Mikroelektroden für die chronische Ableitung und Stimulation neuronaler Aktivität im Kortex

Abstract

For neuroscience an experimental access to the individual neurons is essential to investigate e.g. the interaction of different brain areas. A basic challenge therefor is the long-term stable, electrical interface to the neurons for in-vivo experiments over several months or even years. Due to the inflammatory response of the neural tissue to the foreign body a scar is created around the neural probe with the microelectrodes, so that the electrical access for recording and stimulation of neural activity in the cortex is hindered or even impossible. The present dissertation contains the development of novel neural probes with the goal to reduce the inflammatory response and enable a chronic neural interface. The therefor developed, silicon-based microfabrication process enables a monolithical integration of the neural probes with highly flexible, electrical conducting paths to reduce the mechanical coupling during micromotion of the cortex relative to the skull and thus the irritation of the neural tissue. The developed microfabrication process allows the integration of in total 18 microelectrodes on a linear probe with a rectangular cross section of only 130 Amicrometre x 30 Amicrometre and a highly flexible ribbon cable with a cross section of only 130 Amicrometre x 10 Amicrometre. As flexible insulation materials for the conducting paths to the microelectrodes the biocompatible polymers parylene-C and polyimide were investigated, in which parylene-C revealed as an unsuitable material for this purpose. To guarantee a safe electrical stimulation of neurons, electrode materials with sufficient charge injection capacity have to be used. For this purpose the promising, electrical conductive polymer PEDOT is investigated in the present dissertation, which is deposited on the microelectrodes using an electropolymerization process. In-vitro long-term tests could verify that a degradation of this polymer coating does not occur after short current pulses. Improvements of the polymerization process could furthermore increase the mechanical stability and charge injection capacity of ca. 2 mC/cm2 of this electrode coating. For the implantation of the neural probes an insertion tool was additionally designed and fabricated, which is used to enable a complete and precise insertion of the probe into the cortex. In-vivo experiments could verify the functionality for chronic recording and microstimulation of neural activity using the novel neural probes. Therefore these neural implants have a high potential also for medical applications.