Hermetically sealed coatings for neural implants
Synthesis and Properties of Functional Materials
Final Report Abstract
There are diseases and conditions resulting in damage to the brain or optic nerve. Neural implants can enable communication with the environment e.g. for patients with locked-in syndrome due to a stroke or transfer signals to the brain producing luminous phenomena called phosphenes could be used to create "images" in the brain, restoring a very simple form of vision for blind people. Because the lifespan of neural implants is too short for permanent applications, efforts are made to extend the lifespan. The approach taken here and followed in this work to achieve this is to insert intermediate layers. In this process, oxide layers are introduced between the polyimide (PI) layers so that the conductive gold traces are completely encapsulated. The interlayers are deposited using the HIPIMS process. This process makes it possible to produce denser layers than is usually the case with PVD processes. Polyimide was used as the starting material. In addition to its use for neural implants, producing the samples as flexible foils has the advantage that it can be used to gather knowledge for future implants. Samples with different layers and layer combinations were realized and subjected to a long-term test with accelerated aging in saline solution at certain temperatures. The failure of the specimens was examined electrically and optically. The best results were realized with pretreatment by an oxygen plasma and with intermediate layers of aluminum oxide. The results show that the lifetime of neural implants can be significantly increased. For a technological implementation, further technology development and ultimately in vivo investigations are necessary. Investigating complex geometries and the characterizations of Parylene reveal that Parylene C layers deposited with current methods adsorb moisture. This results in a reduction in impedance, which nevertheless remains sufficiently high for suitably thick films. A critical issue with Parylene C is layer adhesion. The improvement of which remains a research topic. The improvement of the density of thin biocompatible Parylene C layers in the sub-micrometer range is also an interesting scientific issue. In this project, Ta2O5 ALD layers prove to be a promising candidate for the encapsulation of medical implants. The established correlation between deposition condition and the resulting layer stress and layer quality (e.g. pinhole density) is new and will allow a systematic optimization of encapsulation in the future. It is recommended to further investigate Ta2O5 ALD coatings for this purpose and to verify their applicability within possible long-term tests.
Publications
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Adhesion of HIPIMS-Deposited Gold to a Polyimide Substrate. Coatings, 13(2), 250.
Guljakow, Jürgen & Lang, Walter
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Failure Reason of PI Test Samples of Neural Implants. Sensors, 23(3), 1340.
Guljakow, Jürgen & Lang, Walter
