Flexible Bioelectronic Devices Based on Micropatterned Monolithic Carbon Fiber Mats

Abstract

Polymer‐derived carbon can serve as an electrode material in multimodal neural stimulation, recording, and neurotransmitter sensing platforms. The primary challenge in its applicability in implantable, flexible neural devices is its characteristic mechanical hardness that renders it difficult to fabricate the entire device using only carbon. A microfabrication technique is introduced for patterning flexible, cloth‐like, polymer‐derived carbon fiber (CF) mats embedded in polyimide (PI), via selective reactive ion etching. This scalable, monolithic manufacturing method eliminates any joints or metal interconnects and creates electrocorticography electrode arrays based on a single CF mat. The batch‐fabricated CF/PI composite structures, with critical dimension of 12.5 µm, are tested for their mechanical, electrical, and electrochemical stability, as well as to chemicals that mimic acute postsurgery inflammatory reactions. Their recording performance is validated in rat models. Reported CF patterning process can benefit various carbon microdevices that are expected to feature flexibility, material stability, and biocompatibility.

Recent Technological Advances in Fabrication and Application of Organic Electrochemical Transistors

“…[ 117 ] Recently, various fiber structures have been manufactured by advanced nanotechnologies, making it achievable to build electronic devices directly on the surface or inside of single fiber with a typical micrometer‐sized thickness. [ 118–121 ]…”

“…[117] Recently, various fiber structures have been manufactured by advanced nanotechnologies, making it achievable to build electronic devices directly on the surface or inside of single fiber with a typical micrometer-sized thickness. [118][119][120][121] Fibers or textiles are also attractive carriers for OECTs, with great promising applications in wearable electronics such as noninvasive and continuous monitoring of physiological parameters. Unlike FETs that require well defined insulator layer and small feature sizes, [122,123] OECTs present relative ease of manufacture without any narrow and critical dimensions for low voltage operation.…”

Implantable Thin Film Devices as Brain-Computer Interfaces: Recent Advances in Design and Fabrication Approaches

“…Chen et al developed a high-performance indium tin oxide (ITO)/metal grid hybrid flexible transparent microelectrode with high optical transmittance (59%-81%), superior electrochemical impedance (5.4-18.4 Ω•cm 2 ), and excellent sheet resistance (5.6-14.1 Ω•sq −1 ) (Figure 8c) [114]. The hybrid structures retained the superior mechanical properties of [115]); (e) polypyrrole (PPy) electrode materials modified by nanowires through a simple electro-polymerization process (reprinted with permission from [116]); (f) a novel 3D printable conducting polymer ink (reprinted with permission from [77]); (g) stretchable transparent Ag/Au nanowires encapsulated in transparent polymer and connected to hydrogel-coated microelectrodes through silver pads (reprinted with permission from [117]); (h) a neural probe using gallium (Ga) in the probe construction as interconnects (reprinted with permission from [81]).…”

Fabrication and Specific Functionalisation of Carbon Fibers for Advanced Flexible Biosensors

“…The monitoring of brain activity has practical significance for biological physiological health signals. Researchers (Vomero et al, 2019 ) reported that a flexible biosensor probe based on CFs was implanted into mouse brain tissue ( Figure 6 ). A micromachining technology for embedding flexible, cloth-like and polymer-derived CFs pads in polyimide by selective reactive ion etching is introduced.…”

“…(k–p) In vivo characterization of CF-based flexible neural implants. Reproduced with permission from Vomero et al ( 2019 ).…”