Accelerated soak performance of BPDA-PPD polyimide for implantable MEAs

To mature toward real-world applications biomedical sensors should maintain long-term functionality under relatively harsh in-vivo conditions. Microelectrode arrays (MEAs) rely on thin films, such as parylene C or polyimide, the water-barrier of which is crucial for the long-term stability. This work reports on the high water-barrier of BPDA-PPD polyimide. This material was spin-coated on interdigitated microstructures and immersed in saline@60 °C for 170 days. The interdigitated impedance remained stable, higher than parylene C. Curing was crucial for the water-barrier of this polyimide: only long-cured microelectrode arrays remained unchanged in their inter-electrode impedances as compared to short-cured devices when soaked in saline@60 °C for 140 days. Subjecting BPDA-PPD polyimide foils to water-vapour penetration revealed higher performance than parylene C. These results disclose BPDA-PPD polyimide as a promising insulation for implantable MEAs.