Recent advancement of electrocorticography (ECoG) electrodes for chronic neural recording/stimulation

Thin-Film Electrodes Based on Two-Dimensional Nanomaterials for Neural Interfaces

“…Thin-film electrodes made of highly conductive and biocompatible material which can be precisely micropatterned constitute a preferred approach to intracranial electroencephalography (iEEG) with implantable bioelectronics. ,, Both silicon and polymer-based electronics using a conductive metal layer of gold, platinum, titanium, or carbon as neural electrodes, either as an array or as filament, have been investigated as implantable approaches. They have demonstrated passive sensing as well as stimulation capabilities when applied either onto the surface or deeper in the heart and the brain of lab animals. − …”

“…Advanced electrodes for iEEG and neurostimulation can have a variety of shapes and approaches (Figure ), but for simplicity they are mainly classified into three types: flexible filament or wire deep probes, multielectrode microarray probes, and planar microelectrodes. , The planar microelectrodes are typically placed on the surface of the brain cortex to record electrocorticography (ECoG), which offers a superior spatial resolution to noninvasive EEG . A recent example of commercial application of ECoG is demonstrated by “Neuralink” where 96 fibrous electrodes of around 4–6 μm in width are made of three conductive layers of gold, iridium oxide, and the conductive polymer PEDOT/PSS (poly ethylenedioxythiophene doped with polystyrenesulfonate) to lower the impedance (37 ± 5 kΩ at 1 kHz) and enhance the charge-carrying capacity …”

“…Among the potential issues arising are a corrosive interaction of biofluid with the active metallic electronic components and electrical leakage current leading to damage to the surrounding biological tissues . The coating of thin-film membrane electrodes for iEEG with biocompatible polymers (such as polyimide, polyurethane, polydimethylsiloxane, and parylene C) have been shown to improve performance and long-term stability, thanks to minimal contact of the biofluid with the metal (platinum, gold, titanium) electrodes. − Note that in the context of biocompatibility, the availability of miniaturized electrodes using nanomaterials is expected to offer at least a partial relief thanks to their nanometric sizes …”

“…22,39 The planar microelectrodes are typically placed on the surface of the brain cortex to record electrocorticography (ECoG), which offers a superior spatial resolution to noninvasive EEG. 40 A recent example of commercial application of ECoG is demonstrated by "Neuralink" where 96 fibrous electrodes of around 4−6 μm in width are made of three conductive layers of gold, iridium oxide, and the conductive polymer PEDOT/PSS (poly ethylenedioxythiophene doped with polystyrenesulfonate) to lower the impedance (37 ± 5 kΩ at 1 kHz) and enhance the charge-carrying capacity. 38 A critical challenge for implanted interfaces is the ability to ensure a sufficient level of biocompatibility of the used materials and overall system and the ability to stymie adverse effects of long-term implantation on both the biological and the sensing systems.…”

Chronic subdural electrocorticography in nonhuman primates by an implantable wireless device for brain-machine interfaces

“…In contrast to clinical use, in which electrodes are generally implanted for no more than 30 days for epilepsy monitoring, for domestic BMI applications, it is crucial to ensure long-term safety and stable functionality to deliver high-quality neurophysiological data. An ideal device requires good biocompatibility, high selectivity, low invasiveness, and a long working period (11). Several studies have shown that ECoG recordings can record high-frequency activity with reliable performance over multiple years (12)(13)(14)(15).…”