Date of Award

12-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Engineering

First Advisor

Kevin J. Otto

Committee Chair

Kevin J. Otto

Committee Member 1

Edward L/ Barlett

Committee Member 2

Michael G. Heinz

Committee Member 3

Kinam Park

Abstract

Intracortical microelectrodes are devices used in brain-computer interfaces (BCI) to help regain lost motor, sensory, and cognitive functions of individuals with neurological disorders. However, the long-term performance of microelectrode arrays is hampered by a series of inflammatory tissue responses. The consequence of the inflammatory response is the formation of a dense astroglial sheath around the vicinity of the electrode, impeding the electrical conduction between the electrode and neurons. Furthermore, due to the cascade of neuroinflammatory events, the number of neurons is significantly reduced near the electrode, manifested by decrease in signal-to-noise ratio (SNR) and the yield of electrodes. Over time, these issues eventually lead to the functional failure of the implant.

This study aims to investigate mechanical intervention strategies to mitigate the effect of the biological response and prolong the lifetime of the implanted microelectrodes. First, the longitudinal recording performance of a modified site geometry was evaluated. With planar silicon microelectrodes, sites placed on the edge outperformed the sites placed on the center, demonstrated by increased number of detectable single units with enhanced longevity. Second, the stress-strain induced biological response was studied using various flexible electrodes. Flexible electrodes indeed reduced the magnitude of the biological response than the traditional stiff silicon electrodes. Past a certain flexibility level, however, the biological response did not reduce over less soft electrodes, suggesting a flexibility threshold model. Finally, the biological response of electrodes dip-coated with polyethylene glycol (PEG) was evaluated to resolve a potential confound of PEG-coating used for inserting flexible electrodes. Results suggest that dip-coating with PEG do not significantly alter the inflammatory biomarker profiles around the device. Overall, findings from assessing the above mentioned intervention strategies will help devising a complex multimodal solution for prolonging the lifetime of neural implants.

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