Polymer Composite with Carbon Nanofibers Aligned during Thermal Drawing as a Microelectrode for Chronic Neural Interfaces

Abstract

Microelectrodes provide a direct pathway to investigate brain activities electrically from the external world, which has advanced our fundamental understanding of brain functions and has been utilized for rehabilitative applications as brain-machine interfaces. However, minimizing the tissue response and prolonging the functional durations of these devices remain challenging. Therefore, the development of next-generation microelectrodes as neural interfaces is actively progressing from traditional inorganic materials toward biocompatible and functional organic materials with a miniature footprint, good flexibility, and reasonable robustness. In this study, we developed a miniaturized all polymer-based neural probe with carbon nanofiber (CNF) composites as recording electrodes via the scalable thermal drawing process. We demonstrated that in situ CNF unidirectional alignment can be achieved during the thermal drawing, which contributes to a drastic improvement of electrical conductivity by 2 orders of magnitude compared to a conventional polymer electrode, while still maintaining the mechanical compliance with brain tissues. The resulting neural probe has a miniature footprint, including a recording site with a reduced size comparable to a single neuron and maintained impedance that was able to capture neural activities. Its stable functionality as a chronic implant has been demonstrated with the long-term reliable electrophysiological recording with single-spike resolution and the minimal tissue response over the extended period of implantation in wild-type mice. Technology developed here can be applied to basic chronic electrophysiological studies as well as clinical implementation for neuro-rehabilitative applications.

Advanced Multimaterial Electronic and Optoelectronic Fibers and Textiles

“…We envision that the number of recording electrodes can be drastically increased by the incorporation of novel conducting materials that can overcome capillary instability induced breakup during thermal drawing. Long‐term in vivo studies verified that these probes were minimally invasive and featured stable tissue–machine interfaces in the brain …”

A Route Toward Smart System Integration: From Fiber Design to Device Construction

“…Besides the traditional wet‐spinning and melt‐spinning, there is another impressive method, i.e., preform‐to‐fiber drawing technique to fabricate polymer‐based composite fibers . The typical scheme is shown in Figure i .…”

The Rise of Fiber Electronics

“…[38] Low-modulus elastomers showing reduced mechanical mismatches with biological tissue were thus developed to obtain more stable and effective interfaces.F or example, ap olymer-based elastomeric composite with aY oungs modulus five orders of magnitude lower than that of its tungsten counterparts can be extruded. [90][91][92] Additionally, because of the many different encapsulation materials applicable,awide range of elasticities can be obtained;f or example,u pt o5 00 %e lastic deformation has been demonstrated by the utilization of thermoplastic elastomers. [85] Another effective method is to design of nanostructured or microstructured fiber electrodes to achieve better electronic-tissue interfaces.F or example, the bond between the probe and tissue could be greatly enhanced by forming nanometer-sized curves and micrometer-sized needles on as ilicon fiber.…”