This paper introduces the concept of continuous chaotic printing, i.e. the use of chaotic flows for deterministic and continuous extrusion of fibers with internal multilayered micro- or nanostructures. Two free-flowing materials are coextruded through a printhead containing a miniaturized Kenics static mixer (KSM) composed of multiple helicoidal elements. This produces a fiber with a well-defined internal multilayer microarchitecture at high-throughput (>1.0 m min−1). The number of mixing elements and the printhead diameter determine the number and thickness of the internal lamellae, which are generated according to successive bifurcations that yield a vast amount of inter-material surface area (∼102 cm2 cm−3) at high resolution (∼10 µm). This creates structures with extremely high surface area to volume ratio (SAV). Comparison of experimental and computational results demonstrates that continuous chaotic 3D printing is a robust process with predictable output. In an exciting new development, we demonstrate a method for scaling down these microstructures by 3 orders of magnitude, to the nanoscale level (∼150 nm), by feeding the output of a continuous chaotic 3D printhead into an electrospinner. The simplicity and high resolution of continuous chaotic printing strongly supports its potential use in novel applications, including—but not limited to—bioprinting of multi-scale layered biological structures such as bacterial communities, living tissues composed of organized multiple mammalian cell types, and fabrication of smart multi-material and multilayered constructs for biomedical applications.

Graphitic carbons’ unique attributes have attracted worldwide interest towards their development and application. Carbon pyrolysis is a widespread method for synthesizing carbon materials. However, our understanding of the factors that cause differences in graphitization of various pyrolyzed carbon precursors is inadequate. We demonstrate how electro-mechanical aspects of the synthesis process influence molecular alignment in a polymer precursor to enhance its graphitization. Electrohydrodynamic forces are applied via electrospinning to unwind and orient the molecular chains of a non-graphitizing carbon precursor, polyacrylonitrile. Subsequently, exerting mechanical stresses further enhances the molecular alignment of the polymer chains during the formative crosslinking phase. The stabilized polymer precursor is then pyrolyzed at 1000 °C and characterized to evaluate its graphitization. The final carbon exhibits a uniformly graphitized structure, abundant in edge planes, which translates into its electrochemical kinetics. The results highlight the significance of physical synthesis conditions in defining the structure and properties of pyrolytic carbons.

Catalytic substrate, which is devoid of expensive noble metals and enzymes for hydrogen peroxide (H2O2), reduction reactions can be obtained via nitrogen doping of graphite. Here, we report a facile fabrication method for obtaining such nitrogen doped graphitized carbon using polyacrylonitrile (PAN) mats and its use in H2O2 sensing. A high degree of graphitization was obtained with a mechanical treatment of the PAN fibers embedded with carbon nanotubes (CNT) prior to the pyrolysis step. The electrochemical testing showed a limit of detection (LOD) 0.609 µM and sensitivity of 2.54 µA cm−2 mM−1. The promising sensing performance of the developed carbon electrodes can be attributed to the presence of high content of pyridinic and graphitic nitrogens in the pyrolytic carbons, as confirmed by X-ray photoelectron spectroscopy. The reported results suggest that, despite their simple fabrication, the hydrogen peroxide sensors developed from pyrolytic carbon nanofibers are comparable with their sophisticated nitrogen-doped graphene counterparts.

In this study, the bioelectrocatalytic reduction of molecular oxygen by two highly thermostable laccase isoforms from a native strain of Pycnoporus sanguineus CS43 were evaluated and compared to commercially available laccase from Trametes versicolor (TvL). The laccase isoforms (LAC1 and LAC2) and TvL laccase were immobilized by orientation onto anthracene-modified multiwalled carbon nanotubes (AC-MWCNT), which were subsequently immobilized onto carbon nanofiber mat electrodes fabricated using a carbon MEMS (C-MEMS) process. The performances of the isoforms were evaluated at differing pHs, temperatures, and with various inhibitors under hydrodynamic and hydrostatic conditions. Both LAC1 and LAC2 had onset potentials of over +650 mV vs Ag/AgCl at pH 4.0, which are among the highest reported to date for any laccase bioelectrode. High current densities were also obtained, producing 825 ± 88 μA/cm 2 and 1220 ± 106 μA/cm 2 with LAC1 and LAC2, respectively. The bioelectrodes also demonstrated remarkable operational ranges in pH and temperature as well as increased resistance to common laccase inhibitors. In both cases, they maintained over 70% of their maximum current densities after 12 h of continuous operation at 20 °C and over 20% of their maximum current densities after 6 h of continuous operation at 45 °C. In comparison, the TvL cathodes maintained 50% of their maximum current densities after 12 h at 20 °C and lost all catalytic activity after 2 h at 45 °C. The high stability, onset potential, current densities, and increased inhibitor resilience demonstrated by the results of this study make these isoforms very attractive for applications such as biofuel cell cathodes.

In this work, we report on a rapid, efficient electrochemical iodine sensor based on mechanically treated carbon nanofiber (MCNF) electrodes. The electrode’s highly graphitic content, unique microstructure, and the presence of nitrogen heteroatoms in its atomic lattice contribute to increased heterogeneous electron transfer and improved kinetics compared to conventional pyrolytic carbons. The electrode demonstrates selectivity for iodide ions in the presence of both interfering agents and high salt concentrations. The sensor exhibits clinically relevant limits of detection of 0.59 µM and 1.41 µM, in 1X PBS and synthetic urine, respectively, and a wide dynamic range between 5 µM and 700 µM. These results illustrate the advantages of the material’s unique electrochemical properties for iodide sensing, in addition to its simple, inexpensive fabrication. The reported iodine sensor eliminates the need for specimen processing, revealing its aptitude for applications in point-of-care diagnostics.

This review focuses on recent advances in micro-and nano-fabrication techniques and their applications to electrochemical power devices, specifically microfabricated Lithium-ion batteries, enzymatic and microbial fuel cells (biofuel cells), and dye-sensitized solar cells (DSSCs). Although the maturity of these three technologies ranges from market ready (batteries) to fundamental research (biofuel cells) to applied research (DSSCs), advances in MEMS (Micro-Electro-Mechanical Systems) and NEMS (Nano-Electro-Mechanical Systems) techniques, particularly modifications in surface area and surface chemistry, and novel genetic and molecular engineering techniques, significantly improve the electrochemical activity of these technologies across the board. For each of these three categories of power-MEMS devices the review covers: (1) The technical challenges facing the performance and fabrication of electrochemical power devices; (2) Current MEMS and NEMS techniques used to improve efficiency; and (3) Future outlook and suggested improvements of MEMS and NEMS for implementation in electrochemical power devices.

This paper introduces the concept of continuous chaotic printing, i.e., the use of chaotic flows for deterministic and continuous fabrication of fibers with internal multilayered micro-or nanostructures. Two free-flowing materials are coextruded through a printhead containing a miniaturized Kenics static mixer (KSM) composed of multiple helicoidal elements. This produces a fiber with a well-defined internal multilayer microarchitecture at high speeds (>1.0 m min-1). The number of mixing elements and the printhead diameter determine the number and thickness of the internal lamellae, which are generated according to successive bifurcations that yield a vast amount of inter-material surface area (~102 cm2 cm-3) and high resolution features (~10 µm). In an exciting further development, we demonstrate a scale-down of the microstructure by 3 orders of magnitude, to the nanoscale level (~10 nm), by feeding the output of a continuous chaotic 3D printhead into an electrospinner. Comparison of experimental and computational results demonstrates the robust and predictable output and performance of continuous chaotic 3D printing. The simplicity and high resolution of continuous chaotic printing strongly supports its potential use in novel applications, including-but not limited to-bioprinting of multi-scale tissue-like structures, modeling of bacterial communities, and fabrication of smart multi-material and multilayered constructs.

Carbon's electrochemistry depends on its type and microstructure, and how these affect the electrode's electronic density of states. We demonstrate how pyrolysis of electro-mechanically stressed Polyacrylonitrile (PAN) nanofibers, infused with carbon nanotubes, will result in a unique graphitic electrode, which possesses enhanced and multifaceted electrochemical behavior. As corroborated by materials characterization, the microstructure of the stress-activated pyrolytic carbon (SAPC) characteristically contains a high proportion of disorders in the forms of edge planes and embedded heterogeneous nitrogen atoms. These disorders introduce a range of energy states near the Fermi level, yielding enhanced kinetics in the as-synthesized SAPC electrodes. A comprehensive electrochemical study of the SAPC electrode in surface sensitive ([Fe(CN) 6 ] 3-/4-), surface insensitive ([IrCl 6 ] 2-/3-), and adsorption sensitive (dopamine) redox probes demonstrates 5e14-fold increases in its heterogeneous electron transfer rate compared to regular PAN-based carbon electrodes. The fast kinetics of SAPC electrodes in adsorption sensitive analytes translates into its capability for simultaneous detection of dopamine, uric acid, and ascorbic acid. The results point to a new class of pyrolytic carbon electrodes with an attractive electrocatalytic capacity, geared toward electrochemical sensing platforms.