Quantification of safe operation conditions for large-area platinum-iridium electrodes in neurostimulation application

by Elisa Leusmann, Ciamak Abkai, Michael Tittelbach, Wigand Poppendieck

Using electrochemical characterization methods of stimulation electrodes as well as accelerated stimulation examinations, a safe operating field for stimulation is investigated for particularly very large Pt-Ir macroelectrodes in a Laplace configuration.

Traditional methods such as Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and biphasic, charge balanced current pulses were applied on Pt-Ir macroelectrodes in phosphate buffered saline solution to investigate reversible boundaries. These experiments were adapted to approach realistic working conditions.

Investigating operational conditions close to realistic use cases have shown an anti-correlation between higher scan rates and the occurrence of irreversible reactions. In addition, at higher current pulse amplitudes (>3 mA), the voltage dropping across the phase boundary (E_ma and E_mc) saturated. The value of the residual voltage depends on the degree of charge balance of the biphasic pulse. Thus, we have been able to detect more dissolved platinum at high residual voltages—objected by mass spectroscopic measurement.

Residual voltage plays a greater role concerning reversibility in prolonged stimulation and charge imbalance of applied biphasic current pulses. The E_ma saturation is suggested as a new marker for the occurrence of irreversible reactions which needs further investigation. Current amplitudes of 1 mA for the considered single electrode configuration did not lead to a capacitive voltage saturation nor a considerable dissolution of platinum ions and is thus considered as a safe operation configuration.