Bio-Inspired Fractal Electrodes Interfacing with Retinal Cells
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Date
2020-09-24
Authors
Moslehi, Saba
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Neurostimulation implantable devices are used extensively in treating a variety of neurodegenerative conditions such as Parkinson’s, Alzheimer’s and age-related macular degeneration. Current devices fail to provide high enough resolutions due to the lack of understanding of the neuron-implant interface connections and fundamental structural and mechanical differences between the electrodes’ material and geometry to those of the targeted tissue. These differences trigger the immune responses of the nervous system that engulf the implant and push away the targeted neurons from the electrodes’ surface, therefore causing a further drop in the resolution of the device. As long as this issue is unresolved, other approaches for increasing the resolution, such as providing smaller electrode sizes combined with materials with enhanced electrical stimulation/recording properties are not sufficient. In this thesis, an excellent electrode material candidate combined with geometric patterning approach is tested to guide the immune response against the implant into regions away from the surface of the electrodes as well as enhance neuronal adhesion and outgrowth on the electrodes’ surface. First, by introducing a simple Euclidean geometry of rows of vertically aligned carbon nanotube forests separated by rows of silicon, fundamental behavioral trends of retinal neurons and glial cells in encountering two materials with substantial mechanical and topographical differences in neighboring regions are studied. It is shown that the immune response of the glial cells and adhesion and outgrowth of neurons can be controlled and guided by changing the roughness and stiffness of the electrode material vs the substrate. Next, by adopting fractal electrode geometries while using the same materials, it is shown that the driven responses of neurons and glial cells can further be enhanced through fine tuning fractal characteristics of the electrode’s geometry. Furthermore, preliminary results from future work on comparison between fractal and several Euclidean geometries are discussed. By adopting the appropriate materials patterned in an optimal geometry, the immune response of the nervous system towards implants can be controlled and guided to reduce the distance between the implant’s electrodes surface and targeted tissue and hence increase the resolution.