ACCESSING GLIAL SCARRING WITH MICROSENSORS
Prof. Dr. Gerald Urban (Contact PI)
We develop an implantable, polymer-based platform with electrochemical and electrophysiological sensors to study the probe/tissue interface. Different mechanical flexibility of the probes provokes glial scar formation in deep brain structures of rats. Electrochemical sensors are ideal for the study of the probe/tissue interface as they can measure both tissue and electrode properties in high temporal and spatial resolution. The integrated sensors enable monitoring of glial scar structure, metabolites and biomarkers directly at the site of foreign body response. Suggested sensor parameters are impedance, tissue oxygen concentration and appearance of oxidative species. Impedance quantifies fundamental tissue and metal electrode properties, oxygen tissue mass transport and oxidative species the foreign body reaction. We aim to demonstrate the applicability of electrochemical microsensors as an in vivo online monitoring tool to enhance electrophysiology, imaging and histology techniques.
We developed a measurement protocol for oxidizable (reactive species) and reducible species (oxygen) based on Pt electrochemistry. The main challenge was the separation of Pt surface processes from analyte redox processes, which was successfully met by investigation of charge density in potential step experiments. The derived unique amperometric and active potentiometric sensor protocol was successfully characterized. A reproducible, stable behaviour was shown, notably also in the presence of proteins. The protocol was successfully recapitulated on different platforms in the rat brain in vivo: wire tetrodes, concentric stimulation electrodes and polyimide-based thin-film devices. Selectivity, stability and restoration of electrode sensitivity by the cyclic protocol were demonstrated in vivo, up to four weeks after implantation. Our findings provide a framework for different important aspects in neurotechnology: Using existing noble metal electrodes as long-term stable sensors to characterize their biochemical microenvironment; gaining fundamental information on the state of the electrode, towards in situ analysis of electrode degradation/corrosion; and characterization of electrical stimulation along with its charge transfer processes.
Project Related Publications
Weltin A, Ganatra D, König K, Joseph K, Hofmann UG, Urban GA, Kieninger J (2019) New life for old wires: electrochemical sensor method for neural implants, Journal of Neural Engineering, vol. 17, p 016007. https://doi.org/10.1088/1741-2552/ab4c69
Weltin A, Ganatra D, Durisin M, Urban GA, Kieninger J (2019) Electrochemical Protocols Upgrade Conventional Noble Metal Electrodes to Long-term Stable Sensors at the Tissue/Electrode Interface, 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC)
Weltin A, Joseph K , Kieninger J, Hofmann UG, Urban GA (2017) Investigation of Electrical Stimulation By Glutamate Sensing From Brain Slices With Microsensors. 21st International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS), pp 1563–1564.
Weltin A, Kieninger J, Enderle B, Gellner A-K, Fritsch B, Urban G (2014) Polymer-Based, Flexible Glutamate and Lactate Microsensors for in Vivo Applications. Biosensors and Bioelectronics, volume: 61, pp. 192–99.