ultralow Impedance Graphene Microelectrodes with High Optical Transparency for Simultaneous Deep Two‐Photon Imaging in Transgenic Mice

“…PtNPs deposition achieves a 100‐time decrease in the impedance. CV curves of PtNPs/Graphene electrodes show oxide reduction peaks at ≈−270 mV and hydrogen adsorption peaks at −900 to −400 mV (Figure c), all of which indicate that Pt is actively engaged in the charge‐transfer process at electrode/electrolyte interface . As for simultaneous optical imaging or optogenetics experiments, high transmittance is equally important as the low impedance.…”

A Review: Electrode and Packaging Materials for Neurophysiology Recording Implants

“…For example, platinum black and Ir/IrOx are also widely used as stimulating electrodes (Zhang et al, 2015 ; Chen et al, 2019 ). Large charge storage capacity is specifically required for simulating electrodes to achieve better stimulating performance (Hudak et al, 2017 ). Neural stimulators also have the same strict requirements on hermeticity, long-term stability, and biocompatibility of device package (Vanhoestenberghe and Donaldson, 2013 ; Donaldson and Brindley, 2016 ).…”

Alginate-encapsulated brain-derived neurotrophic factor–overexpressing mesenchymal stem cells are a promising drug delivery system for protection of auditory neurons

“…Parameters for safe stimulation of neurons using platinum electrodes in vivo have been determined by Shannon. 63 The pulses used in the current study should theoretically be safe according to calculations by Hudak et al 64 The central electrode with an area of 1.56 ± 0.43 mm 2 and a maximum pulse width of 400 μs could, according to the model, be operated at safe amplitude of 2.3 mA. Clinically used stimulation parameters range for current from about 10.2 to 2000 µA and for pulse width from 8 to 400 µs.…”