Constant-Current Adjustable-Waveform Microstimulator for an Implantable Hybrid Neural Prosthesis

Abstract

Microstimulation of neural tissue has become a widely-used technique for controlling neuronal responses with local electric fields as well as a therapeutic intervention for nervous system disorders such as epilepsy and Parkinson's disease. Of those afflicted by neurological diseases, many are or become tolerant to existing pharmaceuticals and are left with little recourse. Little is known about the necessary design criteria or efficacy of a hybrid neural prosthesis. Assessment of the potential clinical value of a hybrid electro-chemical neural prosthesis was performed through in vitro verification using a prototype microstimulator and P19 cell cultures. We constructed a printed circuit board (PCB) microstimulator as a prototype of a CMOS microstimulator ASIC that was subsequently fabricated in the IBM 7RF 0.18 microm process. Measured results for the prototype are described in this work. An output impedance of 237 kOmega, voltage compliance of 11.3 V, and a linear constant-current output up to +/-600 microA make this microstimulator system a viable option for an implantable hybrid neural prosthesis. Hybrid prostheses could uniquely affect neural modulation with linear glutamate release at physiological amplitudes and frequencies.

High-Side Digitally Current Controlled Biphasic Bipolar Microstimulator

“…In comparison, other research into microstimulators such as the clinically-targeted Bion [22] are much smaller and lower power, but correspondingly much more expensive, less flexible due to their high level of integration, and not matched for the high compliance voltage required by our electrodes. Integrated ASIC microstimulators such as [23] and [24] offer compliance of 11V or less, which is insufficient to drive current through high-impedance (more than 100kΩ) electrodes; full systems described in [25] offer insufficient latency and bandwidth for our experimental requirements. Finally, the current-mirror topology of integrated microstimulators does not guarantee low leakage current, which is critical as DC current will gradually erode the tips of electrodes and damage neural tissue.…”