Monitoring Insertion Force and Electrode Impedance during Implantation of Microwire Electrodes

The electrical impedance and the insertion force were monitored during the implantation of the microwire electrodes. The data reveals distinct phases in the force and impedance profiles corresponding to the different mediums the electrodes pass through. The impedance is shown to be linearly related to the pressure exerted by the electrode on the dura (p < 0.05, R² > 0.8). While both insertion force and the impedance could be used to determine when the electrode touches and breaks through the brain surface, the latter, especially the phase angle of the impedance, is shown to be more consistent and sensitive. It is proposed that the electrode impedance be used to provide more objective and accurate estimation of 1) when the electrode touches the brain; 2) the load distribution among the wires of the microwire array, and 3) the mechanical and immunological interactions between the electrode and the tissue in-vivo. The method can potentially improve the accuracy of electrode placement, and enable the development of better surgical procedures and apparatus. The principle could also be applied to other situations, such as endoscopic and minimum invasive surgeries