Abstracts

Rationale: Successful resection surgery to treat epilepsy depends on accurate seizure localization and cortical mapping. Micro-electrocorticography (µECoG) can more precisely identify seizure foci and detect additional markers of the seizure onset zone such as high-frequency oscillations and microseizures. µECoG arrays have primarily been developed for intra-operative clinical studies. Typical devices have wide, flat ribbons of micro-wiring connecting the array contacts with external data acquisition systems that cannot be safely tunneled and sutured through the dura, skull and scalp. This has posed a challenge to using high-resolution ECoG grids in epilepsy monitoring units (EMUs). To overcome these limitations, we have designed a thin-film ECoG array with round, coiled leads that can be tunneled out of the head and sutured using standard surgical procedures. The device is made of liquid crystal polymer (LCP), a biocompatible material with excellent encapsulation lifetime, and provides both macro and micro contact sizes and spacings to enable direct comparison of seizure localization by µECoG and clinical-standard ECoG. Methods: LCP electrodes were fabricated by Dyconex Micro Systems Technologies and have passed 10993-5 cytotoxicity testing. The hybrid LCP array is 4.2x4.5 cm with 16 macro-contacts (2.3 mm diameter, 1 cm spacing) and 304 micro-contacts (200 µm diameter, 2 mm spacing). The array is split into four strips that are molded together with a 400 µm PDMS silicone backing. Flat ribbons of LCP containing the thin-film wiring are coiled in polyurethane tubing to form round, flexible leads. The leads are connected to a single circuit board for amplification and digital conversion. Adhesion between LCP and PDMS was tested (n = 5) by accelerated soaking in saline (10 g/L) at 60 °C. Electrode surface features were measured by a Dektak150 profilometer. Intra-operative recordings using a similar LCP array with 256 micro-contacts were collected from epilepsy patients (n = 5) during surgical explant of clinical grids. Results: Our LCP array exhibits several potential safety improvements over standard clinical grids. Namely, the array is thinner (400 µm < 700 µm), the surface is smoother (33 µm < 195 µm avg. feature size), and the printing of gold contacts eliminates the risk of protruding metal disks. The design also allows the array to be cut for a smaller size or custom conformability to brain curvature. Ongoing accelerated soak testing has demonstrated no delamination between LCP and PDMS layers for a period equivalent to 10 months at body temperature. We successfully recorded normal cortical signals and interictal spikes from the LCP µECoG arrays during intra-operative testing. The micro-contact recordings revealed spatiotemporal variation in interictal spiking events across the array area, which was undetected by the clinical grid with macro-contacts. Conclusions: Our hybrid ECoG device will allow for simultaneous µECoG and clinical standard recordings. Moreover, our post-processing methods result in device features that may improve surgical safety over current clinical grids.  By enabling the use of µECoG in the EMU to record from the surface of the brain for up to 30 days, we hope to learn how high-resolution recordings may improve surgical outcomes for epilepsy patients. Funding: This work is supported by a CTSA grant (UL1TR002553), NIH U01 NS099697-01 and Finding a Cure for Epilepsy and Seizures (FACES). Florian Solzbacher has financial interest in Blackrock Microsystems. Conflict of interest is managed through University of Utah Conflict of Interest Management.