Evaluating Glial Cell Response to Functional Microelectrode Implants
Creators: Tsui, Christopher Tai Yau
Publisher: name: University of Alberta Library
Year: 2024

<p>Neural interfacing devices are designed to interact with the central nervous system to alleviate functional deficits in people with disabilities arising from neurological injuries or diseases. Such devices often involve the use of an invasive microelectrode implant which is designed to acutely target a site of interest in brain or spinal cord tissue for electrical recording and/or stimulation purposes. However, glial cells in the CNS will react to the presence of implanted electrodes and, over weeks to months, form a glial scar that is detrimental to the functionality of the interfacing device. While strides in biomaterials advances have been made in attenuating glial cell reactivity to the electrodes, comparatively little is known about glial cell responses to actual electrical stimulation especially at the electrode-cell interface. To address this gap in the established literature, a high-throughput in vitro system was designed and developed to assess glial cell responses to both electrode presence and applied electrical stimulation. Platinum-iridium microelectrodes (75 μm diameter) were fabricated and used in electrical stimulation experiments. Primary mixed glial cell cultures were generated from the brains of postnatal day 2 heterozygous C57BL/6J CX3CR-1+/EGFP mice and initially subjected to a biphasic, charge-balanced rectangular stimulation waveform at 0.15 mA and 1.5 mA for 4 h/day over 1, 3, and 7 days. Analysis of immunofluorescence images and scanning electron microscopy images captured the spatiotemporal responses of the glial cells in response to electrical stimulation as well as damage sustained by the electrodes, and validated the feasibility of comparing glial cell responses as a function of different stimulation conditions using the methods employed. Live imaging of EGFP-positive microglia confirmed cell death and formation of a peri-electrode void at close proximity (r &lt; 50 μm) to the electrode tip as a result of electrical stimulation. Follow-up experiments focused on modifying various electrical stimulation paradigm parameters by current, waveform shape, or stimulation frequency reported differential results in glial cell density, biomarker fluorescence intensity and area coverage around the electrode tip after single 4 h rounds of stimulation. Finally, electrochemical testing of the proposed in vitro setup revealed influences of different components of the mixed glial cell cultures towards the electrochemical performance of the microelectrodes in terms of cathodic charge storage capacity, impedance, phase angle, and voltage transient excursions. The work presented in this thesis is intended to function as another set of biological testing tools available to neural interfacing device developers. The described methods are also intended to validate the efficacy and safety of proposed iterations of functional microelectrode designs, and complement data generated in vivo or in a clinical setting that ultimately results in refined designs that are biocompatible, safe, and longer-lasting in patients.</p>