Towards long-term stable polyimide-based flexible electrical insulation for chronically implanted neural electrodes
Open accessAbstract
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 (O2 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 O2 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.
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Leaked substances can disrupt the ionic balance of sodium, potassium, and calcium, leading to excitotoxicity.
“These leaked substances can also disrupt the ionic balance of essential elements like sodium, potassium, and calcium, leading to excitotoxicity—a pathological process causing neuron damage due to excessive neurotransmitter stimulation.”
From Comparative analysis of energy transfer mechanisms for neural implants (2024) · cites this paper as Schander et al., 2021
The Introduction (page unavailable) says that leachables from inadequately processed SU-8 can cause cytotoxicity. It does not say that leaked substances disrupt sodium, potassium, or calcium balance, or that they cause excitotoxicity; the Methods’ discussion of electrolyte concerns an insulation test, not that mechanism. (LLM, conf=0.78)
Experimental — accuracy not yet measuredNeural tissue might undergo fibrosis in response to chemical exposure.
“Lastly, in response to chemical exposure, neural tissue might undergo fibrosis, a defensive yet functionally compromising mechanism (Grisold and Carozzi, 2021; Schander et al., 2021; Yin et al., 2021; World Health Organization: WHO, 2023).”
From Comparative analysis of energy transfer mechanisms for neural implants (2024) · cites this paper as Schander et al., 2021
The Introduction discusses foreign-body responses to neural implants and possible toxic reactions from leachable materials, but it does not say that chemical exposure causes fibrosis in neural tissue. A search of our full copy for fibrosis and chemical exposure found no passage addressing that specific response. (LLM, conf=0.74)
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- Authors
- Schander, A., Gancz, J., Tintelott, M., & Lang, W.
- Affiliations
- University of Bremen (DE)
- Corresponding author
- Schander, Andreas
- Venue
- Micromachines
- Publisher
- MDPI AG
- Published
- 2021-10-20
- Volume
- 12
- Issue
- 11
- Pages
- 1279
- ISSN
- 2072-666X (ISSN-L)
- PMC
- PMC8619170
- OpenAlex
- W3210164395
- Cited by
- 28
- References
- 19
- Citations by year
- 2026: 8 · 2025: 2 · 2024: 8 · 2023: 3 · 2022: 7
- FWCI
- 2.07
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- Locations
- Micromachines (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- RWTH Publications (RWTH Aachen) (submittedVersion, other-oa)
- Funders
- Deutsche Forschungsgemeinschaft (LA 1471/11-2)
- Topics
- Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neuroscience and Neural Engineering
- Physical Sciences › Materials Science › Polymers and Plastics › Conducting polymers and applications
- Physical Sciences › Materials Science › Polymers and Plastics › Synthesis and properties of polymers
- Keywords
- polyimide, electrical insulation, delamination, interlayer bonding, oxygen reactive ion etching, plasma surface treatment, leakage current, accelerated aging test, implant survival
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