ISBN 9783843942225

978-3-8439-4222-5, Reihe Mikrosystemtechnik

Maria Vomero
Development and Assessment of Ultra-Compliant Polyimide-Based Neural Interfaces

152 Seiten, Dissertation Albert-Ludwigs-Universität Freiburg im Breisgau (2019), Softcover, B5

Zusammenfassung / Abstract

Flexible bioelectronic devices often represent the favorable choice as implants for neural applications. Although there are many advantages related to the design versatility and relatively soft nature of their polymeric substrates, many are still the limitations that come with thin-film devices. Long-term stability, miniaturization and integration of non-standard electrode materials are surely some of the most common concerns. Such aspects were addressed in this work and a thorough investigation of different types of polyimide-based neural implants, ranging from intracortical to micro electrocorticography (ECoG) arrays, was performed, in vitro and in vivo, to assess their robustness and reliability. Each device subjected to investigation is peculiar in some way and carries a novel aspect associated either to its mechanical properties or to the electrode material of choice. They are all designed to be highly biostable and to be integrated within the brain by creating a tight biotic/abiotic interface. Hair-size penetrating implants, built upon height rather than width, resulted in some cases completely invisible to the host tissue and could record brain activity chronically and without deteriorating. Ultra-compliant ECoG devices were able to adhere to the brain in a glove-like manner and pick up low and high-frequency signals for several weeks after implantation. The incorporation of pyrolyzed carbon (or glassy carbon) electrodes into polyimide was optimized and the miniaturization and surface activation of those electrodes was extensively studied. A fully flexible and metal-free version of the pyrolyzed carbon electrodes was implemented using a novel fabrication protocol. Finally, laser-induced carbon electrodes were tested to identify their surface composition and evaluate their potential as implantable components. For the completion of the work, standard microfabrication processes were combined and used in non-standard ways.