Evaporative Dry Powders Derived from Cellulose Nanofiber Organogels to Fully Recover Inherent High Viscosity and High Transparency of Water Dispersion.

Water containing low amounts of cellulose nanofiber (CNF) is widely used as a thickening agent owing to its three unique properties: high transparency, viscosity, and controllable viscosity based on the shear rate. CNF dry powders are used to reduce the transportation and storage costs or expand applications as a thickening agent. Herein, the preparation of CNF dry powders that can be used to obtain redispersions while maintaining the aforementioned properties is reported. In this regard, the dehydration and vaporization procedures for a CNF water dispersion without using additives are discussed. When dry powders are prepared by removing water by boiling, their redispersions do not exhibit all their unique properties because of dense aggregations. However, when their redispersions are vigorously stirred to break the dense aggregations, they become transparent, although they do not recover their initial viscosity. Freeze-dried powders recover all their initial properties after redispersion. Nevertheless, their large volume does not reduce the transportation and storage costs. When the liquid is evaporated from the solvent-exchanged CNF organogels, their redispersions also fully recover all their properties. Furthermore, the evaporative dry powders with dense small volumes and good handling contribute to reducing the transportation and storage costs.

Chemically-modified cellulose paper as a microstructured catalytic reactor.

We discuss the successful use of chemically-modified cellulose paper as a microstructured catalytic reactor for the production of useful chemicals. The chemical modification of cellulose paper was achieved using a silane-coupling technique. Amine-modified paper was directly used as a base catalyst for the Knoevenagel condensation reaction. Methacrylate-modified paper was used for the immobilization of lipase and then in nonaqueous transesterification processes. These catalytic paper materials offer high reaction efficiencies and have excellent practical properties. We suggest that the paper-specific interconnected microstructure with pulp fiber networks provides fast mixing of the reactants and efficient transport of the reactants to the catalytically-active sites. This concept is expected to be a promising route to green and sustainable chemistry.

Transparent, conductive, and printable composites consisting of TEMPO-oxidized nanocellulose and carbon nanotube.

Ultrastrong, transparent, conductive and printable nanocomposites were successfully prepared by mixing single-walled carbon nanotubes (CNTs) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs) with abundant sodium carboxyl groups on the crystalline nanocellulose surfaces. The surface-anionic cellulose nanofibrils had reinforcing and nanodispersing effects on the CNTs both in water used as the dispersed medium and in the dried composite film, providing highly conductive and printable nanocomposites with a small amount of CNTs. TOCNs are therefore expected as an effective flexible matrix that can be used as an alternative to conventional polymers for various electrical materials, when nanocomposited with CNTs and also graphene. Our findings provide a promising route to realize green and flexible electronics.

Spatial exosome analysis using cellulose nanofiber sheets reveals the location heterogeneity of extracellular vesicles.

Extracellular vesicles (EVs), including exosomes, are recognized as promising functional targets involved in disease mechanisms. However, the intravital heterogeneity of EVs remains unclear, and the general limitation for analyzing EVs is the need for a certain volume of biofluids. Here, we present cellulose nanofiber (CNF) sheets to resolve these issues. We show that CNF sheets capture and preserve EVs from ~10 µL of biofluid and enable the analysis of bioactive molecules inside EVs. By attaching CNF sheets to moistened organs, we collect EVs in trace amounts of ascites, which is sufficient to perform small RNA sequence analyses. In an ovarian cancer mouse model, we demonstrate that CNF sheets enable the detection of cancer-associated miRNAs from the very early phase when mice did not have apparent ascites, and that EVs from different locations have unique miRNA profiles. By performing CNF sheet analyses in patients, we identify further location-based differences in EV miRNA profiles, with profiles reflecting disease conditions. We conduct spatial exosome analyses using CNF sheets to reveal that ascites EVs from cancer patients exhibit location-dependent heterogeneity. This technique could provide insights into EV biology and suggests a clinical strategy contributing to cancer diagnosis, staging evaluation, and therapy planning.

Direct determination of the degree of fibrillation of wood pulps by distribution analysis of pixel-resolved optical retardation.

We propose a new methodology for direct evaluation of the degree of fibrillation of fibrillating pulp suspensions through the pixel-resolved retardation distribution. Through simple normalization by just injecting a pulp suspension with a certain concentration into a quartz flow channel with a constant cross-sectional shape, the degree of fibrillation (i.e., the degree of bundling of cellulose molecular chains) can be directly mapped by the retardation gradation, reflecting locally high retardation (pulp fibers), smaller retardation (balloons on fibrillating pulps), and much smaller retardation close to water (dispersed nanofibers). Both the average retardation and standard deviation are found to be the direct indicators of the degree of fibrillation. We envision that the proposed methodology will become the future standard for determining the degree of fibrillation by the retardation distribution, and it will pave the way for more precise control of pulp fibrillation and more sophisticated applications of cellulose nanofiber suspensions.

In situ synthesis of Cu nanocatalysts on ZnO whiskers embedded in a microstructured paper composite for autothermal hydrogen production.

Cu nanoparticles (CuNPs) were successfully synthesized in situ on ZnO whiskers as a selective scaffold, which were supported in a microstructured paper matrix composed of inorganic fibers; as-prepared paper composites were easy to handle in practical use and demonstrated excellent catalytic performance in the methanol reforming process for effective hydrogen production.

One-Step Fabrication of Stretchable Copper Nanowire Conductors by a Fast Photonic Sintering Technique and Its Application in Wearable Devices.

Copper nanowire (CuNW) conductors have been considered to have a promising perspective in the area of stretchable electronics due to the low price and high conductivity. However, the fabrication of CuNW conductors suffers from harsh conditions, such as high temperature, reducing atmosphere, and time-consuming transfer step. Here, a simple and rapid one-step photonic sintering technique was developed to fabricate stretchable CuNW conductors on polyurethane (PU) at room temperature in air environment. It was observed that CuNWs were instantaneously deoxidized, welded and simultaneously embedded into the soft surface of PU through the one-step photonic sintering technique, after which highly conductive network and strong adhesion between CuNWs and PU substrates were achieved. The CuNW/PU conductor with sheet resistance of 22.1 Ohm/sq and transmittance of 78% was achieved by the one-step photonic sintering technique within only 20 µs in air. Besides, the CuNW/PU conductor could remain a low sheet resistance even after 1000 cycles of stretching/releasing under 10% strain. Two flexible electronic devices, wearable sensor and glove-shaped heater, were fabricated using the stretchable CuNW/PU conductor, demonstrating that our CuNW/PU conductor could be integrated into various wearable electronic devices for applications in food, clothes, and medical supplies fields.

A highly sensitive and flexible pressure sensor with electrodes and elastomeric interlayer containing silver nanowires.

The next-generation application of pressure sensors is gradually being extended to include electronic artificial skin (e-skin), wearable devices, humanoid robotics and smart prosthetics. In these advanced applications, high sensing capability is an essential feature for high performance. Although surface patterning treatments and some special elastomeric interlayers have been applied to improve sensitivity, the process is complex and this inevitably raises the cost and is an obstacle to large-scale production. In the present study a simple printing process without complex patterning has been used for constructing the sensor, and an interlayer is employed comprising elastomeric composites filled with silver nanowires. By increasing the relative permittivity, εr, of the composite interlayer induced by compression at high nanowire concentration, it has been possible to achieve a maximum sensitivity of 5.54 kPa(-1). The improvement in sensitivity did not sacrifice or undermine the other features of the sensor. Thanks to the silver nanowire electrodes, the sensor is flexible and stable after 200 cycles at a bending radius of 2 mm, and exhibits outstanding reproducibility without hysteresis under similar pressure pulses. The sensor has been readily integrated onto an adhesive bandage and has been successful in detecting human movements. In addition to measuring pressure in direct contact, non-contact pressures such as air flow can also be detected.

Topochemical synthesis and catalysis of metal nanoparticles exposed on crystalline cellulose nanofibers.

Topochemical synthesis of gold nanoparticles (AuNPs) was achieved on crystalline cellulose single nanofibers (CSNFs), which were tailored from native cellulose. Exposed AuNPs@CSNFs composite exhibited an excellent catalytic efficiency: the turnover frequency of the AuNPs@CSNFs was up to 840 times that of conventional polymer-supported AuNPs, for a model aqueous reduction reaction. Our novel strategy provides a promising solution to realize efficient use of limited noble metals using natural bioresources.