Silica sol-gel coatings for neural microelectrodes

Andrew L Pierce, Purdue University

Abstract

While brain computer interfaces and neural prosthetics have enormous potential for use in treating a variety of neurological deficits, their functionality remains hampered by a lack of appropriate biomaterials. The implantation of microelectrodes into the brain initiates a complex immune response. This reactive tissue response results in glial encapsulation and neuronal density loss around the electrode, leading to an increase in impedance and drop in signal to noise ratio, effectively eliminating the ability to record from the electrode. A variety of methods have been investigated to circumvent or overcome this response, yet none have emerged as a widely accepted method. Presented here is an investigation into a novel silica sol-gel coating for microelectrodes as a platform material for mitigation of the reactive tissue response. The state-of-the-art in neural interfaces is presented and the reactive tissue response is discussed at length. Single-shank, 16 site microfabricated electrodes were dip coated in a tetramethoxysilane (TMOS) precursor sol which undergoes a series of condensation reactions to form a nanoporous silica thin film. Fluorescently labeled coatings were used to confirm coating adherence to the electrode. Cyclic voltammetry and impedance spectroscopy were used to evaluate electrical property changes. The sol-gel produced silica was found to successfully adhere to the electrodes as a thin coating. The voltammograms revealed a slight increase in charge carrying capacity of the electrodes following coating. Impedance spectrograms showed a mild increase in impedance at high frequencies but a more pronounced decrease in impedance at mid to low frequencies. These results demonstrate the feasibility of applying sol-gel silica coatings to silicon based microelectrodes and are encouraging for the continued investigation of their use in mitigating the reactive tissue response. The investigation was extended to examine the stability, drug elution rates, and in vivo functionality of the coatings. Further, a circuit model was developed to allow prediction and provide insight into the mechanisms leading to the electrochemical effects of the coating. The development and characterization of these improved biomaterials for neural electrodes will likely accelerate the transition of brain computer interface and neural prosthetic devices from the laboratory to clinical practice.

Degree

M.S.B.M.E.

Advisors

Otto, Purdue University.

Subject Area

Neurosciences|Biomedical engineering

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