(Invited) Microwires Based on Carbon Nanotubes for Medicine and Biology

Abstract

Flexible and biocompatible microwires are generally employed for biomedical implants in medicine, more specifically in neuroscience. These microwires used as electrodes need to be chemically inert and electrically conducting in order to record and stimulate the electrical activity of neurons in the nervous system. The electrodes available today are made of metals and silicon that lack the required flexibility resulting in a mechanical mismatch between soft tissues and rigid metals which induces faster biofouling and inconsistent performance for long-term implants. Biofouling triggered by inflammatory responses dramatically affects the performance of neural electrodes, resulting in decreased signal sensitivity and consistency over time. Thus, long-term clinical applications require electrically conducting flexible electrode materials with reduced dimensions and antibiofouling properties. These characteristics reduce the degree of inflammatory reactions and increase the lifetime of implanted neural electrodes. Carbon nanotubes (CNTs) are well known for their flexibility, electrical conductivity, and chemical inertness. This talk will report the fabrication of CNT fibers and subsequent coating using a biocompatible flexible polymer hydrogenated nitrile butadiene rubber (HNBR). Unlike the gold standard parylene-C coating that requires processing under vacuum, dissolved elastomer HNBR polymer can deposit uniform coating in solutions. Polymer dip-coating has been employed for uniform and continuous coating of meters-long CNT fibers of multiple diameters (26 to 66 mm) to evaluate the robustness of the approach. The polymer was able to provide uniform thickness and pinhole-free coating along the CNT fiber. Furthermore, the polymer has been shown to be biocompatible when tested with in vitro elusions and culturing neurons. The covalent functionalization of CNT microwire cross-section interfacing with the neurons using hydrophilic, anti-biofouling phosphorylcholine molecules displays reduced impedance and increased hydrophilicity. These CNT microwire assemblies are promising for the development of low-impedance neural electrodes with higher hydrophilicity and protein-fouling resistance to inhibit inflammatory responses.