Abstract
Advancements in microfabrication has enabled manufacturing of microscopic neurostimulation electrodes with smaller footprint than ever possible. The smaller electrodes can potentially reduce tissue damage and allow better spatial resolution for neural stimulation. Although electrodes of any shape can easily be fabricated, substantial effort have been focused on identification and characterization of new materials and surface morphology for efficient charge injection, while maintaining simple circular or rectangular Euclidean electrode geometries. In this work we provide a systematic electrochemical evaluation of charge injection capacities of serpentine and fractal-shaped platinum microelectrodes and compare their performance with traditional circular microelectrodes. Our findings indicate that the increase in electrode perimeter leads to an increase in maximum charge injection capacity. Furthermore, we found that the electrode geometry can have even more significant impact on electrode performance than having a larger perimeter for a given surface area. The fractal-shaped microelectrodes, despite having smaller perimeter than other designs, demonstrated superior charge injection capacity. Our results suggest that electrode design can significantly affect both Faradaic and non-Faradaic electrochemical processes, which may be optimized to enable a more energy efficient design for neurostimulation.
Highlights
The reduction in electrode size increases the overall electrical load of battery-powered stimulation systems
Electrochemical impedance spectroscopy (EIS) from circular microscale electrodes with different diameters showed that smaller microelectrode corresponded to a higher impedance, which can be attributed to an increase in the solution resistance and shorter charging time of capacitive double-layer on electrode[26]
We electrochemically examined the role of electrode geometry in terms of perimeter-to-surface area (PSA) ratio and shape using custom microfabricated electrode arrays
Summary
The reduction in electrode size increases the overall electrical load of battery-powered stimulation systems. De Haro et al, demonstrated that electroplated Pt has lower impedance and higher corrosion resistance than sputtered Pt, which can improve the lifetime of the microelectrode[20] Sputtered material such as IrOx and titanium nitride have been demonstrated to be superior than evaporated IrOx due to difference in nanoscale surface morphology[16,17]. Cogan et al confirmed that increasing the PSA ratio of the IrOx microelectrode lowered the electrode impedance and improved the charge injection limit perhaps due to reduction in access resistance and increasing ion flux to the electrode surface[28]. These reports suggest that increasing the PSA may be an effective way of improve electrode performance
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