An experimental study on passive charge balancing

K Sooksood,M Ortmanns,T Stieglitz

doi:10.5194/ars-7-197-2009

K Sooksood, M Ortmanns + Show 1 more

Open Access

https://doi.org/10.5194/ars-7-197-2009

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Abstract

Abstract. This paper presents a simplified analysis of the electrode potential upon mismatched, biphasic stimulation using passive discharge techniques, e.g. by shortening of the electrodes. It turns out that especially for microelectrodes the required shorting intervals become as large as to limit a feasible stimulation interval. If no blocking capacitors can be used due to limited space and the degree of miniaturisation, the passive discharge even imposes severe risks to the surrounding tissue and the electrode.

Highlights

Biomedical implants for functional electrical stimulation (FES), such as the cochlea implant, cardiac pacemaker, and retinal implant have received an increasing interest (Stieglitz and Meyer, 2006; Ortmanns et al, 2007)
In order to avoid these irreversible electrochemical reactions, the stimulating current pulse is typically balanced and biphasic, which ensures that no net charge appears at the electrode after each stimulation cycle and the electrochemical processes are balanced to prevent net dc-currents
Especially when integrated circuitry is used for the stimulator, due to imperfections of the fabrication process more than 1%–5% of mismatch of the current pulses has to be taken into account

Summary

Introduction

Biomedical implants for functional electrical stimulation (FES), such as the cochlea implant, cardiac pacemaker, and retinal implant have received an increasing interest (Stieglitz and Meyer, 2006; Ortmanns et al, 2007). Whenever current is conducted over an electrode into a conducting solution, chemical processes take place at the interface. In order to avoid these irreversible electrochemical reactions, the stimulating current pulse is typically balanced and biphasic, which ensures that no net charge appears at the electrode after each stimulation cycle and the electrochemical processes are balanced to prevent net dc-currents. Especially when integrated circuitry is used for the stimulator, due to imperfections of the fabrication process more than 1%–5% of mismatch of the current pulses has to be taken into account. The only passive, charge balancing measure is to short the electrodes after the mismatched, biphasic stimulation in order to cancel accumulated charge. We model the electrode-electrolyte interface, calculate the net dc-voltage due to imbalance and validate the measurement results by experiments with platinum black electrodes in a 0.9% saline solution

Electrode-electrolyte interface model

Electrode potential calculation

Experiments and discussion

Conclusions