Electron transfer processes occurring on platinum neural stimulating electrodes: pulsing experiments for cathodic-first/charge-balanced/biphasic pulses for 0.566 ≤ k ≥ 2.3 in oxygenated and deoxygenated sulfuric acid

Abstract

The application of a train of cathodic-first/charge-balanced/biphasic pulses applied to a platinum electrode resulted in a positive creep of the anodic phase potential that increases with increasing charge injection but reaches a steady-state value before 1000 pulses have been delivered. The increase follows from the fact that charge going into irreversible reactions occurring during the anodic phase must equal the charge going into irreversible reactions during the cathodic phase for charge-balanced pulses. In an oxygenated electrolyte the drift of the measured positive potential moved into the platinum oxidation region of the i(V e) profile when the charge injection level exceeds k = 1.75. Platinum dissolution may occur in this region and k = 1.75 defines a boundary between damaging and non-damaging levels on the Shannon Plot. In a very low oxygen environment, the positive potential remained below the platinum oxidation region for the highest charge injection values studied, k = 2.3. The results support the hypothesis that platinum dissolution is the defining factor for the Shannon limit, k = 1.75. Numerous instrumentation issues were encountered in the course of making measurements. The solutions to these issues are provided.

Public Regulatory Databases as a Source of Insight for Neuromodulation Devices Stimulation Parameters

“…We employed the Shannon model (8) as a frame of reference because it is often used in peer-reviewed literature (5,6,(11)(12)(13)(14)(15)(16) to estimate the threshold for stimulation-induced neural tissue damage. The model is based on experiments (9,10) performed in cat cerebral cortex with 7 hours of stimulation at 50 Hz using surface disc electrodes of from 0.2 to 50 mm 2 under light anesthesia, which limits its translatability to cases with different conditions.…”

“…This approach is based on studies by McCreery et al performed in acute stimulation experiments in feline cortex (9,10) at a fixed frequency of 50 Hz and fixed biphasic 0.4 millisecond pulses. This model developed by Shannon (8) has become very popular among scholars (5,6,(11)(12)(13)(14)(15)(16). However, since the inception of the Shannon model, medical device manufacturers have performed a substantial number of studies to assess the safety of electrical stimulation in a number of animal models (pig, sheep, monkey, dog, goat); in different anatomical locations (deep brain structures, spinal cord, vagus nerve and other peripheral nerves); stimulation duration (several hours to years of chronic stimulation) with a range of frequencies (from 10 to 10,000 Hz); and a variety of pulse shapes and stimulation amplitudes.…”

Electrical neurostimulation with imbalanced waveform mitigates dissolution of platinum electrodes

“…Pulsing experiments were carried out using a Current-Pulse Capacitor Discharge instrument (CPCDi) manufactured at Case Western Reserve University (Kumsa et al 2016b). For charge-balanced waveforms, passive capacitive discharge was performed using a 1 µ F capacitor.…”

“…For monophasic pulsing, a diode rectifier was employed to allow current to flow only in one direction. The detailed description of the instrument is provided elsewhere (Kumsa et al 2016b). The pulsing was done at 50 Hz with a 100 µ s pulse width and 100 µ s inter-phase delay.…”

Non-clinical and Pre-clinical Testing to Demonstrate Safety of the Barostim Neo Electrode for Activation of Carotid Baroreceptors in Chronic Human Implants

“…The primary cause of stimulation induced tissue damage is still a topic of debate. The two primary theories are cell death brought on by cells being unnaturally stimulated for long periods of time (hyperactivity, excitoxocity) and toxic products due to electron transfer processes (electrochemical reactions Kumsa et al, 2016 ). Although the exact levels of platinum or iridium particulates resulting from chronically implanted electrode dissolution processes necessary to cause cell death are unknown, a common frame of reference is an early study by Rosenberg, et al characterizing the inhibition of cell division in escherichia coli by electrolysis products from a platinum electrode (Rosenberg et al, 1965 ).…”