Chemoselectivity of Pristine Cellulose Nanocrystal Films Driven by Carbohydrate-Carbohydrate Interactions

Improved Cell Adhesion on Self-Assembled Chiral Nematic Cellulose Nanocrystal Films

Chirality is ubiquitous in nature, and closely related to biological phenomena. Nature-originated nanomaterials such as cellulose nanocrystals (CNCs) are able to self-assemble into hierarchical chiral nematic CNC films and impart handedness to nano and micro scale. However, the effects of the chiral nematic surfaces on cell adhesion are still unknown. Herein, this work presents evidence that the left-handed self-assembled chiral nematic CNC films (L-CNC) significantly improve the adhesion of L929 fibroblasts compared to randomly arranged isotropic CNC films (I-CNC). The fluidic force microscopy-based single-cell force spectroscopy is introduced to assess the cell adhesion forces on the substrates of L-CNC and I-CNC, respectively. With this method, a maximum adhesion force of 133.2 nN is quantified for mature L929 fibroblasts after culturing for 24 h on L-CNC, whereas the L929 fibroblasts exert a maximum adhesion force of 78.4 nN on I-CNC under the same condition. Moreover, the instant SCFS reveals that the integrin pathways are involved in sensing the chirality of substrate surfaces. Overall, this work offers a starting point for the regulation of cell adhesion via the self-assembled nano and micro architecture of chiral nematic CNC films, with potential practical applications in tissue engineering and regenerative medicine.

Large-scale production of chiral nematic microspheres

The membrane emulsification technique enables the self-assembly of cellulose nanocrystals (CNCs) confined within a spherical geometry for large-scale production. The resulting solid microspheres show long-range ordering with chiral nematic structures, and this fascinating hierarchical architecture can even be transferred to mesoporous carbon or silica microparticles by a sacrificial template method.

Uncovering the Recent Progress of CNC-Derived Chirality Nanomaterials: Structure and Functions

Cellulose nanocrystal (CNC), as a renewable resource, with excellent mechanical performance, low thermal expansion coefficient, and unique optical performance, is becoming a novel candidate for the development of smart material. Herein, the recent progress of CNC-based chirality nanomaterials is uncovered, mainly covering structure regulations and function design. Undergoing a simple evaporation process, the cellulose nanorods can spontaneously assemble into chiral nematic films, accompanied by a vivid structural color. Various film structure-controlling strategies, including assembly means, physical modulation, additive engineering, surface modification, geometric structure regulation, and external field optimization, are summarized in this work. The intrinsic correlation between structure and performance is emphasized. Next, the applications of CNC-based nanomaterials is systematically reviewed. Layer-by-layer stacking structure and unique optical activity endow the nanomaterials with wide applications in the mineralization, bone regeneration, and synthesis of mesoporous materials. Besides, the vivid structural color broadens the functions in anti-counterfeiting engineering, synthesis of the shape-memory and self-healing materials. Finally, the challenges for the CNC-based nanomaterials are proposed.

Ag Nanoparticle Incorporated Guar Gum-Sodium Alginate-I-Carrageenan Tribiopolymer Blended Cloth Waste Lint Extracted Cellulose Nanocrystal Antimicrobial Composite Film

A biopolymer-based formulation for robust and active food packaging material was developed. This material consisted of a blend of three biopolymers (guar gum-sodium alginate-i-carrageenan) reinforced by cellulose nanocrystals (CNC) alongside the integration of silver nanoparticles (AgNPs) with varying sizes. The CNC utilized in this process was derived from cloth waste lint (CWL) generated from a household cloth dryer machine. This CNC synthesis underwent a series of solvent treatments to yield the CNC used in the composite. CNC and AgNPs were incorporated into the tribiopolymeric blend matrix to construct a nanocomposite film that showed excellent tensile strength (∼90 MPa). The nanocomposite film also exhibited antimicrobial activity against Escherichia coli ATCC 25922 and Bacillus cereus MTCC 1272. In this report, it was demonstrated that the zone of inhibition against E. coli and B. cereus depends on the variation of size and amount of AgNPs inside the polymeric matrix. The practical applicability of such a film was also demonstrated by applying it to sliced bread and the enhancement of the shelf life of the raped bread was compared with a control. Thus, the guar gum-sodium alginate-i-carrageenan tribiopolymer blend with a cloth waste lint extracted cellulose nanocrystal composite film is antimicrobial, hence, an excellent candidate as an active packaging film.

Robust Cellulose Nanocrystal-Based Self-Assembled Composite Membranes Doped with Polyvinyl Alcohol and Graphene Oxide for Osmotic Energy Harvesting

Osmotic energy from the salinity gradients represents a promising energy resource with stable and sustainable characteristics. Nanofluidic membranes can be considered as powerful alternatives to the traditional low-performance ion exchange membrane to achieve high-efficiency osmotic energy harvesting. However, the development of a highly efficient and easily scalable core membrane component from low-cost raw materials remains challenging. Here, a composite membrane based on the self-assembly of cellulose nanocrystals (CNCs) with polyvinyl alcohol (PVA) and graphene oxide (GO) nanoflakes as additives is developed to provide a solution. The introduction of soft PVA polymer significantly improves the mechanical strength and water stability of the composite membrane by forming a nacre-like structure. Benefiting from the abundant negative charges of CNC nanorods and GO nanoflakes and the generated network nanochannels, the composite membrane demonstrates a good cation-selective transport capacity, thus contributing to an optimal osmotic energy conversion of 6.5 W m-2 under a 100-fold salinity gradient and an exemplary stability throughout 25 consecutive days of operation. This work provides an option for the development of nanofluidic membranes that can be easily produced on a large scale from well-resourced and sustainable biomass materials for high-efficiency osmotic energy conversion.

Sustainable, Insoluble, and Photonic Cellulose Nanocrystal Patches for Calcium Ion Sensing in Sweat

Self-assembly of cellulose nanocrystals (CNCs) is invaluable for the development of sustainable optics and photonics. However, the functional failure of CNC-derived materials in humid or liquid environments inevitably impairs their development in biomedicine, membrane separation, environmental monitoring, and wearable devices. Here, a facile and robust method to fabricate insoluble hydrogels in a self-assembled CNC-polyvinyl alcohol (PVA) system is reported. Due to the reconstruction of inter- or intra-molecular hydrogen bond interactions, thermal dehydration makes an optimized CNC/PVA photonic film form a stable hydrogel network in an aqueous solution rather than dissolve. Notably, the resulting hydrogel exhibits superb mechanical performance (stress up to 3.3 Mpa and tough up to 0.73 MJ m^-3 ) and reversible conversion between dry and wet states, enabling it convenient for specific functionalization. Sodium alginate (SA) can be adsorbed into the CNC photonic structure by swelling dry CNC/PVA film in a SA solution. The prepared hydrogel showcases the comprehensive properties of freezing resistance (-20°C), strong adhesion, satisfactory biocompatibility, and highly sensitive and selective Ca²⁺ sensing. The material could act as a portable wearable patch on the skin for the continuous analysis of calcium trends during different physical exercises, facilitating their development in precision nutrition and health monitoring.

A Surface Diffusion Barrier Strategy toward Water-Resistant Photonic Materials for Accurate Detection of Ethanol

Photonic materials that enable visual detection of chemicals have shown great potential for wide applications in chemical, environmental, biotechnological, and food industries, but until now, using hydrophilic photonic materials for tracing water-soluble chemicals remains a major challenge due to the strong water interference. Here, we demonstrate a two-step co-assembly and subsequent surface coating strategy to develop an ethanol-sensitive and anti-water interference photonic crystal film. By using citric acid as a co-assembly phase, high ethanol sensing is realized because of the strong intermolecular affinity. By controlling the thickness of the outer polyvinyl butyral layer, selective ethanol penetration but a water barrier is enabled. Notably, the composite photonic films are free-standing, highly flexible, and controllably structurally colored. We further present using the composite film to quantitatively trace ethanol/water mixtures and potentially track drunk driving as a colorimetric sensor. The heuristic two-step modification strategy proposed in this work not only overcomes the limitation of water interference for hydrophilic colorimetric sensors but also provides references to develop more new photonic materials with water resistance that need to be applied in water/humid environments.

Photonic Cellulose Films with Vivid Structural Colors: Fabrication and Selectively Chemical Response

Recent advances in structural-color cellulose nanocrystal (CNC) materials have been made toward chemical sensing applications; however, such materials lack sufficient color chroma for naked-eye observation, and their selective recognition to given chemicals as well as the corresponding mechanism has rarely been reported. Here, a dopamine-infiltration and post-polymerization approach is proposed to construct vivid structural-color composite films. The chiral nematic structure of CNC enables the structural coloration, while the strong light absorption of the polymeric co-phase, polydopamine (PDA) enhances the color chroma and visibility. By controlling the PDA amount, the composite films can detect organic solvents quantitatively and selectively via visible color changes. From the viewpoint of the compatibility and similitude principle, notably, a critical solubility parameter distance (R₀) between PDA and "active" solvents is defined with a three-dimensional Hansen solubility sphere; this well constructs a rule for the sensing selectivity of the chemochromic composite films. The findings pave the foundation for the design of colorimetric sensors with specifically testing objects.

Highly Tough, Stretchable, and Solvent-Resistant Cellulose Nanocrystal Photonic Films for Mechanochromism and Actuator Properties

Cellulose nanocrystals (CNCs)-derived photonic materials have confirmed great potential in producing renewable optical and engineering areas. However, it remains challenging to simultaneously possess toughness, strength, and multiple responses for developing high-performance sensors, intelligent coatings, flexible textiles, and multifunctional devices. Herein, the authors report a facile and robust strategy that poly(ethylene glycol) dimethacrylate (PEGDMA) can be converged into the chiral nematic structure of CNCs by ultraviolet-triggered free radical polymerization in an N,N-dimethylformamide solvent system. The resulting CNC-poly(PEGDMA) composite exhibits impressive strength (42 MPa), stretchability (104%), toughness (31 MJ m^-3 ), and solvent resistance. Notably, it preserves vivid optical iridescence, displaying stretchable variation from red, yellow, to green responding to the applied mechanical stimuli. More interestingly, upon exposure to spraying moisture, it executes sensitive actuation (4.6° s^-1 ) and multiple complex 3D deformation behaviors, accompanied by synergistic iridescent appearances. Due to its structural anisotropy of CNC with typical left-handedness, the actuation shows the capability to generate a high probability (63%) of right-handed helical shapes, mimicking a coiled tendril. The authors envision that this versatile system with sustainability, robustness, mechanochromism, and specific actuating ability will open a sustainable avenue in mechanical sensors, stretchable optics, intelligent actuators, and soft robots.

Chiral Nematic Cellulose Nanocrystal Films Cooperated with Amino Acids for Tunable Optical Properties

The exploration of functional materials relies greatly on the understanding of material structures and nanotechnologies. In the present work, chiral nematic cellulose nanocrystal (CNC) films were prepared by incorporation with four types of amino acids (AAs, glycine, histidine, phenylalanine, and serine) via evaporation-induced self-assembly. The films present ideal iridescence and birefringence that can be tuned by the amount of AAs added. The intercalation of AAs enlarged the pitch values, contributing to the red-shift trend of the reflective wavelength. Among the AAs, serine presented the most compatible intercalation into cellulose crystals. Interestingly, histidine and phenylalanine composite films showed high shielding capabilities of UV light in diverse wavelength regions, exhibiting multi-optical functions. The sustainable preparation of chiral nematic CNC films may provide new strategies for materials production from biocompatible lignocellulose.

Highly Strong and Solvent-Resistant Cellulose Nanocrystal Photonic Films for Optical Coatings

Cellulose nanocrystals (CNCs) are powerful photonic building blocks for the fabrication of biosourced colored films. A combination of the advantages of self-assembled CNCs and multiple templating agents offers access to the development of novel physicochemical sensors, structural coatings, and optic devices. However, due to the inherent brittleness and water instability of CNC-derived materials, their further applications are widely questionable and restrictive. Here, a soft polymer of poly(vinyl alcohol) (PVA) was introduced into the rigid CNC system to balance molecular interactions, whereafter two hard/soft nanocomposites were fastened through a cross-linking reaction of glutaraldehyde (GA), resulting in a highly flexible, water-stable, and chiral nematic CNC composite film through an evaporation-induced self-assembly technique. For a 1.5 wt % GA-cross-linked 70 wt % CNC loading film, its treatment with harsh hydrophilic exposure (soaking in a strong acid, strong base, and seawater) and various organic solvents show exceptional solvent-resistant abilities. Furthermore, the film can even withstand a weight of 167 g cm^-2 without failure, which is a highly stiff and durable character. Importantly, the film remains a highly ordered chiral nematic organization, being able to act as a highly transparent substrate for selective reflection of left-handed circularly polarized light, preparing fully covered and patterned full-color coatings on various substrates. Our work paves the way for applications in low-cost, durable, and photonic cellulosic coatings.

Functionalized Cellulose Nanocrystals for Cellular Labeling and Bioimaging

Cellulose nanocrystals (CNCs) are unique and promising natural nanomaterials that can be extracted from native cellulose fibers by acid hydrolysis. In this study, we developed chemically modified CNC derivatives by covalent tethering of PEGylated biotin and perylenediimide (PDI)-based near-infrared organic dye and evaluated their suitability for labeling and imaging of different cell lines including J774A.1 macrophages, NIH-3T3 fibroblasts, HeLa adenocarcinoma cells, and primary murine dendritic cells. PDI-labeled CNCs showed a superior photostability compared to similar commercially available dyes under long periods of constant and high-intensity illumination. All CNC derivatives displayed excellent cytocompatibility toward all cell types and efficiently labeled cells in a dose-dependent manner. Moreover, CNCs were effectively internalized and localized in the cytoplasm around perinuclear areas. Thus, our findings demonstrate the suitability of these new CNC derivatives for labeling, imaging, and long-time tracking of a variety of cell lines and primary cells.

Applications of Cellulose Nanomaterials in Stimuli-Responsive Optics

As one of the most abundant biopolymers, cellulose has been a basic but essential building block of human society, with its use dating back thousands of years. With recent developments in nanotechnology and increasing environmental concerns, cellulose-based nanomaterials are now gaining attention as promising green material candidates for many high-value applications as a result of their biocompatibility and advantageous physical and chemical properties. In particular, cellulose nanocrystals are notable for their optical properties that can respond to various environmental stimuli as a result of the unique chiral nematic structure of the material. Compositing cellulosic materials with functional polymers, small molecules, and other nanomaterials can further stabilize and amplify these responsive optical signals and introduce multiple new functionalities. On the basis of these capabilities, many advanced applications of cellulose nanomaterials have been proposed, including chemical sensors, photonic papers, decorative coatings, data security, and smart textiles. In this review, we discuss and summarize recent advances in this emerging field of stimuli-responsive optics based on cellulose nanomaterials.

Dual Response of Photonic Films with Chiral Nematic Cellulose Nanocrystals: Humidity and Formaldehyde

Manipulating functional stimuli-responsive materials has been a hot topic in the research of smart sensors and anticounterfeiting encryption. Here, a novel functional chiral nematic cellulose nanocrystal (CNC) film showing dual responsiveness to humidity and formaldehyde gas was fabricated. The chiral nematic CNC iridescent film could respond to environmental humidity and formaldehyde gas changes by reversible motion. Interestingly, the humidity sensitivity of the CNC iridescent film could be gated by exposing the film to formaldehyde gas. At the same time, the formaldehyde-responsive behavior is strongly affected by the relative humidity (RH), and the response range could be tuned by changing the RH over a wide range. Importantly, the formaldehyde-induced color change could be altered from invisible to visible by the naked eye when the film was exposed to a humid environment. The mechanism of this dual response of the CNC iridescent film is ascribed to the synergistic effect of cooperation and competition between water and formaldehyde molecules by constructing physical cross-linking networks by hydrogen bonds among water, formaldehyde, and CNCs. Furthermore, the "RH-concentration of formaldehyde gas-color" ternary colorimetric system was simulated, which is thought to endow the CNC iridescent film with great potential to act as a sensor in the convenient visible detection of gaseous formaldehyde. Furthermore, this work provided a promising strategy to design multi-gas-sensitive devices with convenient detection, good stability, and excellent reversibility.

Stimuli-responsive self-assembly of cellulose nanocrystals (CNCs): Structures, functions, and biomedical applications

Cellulose nanocrystals (CNCs) have received a significant amount of attention from the researchers. It is used as a nanomaterial for various applications due to its excellent physiochemical properties for the last few decades. Self-assembly is a phenomenon where autonomous reorganization of randomly oriented species occurs elegantly. Self-assembly is responsible for the formation of the hierarchical cholesteric structure of CNCs. This process is highly influenced by several factors, such as the surface chemistry of the nanoparticles, intermolecular forces, and the fundamental laws of thermodynamics. Various conventional experimental designs and molecular dynamics (MD) studies have been applied to determine the possible mechanism of self-assembly in CNCs. Different external factors, like pH, temperature, magnetic/electric fields, vacuum, also influence the self-assembly process in CNCs. Notably, better responses have been observed in CNCs-grafted polymer nanocomposites. These functionalized CNCs with stimuli-responsive self-assembly have immense practical applications in modern biotechnology and medicine. Herein, we have concisely discussed the mechanism of the self-assembled CNCs in the presence of different external factors such as pH, temperature, electric/magnetic fields, and their biomedical applications.

Biomimetic nanochannels for the discrimination of sialylated glycans via a tug-of-war between glycan binding and polymer shrinkage

Sialylated glycans that are attached to cell surface mediate diverse cellular processes such as immune responses, pathogen binding, and cancer progression. Precise determination of sialylated glycans, particularly their linkage isomers that can trigger distinct biological events and are indicative of different cancer types, remains a challenge, due to their complicated composition and limited structural differences. Here, we present a biomimetic nanochannels system integrated with the responsive polymer polyethyleneimine-g-glucopyranoside (Glc-PEI) to solve this problem. By using a dramatic “OFF–ON” change in ion flux, the nanochannels system achieves specific recognition for N-acetylneuraminic acid (Neu5Ac, the predominant form of sialic acid) from various monosaccharides and sialic acid species. Importantly, different “OFF–ON” ratios of the conical nanochannels system allows the precise and sensitive discrimination of sialylated glycan linkage isomers, α2–3 and α2–6 linkage (the corresponding ion conductance increase ratios are 96.2% and 264%, respectively). Analyses revealed an unusual tug-of-war mechanism between polymer-glycan binding and polymer shrinkage. The low binding affinity of Glc-PEI for the α2–6-linked glycan caused considerable shrinkage of Glc-PEI layer, but the high affinity for the α2–3-linked glycan resulted in only a slight shrinkage. This competition mechanism provides a simple and versatile materials design principle for recognition or sensing systems that involve negatively charged target biomolecules. Furthermore, this work broadens the application of nanochannel systems in bioanalysis and biosensing, and opens a new route to glycan analysis that could help to uncover the mysterious and wonderful glycoworld.

A glycan-responsive polymer-modified nanochannels system enables the precise discrimination of sialylated glycan linkage isomers via the different “OFF–ON” changes resulting from a “tug-of-war” between polymer-glycan binding and polymer shrinkage.