Long-Term Stable Neural Interfaces with Nanoporous Graphene Electrodes and Hybrid Polyimide-Aluminium Oxide...

Graphene-based thin film technology holds great promise for next-generation neural interfaces due to graphene´s electrical, electrochemical, and mechanical properties. However, the long-term reliability of this technology remains a challenge, primarily due to the instability of thin-film encapsulation in physiological environments. While standard ceramic encapsulation is robust, it is not compatible with the miniaturization required for minimally invasive implants. This study demonstrates the successful integration of a hybrid encapsulation strategy, combining polyimide with atomic layer deposited (ALD) Al₂O₃, with nanoporous reduced graphene oxide (rGO) microelectrodes, resulting in chronically stable graphene-based neural interfaces. The encapsulation robustness is validated using flexible interdigitated electrodes (IDEs) subjected to accelerated aging and continuous electrical stress. IDEs demonstrated stable performance after soaking for over 1.5 years in phosphate buffer saline (PBS) at 57 °C. Nanoporous graphene microelectrodes combined with the proposed encapsulation retained their structural integrity and electrochemical performance after soaking for 377 days in PBS at 57 °C, withstanding 1 billion biphasic pulses at very high charge density (1 mC cm^{- 2}) and hundreds of bending cycles without noticeable performance deterioration. This work establishes a long-term stable graphene-based neural interface combining nanoporous rGO electrodes and a hybrid polyimide/Al₂O₃ encapsulation, demonstrating a key technology advancement for the use of graphene neural interfaces in chronic brain monitoring and neuromodulation applications.