Lightweight and robust cellulose/MXene/polyurethane composite aerogels as personal protective wearable devices for electromagnetic interference shielding.

The increasing electromagnetic pollution is urgently needed as an electromagnetic interference shielding protection device for wearable devices. Two-dimensional transition metal carbides and nitrides (MXene), due to their interesting layered structure and high electrical conductivity, are ideal candidates for constructing efficient conductive networks in electromagnetic interference shielding materials. In this work, lightweight and robust cellulose/MXene/polyurethane composite aerogels were prepared by mixing cellulose nanofiber (CNF) suspensions with MXene, followed by freeze-drying and coating with polyurethane. In this process, CNF effectively assembled MXene nanosheets into a conductive network by enhancing the interactions between MXene nanosheets. The prepared aerogel exhibited the shielding effectiveness of 48.59 dB in the X-band and an electrical conductivity of 0.34 S·cm-1. Meanwhile, the composite aerogel also possessed excellent thermal insulation, infrared stealth, mechanical and hydrophobic properties, and can be used as a wearable protective device to protect the human body from injuries in different scenarios while providing electromagnetic interference shielding protection.

Preparation of high antioxidant nanolignin and its application in cosmetics.

Lignin, as a natural polyphenol, displays anti-oxidant activity by trapping and binding free radicals through its free phenolic hydroxyl groups. However, the most accessible form, industrial lignins, generally has low phenolic hydroxyl content, which severely limits their application value and scenarios. Herein, we showed that potassium-glycerate deep eutectic solvent (PG-DES) treatment can be combined with laccase oxidation to afford prepared high antioxidant lignin nanoparticles (HA-LNPs) with notably improved anti-oxidant activities benefiting from both the enhanced phenolic hydroxyl content 170.8 % and reduced average particle size (59.0 nm). At concentrations as low as 60 µg/mL, HA-LNPs showed favorable effects in promoting collagen formation. When HA-LNPs were used as an active ingredient in the anti-aging mask formulation, the reactive oxygen species (ROS) scavenging activity of mask samples containing 0.4 % HA-LNPs reached 37.2 %. The data suggest great promise of HA-LNPs as a natural antioxidant for formulating in anti-aging skin care products.

Green, chemical-free, and high-yielding extraction of nanocellulose from waste cotton fabric enabled by electron beam irradiation.

Recycling and high-value reutilization of waste cotton fabrics (WCFs) has attracted a widespread concern. One potential solution is to extract nanocellulose. Sulfuric acid hydrolysis is a conventional method for the production of nanocellulose with high negative charge from WCFs. However, the recycling and disposal of chemicals in nanocellulose production, along with low yields, remain significant challenges. Consequently, there is a pressing need for a sustainable method to produce nanocellulose at higher yield without the use of chemicals. Herein, we propose a green, sustainable and chemical-free method to extract nanocellulose from WCFs. The nanocellulose displayed a rod-like shape with a length of 50-300 nm, a large aspect ratio of 18.4 ± 2 and the highest yield of up to 89.9 %. The combined short-time and efficient two-step process, involving electron beam irradiation (EBI) and high-pressure homogenization (HPH), offers a simple and efficient alternative approach with a low environmental impact, to extract nanocellulose. EBI induced a noticeable degradation in WCFs and HPH exfoliated cellulose to nano-size with high uniformity via mechanical forces. The as-prepared nanocellulose exhibits excellent emulsifying ability as the Pickering emulsion emulsifier. This work provides a facile and efficient approach for nanocellulose fabrication as well as a sustainable way for recycle and reutilization of the waste cotton fabrics.

Electrothermal Phase Change Composite with Flexibility over a Wide Temperature Range for Wearable Thermotherapy.

Flexible electrothermal composite phase change materials (PCMs) are promising candidates for portable thermotherapy. However, a great challenge remains to achieve high PCM loading while maintaining reasonable flexibility. Herein, the polypyrrole-decorated melamine foam (PPy@MF) was fabricated and thereafter applied to confine binary PCM mixtures composed of a high-enthalpy long-chain polyethylene glycol (PEG4000) and its short-chain homologue (PEG200) to make the novel PPy@MF-PEG4000+200 composite PCM. At a high loading of up to 74.1% PEG4000 and a high latent heat energy storage density of 150.1 J/g, the composite PCM remained flexible at temperature (-20 °C) far below its phase transition point thanks to the plasticine effect of PEG200. The composite also demonstrated good Joule heating performance, providing fast heating from 28 to 70 °C at low applied voltages (4.5-6.0 V). The energy could be stored efficiently and released to maintain the composites at the proper temperature. The electrothermal performance of the composite remained undisturbed during curved or repeated bending, showing good potential to be used for personal thermal management and thermotherapy.

A one-pot approach to prepare stretchable and conductive regenerated silk fibroin/CNT films as multifunctional sensors.

Silk fibroin (SF)-based materials are characterized by their outstanding biocompatibility and biodegradability and are considered as the most promising candidates for next-generation flexible electronics. In order to generate such devices, SF can be mixed with carbon nanotubes (CNTs) which feature excellent mechanical, electrical, and thermal properties. However, obtaining regenerated SF with homogeneous dispersion of CNTs in a sustainable manner represents a challenging task, mainly due to the difficulty in overcoming van der Waals forces and strong π-π interactions that hold together the CNT structure. In this study, a one-pot strategy for fabricating SF/CNT films is proposed by designing SF as a modifier of CNTs through non-covalent interactions with the assistance of aqueous phosphoric acid solution. Glycerol (GL) was introduced, endowing the SF/GL/CNT composite film with excellent flexibility and stretchability. The sustainable strategy greatly simplifies the preparation process, avoiding dialysis of SF and the use of artificial dispersants. The as-fabricated SF/GL/CNT films showed an excellent mechanical strength of 1.20 MPa and high sensitivity with a gauge factor of up to 13.7 toward tensile deformation. The composite films had a sensitive monitoring capability for small strains with detection limits as low as 1% and can be assembled into versatile sensors to detect human movement. Simultaneously, the composite films showed a superb thermosensitive capacity (1.64% °C-1), which satisfied the requirement of real-time and continuous skin temperature monitoring. We anticipate that the presented one-pot strategy and the prepared composite films could open a new avenue for forthcoming technologies for electronic skins, personal health monitoring, and wearable electronics.

High-tensile chitin films regenerated from cryogenic aqueous phosphoric acid.

The abuse of non-renewable fossil resources and the resulting plastic pollution have posed a great burden on the environment. Fortunately, renewable bio-macromolecules have shown great potential to replace synthetic plastics in fields ranging from biomedical applications, and energy storage to flexible electronics. However, the potential of recalcitrant polysaccharides, such as chitin, in the above-mentioned fields have not been fully exploited because of its poor processability, which is ultimately due to the lack of suitable, economical, and environmentally friendly solvent for it. Herein, we demonstrate an efficient and stable strategy for the fabrication of high-strength chitin films from concentrated chitin solutions in cryogenic 85 wt% aqueous phosphoric acid (aq. H3PO4). The regeneration conditions, including the nature of the coagulation bath and its temperature are important variables affecting the reassembly of chitin molecules and hence the structure and micromorphology of the films. Uniaxial orientation of the chitin molecules by applying tension to the RCh hydrogels further endows the films with enhanced mechanical properties of up to 235 MPa and 6.7 GPa in tensile strength and Young's modulus, respectively.

Highly stretchable porous regenerated silk fibroin film for enhanced wound healing.

Silk fibroin (SF) has received interest in tissue engineering owing to its biocompatibility, biodegradability, and favorable mechanical properties. However, the complex preparation, brittleness, and lack of pores in the structure of the silk fibroin film limit its application. Herein, we show that facile dissolution of SF in aqueous phosphoric acid followed by regeneration in aqueous ammonium sulfate ((NH4)2SO4) could afford highly stretchable films with nano-pores formed in the nonsolvent-induced phase separation process. The named phase separation, which determines the morphology and mechanical properties of the regeneration silk fibroin (RSF) films, is highly dependent on the (NH4)2SO4 concentration as well as the initial concentration of the SF solution. Therefore, the RSF films exhibit a tunable pore size ranging from 230 to 510 nm and excellent stretchability with tensile strain up to 143 ± 16%. Most interestingly, the RSF films were shown to support the proliferation of human skin fibroblasts in vitro as well as speed up full-thickness skin wound healing in a rat model. This work establishes an easy and feasible method to access porous RSF membranes that can be used for wound dressing in clinical settings.

Composite hydrogel based oxidated sodium carboxymethyl cellulose and gelatin loaded carboxymethylated cotton fabric for hemostasis and infected wound treatment.

The fabric-based wound dressings are hard to maintain a moist environment for wound healing while the hemostatic property and gas permeability of some hydrogel-based wound dressings are not ideal. This study first put forward a strategy of checkerboard-pattern wound dressing: 1) preparing the base fabric with hemostatic property, 2) printing multifunctional hydrogels onto one side of the base fabric to form checkerboard patterns, 3) modifying the other side of the base fabric to be hydrophobic. In this manner, the composite dressing not only maintained the advantages of hydrogels, but also inherited good mechanical property, hemostatic property, and gas permeability from the base fabric. Here, the cotton fabric was carboxymethylated to be MCF. To obtain multifunctional hydrogel, sodium carboxymethylcellulose was oxidated to introduce aldehyde groups to form Schiff base with amino groups in gelatin, besides, dopamine and Ag nanoparticles were introduced to endow the hydrogel with antioxidant property and antibacterial activity. The multifunctional hydrogel was printed onto one side of MCF, subsequently, the deposition of paraffin made the other side of this dressing become hydrophobic. The good performance of the obtained dressing in hemostatic process and wound healing demonstrated its potential in the field of wound treatment.

Morphology-Controlled Synthesis of Polyphosphazene-Based Micro- and Nano-Materials and Their Application as Flame Retardants.

Common flame retardants, such as halogen-based materials, are being phased-out owing to their harmful environmental and health effects. We prepared poly-(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS) microspheres, nanotubes, capsicum-like nanotubes, and branched nanotubes as flame retardants. An increase in reaction temperature changed the morphology from nanotubes to microspheres. A PZS shape had a positive effect on the flame retardancy of polyethylene terephthalate (PET). The PZS with a capsicum-like nanotube morphology had the best flame retardancy, and the PET limiting oxygen index increased from 25.2% to 34.4%. The flame retardancy capability was followed by PZS microspheres (33.1%), branched nanotubes (32.8%), and nanotubes (32.5%). The capsicum-like nanotubes promote the formation of highly dense and continuous carbon layers, and they release a non-combustible gas (CO2). This study confirms polyphosphazene-based flame retardants as viable and environmentally-friendly alternatives to common flame retardants. It also presents a novel and facile design and synthesis of morphology-controlled nanomaterials with enhanced flame retardant properties.

Integrated Janus cellulosic composite with multiple thermal functions for personalized thermal management.

The effective integration of multiple thermal functions into one material is highly attractive in personal thermal management, taking the complex application environment into consideration. Herein, a multifunctional Janus cellulosic composite encompassing superior electrical heating, energy storage, thermal insulation, and infrared camouflage performance was firstly developed by integrating Janus cellulose nanofibers (CNF) aerogel, polypyrrole (PPy), and polyethylene glycol (PEG). In practice, the active heating-thermal regulation layer (PPy@CNFphilic-PEG) of multifunctional Janus cellulosic composite is faced inward to provide heating on-demand through the joint action of the electrically conductive PPy and thermally regulative PEG. The outward-facing hydrophobic aerogel layer (CNFphobic) serves as the thermal insulator, which simultaneously enables infrared camouflage by reducing heat loss to the environment via infrared radiation. This work presents an effective and facile strategy toward multifunctional Janus materials for efficient personal thermal management, showing great promise for potential applications, such as thermal comfort, infrared camouflage, and security protection.

Antibacterial thyme oil-loaded zwitterionic emulsion hydrogels.

Emulsion hydrogels are structurally composite materials combining the advantages of emulsions and hydrogels with the ability to accommodate hydrophobic and hydrophilic components in one system. It is a promising strategy for the excellent encapsulation and delivery of many bioactive ingredients. In this work, the thyme oil-loaded zwitterionic emulsion hydrogels are constructed by the cellulose acetoacetate-horseradish peroxidase-hydrogen peroxide-initiated (CAA-HRP-H2O2-initiated) ternary enzyme-mediated polymerization of the thyme oil-in-water (O/W) emulsions stabilized by cellulose acetoacetate (CAA). CAA is the key component in the system, acting as the emulsifier and the polymerization mediator simultaneously. The formed zwitterionic poly(sulfobetaine methacrylate) (PSBMA) hydrogel network provides emulsion hydrogels with good hydration capacity and potential anti-fouling performance. The thyme oil-loaded zwitterionic emulsion hydrogels exhibit interconnected, uniform, and adjustable porous structures with tunable mechanical properties, antifouling performance, good biocompatibility, and excellent antibacterial activity against S. aureus and E. coli. These results all demonstrate that the ternary enzyme-mediated polymerization of zwitterionic monomers in the continuous phase of O/W emulsion templates is a facile and efficient strategy to encapsulate hydrophobic bioactive ingredients.

High-tensile regenerated cellulose films enabled by unexpected enhancement of cellulose dissolution in cryogenic aqueous phosphoric acid.

We have demonstrated, for the first time, high-efficient non-destructive and non-derivative dissolution of cellulose could be achieved in cryogenic aqueous phosphoric acid. Cellulose from different sources and of varying degree of polymerization from 200 (MCC) to 2200 (cotton fabric) could be dissolved completely to afford solutions containing 5 wt%-18 wt% cellulose, from which ultra-strong and tough cellulose films of tensile strength as high as 707 MPa could be obtained using water as the coagulant. These solutions can be stored at -18 °C for extended time without noticeable degradation while desired degree of polymerization is also attainable by tuning the storage conditions. The findings of this work call for renewal attention on phosphoric acid as a promising cellulose solvent for being non-toxic, non-volatile, easy to handle, and cost-effective.

A Nature-Inspired Monolithic Integrated Cellulose Aerogel-Based Evaporator for Efficient Solar Desalination.

Solar-driven seawater desalination is a prospective approach to tackle the problem of freshwater shortage. Establishing a robust, efficient solar-thermal water evaporator with great salt-resistance through a facile and scalable fabrication technique is still a challenge. In this study, a floatable and robust monolithic integrated cellulose aerogel-based evaporator (MiCAE) with high performance is fabricated by carefully designing and integrating three functional components, namely, a hydrophilic cellulose-PVA aerogel (CPA), hydrophobic silylated cellulose aerogel (SCA), and multiwalled carbon nanotube (MCNT) coating layer (CPA@CNT), through the heterogeneous mixing and freeze-drying aerogel fabrication step in situ. Inspired by woods and mushrooms, the incorporation of SCA with mushroom-shaped CPA possessing wood-like structures in MiCAE can realize heat localization and effectively suppress irreversible heat dissipation. Meanwhile, CPA endows the evaporator with the rapid water transportation and great salt excretion capability because of its low-tortuosity porous structure. Thanks to the synergistic effect of the integrated functional structures, in the highly concentrated brine (17.5 wt %), the MiCAE can still realize the combination of high efficiency and obvious salt-resistance behavior. This work offers a facile, efficient salt-resistance solution for seawater desalination.

Self-healing and acidochromic polyvinyl alcohol hydrogel reinforced by regenerated cellulose.

Recently, integration of self-healing, color-tunable, sol-gel converted properties into hydrogel has attracted interest for preparing a reinforced multifunctional hydrogel. Herein, acidochromic regenerated cellulose (ARC) was incorporated into the polyvinyl alcohol/borax (PB) matrix for constructing a tough, self-healing, multicolor and sol-gel converted smart hydrogel (PB/ARC). The mechanical properties of PB/ARC hydrogel were improved after introducing ARC, which could bear a weight of 200 g and had high maximum tensile strength (6.8 times) and compressive strength (2.3 times). PB/ARC hydrogel automatically fused within 15 s after being cut and quickly recovered to the original state after being subjected to high shear strain, showing excellent self-healing ability. The color of hydrogel could be tuned between yellow and purple by altering pH values (5-12). In addition, PB/ARC hydrogel exhibited reversible sol-gel conversion in response to the change of acidity and alkalinity. This study offers a new and facile strategy for developing multifunctional smart hydrogel.

In situ growth of CuS NPs on 3D porous cellulose macrospheres as recyclable biocatalysts for organic dye degradation.

Aiming at recyclable catalyst carriers, porous cellulose macrospheres from wood pulp dissolved in an alkaline urea system were regenerated by simple injection regeneration. After solvent exchange, porous cellulose macrospheres (CMs) with a high specific surface area of 325.3 m2 g-1 were obtained by lyophilization, and CuS nanoparticles (CuS NPs) were coated on CMs by in situ growth in the liquid phase to achieve CuS-supported CM macrospheres (CuS@CM). The results indicated that the CuS@CM biocatalyst was successfully prepared with an average diameter of approximately 1.2 mm. In addition, CuS@CM was further used as a heterogeneous catalyst for the catalytic degradation of methylene blue (MB) and methyl orange (MO) model dyes during the oxidation of hydrogen peroxide (H2O2). In the presence of low doses of H2O2, the degradation rate of MB reached 94.8% within 10 min, showing high catalytic activity under neutral and alkaline conditions. After five cycles, 90.1% of the original catalytic activity was still retained, indicating that the prepared CuS@CM composite possessed excellent catalytic activity and reusability.

Robust Fabrication of Fluorescent Cellulosic Materials via Hantzsch Reaction.

Hantzsch reaction is one of the typical multicomponent reactions (MCRs), and it is employed herein to endow cellulosic materials with fluorescent properties. For example, acetoacetyl (ACAC)-bearing cotton fabric prepared via transesterification with tert-butyl acetoacetate is subjected to an aqueous Hantzsch reaction with formaldehyde and ammonium acetate at ambient temperature. A strong fluorescent emission around 460 nm is achieved within 10 min. XPS, fluorescent spectroscopy, and elemental analysis are used to confirm the presence of 1,4-dihydropyridine (DHP) rings on the surface of the fabric. TGA, SEM, XRD, and mechanical testing results show that the modification process has minimum impact on intrinsic properties of the fabric. The strategy is also shown to be generally applicable to various forms of cellulosic materials and different aldehydes. This fast and simple approach enriches the application of MCR in modification of cellulose and cellulose derivatives.

Synthetic semicrystalline cellulose oligomers as efficient Pickering emulsion stabilizers.

Nanocellulose are promising Pickering emulsion stabilizers for being sustainable and non-toxic. In this work, semicrystalline cellulose oligomers (SCCO), which were synthesized from maltodextrin using cellobiose as primer by in vitro enzymatic biosystem, were exploited as stabilizers for oil-in-water Pickering emulsions. At first, the morphology, structure, thermal and rheological properties of SCCO suspensions were characterized, showing that SCCO had a sheet morphology and typical cellulose-Ⅱ structure with 56 % crystallinity. Then the kinetic stabilities of emulsions containing various amounts of SCCO were evaluated against external stress such as pH, ionic strength, and temperature. Noting that SCCO-Pickering emulsions exhibited excellent stabilities against changes in centrifugation, pH, ionic strengths, and temperatures, and it was also kinetically stable for up to 6 months. Both SCCO suspensions and their emulsions exhibited gel-like structures and shear-thinning behaviors. These results demonstrated great potential of SCCO to be applied as nanocellulosic emulsifiers in food, cosmetic and pharmaceutical industries.

The effect of the degree of substitution on the solubility of cellulose acetoacetates in water: A molecular dynamics simulation and density functional theory study.

The effect of the degree of substitution (DS) on the aqueous solubility of cellulose acetoacetates (CAA) was investigated by molecular dynamics simulations and density functional theory calculations. Using average non-covalent interaction and the electrostatic potential analyses done on cellobiose as the model, it was showed both polar and non-polar areas of the system increased as the more hydroxyls were replaced by acetoacetate groups. Analyses of the solvation free energies of a celludecose (glucan containing 10 monosaccharide sugar units) at constant pressure and temperature showed the polar solvation free energies and the number of decose-water hydrogen bonds increased as DS was varied from 0.3 to 0.8, which contributes to higher solubility in water. When the DS of CAA increased from 0.8 to 1.5, it became insoluble again because the plateaued increase in solvation free energy could no longer compensate for the decreasing CAA-water hydrogen bonding interactions. The growing van der Waals interactions among CAA molecules as the molecule grows bigger with each attached AA group also contributes to the decreasing water solubility.

Sponges with Janus Character from Nanocellulose: Preparation and Applications in the Treatment of Hemorrhagic Wounds.

The development of a rapid and effective hemostatic dressing is highly desired in the treatment of hemorrhagic wounds. In this study, sponges with Janus character are developed using cellulose nanofibers (CNFs) that exhibit materials facets of different wettability characteristics using heterogeneous mixing and freeze-drying. The bonding of the interface between the hydrophilic and hydrophobic facets is achieved by using interpenetrating chemical cross-linking between CNFs and organosilanes. The hydrophilic layer absorbs water from blood and works synergistically with the inherent hemostatic chitosan-rich complementary layer to accelerate blood clotting, displaying both active and passive hemostatic mechanisms. The hydrophobic layer prevents blood penetration into the construct and exerts proper pressure on the wound. Compared with the hydrophilic control samples and commercial gauzes, the Janus sponges can achieve effective bleeding control with nearly 50% less blood loss in a femoral artery injury model and prolong the survival time in a carotid artery injury model. Compared with the only hydrophilic layer, the time to hemostasis of Janus sponge are reduced from 165 ± 20 to 131 ± 26 s in femoral artery injury model and from 102 ± 21 to 83 ± 15 s in liver femoral artery injury model.

Preparation and characterization of carboxymethylated cotton fabrics as hemostatic wound dressing.

Uncontrolled hemorrhage is a large cause of death in the global scope, thus leading to an urgent demand to develop efficient hemostatic materials. In this study, a series of modified cotton fabrics (MCFs) with different carboxymethyl group contents were prepared from cotton fabric (CF) by a carboxymethylation process to choose the appropriate one with the best hemostatic performance. The carboxymethyl group contents of MCFs rose up as the dosages of ClCH2COOH increased. The crystallinity of CF decreased after carboxymethylation, and MCFs can dissolve slightly with the phenomenon that there were vague boundaries between fibers after being treated with water. Furthermore, the MCF with the carboxymethyl group content at 0.77 mmol/g (MCF-0.77) could absorb the blood quickly, achieve dense distribution of blood cells and have high viscosity of leaching liquor. In addition, the MCF-0.77 with good biocompatibility accelerated the hemostasis time to 46.6 ± 8.4 s compared with the CF (88.8 ± 31.5 s) in a rat model of liver injury. In summary, the prepared MCF-0.77 is a potential hemostatic wound dressing for clinical use since every second counts for pre-hospital care.