Abstracts

Rationale: Intracranial EEG (iEEG) electrode arrays for prolonged recoding (under 30 days) are critical for brain mapping to identify normal and pathological brain for subsequent resection or direct brain electrical stimulation. Clinical iEEG recording array technology has not changed since the original FDA 510(k) awarded for the subdural electrodes in 1985. Currently subdural electrode arrays are manufactured by hand, and limited to simple, low spatial density electrode designs that do not optimally conform to brain convolutions. They can cause visible dents on the brain surface after multiple days of monitoring and are associated with clear histological changes. Subdural electrode grid design flexibility, brain conformability, and biocompatibility can be improved by development of thin, flexible, polyimide substrate electrodes. Methods: Multiple configurations of thin film electrode arrays were manufactured (60 µm polyimide film with exposed platinum contacts). All electrode arrays (8x8, 4x4, 1x2 configurations) had a single tail terminating in a zero insertion force connector. Electrical and mechanical testing of was performed in a bench-top phantom and an acute porcine model of epilepsy. Results: Electrode arrays (3 mm diameter, 10 mm pitch, 60 µm film thickness) were fabricated. The mean electrode impedance was 5 Ohm ± 10% at 1 kHz. The electrode arrays were tested after 2 weeks of continuous current stimulation (15 mA, 120 µs pulse width, at 50 Hz) without any electrical performance degradation. Preliminary tensile load and flexibility of the NeuroOne electrode was tested by wrapping the electrode around silicone rods and tracking electrical properties. Conclusions: Thin, flexible polyimide substrate electrodes with metallic contacts provide comparable electrophysiological data to standard clinical electrodes, but with improved mechanical properties. Previously, we have shown the improved flexibility and reduced volume of polyimide electrodes reduces the immunological response. The single electrode tail exiting the brain should reduce infection risk. Funding: NeuroOne Inc. supplied the electrodes for testing