A Wireless Neurostimulator System with an Embedded ARM™ Microprocessor

A portable neurostimulator circuit with anodic bias enhances stimulation injection capacity

Objective.Electrochemically safe and efficient charge injection for neural stimulation necessitates monitoring of polarization and enhanced charge injection capacity of the stimulating electrodes. In this work, we present improved microstimulation capability by developing a custom-designed multichannel portable neurostimulator with a fully programmable anodic bias circuitry and voltage transient monitoring feature.Approach.We developed a 16-channel multichannel neurostimulator system, compared charge injection capacities as a function of anodic bias potentials, and demonstrated convenient control of the system by a custom-designed user interface allowing bidirectional wireless data transmission of stimulation parameters and recorded voltage transients. Charge injections were conducted in phosphate-buffered saline with silicon-based iridium oxide microelectrodes.Main results.Under charge-balanced 200µs cathodic first pulsing, the charge injection capacities increased proportionally to the level of anodic bias applied, reaching a maximum of ten-fold increase in current intensity from 10µA (100µC cm-2) to 100µA (1000µC cm-2) with a 600 mV anodic bias. Our custom-designed and completely portable 16-channel neurostimulator enabled a significant increase in charge injection capacityin vitro. Significance.Limited charge injection capacity has been a bottleneck in neural stimulation applications, and our system may enable efficacious behavioral animal study involving chronic microstimulation while ensuring electrochemical safety.

A Diagnostic Circuit for Crosstalk Detection in Microelectrode Arrays

Current leakage between channels in microelectrode arrays is a sign of device failure and can lead to shorting of neural signals. The purpose of this project is to detect crosstalk between 32 channels of electrodes. We designed an embedded crosstalk detection system that can stimulate each electrode individually with a constant-current pulse and record voltage transients of the stimulated and adjacent electrodes to generate a matrix of crosstalk values. Charge injection in a phosphate buffered saline solution was used to check the condition of each electrode. A semi-wet condition was then used to determine the percent crosstalk between the channels. The analysis showed that there was minimal crosstalk between the electrodes, except for a known physical defect on the probe. The measurement technique enabled by the electronics circuit has the potential to be used in functional testing and screening of implantable devices.

Maximizing Charge Injection Limits of Iridium Oxide Electrodes with a Programmable Anodic Bias Circuit

Efficacious stimulation of neural tissues requires high charge injection capacity while minimizing electrode polarization. Applying anodic bias on certain electrode materials is a way to enhance charge injection both in vitro and in vivo. We developed an embedded neurostimulator system that enabled a digital control of user-defined bias levels, without requiring a potentiometer or external voltage source. Comparison of charge injection with and without anodic-bias, as well as at different bias potentials were conducted in phosphate-buffered saline with Blackrock iridium oxide microelectrodes. Results showed that a nine-fold increase in current intensity and charge injection capacity, was achieved with a 0.7 V anodic bias and within electrochemically safe limits.