Electrochemical performance of platinum electrodes within the multi-electrode spiral nerve cuff

In this study, the electrochemical performance of platinum electrodes within a multi-electrode spiral cuff to be used for selective nerve stimulation was investigated. The original cuff, simplified into a half-cuff, contained a single row of nine electrodes (0.5 × 2 mm) at a distance of 2 mm from its inner surface. Cyclic voltammetry was used to investigate the electrochemical reactions at the electrode-electrolyte interface, to define a potential window within which the electrode could be safely used in selective nerve stimulation, to calculate the charge injection capacity and cathodal charge storage capacity. Voltage transients retrieved during excitation with quasitrapezoidal biphasic current pulses, tested by selective nerve stimulation of the isolated porcine left cervical vagus nerve segment, were used to determine the maximum polarization across the electrode-electrolyte interface and to calculate cathodic charge injection capacity of the electrode. The results show that the most negative and most positive potentials across the electrode-electrolyte interface reached -0.54 and 0.59 V; these did not exceed the safe potential limits for water electrolysis. Furthermore, the time integral of the cathodic current by cyclic voltammetry measured over the potential range of water electrolysis, actually representing the cathodal charge storage capacity, was approximately -4 mC cm(-2). The charge injection capacity, representing the maximum charge density injected in a current stimulation pulse, using only reversible processes, however, was around 75 µC cm(-2). In conclusion, both, the tested stimulation pulse and electrode are suitable for efficient and safe selective nerve stimulation.