Thin-film microfabrication and intraoperative testing of µECoG and iEEG depth arrays for sense and stimulation

Abstract

Objective. Intracranial neural recordings and electrical stimulation are tools used in an increasing range of applications, including intraoperative clinical mapping and monitoring, therapeutic neuromodulation, and brain computer interface control and feedback. However, many of these applications suffer from a lack of spatial specificity and localization, both in terms of sensed neural signal and applied stimulation. This stems from limited manufacturing processes of commercial-off-the-shelf (COTS) arrays unable to accommodate increased channel density, higher channel count, and smaller contact size. Approach. Here, we describe a manufacturing and assembly approach using thin-film microfabrication for 32-channel high density subdural micro-electrocorticography (µECoG) surface arrays (contacts 1.2 mm diameter, 2 mm pitch) and intracranial electroencephalography (iEEG) depth arrays (contacts 0.5 mm × 1.5 mm, pitch 0.8 mm × 2.5 mm). Crucially, we tackle the translational hurdle and test these arrays during intraoperative studies conducted in four humans under regulatory approval. Main results. We demonstrate that the higher-density contacts provide additional unique information across the recording span compared to the density of COTS arrays which typically have electrode pitch of 8 mm or greater; 4 mm in case of specially ordered arrays. Our intracranial stimulation study results reveal that refined spatial targeting of stimulation elicits evoked potentials with differing spatial spread. Significance. Thin-film, μECoG and iEEG depth arrays offer a promising substrate for advancing a number of clinical and research applications reliant on high-resolution neural sensing and intracranial stimulation.

Flexible Electrodes for Brain–Computer Interface System

“…Regardless of the type of electrodes, the basic thought is to improve the quality of recorded EEG signals while improving the level of comfort and minimizing the trauma to patients. As a result, the electrodes may potentially serve as core PI/Pt/Ir [ 120] Thin-film microfabrication / Biocompatible / Hydrogel/PEI/PC/COC/Sn [70] Thermal drawing Parylene/AgNWs/IZO/Ti/Au [ 119] Deposition/Pattering/Etching PEN/Au [121] Inkjet-printing [ 122] Laser patterning/Encapsulation 3015(± 333) S•m −1 / / SEBS/GFG/Cu [128] Electrospinning When it comes to the additional requirements for flexible electrodes, the major properties are pursued by all BCI electrodes, such as mechanical property, adhesion, and biocompatibility. Furthermore, the biodegradability may play a more important role in intracranial electrodes for placement and drug delivery.…”

“…Sellers microfabricated thin‐film surface and depth electrode arrays, which provides increased spatial specificity and precision for both sensing and stimulation. [ 120 ] By bending the flexible array around thermoplastic tubing and bonding it in place, the electrode could get enough rigidity for insertion into the brain. The thin‐film microfabrication allows for highly customized designs to meet the needs of personalization.…”

“…[119] Sellers et al use co-deposited platinumiridium to lower impedance without additional surface processing, the platinum-iridium electrode have a thickness of 0.25 μm and a double-layer capacitance (Q) of 3.1 mF cm −2 to maintain sufficient SNR. [120] Gold has demonstrated its superior stability and inertness in biological fluids and the gold electrode array with an ultrathin substrate achieves high flexibility in implantable applications. [121] Driscoll et al developed flexible high-density bioelectronic interfaces using Ti 3 C 2 MXene by the highly scalable method they developed, which enabled them to fabricate multichannel electrode arrays of an arbitrary size and geometry.…”

“…[ 119 ] Sellers et al use co‐deposited platinum‐iridium to lower impedance without additional surface processing, the platinum‐iridium electrode have a thickness of 0.25 µm and a double‐layer capacitance ( Q ) of 3.1 mF cm −2 to maintain sufficient SNR. [ 120 ] Gold has demonstrated its superior stability and inertness in biological fluids and the gold electrode array with an ultrathin substrate achieves high flexibility in implantable applications. [ 121 ] Driscoll et al.…”

Flexible, Scalable, High Channel Count Stereo-Electrode for Recording in the Human Brain

“…To increase the spatial resolution and channel count of electrodes that can record from either the lateral grey matter or deep brain structures, recent engineering approaches have focused on rolling or adhering conformable and photolithographically defined polyimide electrodes around or on medical-grade tubing used in clinical depth electrodes (25)(26)(27)(28). These hybrid integration approaches impose a limitation on the size of the electrode such that the starting diameter is predetermined by the clinical depth electrode diameter.…”