Stability of flexible thin-film metallization stimulation electrodes: analysis of explants after first-in-human study and improvement of in vivo performance

Paul Čvančara (1) , Tim Boretius (2) , Víctor López-Álvarez (3) , Pawel Maciejasz (4, 5) , David Andreu (5) , Stanisa Raspopovic (6) , Francesco M. Petrini (7) , Silvestro Micera (8) , Giuseppe Granata (9) , Eduardo Fernandez (10) , Paolo Rossini (10) , Ken Yoshida (11) , Winnie Jensen (12) , Jean-Louis Divoux (13) , David Guiraud (5) , Xavier Navarro (3) , Thomas Stieglitz (2)

1 BCF - Bernstein Center Freiburg
2 IMTEK - Department of Microsystems Engineering [Freiburg]
3 UAB - Universitat Autònoma de Barcelona = Autonomous University of Barcelona = Universidad Autónoma de Barcelona
4 Otto Bock Healthcare GmbH
5 CAMIN - Contrôle Artificiel de Mouvements et de Neuroprothèses Intuitives
6 ETH Zürich - Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich]
7 Fondation Bertarelli Chair inTranslational Neuroscience and Neuroengineering [Lausanne]
8 SSSA - Scuela Santa Anna
9 Fondazione Policlinico Universitario Agostino Gemelli IRCCS
10 Unicatt - Università cattolica del Sacro Cuore [Piacenza e Cremona]
11 Perdue University
12 SMI - Center for Sensory-Motor Interaction
13 AXONIC - OBELIA dept

Objective. Micro-fabricated neural interfaces based on polyimide (PI) are achieving increasing importance in translational research. The ability to produce well-defined micro-structures with properties that include chemical inertness, mechanical flexibility and low water uptake are key advantages for these devices. Approach. This paper reports the development of the transverse intrafascicular multichannel electrode (TIME) used to deliver intraneural sensory feedback to an upper-limb amputee in combination with a sensorized hand prosthesis. A failure mode analysis on the explanted devices was performed after a first-inhuman study limited to 30 d. Main results. About 90% of the stimulation contact sites of the TIMEs maintained electrical functionality and stability during the full implant period. However, optical analysis post-explantation revealed that 62.5% of the stimulation contacts showed signs of delamination at the metallization-PI interface. Such damage likely occurred due to handling during explantation and subsequent analysis, since a significant change in impedance was not observed in vivo. Nevertheless, whereas device integrity is mandatory for long-term functionality in chronic implantation, measures to increase the bonding strength of the metallization-PI interface deserve further investigation. We report here that silicon carbide (SiC) is an effective adhesion-promoting layer resisting heavy electrical stimulation conditions within a rodent animal trial. Optical analysis of the new electrodes revealed that the metallization remained unaltered after delivering over 14 million pulses in vivo without signs of delamination at the metallization-PI interface. Significance. Failure mode analysis guided implant © 2020 IOP Publishing Ltd J. Neural Eng. 17 (2020) 046006 PČvančara et al stability optimization. Reliable adhesion of thin-film metallization to substrate has been proven using SiC, improving the potential transfer of micro-fabricated neural electrodes for chronic clinical applications. (Document number of Ethical Committee: P/905/CE/2012; Date of approval: 2012-10-04)

Mots clés: Neural interfaces; Polyimide; Thin-film; Electrode; Stability

Domaines: Automatique / Robotique; Physiologie [q-bio.TO]; Neurobiologie

Paul Čvančara, Tim Boretius, Víctor López-Álvarez, Pawel Maciejasz, David Andreu, et al.. Stability of flexible thin-film metallization stimulation electrodes: analysis of explants after first-in-human study and improvement of in vivo performance. Journal of Neural Engineering, 2020, 17 (4), pp.#046006. ⟨10.1088/1741-2552/ab9a9a⟩. ⟨hal-02907515⟩