Renae Burke

Renae Burke

Optimizing Neuroprosthesis Longevity via Electrode Design: The Role of Electrode-Site Area


Burke R.G., Urdaneta M.E., Veit N.C., Otto K.J.


Dr. Kevin Otto


Herbert Wertheim College of Engineering


The potential of intracortical devices to treat neurological diseases such as paralysis via brain machine interfaces has propelled the design of novel implantable devices. Developing a bidirectional brain-machine interface to provide sensory feedback from prosthetic hands relies on the chronic performance of neuroprostheses in both recording and stimulation. A better understanding of the electrode-tissue interface and electrode design is critical to improve the chronic stability of such devices. Size plays an important role in the design of neuroprosthetic devices and it can improve the longitudinal functionality of these devices. However, the role of electrode-site area remains uncertain. A custom-made silicon planar array with four circular electrode sites of varying areas, 800, 2400, 7200, and 21600 µm2 was implanted in the somatosensory cortex of rats. Electrophysiological recordings, microstimulation thresholds and electrochemical features were repeatedly measured for several weeks. Electrochemical Impedance Spectroscopy (EIS) and Voltage Transient (VT) measurement techniques provide information about the frequency dependent components of the electrode as well as the electron transfer rate of reaction in the electrode-electrolyte interface. EIS results show a gradual increase of the impedance magnitude as electrode’s size decreases, which confirm the anticipated inverse relationship between electrode-site size and impedance magnitude. Overall, threshold detection from stimulation trend toward smaller site areas having slightly greater, and more variable, thresholds than larger site sizes. Electrophysiological recordings were analyzed to measure each electrode-site longitudinal signal-to-noise ratio (SNR) profile. Preliminary analysis suggests that spike activity is greater in both amplitude and SNR at deeper cortical layers. These insights show that both electrode-site area and depth are important to consider in the design and development of chronically stable neuroprosthetic devices that can efficiently record and stimulate in a brain-machine interface.


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