Sandwich-Structured Mxene/Waste Polyurethane Foam Composites For Highly Efficient Electromagnetic Interference, Infrared Shielding and Joule Heating.

Electromagnetic interference (EMI) shielding and infrared (IR) stealth materials have attracted increasing attention owing to the rapid development of modern communication and military surveillance technologies. However, to realize excellent EMI shielding and IR stealth performance simultaneously remains a great challenge. Herein, a facile strategy is demonstrated to prepare high-efficiency EMI shielding and IR stealth materials of sandwich-structured MXene-based thin foam composites (M-W-M) via filtration and hot-pressing. In this composite, the conductive Ti3C2Tx MXene/cellulose nanofiber (MXene/CNF) film serves as the outer layer, which reflects electromagnetic waves and reduces the IR emissivity. Meanwhile, the middle layer is composed of a porous waste polyurethane foam (WPUF), which not only improves thermal insulation capacity but also extends electromagnetic wave propagation paths. Owing to the unique sandwich structure of "film-foam-film", the M-W-M composite exhibits a high EMI shielding effectiveness of 83.37 dB, and in the meantime extremely low emissivity (22.17%) in the wavelength range of 7-14 µm and thermal conductivity (0.19 W m-1 K-1), giving rise to impressive IR stealth performance at various surrounding temperatures. Remarkably, the M-W-M composite also shows excellent Joule heating properties, capable of maintaining the IR stealth function during Joule heating.

Structural, Optical, and Mechanical Insights into Cellulose Nanocrystal Chiral Nematic Film Engineering by Two Assembly Techniques.

Iridescent cellulose nanocrystal (CNC) films with chiral nematic nanostructures exhibit great potential in optical devices, sensors, painting, and anticounterfeiting applications. CNCs can assemble into a chiral nematic liquid crystal structure by evaporation-assisted self-assembly (EISA) and vacuum-assisted self-assembly (VASA) techniques. However, there is a lack of comprehensive examinations of their structure-property correlations, which are essential for fabricating materials with unique properties. In this work, we gained insights into the optical, mechanical, and structural differences of CNC films engineered using the two techniques. In contrast to the random self-assembly at the liquid-air interface in EISA, the continuous external pressure in the VASA process forces CNCs to assemble at the filter-liquid interface. This results in fewer defects in the interfaces between tactoids and highly ordered cholesteric phases. Owing to the distinct CNC assembly behaviors, the films prepared by these two methods show great differences in the nanostructure, microstructure, and macroscopic morphology. Consequently, the highly ordered cholesteric structure gives VASA-CNC films a more uniform structural color and enhanced mechanical performance. These fundamental understandings of the relationship of structure-property nanoengineering through various assembly techniques are essential for designing and constructing high-performance chiral iridescent CNC materials.

Chiroptical Nanocellulose Bio-Labels for Independent Multi-Channel Optical Encryption.

Advanced multiplexing optical labels with multiple information channels provide a powerful strategy for large-capacity and high-security information encryption. However, current optical labels face challenges of difficulty to realize independent multi-channel encryption, cumbersome design, and environmental pollution. Herein, multiplexing chiroptical bio-labels integrating with multiple optical elements, including structural color, photoluminescence (PL), circular polarized light activity, humidity-responsible color, and micro/nano physical patterns, are constructed in complex design based on host-guest self-assembly of cellulose nanocrystals and bio-gold nanoclusters. The thin nanocellulose labels exhibit tunable circular polarized structural color crossover the entire visible wavelength and circularly polarized PL with the highest-recorded dissymmetry factor up to 1.05 due to the well-ordered chiral organization of templated gold nanoclusters. Most importantly, these elements can independently encode customized anti-counterfeiting information to achieve five independent channels of high-level anti-counterfeiting, which are rarely achieved in traditional materials and design counterparts. Considering the exceptional seamless integration of five independent encryption channels and the recyclable features of labels, the bio-labels have great potential for the next generation anti-counterfeiting materials technology.

One-pot superhydrophilic surface modification of waste polyurethane foams for high-efficiency oil/water separation.

Despite of the fact that polymers have brought tremendous convenience to human life, they have also inevitably caused considerable environmental pollution after their service life. Therefore, a feasible strategy that can effectively recycle waste polymers and endow them with high added value is much desired. Superwetting materials have shown great promise in oily wastewater treatment because of their high oil/water separation efficiency. However, most of these materials present some limitations, such as complex preparation procedures and poor salt tolerance, which hamper their practical applications. In this study, an iron hydroxide@polydopamine@waste polyurethane foam (Fe(OH)3@PDA@WPU) was synthesized via a facile and mild "one-pot" reaction. During this process, polymerization of dopamine and in situ growth of Fe(OH)3 were simultaneously realized, and the resultant PDA and Fe(OH)3 nanoparticles were firmly attached to the surface of WPU. Due to the abundant hydrophilic groups from PDA and Fe(OH)3 coupled with the surface roughness created by Fe(OH)3 nanoparticles, the surface properties of the foam could be changed from hydrophobic to superhydrophilic. Remarkably, the Fe(OH)3@PDA@WPU was capable of separating various oil/water mixtures even under some severe conditions (e.g. erosion in a saturated sodium chloride solution and longtime sonication), demonstrating high potential in marine oily sewage treatment. Moreover, this work also paved a new path for reducing the negative impact of waste polymer foams on our environment, and in the meantime realizing their high value utilization.

Amyloid Fibril-Templated High-Performance Conductive Aerogels with Sensing Properties.

Amyloid fibrils have garnered increasing attention as viable building blocks for functional material design and synthesis, especially those derived from food and agricultural wastes. Here, amyloid fibrils generated from ß-lactoglobulin, a by-product from cheese industries, have been successfully used as a template for the design of a new class of high-performance conductive aerogels with sensing properties. These mechanically stable aerogels with three-dimensional porous architecture have a large surface area (≈159 m2 g-1), low density (≈0.044 g cm-3), and high electrical conductivity (≈0.042 S cm-1). A pressure sensing device is developed from these aerogels based on their combined electrical conductivity and compressible properties. More interestingly, these aerogels can be employed to design novel enzyme sensors by exploiting the proteinaceous nature of amyloid fibrils. This study expands the scope of structured amyloid fibrils as scaffolds for in situ polymerization of conducting polymers, offering new opportunities to design materials with multiple functionalities.

Self-Healing Sensors Based on Dual Noncovalent Network Elastomer for Human Motion Monitoring.

Nowadays, it is still a challenge to prepare flexible sensors with great mechanical strength, stretchability, high sensitivities, and excellent self-healing (SH) abilities. Herein, a nanostructured supramolecular elastomer is reported with a dual noncovalent network of hydrogen bonding interactions and metal-ligand coordination. The resultant flexible sensor presents ultrafast (30 s), autonomous, and repeatable SH ability with high healing efficiency (80% after the 3rd healing process), as well as enhanced mechanical properties. Benefitting from the 3D conductive network, the sensor exhibits high electrical sensitivity and very low detection limit (0.2% strain). As a result, the flexible sensor is capable of precisely monitoring small strains of human motions (such as vocal-cord vibration), and exhibits reproducible and recognizable current signals after cutting-healing process. The dual noncovalent network design proposed here opens up a new opportunity for scalable fabrication of high performance SH sensors and other electronic devices.

Hierarchically structured composites for ultrafast liquid sensing and smart leak-plugging.

Conductive polymer composites (CPCs) have been intensively exploited as remarkable liquid sensing materials based on variations in their conductivity under liquid stimuli. However, most advances in liquid sensing CPCs are limited to bulk materials. Due to the slow permeation of liquids into the compact CPCs, sluggish responses are inevitable for most existing CPC-based liquid sensing materials. Here, we developed a new class of liquid sensing materials via a hierarchical structure design. Specifically, a thin CPC layer with a segregated conductive network was coated on porous polyurethane (PU) skeletons by layer-by-layer assembly, forming an elaborately designed hierarchical structure in the prepared CPC@PU composites. With this hierarchical structure, the CPC@PU composites exhibited ultrafast responses (0.05-0.15 s) to solvent stimuli, which are ∼3 orders of magnitude faster than the state-of-the-art composites. After liquid sensing, quick regeneration (within 10 s) could be achieved under hot-air. Accordingly, organic liquid and gas sensors and liquid-sensing electronic skins were fabricated. Furthermore, we prepared smart and fast leak-plugging materials using the CPC@PU composites based on the swelling-induced blocking of micropores in the materials. This structural strategy proposed here opens up exciting avenues towards manufacturing real-time liquid sensing and plugging materials, revealing potential applications in oilfield exploitation, solvent storage/transportation, environmental monitoring, etc.

Multiple Hydrogen Bonding Enables the Self-Healing of Sensors for Human-Machine Interactions.

Despite its widespread use in signal collection, flexible sensors have been rarely used in human-machine interactions owing to its indistinguishable signal, poor reliability, and poor stability when inflicted with unavoidable scratches and/or mechanical cuts. A highly sensitive and self-healing sensor enabled by multiple hydrogen bonding network and nanostructured conductive network is demonstrated. The nanostructured supramolecular sensor displays extremely fast (ca. 15 s) and repeatable self-healing ability with high healing efficiency (93 % after the third healing process). It can precisely detect tiny human motions, demonstrating highly distinguishable and reliable signals even after cutting-healing and bending over 20 000 cycles. Furthermore, a human-machine interaction system is integrated to develop a facial expression control system and an electronic larynx, aiming to control the robot to assist the patient's daily life and help the mute to realize real-time speaking.

Tailoring percolating conductive networks of natural rubber composites for flexible strain sensors via a cellulose nanocrystal templated assembly.

Conductive polymer composites (CPCs) just above the percolation threshold exhibit a unique strain-reversible electric response upon application of tensile strain, which can be used to prepare strain sensors. However, it is difficult to balance the electric conductivity which is fundamental to a stable output signal and the strain sensing sensitivity due to the relatively dense conductive pathways of the traditional CPCs. Constructing a "brittle" but effective conductive network structure in CPCs is the essential foundation of a desirable sensing material. Here, we demonstrate for the first time that highly flexible, stretchable, sensitive, and reversible strain sensors can be fabricated by a facile latex assembly approach, in which nontoxic, sustainable and biodegradable cellulose nanocrystals played a key role in tailoring the percolating network of conductive natural rubber (NR)/carbon nanotube (CNT) composites. The resulting nanocomposites with a continuous 3D conductive structure exhibited a very low electrical conductivity percolation threshold (4-fold lower than that of the conventional NR/CNT composites), high resistivity and sensitivity (gauge factor ≈ 43.5) and meanwhile good reproducibility of up to 100% strain. The proposed materials and principles in this study open up a novel practical approach to design high performance flexible sensors for a broad range of multifunctional applications.

Uniaxially aligned electrospun all-cellulose nanocomposite nanofibers reinforced with cellulose nanocrystals: scaffold for tissue engineering.

Uniaxially aligned cellulose nanofibers with well oriented cellulose nanocrystals (CNCs) embedded were fabricated via electrospinning using a rotating drum as the collector. Scanning electron microscope (SEM) images indicated that most cellulose nanofibers were uniaxially aligned. The incorporation of CNCs into the spinning dope resulted in more uniform morphology of the electrospun cellulose/CNCs nanocomposite nanofibers (ECCNN). Polarized light microscope (PLM) and transmission electron microscope (TEM) showed that CNCs dispersed well in ECCNN nonwovens and achieved considerable orientation along the long axis direction. This unique hierarchical microstructure of ECCNN nonwovens gave rise to remarkable enhancement of their physical properties. By incorporating 20% loading (in weight) of CNCs, the tensile strength and elastic modulus of ECCNN along the fiber alignment direction were increased by 101.7 and 171.6%, respectively. Their thermal stability was significantly improved as well. In addition, the ECCNN nonwovens were assessed as potential scaffold materials for tissue engineering. It was elucidated from MTT tests that the ECCNN were essentially nontoxic to human cells. Cell culture experiments demonstrated that cells could proliferate rapidly not only on the surface but also deep inside the ECCNN. More importantly, the aligned nanofibers of ECCNN exhibited a strong effect on directing cellular organization. This feature made the scaffold particularly useful for various artificial tissues or organs, such as blood vessel, tendon, nerve, and so on, in which cell orientation was crucial for their performance.

Biomimetic Mechanically Robust Chiroptical Hydrogel Enabled by Hierarchical Bouligand Structure Engineering.

Natural bouligand structures enable crustacean exoskeletons and fruits to strike a combination of exceptional mechanical robustness and brilliant chiroptical properties owing to multiscale structural hierarchy. However, integrating such a high strength-stiffness-toughness combination and photonic functionalities into synthetic hydrogels still remains a grand challenge. In this work, we report a simple yet general biomimetic strategy to construct an ultrarobust chiroptical hydrogel by closely mimicking the natural bouligand structure at multilength scale. The hierarchical structural engineering of long-range ordered cellulose nanocrystals' bouligand structure, well-defined poly(vinyl alcohol) nanocrystalline domains, and dynamic interfacial interaction synergistically contributes to the integration of high strength (23.3 MPa), superior modulus (264 MPa), and high toughness (54.7 MJ m-3), as well as extraordinary impact resistance, which far exceed their natural counterparts and synthetic photonic hydrogels. More importantly, seamless chiroptical and solvent-responsive patterns with high resolution can also be scalably integrated into the hydrogel by localized manipulation of the photonic band, while maintaining good ionic conductivity. Such exceptional mechanical-photonic combination holds tremendous potential for applications in wearable sensors, encryption, displays, and soft robotics.

Diverse immune responses in vaccinated individuals with and without symptoms after omicron exposure during the recent outbreak in Guangzhou, China.

Objectives: During the recent wave of coronavirus disease 2019 (COVID-19) infections in China, most individuals have been vaccinated and exposed to the omicron variant. In the present study, two cohorts were observed in the vaccinated population: vaccinated individuals with symptoms (VIWS) and those without symptoms (VIWOS). Our study aimed to characterize the antibody response in two cohorts: VIWS and VIWOS. Methods: A questionnaire survey was conducted in the community. Blood and saliva samples were collected from 124 individuals in the VIWS and VIWOS cohorts. Capture enzyme-linked immunosorbent assay (ELISA) was performed to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific antibodies. Results: The questionnaire survey revealed that 30.0 % (302/1005) of individuals in the older adult group (≥65 years) experienced no symptoms, whereas the rate of individuals without symptoms in the younger group (<65 years) was 17.8 % (166/932). Nucleocapsid (N)-specific IgM (N-IgM) was detected in the blood samples at a rate of 69.2 % (54/78) in the VIWS cohort. The positivity rate for N-specific IgA (N-IgA) was 93.6 % (73/78). In addition, the positivity rates of spike (S)-specific IgA (S-IgA) and N-IgA detected in saliva samples were 42 % (21/50) and 54 % (27/50), respectively. Both N-IgA positivity and negativity were observed in the VIWOS cohort. The detection rate of N-IgM positivity was 57.1 % (12/21) in the N-IgA-positive group. In addition, 54.3 % (25/46) of the vaccinated individuals without symptoms were IgA-negative. Conclusions: Our study indicates that substantial N-specific antibodies were induced during omicron infection and that testing for N-IgA in both blood and saliva may aid in the diagnosis of SARS-CoV-2 infection in vaccinated populations.

Facile fabrication of 3D Janus foams of electrospun cellulose nanofibers/rGO for high efficiency solar interface evaporation.

Solar-powered interfacial evaporation is one of the most efficient state-of-the-art technologies for producing clean water via desalination. Herein, we report a novel bio-based nanofibrous foam for high efficiency solar interface evaporation. To this end, a hybrid membrane of cellulose nanofibers/graphene oxide (GO) is first fabricated by electrospinning coupled with in situ layer-by-layer self-assembly technique. After that, the membrane is subjected to a foaming process in an aqueous NaBH4, which effectively transforms the 2D membrane into a 3D foam. This structure can improve the photothermal conversion efficiency and also facilitate the water transport at the gas-water interface. In the meantime, the GO is converted to the reduced GO (rGO) with a higher light absorption efficiency. Finally, one side of the foam is hydrophobically modified via spray-coating with a fluorocarbon resin (FR) to obtain the Janus type 3D foam, namely FR@EC/rGO. The resultant 3D foam combines the functions of solar energy absorption in the upper layer and water pumping capability in the lower layer. It exhibits an extraordinary solar vapor conversion efficiency of 94.2 % and a fast evaporation rate of 1.83 kg m-2 h-1, showing high potential in future seawater desalination.

Facile fabrication of three-dimensional nanofibrous foams of cellulose@g-C3N4@Cu2O with superior visible-light photocatalytic performance.

In this work, a unique three-dimensional nanofibrous foam of cellulose@g-C3N4@Cu2O was prepared via electrospinning followed by a foaming process. A cellulose solution in DMAc/LiCl containing g-C3N4 and CuSO4 was applied for electrospinning, while aqueous alkali was used as the coagulation bath. The solidification of electrospun cellulose/g-C3N4 nanofibers would be accompanied with in-situ formation of Cu(OH)2 nanoparticles. Interestingly, the hydrogen gas (H2) generated from NaBH4 could transform the two-dimensional membrane into a three-dimensional foam, leading to the increased specific surface area and porosity of the material. Meanwhile, the Cu(OH)2 nanoparticles attached on the electrospun nanofibers were reduced to Cu2O to form a p-n heterostructure between Cu2O and g-C3N4. The as-prepared cellulose@g-C3N4@Cu2O foam exhibited a high degradation efficiency (99.5 %) for the dye of Congo Red under visible light radiation. And ·O2- was discovered to be the dominant reactive species responsive for dye degradation. Moreover, the cellulose@g-C3N4@Cu2O could maintain its initial degradation efficiency even after seven cycles of reuse, suggesting the excellent stability and cycling performance.

Acidic deep eutectic solvent assisted mechanochemical delignification of lignocellulosic biomass at room temperature.

Lignocellulosic biomass is the most abundant natural polymer on Earth, but the efficient fractionation and refinery of all its components remain challenging. Acidic deep eutectic solvents refining is a promising method, while it is likely to cause lignin condensation and carbohydrates degradation, especially at server operation conditions. Here we propose the use of acidic deep eutectic solvent (DES), choline chloride/p-toluenesulfonic acid assisted mechanochemical pretreatment (DM) for efficient lignocellulose fractionation at mild condition. Four representative lignocellulose, wheat straw, moso bamboo, poplar wood and pine wood were selected at varied milling time (3, 6 h) to assess the fractionation ability of this strategy. This DM pretreatment demonstrated a rather high cellulose retentions (∼90 %) and extent of delignification for wheat straw and bamboo biomass, which corresponds to a high extent of enzymatic hydrolysis (∼75.5 %) for sugar platform pursuing. The extracted lignin showed rather high content of ß-O-4' leakages due to the swelling effect of deep eutectic solvent and mild operation conditions. This work provided a promising strategy to fractionate lignocellulose using deep eutectic solvents with the goal of simultaneous cellulose hydrolysis and reactive lignin obtaining that is usually difficult to realize using traditional chemical fractionation approach.

Bioinspired Stabilization of Amorphous Calcium Carbonate by Carboxylated Nanocellulose Enables Mechanically Robust, Healable, and Sensing Biocomposites.

Nature builds numerous structurally complex composites with fascinating mechanical robustness and functionalities by harnessing biopolymers and amorphous calcium carbonate (ACC). The key to successfully mimicking these natural designs is efficiently stabilizing ACC, but developing highly efficient, biodegradable, biocompatible, and sustainable stabilizing agents remains a grand challenge since anhydrous ACC is inherently unstable toward crystallization in the wet state. Inspired by the stabilized ACC in crustacean cuticles, we report the efficient stabilization ability of the most abundant biopolymer-cellulose nanofibrils (CNFs) for ACC. Through the cooperative stabilizing effect of surface carboxyl groups and a rigid segregated network, the CNFs exhibit long-term stability (more than one month) and achieved a stabilization efficiency of 3.6 and 4.4 times that of carboxymethyl cellulose (CMC) and alginate, respectively, even higher than poly(acrylic acid). The resulting CNF/ACC dispersions can be constructed into transparent composite films with the high strength of 286 MPa and toughness up to 28.5 MJ/m3, which surpass those of the so far reported synthetic biopolymer-calcium carbonate/phosphate composites. The dynamic interfacial interaction between nanocomponents also provides the composite films with good self-healing properties. Owing to their good wet stability, the composite films present high humidity sensitivity for monitoring respiration and finger contact.

Interfacial Electrostatic Self-Assembly of Amyloid Fibrils into Multifunctional Protein Films.

Amyloid fibrils have generated steadily increasing traction in the development of natural and artificial materials. However, it remains a challenge to construct bulk amyloid films directly from amyloid fibrils due to their intrinsic brittleness. Here, a facile and general methodology to fabricate macroscopic and tunable amyloid films via fast electrostatic self-assembly of amyloid fibrils at the air-water interface is introduced. Benefiting from the excellent templating properties of amyloid fibrils for nanoparticles (such as conductive carbon nanotubes or magnetic Fe3 O4 nanoparticles), multifunctional amyloid films with tunable properties are constructed. As proof-of-concept demonstrations, a magnetically oriented soft robotic swimmer with well-confined movement trajectory is prepared. In addition, a smart magnetic sensor with high sensitivity to external magnetic fields is fabricated via the combination of the conductive and magnetic amyloid films. This strategy provides a convenient, efficient, and controllable approach for the preparation of amyloid-based multifunctional films and related smart devices.

Sustainable Starch/Lignin Nanoparticle Composites Biofilms for Food Packaging Applications.

Construction of sustainable composite biofilms from natural biopolymers are greatly promising for advanced packaging applications due to their biodegradable, biocompatible, and renewable properties. In this work, sustainable advanced food packaging films are developed by incorporating lignin nanoparticles (LNPs) as green nanofillers to starch films. This seamless combination of bio-nanofiller with biopolymer matrix is enabled by the uniform size of nanofillers and the strong interfacial hydrogen bonding. As a result, the as-prepared biocomposites exhibit enhanced mechanical properties, thermal stability, and antioxidant activity. Moreover, they also present outstanding ultraviolet (UV) irradiation shielding performance. As a proof of concept in the application of food packaging, we evaluate the effect of composite films on delaying oxidative deterioration of soybean oil. The results indicate our composite film could significantly decrease peroxide value (POV), saponification value (SV), and acid value (AV) to delay oxidation of soybean oil during storage. Overall, this work provides a simple and effective method for the preparation of starch-based films with enhanced antioxidant and barrier properties for advanced food packaging applications.

Bioinspired Chiral Template Guided Mineralization for Biophotonic Structural Materials.

Nature provides numerous biomineral design inspirations for constructing structural materials with desired functionalities. However, large-scale production of damage-tolerant Bouligand structural materials with biologically comparable photonics remains a longstanding challenge. Here, an efficient and scalable artificial molting strategy, based on self-assembly of cellulose nanocrystals and subsequent mineralization of amorphous calcium carbonate, is developed to produce biomimetic materials with an exceptional combination of mechanical and photonic properties that are usually mutually exclusive in synthetic materials. These biomimetic composites exhibit tunable mechanics from "strong and flexible", which exceeds the benchmark of natural chiral materials, to "stiff and hard", which is comparable to natural and synthetic counterparts. Especially, the biomimetic composites possess ultrahigh stiffness of 2 GPa in their fully water-swollen state-a value well beyond hydrated crab exoskeleton, cartilage, tendon, and stiffest synthetic hydrogels, combined with exceptional strength and resilience. Additionally, these composites are distinguished by the tunable chiral structural color and water-triggered switchable photonics that are absent in most artificial mineralized materials, as well as unique hydroplastic properties. This study opens the door for a scalable synthesis of resilient biophotonic structural materials in practical bulk form.

Mechanically Strong and Electrically Conductive Polyethylene Oxide/Few-Layer Graphene/Cellulose Nanofibrils Nanocomposite Films.

In this work, a cellulose nanofibrils (CNFs)/few-layer graphene (FLG) hybrid is mechanically stripped from bamboo pulp and expanded graphene (EG) using a grinder. This strategy is scalable and environmentally friendly for high-efficiency exfoliation and dispersion of graphene in an aqueous medium. The in situ-generated CNFs play a key role in this process, acting as a "green" dispersant. Next, the obtained CNFs-FLG is used as a functional filler in a polyoxyethylene (PEO) matrix. When the composition of CNFs-FLG is 50 wt.%, the resultant PEO/CNFs-FLG nanocomposite film exhibits a Young's modulus of 1.8 GPa and a tensile strength of 25.7 MPa, showing 480% and 260% enhancement as compared to those of the pure PEO film, respectively. Remarkably, the incorporation of CNFs-FLG also provides the nanocomposite films with a stunning electrical conductivity (72.6 S/m). These attractive features make PEO/CNFs-FLG nanocomposite films a promising candidate for future electronic devices.