Objective. Chronically-implanted neural microelectrodes are powerful tools for neuroscience research and emerging clinical applications, but their usefulness is limited by their tendency to fail after months in vivo. One failure mode is the degradation of insulation materials that protect the conductive traces from the saline environment. Approach. Studies have shown that material degradation is accelerated by mechanical stresses, which tend to concentrate on raised topographies such as conducting traces. Therefore, to avoid raised topographies, we developed a fabrication technique that recesses (buries) the traces in dry-etched, self-aligned trenches. Main results. The fabrication technique produced flatness within approximately 15 nm. Finite element modeling showed that the recessed geometry would be expected to reduce intrinsic stress concentrations in the insulation layers. Finally, in vitro electrochemical tests confirmed that recessed traces had robust recording and stimulation capabilities that were comparable to an established non-recessed device design. Significance. Our recessed trace fabrication technique requires no extra masks, is easy to integrate with existing processes, and is likely to improve the long-term performance of implantable neural devices.
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 sixteen-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 200 µs 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 10 µA (100 µC/cm2) to 100 µA (1000 µC/cm2) with a 600 mV anodic bias. Our custom-designed and completely portable sixteen-channel neurostimulator enabled a significant increase in charge injection capacity in 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.
In this study, a novel multi-layer printed circuit board (PCB)-based neurostimulator system with an embedded microprocessor is presented for applications in neuroprosthesis. The system integrates rechargeable batteries, a power management block, adjustable constant-current waveforms, voltage transient monitoring, and evoked neural response recording. The system can be configured to select channels among the 16 stimulation channels via Bluetooth communication wirelessly. Bench top measurements demonstrated that the system generated biphasic current waveforms with various stimulation parameters with approximately 407 mW of power consumption. Additional testing and validation with microelectrodes are underway.
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