Chitin Nanofibers Enable the Colloidal Dispersion of Carbon Nanomaterials in Aqueous Phase and Hybrid Material Coassembly.

Chitin nanofibrils (ChNF) sourced from discarded marine biomass are shown as effective stabilizers of carbon nanomaterials in aqueous media. Such stabilization is evaluated for carbon nanotubes (CNT) considering spatial and temporal perspectives by using experimental (small-angle X-ray scattering, among others) and theoretical (atomistic simulation) approaches. We reveal that the coassembly of ChNF and CNT is governed by hydrophobic interactions, while electrostatic repulsion drives the colloidal stabilization of the hybrid ChNF/CNT system. Related effects are found to be transferable to multiwalled carbon nanotubes and graphene nanosheets. The observations explain the functionality of hybrid membranes obtained by aqueous phase processing, which benefit from an excellent areal mass distribution (correlated to piezoresistivity), also contributing to high electromechanical performance. The water resistance and flexibility of the ChNF/CNT membranes (along with its tensile strength at break of 190 MPa, conductivity of up to 426 S/cm, and piezoresistivity and light absorption properties) are conveniently combined in a device demonstration, a sunlight water evaporator. The latter is shown to present a high evaporation rate (as high as 1.425 kg water m-2 h-1 under one sun illumination) and recyclability.

Solid Wood Modification toward Anisotropic Elastic and Insulative Foam-Like Materials.

The methods used to date to produce compressible wood foam by top-down approaches generally involve the removal of lignin and hemicelluloses. Herein, we introduce a route to convert solid wood into a super elastic and insulative foam-like material. The process uses sequential oxidation and reduction with partial removal of lignin but high hemicellulose retention (process yield of 72.8%), revealing fibril nanostructures from the wood's cell walls. The elasticity of the material is shown to result from a lamellar structure, which provides reversible shape recovery along the transverse direction at compression strains of up to 60% with no significant axial deformation. The compressibility is readily modulated by the oxidation degree, which changes the crystallinity and mobility of the solid phase around the lumina. The performance of the highly resilient foam-like material is also ascribed to the amorphization of cellulosic fibrils, confirmed by experimental and computational (molecular dynamics) methods that highlight the role of secondary interactions. The foam-like wood is optionally hydrophobized by chemical vapor deposition of short-chained organosilanes, which also provides flame retardancy. Overall, we introduce a foam-like material derived from wood based on multifunctional nanostructures (anisotropically compressible, thermally insulative, hydrophobic, and flame retardant) that are relevant to cushioning, protection, and packaging.

Control of the Colloidal and Adsorption Behaviors of Chitin Nanocrystals and an Oppositely Charged Surfactant at Solid, Liquid, and Gas Interfaces.

Chitin has a unique hierarchical structure, spanning the macro- and nanoscales, and presents chemical characteristics that make it a suitable component of multiphase systems. Herein, we elucidate the colloidal interactions between partially deacetylated chitin nanocrystals (cationic ChNC) and an anionic surfactant, sodium dodecyl sulfate (SDS). We investigate charge neutralization and association (electrophoretic mobility, surface tensiometry, and quartz crystal microgravimetry) and their role in the stabilization of Pickering emulsions. We find SDS adsorption and association with ChNC under distinctive regimes: At low SDS concentration, submonolayer assemblies form on ChNC, driven by the hydrophobic effect and electrostatic interactions. With the increased SDS concentration, bilayers or patchy bilayers form, followed by adsorbed hemimicelles and micelles. We further suggested the role of hydrophobic effects in the observed colloidal transitions and complex conformations. At the highest SDS concentration tested, charge neutralization and SDS/ChNC flocculation take place. Remarkably, at given concentrations, adsorbed SDS endows the chitin nanoparticles with an effective hydrophobicity that opens the opportunity to achieve tailorable Pickering stabilization. Hence, a facile route is proposed by in situ modification by SDS physisorption, which extends the potential of renewable nanoparticles in the formulation of complex fluids, for instance, those relevant to household and healthcare products.

Structured Emulgels by Interfacial Assembly of Terpenes and Nanochitin.

Interfacial assemblies formed by colloidal complexation are effective in multiphase stabilization, as shown in structured liquids and Pickering emulgels. Herein, we demonstrate a type of biobased colloidal system that spontaneously stabilizes an organic phase in a continuous hydrogel phase. Specifically, a triterpene extracted from bark (betulin, BE) is added to an organic phase containing a coniferous resin (rosin acid, a diterpene). BE is shown to take part in strong noncovalent interactions with the nanochitin dispersed in the aqueous (hydrogel) phase, leading to a complex of high interfacial activity. The viscoelastic response of the system is rationalized by the presence of a superstable structured dual network. When used as a templating material, the emulgel develops into structured liquids and cryogels. The herein introduced all-biobased type of nanoparticle surfactant system forms a gel ("emulsion-filled" with "aggregated droplets") that features the functional benefits of both betulin and nanochitin.

Efficient ultraviolet blocking film on the lignin-rich lignocellulosic nanofibril from bamboo.

The ultraviolet (UV) blocking performance of current bio-based devices is always limited by delignification and exploited chemical treatment. Lignocellulosic nanofibril (LCNF) is a promising green alternative that could efficiently impede UV radiation. Herein, we proposed a robust LCNF film that achieved 99.8 ± 0.19 % UVB blocking, 96.1 ± 0.23 % UVA blocking, and was highly transparent without complex chemical modification. Compared to conventional lignin composites, this LCNF method involves 29.5 ± 2.31 % lignin content directly extracted from bamboo as a broad-spectrum sun blocker. This bamboo-based LCNF film revealed an excellent tensile strength of 94.9 ± 3.6 MPa and outstanding stability, adapting to the natural environment's variability. The residual hemicellulose could also embed the link between lignin and cellulose, confirming high lignin content in the network. The connection between lignin and hemicelluloses in the cellulose network was explored and described for the fibrillation of lignocellulosic nanofibrils. This research highlights the promising development of LCNFs for UV protection and bio-based solar absorption materials.

Layer-by-Layer Deposition of Low-Solid Nanochitin Emulgels Creates Porous Structures for High Cell Attachment and Proliferation.

Direct ink writing (DIW) is a customizable platform to engineer complex constructs from biobased colloids. However, the latter usually display strong interactions with water and lack interparticle connectivity, limiting one-step processing into hierarchically porous structures. We overcome such challenges by using low-solid emulgel inks stabilized by chitin nanofibrils (nanochitin, NCh). By using complementary characterization platforms, we reveal NCh structuring into spatially controlled three-dimensional (3D) materials that generate multiscale porosities defined by emulsion droplet size, ice templating, and DIW infill density. The extrusion variables, key in the development of surface and mechanical features of printed architectures, are comprehensively analyzed by using molecular dynamics and other simulation approaches. The obtained scaffolds are shown for their hierarchical porous structures, high areal density, and surface stiffness, which lead to excellent modulation of cell adhesion, proliferation, and differentiation, as tested with mouse dermal fibroblast expressing green fluorescent proteins.

Insulative Biobased Glaze from Wood Laminates Obtained by Self-Adhesion.

The combination of optical transparency and mechanical strength is a highly desirable attribute of wood-based glazing materials. However, such properties are typically obtained by impregnation of the highly anisotropic wood with index-matching fossil-based polymers. In addition, the presence of hydrophilic cellulose leads to a limited water resistance. Herein, this work reports on an adhesive-free lamination that uses oxidation and densification to produce transparent all-biobased glazes. The latter are produced from multilayered structures, free of adhesives or filling polymers, simultaneously displaying high optical clarity and mechanical strength, in both dry and wet conditions. Specifically, high values of optical transmittance (≈85.4%), clarity (≈20% with low haze) at a thickness of ≈0.3 mm, and highly isotropic mechanical strength and water resistance (wet strength of ≈128.25 MPa) are obtained for insulative glazes exhibiting low thermal conductivity (0.27 W m-1 K-1 , almost four times lower than glass). The proposed strategy results in materials that are systematically tested, with the leading effects of self-adhesion induced by oxidation rationalized by ab initio molecular dynamics simulation. Overall, this work demonstrates wood-derived materials as promising solutions for energy-efficient and sustainable glazing applications.

Super-Macroporous Lightweight Materials Templated from Bicontinuous Intra-Phase Jammed Emulsion Gels Based on Nanochitin.

Non-equilibrium multiphase systems are formed by mixing two immiscible nanoparticle dispersions, leading to bicontinuous emulsions that template cryogels with interconnected, tortuous channels. Herein, a renewable, rod-like biocolloid (chitin nanocrystals, ChNC) is used to kinetically arrest bicontinuous morphologies. Specifically, it is found that ChNC stabilizes intra-phase jammed bicontinuous systems at an ultra-low particle concentration (as low as 0.6 wt.%), leading to tailorable morphologies. The synergistic effects of ChNC high aspect ratio, intrinsic stiffness, and interparticle interactions produce hydrogelation and, upon drying, lead to open channels bearing dual characteristic sizes, suitably integrated into robust bicontinuous ultra-lightweight solids. Overall, it demonstrates the successful formation of ChNC-jammed bicontinuous emulsions and a facile emulsion templating route to synthesize chitin cryogels that form unique super-macroporous networks.

Mechanically strong all-chitin filaments: Wet-spinning of ß-chitin nanofibers in aqueous NaOH.

Herein, a facile wet-spinning strategy was used for the fabrication of mechanically strong all-chitin filaments from an aqueous NaOH solution using ß-chitin nanofibers (ß-ChNFs). It is hypothesized that to reach high mechanical performance it is important to preserve the crystalline structure of chitin during fabrication. To explore this possibility, ß-ChNFs were disintegrated from squid pens by a mild procedure and showed a uniform diameter of 10-25 nm, length of a few microns, and a high aspect ratio of more than 200. An interesting finding was that gel-like ß-ChNF filaments were directly formed in aqueous NaOH without using any organic or ionic agents. The gelation of ß-ChNFS under alkali treatments contributed to the construction of strong nanonetworks and thus facilitated the formation of high-strength filaments. The resulting all-chitin filaments showed a high tensile strength and Young's modulus of 251.3 ± 12.45 MPa and 12.1 ± 0.72 GPa, respectively, which were further investigated for utilization as flexible sensors. The advantages of this strategy included the lack of use of any toxic solvents and the achievement of high mechanical performance for the all-chitin filaments. We believe that this wet-spinning approach may promote the functional utilization of chitin to develop high-strength filaments in smart textiles, biosensors, and structural reinforcements.

Strong, Water-Resistant, and Ionic Conductive All-Chitosan Film with a Self-Locking Structure.

Renewable and biodegradable natural polymeric materials are attractive candidates for replacing nonbiodegradable plastics. However, it is challenging to fabricate polysaccharide-based materials (such as cellulose and chitin) that can be used in humid or even watery environments due to their inferior stability against water. Here, a self-locking structure is constructed to develop a strong, water-resistant, and ionic conductive all-chitosan film without other additives. The densely packed self-locking structure introduces strong interactions between chitosan nanofibers, preventing the fibers from disentangling even in watery environments. The resulting film exhibits outstanding tensile strength of ∼144 MPa, superior wet strength of ∼54.3 MPa, and high ionic conductivity of 0.0012 S/cm at 10-4 M KCl, which are significantly higher than those of conventional polysaccharide-based materials and many commercially used plastics. Additionally, it also possesses outstanding flexibility, excellent thermal stability, good antimicrobial ability, and biodegradability, which make it a promising eco-friendly alternative to plastics for many potential applications, such as packaging bags, drinking straws, and ion regulation membranes.

Mechanisms of Strain-Induced Interfacial Strengthening of Wet-Spun Filaments.

We investigate the mechanism of binding of dopamine-conjugated carboxymethyl cellulose (DA-CMC) with carbon nanotubes (CNTs) and the strain-induced interfacial strengthening that takes place upon wet drawing and stretching filaments produced by wet-spinning. The filaments are known for their tensile strength (as high as 972 MPa and Young modulus of 84 GPa) and electrical conductivity (241 S cm-1). The role of axial orientation in the development of interfacial interactions and structural changes, enabling shear load bearing, is studied by molecular dynamics simulation, which further reveals the elasto-plasticity of the system. We propose that the reversible torsion of vicinal molecules and DA-CMC wrapping around CNTs are the main contributions to the interfacial strengthening of the filaments. Such effects play important roles in impacting the properties of filaments, including those related to electrothermal heating and sensing. Our findings contribute to a better understanding of high aspect nanoparticle assembly and alignment to achieve high-performance filaments.

Toward Strong and Tough Wood-Based Hydrogels for Sensors.

The purpose of this research is to develop strong and tough wood-based hydrogels, which are reinforced by an aligned cellulosic wood skeleton. The hypothesis is that improved interfacial interaction between the wood cell wall and a polymer is of great importance for improving the mechanical performance. To this end, a facile and green approach, called ultraviolet (UV) grafting, was performed on the polyacrylamide (PAM)-infiltrated wood skeleton without using initiators. An important finding was that PAM-grafted cellulose nanofiber (CNF) architectures formed in the obtained hydrogels under UV irradiation, where CNFs themselves serve as both initiators and cross-linkers. Moreover, an alkali swelling treatment was utilized to improve the accessibility of the wood cell wall before UV irradiation and thus facilitate grafting efficiency. The resulting alkali-treated Wood-g-PAM hydrogels exhibited significantly higher tensile properties than those of the Wood/PAM hydrogel and were further assembled into conductive devices for sensor applications. We believe that this UV grafting strategy may facilitate the development of strong wood-based composites with interesting features.

Antimicrobial/Biocompatible Hydrogels Dual-Reinforced by Cellulose as Ultrastretchable and Rapid Self-Healing Wound Dressing.

Hydrogels as a wound dressing, integrated with ultrastretchability, rapid self-healing, and excellent antimicrobial activity, are in high demand, particularly for joint skin wound healing. Herein, a multifunctional and ductile composite hydrogel was developed using poly(vinyl alcohol) (PVA)-borax gel as a matrix that was synergized or dual-reinforced with dopamine-grafted oxidized carboxymethyl cellulose (OCMC-DA) and cellulose nanofibers (CNF). Moreover, neomycin (NEO), an aminoglycoside antibiotic with multifunctional groups, was incorporated into the hydrogel network as both an antibacterial agent and a cross-linker. The dynamic reversible borate ester linkages and hydrogen bonds between OCMC-DA, PVA, and CNF, along with dynamic cross-linking imine linkages between NEO and OCMC-DA, endowed the hydrogel with excellent self-healing ability and stretchability (3300%). The as-reinforced networks enhanced the mechanical properties of hydrogels significantly. More remarkably, the composite hydrogel with improved biodegradability and biocompatibility is pH-responsive and effective against a broad spectrum of bacteria, which is attributed to the controllable release of NEO for steady availability of the antibiotic on the wound location. Overall, the antimicrobial hydrogel with rapid self-healing and reliable mechanical properties holds significant promise as dressing material for wound healing.

Multifunctional Wet-Spun Filaments through Robust Nanocellulose Networks Wrapping to Single-Walled Carbon Nanotubes.

Cellulose nanofibrils (CNFs) and single-walled carbon nanotubes (SWNTs) hold potential for fabricating multifunctional composites with remarkable performance. However, it is technically tough to fabricate materials by CNFs and SWNTs with their intact properties, mainly because of the weakly synergistic interaction. Hence, constructing sturdy interfaces and sequential connectivity not only can enhance mechanical strength but also are capable of improving the electrical conductivity. In that way, we report CNF/SWNT filaments composed of axially oriented building blocks with robust CNF networks wrapping to SWNTs. The composite filaments obtained through the combination of three-mill-roll and wet-spinning strategy display high strength up to ∼472.17 MPa and a strain of ∼11.77%, exceeding most results of CNF/SWNT composites investigated in the previous literature. Meanwhile, the filaments possess an electrical conductivity of ∼86.43 S/cm, which is also positively dependent on temperature changes. The multifunctional filaments are further manufactured as a strain sensor to measure mass variation and survey muscular movements, leading to becoming optimistic incentives in the fields of portable gauge measuring and wearable bioelectronic therapeutics.