333 First FDA Cleared Thin Film Electrode for Intracranial Recording and Monitoring of Brain Activity – Device Testing and Initial Clinical Use

Abstract

INTRODUCTION: Subdural strip and grid (SDG) electrodes are routinely used for pre-surgical evaluation of patients with drug resistant epilepsy (DRE). Although these electrodes have been in the US market since their first FDA clearance in 1985, their fabrication, materials and properties have hardly changed. They are made of silicone, are thick (>0.5 mm), manufactured by hand, and do not optimally conform to brain convolutions. Technological solutions that overcome these limitations are needed. METHODS: Thin film electrode (0.08 mm) arrays were manufactured from polyimide with platinum contacts (multiple configurations, 3 mm contact diameter, spaced 10 mm apart). Electrochemical and electrical testing include electrolyte interface impedance, cyclic voltammetry and other impedance and isolation tests, according to the International Electrotechnical Commission 60601 for proving device safety and performance. Biocompatibility was tested using standard methods according to International Organization for Standardization 10993. Post-market data were collected employing a user feedback questionnaire using a rating scale (1 to 5, with 5 being the highest). RESULTS: Thin film electrodes passed all electrochemical, electrical and biocompatibility testing required for FDA clearance (obtained Nov 2019). Electrodes (n = 19) were used in clinical practice between Nov 23, 2020 and May 3, 2021 in the epilepsy monitoring units and for intraoperative monitoring (IOM) for recording brain activity in (a) DRE patients undergoing evaluation for potential surgical resection, and (b) patients undergoing tumor resection. Users (neurosurgeons; n = 6) provided ratings between 4 and 5 regarding the properties (thickness, flexibility, weight), features (ease of placement, conformability to the brain areas) and performance (qualitative signal recording quality) of the electrodes during surgical implantation. CONCLUSION: This is the first thin film electrode technology FDA cleared for use in clinical practice. The properties of these thin, flexible polyimide electrode arrays may overcome many limitations of the existing technology. Initial clinical use indicated that the technology is feasible for surgical implantation with greater flexibility compared to silicone based cortical electrodes.