Application of implantable wireless biomicrosystem for monitoring electrode-nerve impedance of animal after sciatic nerve injury

In neural prosthetic applications, it is imperative to monitor the impedance of implantable cuff electrode for the effective sensing and stimulating schemes. With the development of an implantable biomicrosystem, this study was conducted to monitor the time-course changes of electrode-nerve impedance as well as to elicit constant stimulation current for aiding nerve repair in an experimental sciatic nerve injury animal model. For continuous in vivo impedance monitoring, a transcutaneous magnetic coupling technique was adopted for transmitting power and command into the internal module and sending outwards the impedance measurement. The two-terminal and four-terminal methods were adopted for measuring the electrode-tissue interfacing impedance and tissue impedance. To avoid high sampling rate required, a gain-phase detector was utilized for direct output of the magnitude and phase shift of the impedance measurement. Validation tests of impedance measurement and microstimulation function were first performed in an in-vitro impedance model. The differences of measured impedance were less than 10 % in comparison with those measured by precision LCR meter. A self-sizing spiral cuff electrode was fabricated and wrapped around the injured sciatic nerve of New Zealand rabbit for monitoring the changes of electrode-nerve impedance when the animal was awake but partly constrained in a restrainer. In addition, commands for varied level of constant current can be delivered via the magnetic coupling in an attempt to assist the nerve repair.