PEDOT-CNT-Coated Low-Impedance, Ultra-Flexible, and Brain-Conformable Micro-ECoG Arrays

Abstract

Electrocorticography (ECoG) is becoming a common tool for clinical applications, such as preparing patients for epilepsy surgery or localizing tumor boundaries, as it successfully balances invasiveness and information quality. Clinical ECoG arrays use millimeter-scale electrodes and centimeter-scale pitch and cannot precisely map neural activity. Higher-resolution electrodes are of interest for both current clinical applications, providing access to more precise neural activity localization and novel applications, such as neural prosthetics, where current information density and spatial resolution is insufficient to suitably decode signals for a chronic brain-machine interface. Developing such electrodes is not trivial because their small contact area increases the electrode impedance, which seriously affects the signal-to-noise ratio, and adhering such an electrode to the brain surface becomes critical. The most straightforward approach requires increasing the array conformability with flexible substrates while improving the electrode performance using materials with superior electrochemical properties. In this paper, we propose an ultra-flexible and conformable polyimide-based micro-ECoG array of submillimeter recording sites electrochemically coated with high surface area conductive polymer-carbon nanotube composites to improve their brain-electrical coupling capabilities. We characterized our devices both electrochemically and by recording from rat somatosensory cortex in vivo. The performance of the coated and uncoated electrodes was directly compared by simultaneously recording the same neuronal activity during multiwhisker deflection stimulation. Finally, we assessed the effect of electrode size on the extraction of somatosensory evoked potentials and found that in contrast to the normal high-impedance microelectrodes, the recording capabilities of our low-impedance microelectrodes improved upon reducing their size from 0.2 to 0.1 mm.

Silicon-Integrated High-Density Electrocortical Interfaces

“…(g) A transparent ECoG electrode array with platinum electrodes on a Parylene C substrate [27]. (h) An electrode array with poly (3, 4-ethylenedioxythiophene) (PDOT) and PEDOT-carbon nanotube (CNT) composite coatings for lower electrode interface impedance [28]. (i) A flexible electrode array on a bioresorbable substrates of silk fibroin [29].…”

“…Such limitations have been addressed by micropatterning increased surface area, and carbon nanotube [34] or conductive polymer coatings [ Fig. 4(h)] [28]. Flexible substrates have also reduced the effective distance between source and electrodes through tight, conformal geometries [24], [26].…”

Monitoring the evolution of boron doped porous diamond electrode on flexible retinal implant by OCT and in vivo impedance spectroscopy

“…nanotubes [22]. The electrochemical impedance modulus of the electrode in the observed spectral range (100 Hz-50 kHz) does not compete with the best materials reported in the literature such as carbon nanotubes (CNTs) [31], PEDOT [32] or porous platinum [33], but it is also interestingly significantly lower than the value reported in the literature for nanocrystalline diamond (NCD) electrode [34] and close to other porous diamond electrode.…”

Electrodes based on PPy polymer for electrocardiography and impedance plethysmography

“…The microelectrodes are another area were the PPy electrodes can assume the same roll of other used substance like Indium oxide (ITO), typically used in micro arrays as occur with other conductive polymers [13]. Moreover, brainmachine interfaces or recent active bioprosthesis depend on the electrode tissue contacts.…”

“…In this context, with the polymer electrodes, the contact area has been increased and improved as a consequence of their flexibility and adaptability to a large number of flat or curved surfaces. Typically the non-metallic bioelectrodes presented now a days have probed their efficacy in electrocardiography (ECG) and electroencephalography (EEG) records [10][11][12][13]. However, bioelectrodes are required in other kind of useful non-invasive medical test.…”