MEASUREMENT OF BIO-IMPEDANCE ON AN ISOLATED RAT SCIATIC NERVE OBTAINED WITH SPECIFIC CURRENT STIMULATING PULSES

In this study we designed and tested a four-probe, bio-impedance measurement set-up for peripheral nerves, based on the Red Pitaya open-source measurement and control tool. The set-up was tested on an isolated rat sciatic nerve (RSN) while it was stimulated with specific current stimulating pulses. The measurements tested the hypothesis that the specific waveform of a stimulating pulse elicits current differences at the double layer (DL) interface between the platinum (Pt) stimulating electrode and the nerve tissue. Impedance spectroscopy was used to electrically characterize the interface between the Pt electrode and the nerve tissue and measure the interface electrical impedance (Z). An analysis of the frequency response and the impedance, with specific current stimulating pulses, characterised the structure and the composition-related electrical properties of the RSN. An analysis of the voltage responses (VRs), measured at the same time, showed that the maximum negative polarization across the electrode-electrolyte interface (E-mc) and the maximum positive polarization across the electrode-electrolyte interface (E-ma) did not exceed the safety limits for water electrolysis. We conclude that the voltage and current changes, elicited at the DL of the interface between the Pt stimulating electrode and the nerve tissue, do not lead to tissue damage. Based on the obtained electrophysiological results we conclude that the developed stimulating electrodes and the stimulus pattern could act as a useful tool for developing nerve-stimulating electrodes.