Electrochemical Impedance Behavior under Various Test Configurations for Electrodes in Implantable Neurostimulators.

Implantable neurostimulators are key devices for treating neurological disorders such as Parkinson's disease and epilepsy by delivering electrical pulses to specific neural tissues. The electrochemical impedance at the electrode-tissue interface significantly influences therapeutic effects and impacts the quality of closed-loop brain signal acquisition. While the real-time and accurate impedance is difficult to measure in vivo, since reference electrodes cannot be implanted for a long time. This study aims to quantify the differences in electrochemical impedance spectroscopy of various electrode configurations by utilizing equivalent circuit models. In this work, 2-electrode, 3-electrode and bipolar systems of clinical deep brain stimulation electrodes were tested in vitro, and the in-body practicality were discussed. 2-electrode and 3-electrode model showed similar impedance spectroscopy results, supporting the possibility of using simpler configuration in vivo. However, the study reveals obvious impedance differences in bipolar mode, almost doubling those in monopolar stimulation. These findings provide essential methodological support for modeling tissue interfaces in implantable neural stimulators, ensuring safety and therapeutic effectiveness. It also has key clinical implications for the development of microelectrodes and the advancement of closed-loop therapies.Clinical Relevance- This provides a theoretical reference for the accurate evaluation of the long-term in vivo impedance of implantable electrodes.