Abstracts

Rationale: Stereoelectroencephalography (sEEG) is a minimally invasive intracranial monitoring procedure that uses depth electrodes stereotactically implanted into deep brain structures to map the origin and propagation of seizures in epileptic patients. Driven by a constant need to develop new sEEG electrodes with novel materials and features, here we describe a new thin film polyimide sEEG electrode and a battery of electrochemical and biocompatibility tests to evaluate electrode safety and performance.

Methods: sEEG electrodes were manufactured from thin-film polyimide with platinum contacts (5-16 contacts, 2 mm height, 1.5-3.2 mm spacing, 0.8 mm diameter). The electrodes feature an anchor bolt to ensure implant stability and a stylet to aid with placement. Electrochemical testing included impedance measurements, electrochemical impedance spectroscopy, cyclic voltammetry, voltage transient polarization, and a 29-day simulated implant followed by stimulation (≤150µC/cm²) and detection. Biocompatibility included cytotoxicity, hemolysis, sensitization, irritation, acute systemic toxicity, pyrogenicity, hemolysis, a 29-day electrode implant in sheep brain, and a 29-day anchor bolt implant in rabbit bone, performed per ISO-10993 guidelines.

Results: Electrochemistry showed that impedance was appropriate for high quality neural recordings (range, 248±36.9 Ohm at 1KHz, n=15). Following simulated implant, electrodes were electrically stable for delivering clinically relevant stimulation without leaching metals (n=32 contact pairs). Biocompatibility indicated that the electrodes were non-cytotoxic and non-hemolytic, produced no sensitization and irritation, no weight loss and no temperature increase in animal testing. Histological examination of the sheep brain tissue showed no or minimal immune cell accumulation, necrosis, neovascularization, fibrosis, and astrocyte infiltration, with no differences from the control material (n=10, 12 implants from 5, 4 test and control animals, respectively). Cellular response at the anchor bolt - bone tissue interface (n=10 implants from 5 animals) was absent or minimal, with rare presence of giant cells, macrophages, narrow fibrosis band and minimal capillaries. Necrosis and fatty infiltration were absent.

Conclusions: These results demonstrate safety and performance of a new thin-film polyimide sEEG electrode, which is now FDA cleared for < 30 days use.

Funding: NeuroOne Medical Technology Corporation