title: Concept and Development of an Electronic Framework Intended for Electrode and Surrounding Environment Characterization In Vivo.
abstract: There has been substantial progress over the last decade towards miniaturizing implantable microelectrodes for use in Active Implantable Medical Devices (AIMD). Compared to the rapid development and complexity of electrode miniaturization, methods to monitor and assess functional integrity and electrical functionality of these electrodes, particularly during long term stimulation, have not progressed to the same extent. Evaluation methods that form the gold standard, such as stimulus pulse testing, cyclic voltammetry and electrochemical impedance spectroscopy, are either still bound to laboratory infrastructure (impractical for long term in vivo experiments) or deliver no comprehensive insight into the material's behaviour. As there is a lack of cost effective and practical predictive measures to understand long term electrode behaviour in vivo, material investigations need to be performed after explantation of the electrodes. We propose the analysis of the electrode and its environment in situ, to better understand and correlate the effects leading to electrode failure. The derived knowledge shall eventually lead to improved electrode designs, increased electrode functionality and safety in clinical applications. In this paper, the concept, design and prototyping of a sensor framework used to analyse the electrode's behaviour and to monitor diverse electrode failure mechanisms, even during stimulation pulses, is presented. We focused on the electronic circuitry and data acquisition techniques required for a conceptual multi-sensor system. Functionality of single modules and a prototype framework have been demonstrated, but further work is needed to convert the prototype system into an implantable device. In vitro studies will be conducted first to verify sensor performance and reliability.
authors.affiliation: Laboratory for Biomedical Microtechnology, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Köhler-Allee 102, 79110 Freiburg, Germany. stefan.rieger.imtek@gmail.com.|Cortec GmbH, Georges-Köhler Allee 010, 79110 Freiburg, Germany. stefan.rieger.imtek@gmail.com.
authors.forename: Stefan B
authors.initials: SB
authors.lastname: Rieger
authors.affiliation: Laboratory for Biomedical Microtechnology, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Köhler-Allee 102, 79110 Freiburg, Germany. jsordonez@gmail.com.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Pfau
authors.affiliation: Laboratory for Biomedical Microtechnology, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Köhler-Allee 102, 79110 Freiburg, Germany. thomas.stieglitz@imtek.uni-freiburg.de.|BrainLinks-BrainTools Center, University of Freiburg, Georges-Köhler-Allee 79, 79110 Freiburg, Germany. thomas.stieglitz@imtek.uni-freiburg.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Stieglitz
authors.affiliation: Laboratory for Biomedical Microtechnology, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Köhler-Allee 102, 79110 Freiburg, Germany. maria.asplund@imtek.uni-freiburg.de.|BrainLinks-BrainTools Center, University of Freiburg, Georges-Köhler-Allee 79, 79110 Freiburg, Germany. maria.asplund@imtek.uni-freiburg.de.
authors.forename: Maria
authors.initials: M
authors.lastname: Asplund
authors.affiliation: Laboratory for Biomedical Microtechnology, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Köhler-Allee 102, 79110 Freiburg, Germany. jennifer.pfau@imtek.uni-freiburg.de.|Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Albertstraße 19, 79104 Freiburg, Germany. jennifer.pfau@imtek.uni-freiburg.de.|Medtronic, Medtronic Eindhoven Design Center, Neuromodulation High Tech Campus 41, 5656 AE Eindhoven, The Netherlands. jennifer.pfau@imtek.uni-freiburg.de.
authors.forename: Juan S
authors.initials: JS
authors.lastname: Ordonez
keywords: failure mechanisms; impedance measurements; neural implant; pH measurements; stress measurements; temperature measurements; thin-film microelectrodes