Preparation of Monodisperse Biodegradable Polymer Microparticles Using a Microfluidic Flow‐Focusing Device for Controlled Drug Delivery

Degradable microparticles have broad utility as vehicles for drug delivery and form the basis of several therapies approved by the US Food and Drug Administration. Conventional emulsion‐based methods of manufacturing produce particles with a wide range of diameters (and thus kinetics of release) in each batch. This paper describes the fabrication of monodisperse, drug‐loaded microparticles from biodegradable polymers using the microfluidic flow‐focusing (FF) devices and the drug‐delivery properties of those particles. Particles are engineered with defined sizes, ranging from 10 µm to 50 µm. These particles are nearly monodisperse (polydispersity index = 3.9%). A model amphiphilic drug (bupivacaine) is incorporated within the biodegradable matrix of the particles. Kinetic analysis shows that the release of the drug from these monodisperse particles is slower than that from conventional methods of the same average size but a broader distribution of sizes and, most importantly, exhibit a significantly lower initial burst than that observed with conventional particles. The difference in the initial kinetics of drug release is attributed to the uniform distribution of the drug inside the particles generated using the microfluidic methods. These results demonstrate the utility of microfluidic FF for the generation of homogenous systems of particles for the delivery of drugs.     

Carbon‐MEMS‐Based Alternating Stacked MoS2@rGO‐CNT Micro‐Supercapacitor with High Capacitance and Energy Density

A novel process to fabricate a carbon‐microelectromechanical‐system‐based alternating stacked MoS₂@rGO–carbon‐nanotube (CNT) micro‐supercapacitor (MSC) is reported. The MSC is fabricated by successively repeated spin‐coating of MoS₂@rGO/photoresist and CNT/photoresist composites twice, followed by photoetching, developing, and pyrolysis. MoS₂@rGO and CNTs are embedded in the carbon microelectrodes, which cooperatively enhance the performance of the MSC. The fabricated MSC exhibits a high areal capacitance of 13.7 mF cm^?2 and an energy density of 1.9 µWh cm^?2 (5.6 mWh cm^?3), which exceed many reported carbon‐ and MoS₂‐based MSCs. The MSC also retains 68% of capacitance at a current density of 2 mA cm^?2 (5.9 A cm^?3) and an outstanding cycling performance (96.6% after 10 000 cycles, at a scan rate of 1 V s^?1). Compared with other MSCs, the MSC in this study is fabricated by a low‐cost and facile process, and it achieves an excellent and stable electrochemical performance. This approach could be highly promising for applications in integration of micro/nanostructures into microdevices/systems.     

Flow‐Regulated Growth of Titanium Dioxide (TiO2) Nanotubes in Microfluidics

Electrochemical anodization of titanium (Ti) in a static, bulk condition is used widely to fabricate self‐organized TiO₂ nanotube arrays. Such bulk approaches, however, require extended anodization times to obtain long TiO₂ nanotubes and produce only vertically aligned nanotubes. To date, it remains challenging to develop effective strategies to grow long TiO₂ nanotubes in a short period of time, and to control the nanotube orientation. Here, it is shown that the anodic growth of TiO₂ nanotubes is significantly enhanced (≈16–20 times faster) under flow conditions in microfluidics. Flow not only controls the diameter, length, and crystal orientations of TiO₂ nanotubes, but also regulates the spatial distribution of nanotubes inside microfluidic devices. Strikingly, when a Ti thin film is deposited on silicon substrates and anodized in microfluidics, both vertically and horizontally aligned (relative to the bottom substrate) TiO₂ nanotubes can be produced. The results demonstrate previously unidentified roles of flow in the regulation of growth of TiO₂ nanotubes, and provide powerful approaches to effectively grow long, oriented TiO₂ nanotubes, and construct hierarchical TiO₂ nanotube arrays on silicon‐based materials.     

Embedded Fin‐Like Metal/CNT Hybrid Structures for Flexible and Transparent Conductors

In this paper, an embedded fin‐like metal‐coated carbon nanotube (Fin‐M/CNT) structure is demonstrated for flexible and transparent conductor wire applications. Embedded in a polydimethylsiloxane polymeric substrate, Fin‐M/CNT wires with a minimum width of 5 μm and a minimum pitch of 10 μm have been achieved. Direct current resistances of single Fin‐M/CNT wires, where the supporting CNT structures have been covered by Ti/Al/Au metal coatings of different thicknesses, have been measured. The high aspect ratio of the fin‐like structures not only improves the adhesion between the wires and the polymeric substrate, but also yields a low resistance at a small surface footprint. In addition, transparent Fin‐M/CNT grid lines with hexagonal patterns, with a sheet resistance of as low as 45 Ω sq^?1, have been achieved at an optical transmittance of 88%. The robustness of the Fin‐M/CNT structures has been demonstrated in bending tests up to 500 cycles and no significant changes in wire resistances are observed.     

Nanomanufacturing of RGO‐CNT Hybrid Film for Flexible Aqueous Al‐Ion Batteries

A highly electrically conductive film‐type current collector is an essential part of batteries. Apart from the metal‐based current collectors, lightweight and highly conductive carbon materials such as reduced graphene oxide (RGO) and carbon nanotubes (CNTs) show great potential as current collectors. However, traditional RGO manufacturing usually requires a long time and high energy, which decreases the product yielding rate and manufacturing efficiency. Moreover, the performance of the manufactured RGO needs to be further improved. In this work, CNT and GO are evenly mixed into GO‐CNT, which can be directly reduced into RGO‐CNT by Joule heating at 2936 K within less than 1 min. The fabricated RGO‐CNT achieves a high electrical conductivity of 2750 S cm^?1, and realizes a 10⁶‐fold increase. The assembled flexible aqueous Al‐ion battery with RGO‐CNT as the current collector exhibits impressive electrochemical performance in terms of superior cycling stability and exceptional rate capability, and excellent mechanical ability regarding the tolerance to mechanical damage such as bending, folding, piercing, and cutting without detrimental consequences.     

Rational Design and Synthesis of Extremely Efficient Macroporous CoSe2–CNT Composite Microspheres for Hydrogen Evolution Reaction

Uniquely structured CoSe₂–carbon nanotube (CNT) composite microspheres with optimized morphology for the hydrogen‐evolution reaction (HER) are prepared by spray pyrolysis and subsequent selenization. The ultrafine CoSe₂ nanocrystals uniformly decorate the entire macroporous CNT backbone in CoSe₂–CNT composite microspheres. The macroporous CNT backbone strongly improves the electrocatalytic activity of CoSe₂ by improving the electrical conductivity and minimizing the growth of CoSe₂ nanocrystals during the synthesis process. In addition, the macroporous structure resulting from the CNT backbone improves the electrocatalytic activity of the CoSe₂–CNT microspheres by increasing the removal rate of generated H₂ and minimizing the polarization of the electrode during HER. The CoSe₂–CNT composite microspheres demonstrate excellent catalytic activity for HER in an acidic medium (10 mA cm^?2 at an overpotential of ≈174 mV). The bare CoSe₂ powders exhibit moderate HER activity, with an overpotential of 226 mV at 10 mA cm^?2. The Tafel slopes for the CoSe₂–CNT composite and bare CoSe₂ powders are 37.8 and 58.9 mV dec^?1, respectively. The CoSe₂–CNT composite microspheres have a slightly larger Tafel slope than that of commercial carbon‐supported platinum nanoparticles, which is 30.2 mV dec^–1.     

Ultra‐High Optical Absorption Efficiency from the Ultraviolet to the Infrared Using Multi‐Walled Carbon Nanotube Ensembles

The optical absorption efficiencies of vertically aligned multi‐walled (MW)‐carbon nanotube (CNT) ensembles are characterized in the 350?7000 nm wavelength range where CNT site densities > 1 × 10¹¹/cm² are achieved directly on metallic substrates. The site density directly impacts the optical absorption characteristics, and while high‐density arrays of CNTs on electrically insulating and non‐metallic substrates have been commonly reported, achieving high site‐densities on metals has been challenging and remains an area of active research. These absorber ensembles are ultra‐thin (<10 μm) and yet they still exhibit a reflectance as low as ～0.02%, which is 100 times lower than the reference; these characteristics make them potentially attractive for high‐sensitivity and high‐speed thermal detectors. In addition, the use of a plasma‐enhanced chemical vapor deposition process for the synthesis of the absorbers increases the portfolio of materials that can be integrated with such absorbers due to the potential for reduced synthesis temperatures. The remarkable ruggedness of the absorbers is also demonstrated as they are exposed to high temperatures in an oxidizing ambient environment, making them well‐suited for extreme thermal environments encountered in the field, potentially for solar cell applications. Finally, a phenomenological model enables the determinatiom of the extinction coefficients in these nanostructures and the results compare well with experiment.     

Dendrite‐Free Zinc Deposition Induced by Multifunctional CNT Frameworks for Stable Flexible Zn‐Ion Batteries

The current boom of safe and renewable energy storage systems is driving the recent renaissance of Zn‐ion batteries. However, the notorious tip‐induced dendrite growth on the Zn anode restricts their further application. Herein, the first demonstration of constructing a flexible 3D carbon nanotube (CNT) framework as a Zn plating/stripping scaffold is constituted to achieve a dendrite‐free robust Zn anode. Compared with the pristine deposited Zn electrode, the as‐fabricated Zn/CNT anode affords lower Zn nucleation overpotential and more homogeneously distributed electric field, thus being more favorable for highly reversible Zn plating/stripping with satisfactory Coulombic efficiency rather than the formation of Zn dendrites or other byproducts. As a consequence, a highly flexible symmetric cell based on the Zn/CNT anode presents appreciably low voltage hysteresis (27 mV) and superior cycling stability (200 h) with dendrite‐free morphology at 2 mA cm^?2, accompanied by a high depth of discharge (DOD) of 28%. Such distinct performance overmatches most of recently reported Zn‐based anodes. Additionally, this efficient rechargeability of the Zn/CNT anode also enables a substantially stable Zn//MnO₂ battery with 88.7% capacity retention after 1000 cycles and remarkable mechanical flexibility.