Towards Long-Term Stable Polyimide-Based Flexible Electrical Insulation for Chronically Implanted Neural Electrodes

For chronic applications of flexible neural implants, e.g., intracortical probes, the flexible substrate material has to encapsulate the electrical conductors with a long-term stability against the saline environment of the neural tissue. The biocompatible polymer polyimide is often used for this pu...

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Autores principales:	Andreas Schander, Julia M. Gancz, Marcel Tintelott, Walter Lang
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	polyimide neural interfaces flexible implants long-term stability interdigital electrode array electrical insulation stability Mechanical engineering and machinery TJ1-1570
Acceso en línea:	https://doaj.org/article/e36ceaf2b2ad4b6a863dcd528ed0f8a2
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id	oai:doaj.org-article:e36ceaf2b2ad4b6a863dcd528ed0f8a2
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spelling	oai:doaj.org-article:e36ceaf2b2ad4b6a863dcd528ed0f8a22021-11-25T18:22:44ZTowards Long-Term Stable Polyimide-Based Flexible Electrical Insulation for Chronically Implanted Neural Electrodes10.3390/mi121112792072-666Xhttps://doaj.org/article/e36ceaf2b2ad4b6a863dcd528ed0f8a22021-10-01T00:00:00Zhttps://www.mdpi.com/2072-666X/12/11/1279https://doaj.org/toc/2072-666XFor chronic applications of flexible neural implants, e.g., intracortical probes, the flexible substrate material has to encapsulate the electrical conductors with a long-term stability against the saline environment of the neural tissue. The biocompatible polymer polyimide is often used for this purpose. Due to its chemical inertness, the adhesion between two polyimide layers is, however, a challenge, which can lead to delamination and, finally, to short circuits. The state-of-the-art method to improve the adhesion strength is activating the polyimide surface using oxygen reactive ion etching (O<sub>2</sub> RIE). However, the influence of the process variations (etching time, bias power) on the long-term stability is still unclear. Therefore, we establish a test method, where the aging of a gold interdigital structure embedded in two polyimide layers and immersed in saline solution is accelerated using an elevated temperature, mechanical stress and an electrical field. A continuous measurement of a leakage current is used to define the failure state. The results show that the variation of the O<sub>2</sub> RIE plasma process has a significant effect on the long-term stability of the test samples. Comparing the two different plasma treatments 0.5 min at 25 W and 1 min at 50 W, the long-term stability could be increased from 20.9 ± 19.1 days to 44.9 ± 18.9 days. This corresponds to more than a doubled lifetime. An ideal solution for the delamination problem is still not available; however, the study shows that the fine-tuning of the fabrication processes can improve the long-term stability of chronically implanted neural electrodes.Andreas SchanderJulia M. GanczMarcel TintelottWalter LangMDPI AGarticlepolyimideneural interfacesflexible implantslong-term stabilityinterdigital electrode arrayelectrical insulation stabilityMechanical engineering and machineryTJ1-1570ENMicromachines, Vol 12, Iss 1279, p 1279 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	polyimide neural interfaces flexible implants long-term stability interdigital electrode array electrical insulation stability Mechanical engineering and machinery TJ1-1570
spellingShingle	polyimide neural interfaces flexible implants long-term stability interdigital electrode array electrical insulation stability Mechanical engineering and machinery TJ1-1570 Andreas Schander Julia M. Gancz Marcel Tintelott Walter Lang Towards Long-Term Stable Polyimide-Based Flexible Electrical Insulation for Chronically Implanted Neural Electrodes
description	For chronic applications of flexible neural implants, e.g., intracortical probes, the flexible substrate material has to encapsulate the electrical conductors with a long-term stability against the saline environment of the neural tissue. The biocompatible polymer polyimide is often used for this purpose. Due to its chemical inertness, the adhesion between two polyimide layers is, however, a challenge, which can lead to delamination and, finally, to short circuits. The state-of-the-art method to improve the adhesion strength is activating the polyimide surface using oxygen reactive ion etching (O<sub>2</sub> RIE). However, the influence of the process variations (etching time, bias power) on the long-term stability is still unclear. Therefore, we establish a test method, where the aging of a gold interdigital structure embedded in two polyimide layers and immersed in saline solution is accelerated using an elevated temperature, mechanical stress and an electrical field. A continuous measurement of a leakage current is used to define the failure state. The results show that the variation of the O<sub>2</sub> RIE plasma process has a significant effect on the long-term stability of the test samples. Comparing the two different plasma treatments 0.5 min at 25 W and 1 min at 50 W, the long-term stability could be increased from 20.9 ± 19.1 days to 44.9 ± 18.9 days. This corresponds to more than a doubled lifetime. An ideal solution for the delamination problem is still not available; however, the study shows that the fine-tuning of the fabrication processes can improve the long-term stability of chronically implanted neural electrodes.
format	article
author	Andreas Schander Julia M. Gancz Marcel Tintelott Walter Lang
author_facet	Andreas Schander Julia M. Gancz Marcel Tintelott Walter Lang
author_sort	Andreas Schander
title	Towards Long-Term Stable Polyimide-Based Flexible Electrical Insulation for Chronically Implanted Neural Electrodes
title_short	Towards Long-Term Stable Polyimide-Based Flexible Electrical Insulation for Chronically Implanted Neural Electrodes
title_full	Towards Long-Term Stable Polyimide-Based Flexible Electrical Insulation for Chronically Implanted Neural Electrodes
title_fullStr	Towards Long-Term Stable Polyimide-Based Flexible Electrical Insulation for Chronically Implanted Neural Electrodes
title_full_unstemmed	Towards Long-Term Stable Polyimide-Based Flexible Electrical Insulation for Chronically Implanted Neural Electrodes
title_sort	towards long-term stable polyimide-based flexible electrical insulation for chronically implanted neural electrodes
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/e36ceaf2b2ad4b6a863dcd528ed0f8a2
work_keys_str_mv	AT andreasschander towardslongtermstablepolyimidebasedflexibleelectricalinsulationforchronicallyimplantedneuralelectrodes AT juliamgancz towardslongtermstablepolyimidebasedflexibleelectricalinsulationforchronicallyimplantedneuralelectrodes AT marceltintelott towardslongtermstablepolyimidebasedflexibleelectricalinsulationforchronicallyimplantedneuralelectrodes AT walterlang towardslongtermstablepolyimidebasedflexibleelectricalinsulationforchronicallyimplantedneuralelectrodes
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Towards Long-Term Stable Polyimide-Based Flexible Electrical Insulation for Chronically Implanted Neural Electrodes

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