Three-Dimensional-Moldable Nanofiber-Reinforced Transparent Composites with a Hierarchically Self-Assembled "Reverse" Nacre-like Architecture

Enhancing Mechanical Durability of Water-Soluble Microneedles with Cellulose Nanofibers via Thermal Imprinting

The study demonstrates the effectiveness of ultrahigh-pressure homogenizer (UHPH) cellulose nanofibers (CNFs) in improving the mechanical properties of poly(vinyl alcohol) (PVA) microneedle arrays (MNA). CNFs were incorporated into PVA nanocomposite films at concentrations of 0, 5, and 8 wt % using solvent casting and a nickel mold coated with a fluoropolymer was used to thermally imprint the films with MNA micropatterns at optimal mold temperatures and pressing pressure. The integration of CNFs substantially enhanced the morphological properties, surface modulus, and the accuracy of pattern replication in the nanocomposite. The augmented mechanical strength observed in the micropatterns, attributed to CNFs and subjected to UHPH treatment, can be ascribed to the physical entanglement and hydrogen bonding facilitating formation within the MNA micropattern.

An Investigation of the Mechanical Properties of Ti Films Reinforced with Wood Composites by Growing Ti Particles on a Wood Substrate

Table tennis racquet blades (TTRBs) are specialized wood materials known for their excellent mechanical properties. As one of the widely used physical vapor deposition technologies, magnetron sputtering has become the most effective method for preparing various thin film materials. In this study, the surface of the TTRB is coated with a Ti film with different thicknesses by magnetron sputtering to improve the performance of the TTRB. The surface roughness, crystal structure, viscoelasticity of the TTRB were analyzed by means of non-contact surface profilometry, X-ray diffraction (XRD), and dynamic mechanical analysis (DMA). In order to effectively test TTRB properties, three types of testing devices were designed, including free-fall rebound, laser vibration measurement, and the dynamic rebound test. The results reveal that the deposition of a Ti film on the surface of the TTRB improves the rigidity and rebound efficiency of the TTRB. Under optimized conditions, the initial amplitude, vertical rebound distance, and rebound rate can reach 2.1 μm, 23.7 cm, 13.7%, respectively, when the deposition thickness is 5 μm. It is anticipated that the modification and the corresponding detection methods developed in this study can foster innovative product development, standardize the TTRB industry, and contribute to the advancement of table tennis.

Biomimetic Mechanical Robust Cement-Resin Composites with Machine Learning-Assisted Gradient Hierarchical Structures

Biological materials relying on hierarchically ordered architectures inspire the emergence of advanced composites with mutually exclusive mechanical properties, but the efficient topology optimization and large-scale manufacturing remain challenging. Herein, this work proposes a scalable bottom-up approach to fabricate a novel nacre-like cement-resin composite with gradient brick-and-mortar (BM) structure, and demonstrates a machine learning-assisted method to optimize the gradient structure. The fabricated gradient composite exhibits an extraordinary combination of high flexural strength, toughness, and impact resistance. Particularly, the toughness and impact resistance of such composite attractively surpass the cement counterparts by factors of approximately 700 and 600 times, and even outperform natural rocks, fiber-reinforced cement-based materials and even some alloys. The strengthening and toughening mechanisms are clarified as the regional-matrix densifying and crack-tip shielding effects caused by the gradient BM structure. The developed gradient composite not only endows a promising structural material for protective applications in harsh scenarios, but also paves a new way for biomimetic metamaterials designing.

Nanocellulose-stabilized Pickering emulsions: Fabrication, stabilization, and food applications

Pickering emulsions have been widely studied due to their good stability and potential applications. Nanocellulose including cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and bacterial cellulose nanofibrils (BCNFs) has emerged as sustainable stabilizers/emulsifiers in food-related Pickering emulsions due to their favorable properties such as renewability, low toxicity, amphiphilicity, biocompatibility, and high aspect ratio. Nanocellulose can be widely obtained from different sources and extraction methods and can effectively stabilize Pickering emulsions via the irreversible adsorption onto oil-water interface. The synergistic effects of nanocellulose and other substances can further enhance the interfacial networks. The nanocellulose-based Pickering emulsions have potential food-related applications in delivery systems, food packaging materials, and fat substitutes. Nanocellulose-based Pickering emulsions as 3D printing inks exhibit good injectable and gelling properties and are promising to print spatial architectures. In the future, the utilization of biomass waste and the development of "green" and facile extraction methods for nanocellulose production deserve more attention. The stability of nanocellulose-based Pickering emulsions in multi-component food systems and at various conditions is an utmost challenge. Moreover, the case-by-case studies on the potential safety issues of nanocellulose-based Pickering emulsions need to be carried out with the standardized assessment procedures. In this review, we highlight key fundamental work and recent reports on nanocellulose-based Pickering emulsion systems. The sources and extraction of nanocellulose and the fabrication of nanocellulose-based Pickering emulsions are briefly summarized. Furthermore, the synergistic stability and food-related applications of nanocellulose-stabilized Pickering emulsions are spotlighted.

Cellulose or chitin nanofibril-stabilized latex for medical adhesion via tailoring colloidal interactions

The objective of this research is to develop a functional medical adhesive from natural nanofibril-stabilized latex through an aqueous process. Surface charged cellulose or chitin nanofibrils are used to form Pickering emulsions of acrylic monomers, followed by in situ polymerization. Charged initiators are selected to tailor the interactions between them and nanofibrils, and it is found that the repulsive electrostatic interactions play a key role in stabilizing the heterogeneous system. As a result, poly(2-ethylhexyl acrylate-co-methyl methacrylate) latexes are successfully prepared for surfactant-free adhesives with a high shear strength of 72.0 ± 6.5 kPa. In addition, drug can be easily incorporated in the nanopaper substrate or adhesive layer to form a medical tape, exhibiting long-term drug release and antibacterial behaviors. We managed developing a facile method to integrate green synthesis, versatile functionalities and excellent adhesion into one adhesive, which remains a great challenge.

High internal phase Pickering emulsions stabilized by co-assembled rice proteins and carboxymethyl cellulose for food-grade 3D printing

In this study, high internal phase Pickering emulsions (HIPPEs) stabilized by protein-polysaccharide complexes were used as inks for food-grade three-dimensional printing (3DP). The complexes (RCs) structured by synergistic interactions between rice proteins (RPs) and carboxymethyl cellulose (CMC) displayed outstanding biphasic wettability with excellent ability to reduce the oil/water interfacial tension. The interfacial structures formed by RCs provided a steric barrier and sufficient electrostatic repulsion, preventing droplet coalescence against heating treatment as well as long-term storage. Moreover, the rheological behaviors of the HIPPEs can be tuned by the substitution degree (DS) of CMC for tailorable hydrophobic/hydrophilic properties of RCs, allowing their controllable injectability and printability during 3DP. The HIPPEs stabilized by RCs with a DS 1.2 showed the most favorable printing resolution, hardness, adhesiveness, and chewiness. Associating the hydrophobic RPs with hydrophilic CMC, our study enabled on-demand amphiphilicity of RCs for effective stabilization of HIPPEs that can be manipulated for 3DP.

Surface and Interface Engineering for Nanocellulosic Advanced Materials

How do trees support their upright massive bodies? The support comes from the incredibly strong and stiff, and highly crystalline nanoscale fibrils of extended cellulose chains, called cellulose nanofibers. Cellulose nanofibers and their crystalline parts-cellulose nanocrystals, collectively nanocelluloses, are therefore the recent hot materials to incorporate in man-made sustainable, environmentally sound, and mechanically strong materials. Nanocelluloses are generally obtained through a top-down process, during or after which the original surface chemistry and interface interactions can be dramatically changed. Therefore, surface and interface engineering are extremely important when nanocellulosic materials with a bottom-up process are fabricated. Herein, the main focus is on promising chemical modification and nonmodification approaches, aiming to prospect this hot topic from novel aspects, including nanocellulose-, chemistry-, and process-oriented surface and interface engineering for advanced nanocellulosic materials. The reinforcement of nanocelluloses in some functional materials, such as structural materials, films, filaments, aerogels, and foams, is discussed, relating to tailored surface and/or interface engineering. Although some of the nanocellulosic products have already reached the industrial arena, it is hoped that more and more nanocellulose-based products will become available in everyday life in the next few years.

Double-crosslinked cellulose nanofiber based bioplastic films for practical applications

While green bioplastic based on carbohydrate polymers have showed considerable promise, the methods typically used to prepare them in a single material have remained a significant challenge. In this study, a simple approach is proposed to fabricate high performance cellulose films composed of chemically and physically dual-crosslinked 2,2,6,6-tetramethylpiperidine-1-oxy-oxidized cellulose nanofibers (DC TEMPO-CNFs). The hydroxyl groups of TEMPO-CNF suspensions were firstly crosslinked chemically with epichlorohydrin (ECH), and subsequently TEMPO-CNF matrices were crosslinked physically via the strong electrostatic interaction between carboxylate and Ca²⁺ ions. It was found that the optimized DC TEMPO-CNF films exhibit a good transmittance (90 %) and a high tensile strength (303 MPa). Furthermore, these DC TEMPO-CNF films revealed superior thermal stability and excellent water resistance compared to neat TEMPO-CNF films without crosslinked domains. We believe that these results will pave the way to preparing practical polysaccharide bioplastics with simple, environmentally-friendly manufacturing processes.

Developing fibrillated cellulose as a sustainable technological material

Cellulose is the most abundant biopolymer on Earth, found in trees, waste from agricultural crops and other biomass. The fibres that comprise cellulose can be broken down into building blocks, known as fibrillated cellulose, of varying, controllable dimensions that extend to the nanoscale. Fibrillated cellulose is harvested from renewable resources, so its sustainability potential combined with its other functional properties (mechanical, optical, thermal and fluidic, for example) gives this nanomaterial unique technological appeal. Here we explore the use of fibrillated cellulose in the fabrication of materials ranging from composites and macrofibres, to thin films, porous membranes and gels. We discuss research directions for the practical exploitation of these structures and the remaining challenges to overcome before fibrillated cellulose materials can reach their full potential. Finally, we highlight some key issues towards successful manufacturing scale-up of this family of materials.

High Internal Phase Emulsion for Food-Grade 3D Printing Materials

Three-dimensional printing (3DP) has attracted significant attention for its use in additive manufacturing techniques because it provides customizability and flexibility for fabricating structures with arbitrary shapes. Certain applications in the food and medicine industries require 3D printable materials that are both biocompatible and biodegradable. Consequently, this study reports 3D printable materials constructed from food-grade high internal phase emulsions (HIPEs). The studied HIPEs (phase ratio 85%) were stabilized by the efficient adsorption behavior of cod proteins (concentration range, 10-50 mg mL^-1) at the oil-water interface. The stability of the oil-in-water HIPEs was improved by the formation of a concentration-dependent percentage of adsorbed proteins and cross-linking networks, and homogeneous and self-supporting structures were generated after 7 days of storage at 4 °C. The gel-like shear thinning rheological behavior induced by the cross-linking networks in the studied HIPEs can be tuned to obtain the desired printability and extrudability during 3DP. In the present study, the HIPEs stabilized with 50 mg mL^-1 of cod proteins exhibited the highest printing resolution, gel strength, hardness, adhesiveness, and chewiness during 3DP. These food-grade HIPE inks have the potential to diversify the applications of 3DP in foods, cosmetics, drug delivery systems, and packaging materials.

Material design of nanocellulose/polymer composites via Pickering emulsion templating

Cellulose nanofiber (CNF) is a crystalline fiber composed of a bundle of cellulose molecular chains and is expected to be used as a new biomass-derived nanomaterial. The CNF has a unique morphology: a few to tens of nanometer width and a submicrometer to micrometer length. Its application to various materials, in particular its utilization as a polymer reinforcing material, has been anticipated due to its excellent mechanical properties. However, CNFs and plastics are generally hard to mix, and thus, it is difficult to combine them at the nanolevel. In this review, we describe the CNF/polymer nanocompositing process from Pickering emulsion. We use ~3 nm-wide wood-derived CNFs and report on the preparation of CNF/polymer homogenous composite films. We also introduce a new type of CNF/polymer composite, a core-shell microparticle, using this Pickering emulsion as a template.

Optically Transparent Multiscale Composite Films for Flexible and Wearable Electronics

One of the key breakthroughs enabling flexible electronics with novel form factors is the deployment of flexible polymer films in place of brittle glass, which is one of the major structural materials for conventional electronic devices. Flexible electronics requires polymer films with the core properties of glass (i.e., dimensional stability and transparency) while retaining the pliability of the polymer, which, however, is fundamentally intractable due to the mutually exclusive nature of these characteristics. An overview of a transparent fiber-reinforced polymer, which is suggested as a potentially viable structural material for emerging flexible/wearable electronics, is provided. This includes material concept and fabrication and a brief review of recent research progress on its applications over the past decade.

Metal Mimics: Lightweight, Strong, and Tough Nanocomposites and Nanomaterial Assemblies

The ideal structural material would have high strength and stiffness with a tough ductile failure, all with a low density. Historically, no such material exists, and materials engineers have had to sacrifice a desired property during materials selection, with metals (high density), fiber composites (brittle failure), and polymers (low stiffness) having fundamental limitations on at least one front. The ongoing revolution of nanomaterials provides a potential route to build on the potential of fiber-reinforced composites, matching their strength while integrating toughening behaviors akin to metal deformations, all while using low-weight constituents. Here, the challenges, approaches, and recent developments of nanomaterials for structural applications are discussed, with an emphasis on improving toughening mechanisms, which is often the neglected factor in a field that chases strength and stiffness.

Preparation of Transparent and Thick CNF/Epoxy Composites by Controlling the Properties of Cellulose Nanofibrils

Cellulose nanofibrils (CNFs) have been used as reinforcing elements in optically transparent composites by combination with polymer matrices. In this study, strong, optically transparent, and thick CNF/epoxy composites were prepared by immersing two or four layers of CNF sheets in epoxy resin. The morphology of the CNF, the preparation conditions of the CNF sheet, and the grammage and layer numbers of the CNF sheets were controlled. The solvent-exchanged CNF sheets resulted in the production of a composite with high transparency and low haze. The CNF with smaller width and less aggregated fibrils, which are achieved by carboxymethylation, and a high number of grinding passes are beneficial in the production of optically transparent CNF/epoxy composites. Both the grammage and number of stacked layers of sheets in a composite affected the optical and mechanical properties of the composite. A composite with a thickness of 450-800 μm was prepared by stacking two or four layers of CNF sheets in epoxy resin. As the number of stacked sheets increased, light transmittance was reduced and the haze increased. The CNF/epoxy composites with two layers of low grammage (20 g/m²) sheets exhibited high light transmittance (>90%) and low haze (<5%). In addition, the composites with the low grammage sheet had higher tensile strength and elastic modulus compared with neat epoxy and those with high grammage sheets.

Highly recyclable and super-tough hydrogel mediated by dual-functional TiO2 nanoparticles toward efficient photodegradation of organic water pollutants

A novel photocatalytic hydrogel was prepared by loading TiO₂ nanoparticles (TiO₂ NPs) onto the surface of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized chitin nanofibers (TOCNs), which were further incorporated into the polyacrylamide (PAM) matrix. The resultant hydrogel exhibited a macro-porous structure with a low density (~1.45 g/cm³) and high water content (~80%). The well-dispersed TiO₂ NPs not only acted as a crosslinking agent for bridging the three-dimensional porous network structure, but also endowed the hydrogel with good catalytic activity. After the introduction of TiO₂ accounting for 10 wt% of the hydrogel mass, the hydrogels showed compressive strength of 1.46 MPa at 70% strain, tensile stress of 316 kPa, tensile strain of 310%, toughness of 47.25 kJ/m³ and fatigue resistance. Compared with neat TOCN-PAM hydrogel, the uniaxial compressive and tensile strengths of the TiO₂-TOCN-PAM10 hydrogel increased 6.35-fold and 3.70-fold, respectively. Furthermore, the removal of methyl orange (MO) was attributed to the synergistic effect of the adsorption and photocatalytic degradation of the hydrogels. The hydrogels adsorbed up to 8.5% of MO after 150 min of adsorption and a photocatalytic degradation rate of 97.3% achieved after 90 min of UV irradiation at pH = 2. Especially, the TiO₂-TOCN-PAM10 hydrogel exhibited excellent recycling performance: its MO removal efficiency was around 96% even after 10 reuse cycles. The as-prepared hydrogels, with characteristics of excellent stretchability, photocatalytic activity and recyclability, are expected to be used in alleviating organic pollutants in practical wastewater treatments.

Thermally Superstable Cellulosic-Nanorod-Reinforced Transparent Substrates Featuring Microscale Surface Patterns

The recent rapid expansion of thin-film, bendable, and wearable consumer (opto)electronics demands flexible and transparent substrates other than glass. Plastics are the traditional choice, but they require amelioration because of their thermal instability. Here, we report the successful conversion of a soft and thermally vulnerable polymer into a highly thermally stable transparent nanocomposite material. This is achieved by the meticulous choice of a polymer with a glass-transition temperature below 0 °C that gives stable mechanics above room temperature, reinforcing the polymer with a load-bearing hierarchical network of the incredibly strong and stable natural material: cellulose nanorods. Owing to the Pickering emulsification process, the nanocomposites inherit the self-assembled structural hierarchy from the cellulose nanorod-encapsulated resin droplets. The ameliorated nanocomposites have highly desirable high-temperature endurance (∼150-180 °C) in terms of the thermomechanical, thermodimensional, and thermo-optical performance. Any photonic nano- or microstructures can be directly molded on the surface of the nanocomposites in high precision for better light management in photonic and opto-electronic applications. The highlight of this work is the demonstration of a highly thermally stable microlens array on the ameliorated transparent nanocomposite.