Three-Dimensional Carbon Nanotube Electrodes for Extracellular Recording of Cardiac Myocytes

Advances in Carbon-Based Microfiber Electrodes for Neural Interfacing

Neural interfacing devices using penetrating microelectrode arrays have emerged as an important tool in both neuroscience research and medical applications. These implantable microelectrode arrays enable communication between man-made devices and the nervous system by detecting and/or evoking neuronal activities. Recent years have seen rapid development of electrodes fabricated using flexible, ultrathin carbon-based microfibers. Compared to electrodes fabricated using rigid materials and larger cross-sections, these microfiber electrodes have been shown to reduce foreign body responses after implantation, with improved signal-to-noise ratio for neural recording and enhanced resolution for neural stimulation. Here, we review recent progress of carbon-based microfiber electrodes in terms of material composition and fabrication technology. The remaining challenges and future directions for development of these arrays will also be discussed. Overall, these microfiber electrodes are expected to improve the longevity and reliability of neural interfacing devices.

Carbon Nanotube Modified Microelectrode Array for Neural Interface

Carbon nanotubes (CNTs) coatings have been shown over the past few years as a promising material for neural interface applications. In particular, in the field of nerve implants, CNTs have fundamental advantages due to their unique mechanical and electrical properties. In this study, carbon nanotubes multi-electrode arrays (CNT-modified-Au MEAs) were fabricated based on gold multi-electrode arrays (Au-MEAs). The electrochemical impedance spectra of CNT-modified-Au MEA and Au-MEA were compared employing equivalent circuit models. In comparison with Au-MEA (17 Ω), CNT-modified-Au MEA (8 Ω) lowered the overall impedance of the electrode at 1 kHz by 50%. The results showed that CNT-modified-Au MEAs have good properties such as low impedance, high stability and durability, as well as scratch resistance, which makes them appropriate for long-term application in neural interfaces.

Bioelectronics with nanocarbons

Characterizing the electrical activity of cardiomyocytes and neurons is crucial in understanding the complex processes in the heart and brain tissues, both in healthy and diseased states. Micro- and nanotechnologies have significantly improved the electrophysiological investigation of cellular networks. Carbon-based nanomaterials or nanocarbons, such as carbon nanotubes (CNTs), nanodiamonds (NDs) and graphene are promising building blocks for bioelectronics platforms owing to their outstanding chemical and physical properties. In this review, we discuss the various bioelectronics applications of nanocarbons and their derivatives. Furthermore, we touch upon the challenges that remain in the field and describe the emergence of carbon-based hybrid-nanomaterials that will potentially address those limitations, thus improving the capabilities to investigate the electrophysiology of excitable cells, both as a network and at the single cell level.

Transparent poly(3,4-ethylenedioxythiophene)-based microelectrodes for extracellular recording

It is well known that at the interface between neuronal tissue and recording electrode low electrical impedance is required. However, if simultaneous optical detection or stimulation is an issue, good optical transmittance of the electrode material is desirable as well. State-of-the-art titanium nitride electrodes provide superior low impedance compared to gold or iridium, but are nontransparent. Transparent electrode materials like the transparent conducting oxide, indium tin oxide (ITO), or graphene offer high light transmittance (>80%) but reveal relatively high impedance. In this paper, the authors propose the conducting polymer poly(3,4-ethylenedioxythiophene) with the counter ion NO₃^- as the electrode material for low impedance and good optical transmittance properties. The polymer is electrochemically deposited onto ITO improving the relatively high impedance of ITO. This multilayer electrode allows not only for electrophysiological recordings of cardiomyocytes but also for monitoring of cell contraction under the microscope. Electrochemical impedance spectroscopy and action potential recordings reveal that the new transparent electrodes are a good compromise in terms of low impedance and transparency if deposition parameters are optimized.

Carbon-Nanotube-Wrapped Spider Silks for Directed Cardiomyocyte Growth and Electrophysiological Detection

The combination of nanostructures with biomaterials offers great opportunities in constructing innovative functional devices such as biosensors and actuators. Here, we create a multifunctional fiber by wrapping a thin film of carbon nanotubes (CNTs) on naturally found spider silks, which shows great flexibility and conductivity. The hybrid CNT-silk fiber demonstrates intimate contact with cardiomyocytes and can direct the cell growth and simultaneously record potential signals evoked from cell beating. Cell activities reflected in the form of potential signals have been monitored clearly and reliably through the CNT-silk fibers without degradation over the long term.

Vertically Aligned Carbon Nanotubes as Platform for Biomimetically Inspired Mechanical Sensing, Bioactive Surfaces, and Electrical Cell Interfacing

Vertically aligned carbon nanotubes (VACNTs) are one dimensional carbon objects anchored atop of a solid substrate. They are geometrically fixed in contrast to their counterparts, randomly oriented carbon nanotubes (CNTs). In this progress report, the breadth in which these one dimensional, mechanically flexible, though robust and electrical conducting carbon nanostructures can be employed as functional material is shown and our research is put in perspective to work in the last five to ten years. The connection between the different areas touched in this report is the biomimetic-materials approach, which rely on the hairy morphology of VACNTs. These properties in connection with their electrical conductivity offer possibilities towards new functional features and applications of VACNTs. To appreciate the possibilities of biomimetic research with VACNTs, first their material characteristics are given to make the reader familiar with specific features of their synthesis, the peculiarities in arranging and controlling the morphology of CNTs in a vertical alignment as well as a current understanding of these properties on a microscopic basis. In doing so, similarities as well as differences, which offer new possibilities for biomimetic studies of VACNTS with respect to multiwalled randomly oriented CNTs, will become clear.

Electrophysiologic and cellular characteristics of cardiomyocytes after X-ray irradiation

The aim of this study was to investigate possible effects of ionizing irradiation on the electrophysiological functionality of cardiac myocytes in vitro. Primary chicken cardiomyocytes with spontaneous beating activity were irradiated with X-rays (dose range of 0.5-7 Gy). Functional alterations of cardiac cell cultures were evaluated up to 7 days after irradiation using microelectrode arrays. As examined endpoints, cell proliferation, apoptosis, reactive oxygen species (ROS) and DNA damage were evaluated. The beat rate of the cardiac networks increased in a dose-dependent manner over one week. The duration of single action potentials was slightly shortened. Additionally, we observed lower numbers of mitotic and S-phase cells at certain time points after irradiation. Also, the number of cells with γH2AX foci increased as a function of the dose. No significant changes in the level of ROS were detected. Induction of apoptosis was generally negligibly low. This is the first report to directly show alterations in cardiac electrophysiology caused by ionizing radiation, which were detectable up to one week after irradiation.

Rigid and flexible organic electrochemical transistor arrays for monitoring action potentials from electrogenic cells

Rigid and flexible organic electrochemical transistor arrays are successfully implemented for monitoring cardiac action potentials. Excellent signal to noise ratios are achieved with values routinely larger than 4. These devices are promising to be used in both conventional and emerging areas.

Growth and structural discrimination of cortical neurons on randomly oriented and vertically aligned dense carbon nanotube networks

The growth of cortical neurons on three dimensional structures of spatially defined (structured) randomly oriented, as well as on vertically aligned, carbon nanotubes (CNT) is studied. Cortical neurons are attracted towards both types of CNT nano-architectures. For both, neurons form clusters in close vicinity to the CNT structures whereupon the randomly oriented CNTs are more closely colonised than the CNT pillars. Neurons develop communication paths via neurites on both nanoarchitectures. These neuron cells attach preferentially on the CNT sidewalls of the vertically aligned CNT architecture instead than onto the tips of the individual CNT pillars.

Enhanced human bone marrow mesenchymal stem cell functions in novel 3D cartilage scaffolds with hydrogen treated multi-walled carbon nanotubes

Cartilage tissue is a nanostructured tissue which is notoriously hard to regenerate due to its extremely poor inherent regenerative capacity and complex stratified architecture. Current treatment methods are highly invasive and may have many complications. Thus, the goal of this work is to use nanomaterials and nano/microfabrication methods to create novel biologically inspired tissue engineered cartilage scaffolds to facilitate human bone marrow mesenchymal stem cell (MSC) chondrogenesis. To this end we utilized electrospinning to design and fabricate a series of novel 3D biomimetic nanostructured scaffolds based on hydrogen (H2) treated multi-walled carbon nanotubes (MWCNTs) and biocompatible poly(L-lactic acid) (PLLA) polymers. Specifically, a series of electrospun fibrous PLLA scaffolds with controlled fiber dimension were fabricated in this study. In vitro MSC studies showed that stem cells prefer to attach in the scaffolds with smaller fiber diameter. More importantly, the MWCNT embedded scaffolds showed a drastic increase in mechanical strength and a compressive Young's modulus matching to natural cartilage. Furthermore, our MSC differentiation results demonstrated that incorporation of the H2 treated carbon nanotubes and poly-L-lysine coating can induce more chondrogenic differentiations of MSCs than controls. After two weeks of culture, PLLA scaffolds with H2 treated MWCNTs and poly-L-lysine can achieve the highest glycosaminoglycan synthesis, making them promising for further exploration for cartilage regeneration.

Improving cardiac myocytes performance by carbon nanotubes platforms

The application of nanotechnology to the cardiovascular system has increasingly caught scientists' attention as a potentially powerful tool for the development of new generation devices able to interface, repair, or boost the performance of cardiac tissue. Carbon nanotubes (CNTs) are considered as promising materials for nanomedicine applications in general and have been recently tested toward excitable cell growth. CNTs are cylindrically shaped structures made up of rolled-up graphene sheets, with unique electrical, thermal, and mechanical properties, able to effectively conducting electrical current in electrochemical interfaces. CNTs-based scaffolds have been recently found to support the in vitro growth of cardiac cells: in particular, their ability to improve cardiomyocytes proliferation, maturation, and electrical behavior are making CNTs extremely attractive for the development and exploitation of interfaces able to impact on cardiac cells physiology and function.