Sharpened and Mechanically Durable Carbon Fiber Electrode Arrays for Neural Recording

Abstract

Bioelectric medicine treatments target disorders of the nervous system unresponsive to pharmacological methods. While current stimulation paradigms effectively treat many disorders, the underlying mechanisms are relatively unknown, and current neuroscience recording electrodes are often limited in their specificity to gross averages across many neurons or axons. Here, we develop a novel, durable carbon fiber electrode array adaptable to many neural structures for precise neural recording. Carbon fibers (6.8 µm diameter) were sharpened using a reproducible blowtorch method that uses the reflection of fibers against the surface of a water bath. The arrays were developed by partially embedding carbon fibers in medical-grade silicone to improve durability. We recorded acute spontaneous electrophysiology from the rat cervical vagus nerve (CVN), feline dorsal root ganglia (DRG), and rat brain. Blowtorching resulted in fibers of 72.3 ± 33.5-degree tip angle with 146.8 ± 17.7 µm exposed carbon. Observable neural clusters were recorded using sharpened carbon fiber electrodes from rat CVN (41.8 µVpp), feline DRG (101.1 µVpp), and rat brain (80.7 µVpp). Recordings from the feline DRG included physiologically relevant signals from increased bladder pressure and cutaneous brushing. These results suggest that this carbon fiber array is a uniquely durable and adaptable neural recording device. In the future, this device may be useful as a bioelectric medicine tool for diagnosis and closedloop neural control of therapeutic treatments and monitoring systems.

Electrodeposited Platinum Iridium Enables Microstimulation With Carbon Fiber Electrodes

“…The development of small microelectrodes for localized neural stimulation is the key challenge facing neural interfaces. CFEA have proven to effectively provide neural recording from the motor cortex (Patel et al, 2015(Patel et al, , 2016Massey et al, 2019) as well as from the peripheral nerve (Gillis et al, 2018;Dehdashtian et al, 2020;Welle et al, 2021). We recently (Della Valle et al, 2021) demonstrated how electroplated PtIr can decrease CF impedance with a good coating adherence.…”

“…The carbon fiber electrode arrays (CFEA) consist of eight sharpened CFs coated with a Parylene C insulation layer (800 nm) and are attached to a small printed circuit board [ZIF Probe, ZIF, (Patel et al, 2016)]. Insulation is removed at the tip using a blowtorching process (Welle et al, 2021) to expose 100-150 μm of carbon with sharpened tips. The final tip diameter tapers from 8.4 to ∼2 μm diameter at the tip.…”

“…Polyimide is an example of an electrode substrate that requires a stiffener while silicon is an example of an electrode that is stiff but brittle at dimensions below 15 microns. Carbon fiber (CF) ultramicroelectrodes have proven to be strong enough to penetrate the cortex (Patel et al, 2015;Patel et al, 2016;Massey et al, 2019) and peripheral nerve (Gillis et al, 2018;Dehdashtian et al, 2020) yet small enough to evoke minimal foreign body reaction (Deku et al, 2018;Kozai et al, 2012;Patel et al, 2016;Welle et al, 2020Welle et al, , 2021. Since carbon is also conductive, it can serve as both a mechanical substrate and electrical conductor for an ultramicroelectrode (Kozai et al, 2012;Patel et al, 2016;Jiman et al, 2020).…”

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

“…[104] Carbon fibers are typically thinner, more flexible, and as biocompatible as thin metal films [105] and are particularly compatible with processing of thin polymeric films. [106] The fibers can be commercially purchased, even preinsulated at micrometer-scale diameters, and arranged in various geometries to fabricate electrical tracks [107][108][109][110][111] or can form a "carbon fabric" that can be cut to form the electrical tracks. [77] Carbon macroparticles, such as carbon black, can be mixed with a polymeric matrix and screen printed, extruded, or 3D-printed for further control over the formulation and pattering.…”

Ultraflexible and Stretchable Intrafascicular Peripheral Nerve Recording Device with Axon‐Dimension, Cuff‐Less Microneedle Electrode Array

“…[4,5] The development of intrafascicular devices enabled researchers to detect and modulate neural activities at a higher resolution. To date, a variety of intrafascicular recording and/or stimulation methods have been achieved using thin-film polymer devices, [6,7] carbon fiber electrode arrays, [8,9] highly conductive carbon-based threads with low electrochemical impedance, [10][11][12] Utah arrays, [13,14] flexible microneedle electrode arrays, [15][16][17] and regenerative devices. [18] With implantation of such devices, researchers were able to map and decode Peripheral nerve mapping tools with higher spatial resolution are needed to advance systems neuroscience, and potentially provide a closed-loop biomarker in neuromodulation applications.…”