Utilization of polymer insulator layers, which can be processed by microelectromechanical system (MEMS) technology, makes the realization of flexible microelectrode arrays possible. These systems are suitable devices for neurophysiological measurements because of their excellent biocompatibility.
It is possible to measure local field potential changes with high resolution using foil electrodes placed onto the surface of the cerebral cortex. With sensors implanted into the extracellular space of the brain, unit activities, i.e. action potentials of the neurons nearby the sensor can be detected. In the clinics, local field potential measurements can be employed for epilepsy diagnosis and epileptic focus localization. By surgically removing the foci, the illness can be cured. With the utilization of the sensors, the extent of the necessary lesion can be minimized.
I present the development of a polymer-based flexible microelectrode system, fabricated at the Institute for Technical Physics and Materials Science, RCNS, HAS. My goal was to create a combined sensor structure consisting of two main components: a needle-like microelectrode array for the measurement of extracellular signals and a sheet-like array attached perpendicularly to the axis of the needle for recording electrocorticographic (ECoG) signals from the brain surface.
In the first part of the thesis I’m reviewing the biological background of neural activities and their measurement methods. In the second part I’m presenting the properties of the applied materials, the design of the electrode system and the steps of the microtechnological process flow, including fabrication of polyimide and SU-8 layers and platinum lift-off technology. Finally, I’m demonstrating the validation of the assembled devices with in vitro electrochemical impedance spectroscopic (EIS) measurements in physiological saline and with in vivo functionality tests, performed in rat neocortex.