MRI‐Compatible and Conformal Electrocorticography Grids for Translational Research

Abstract

Intraoperative electrocorticography (ECoG) captures neural information from the surface of the cerebral cortex during surgeries such as resections for intractable epilepsy and tumors. Current clinical ECoG grids come in evenly spaced, millimeter‐sized electrodes embedded in silicone rubber. Their mechanical rigidity and fixed electrode spatial resolution are common shortcomings reported by the surgical teams. Here, advances in soft neurotechnology are leveraged to manufacture conformable subdural, thin‐film ECoG grids, and evaluate their suitability for translational research. Soft grids with 0.2 to 10 mm electrode pitch and diameter are embedded in 150 µm silicone membranes. The soft grids are compatible with surgical handling and can be folded to safely interface hidden cerebral surface such as the Sylvian fold in human cadaveric models. It is found that the thin‐film conductor grids do not generate diagnostic‐impeding imaging artefacts (<1 mm) nor adverse local heating within a standard 3T clinical magnetic resonance imaging scanner. Next, the ability of the soft grids to record subdural neural activity in minipigs acutely and two weeks postimplantation is validated. Taken together, these results suggest a promising future alternative to current stiff electrodes and may enable the future adoption of soft ECoG grids in translational research and ultimately in clinical settings.

Biomedical Microtechnologies Beyond Scholarly Impact

“…Soft elastomers such as polydimethylsiloxane silicone (PDMS), popularly used as biocompatible molded external shell for implanted devices of different sorts [21,22], have now been shown to be compatible with full integration into wafer-scale microfabrication processes [23]. Examples of devices microfabricated on silicone elastomer include implantable neural interfaces for the central nervous system [24,25] and peripheral nerves [26], as well as wearable electronic sensors that conform the human skin [27]. Other important research directions stem from the inclusion of biodegradable electronic materials in transient implantable devices that are designed to be metabolized once they have served their purpose inside the body [28].…”

Materials for Implantable Surface Electrode Arrays: Current Status and Future Directions

“…Surface mounted connectors that are ribbon-like minimize the bulkiness of the overall array and offer a flexible interface to the tracks. [29,143,174] There are various commercially available ribbon connector pieces, and pieces can be custom designed with an appropriate pitch of electronics that are encapsulated by polyimide films or tapes. The latter allows for various geometrical arrangements of the connector pins, including a "comb-like" structure that can minimize short-circuits of the pads.…”

“…The electrodes found in most clinical grids are fabricated from bulk metal disks. These relatively thick, millimeter‐thickness and millimeter‐diameter disks are most often stainless steel or platinum–iridium, [ 143 ] and arranged in a rectangular grid. The metal is attached to the underlying track, which must also be composed of metal to allow soldering.…”

Applications for Flexible TFT Arrays Emerge in the Biomedical Domain

“…For in vivo electrophysiology implantable arrays, the goal is to spatially measure electrical activity from the cerebral cortex (i.e., electrocorticography; ECoG). [14][15][16] ECoG could be the basis for so-called electroceuticals-devices to treat diseases with electrical signals-and is a promising technique for brain-computer interfaces. However, two challenges must be resolved for this application: non-invasiveness and array stiffness (Fig.…”