Unwinding a spiral of cellulose nanocrystals for stimuli-responsive stretchable optics

Stimuli-Responsive Chiral Cellulose Nanocrystals Based Self-Assemblies for Security Measures to Prevent Counterfeiting: A Review

The proliferation of misleading information and counterfeit products in conjunction with technical progress presents substantial worldwide issues. To address the issue of counterfeiting, many tactics, such as the use of luminous anticounterfeiting systems, have been investigated. Nevertheless, traditional fluorescent compounds have a restricted effectiveness. Cellulose nanocrystals (CNCs), known for their renewable nature and outstanding qualities, present an excellent opportunity to develop intelligent, optically active materials formed due to their self-assembly behavior and stimuli response. CNCs and their derivatives-based self-assemblies allow for the creation of adaptable luminous materials that may be used to prevent counterfeiting. These materials integrate the photophysical characteristics of optically active components due to their stimuli-responsive behavior, enabling their use in fibers, labels, films, hydrogels, and inks. Despite substantial attention, existing materials frequently fall short of practical criteria due to limited knowledge and poor performance comparisons. This review aims to provide information on the latest developments in anticounterfeit materials based on stimuli-responsive CNCs and derivatives. It also includes the scope of artificial intelligence (AI) in the near future. It will emphasize the potential uses of these materials and encourage future investigation in this rapidly growing area of study.

3D Printing Photonic Crystals: A Review

Living organisms in nature possess diverse and vibrant structural colors generated from their intrinsic surface micro/nanostructures. These intricate micro/nanostructures can be harnessed to develop a new generation of colorful materials for various fields such as photonics, information storage, display, and sensing. Recent advancements in the fabrication of photonic crystals have enabled the preparation of structurally colored materials with customized geometries using 3D printing technologies. Here, a comprehensive review of the historical development of fabrication methods for photonic crystals is provided. Diverse 3D printing approaches along with the underlying mechanisms, as well as the regulation methods adopted to generate photonic crystals with structural color, are discussed. This review aims to offer the readers an overview of the state-of-the-art 3D printing techniques for photonic crystals, present a guide and considerations to fabricate photonic crystals leveraging different 3D printing methods.

Dynamically crosslinked chiral optics sensing for ultra-sensitive VOCs detection

Chiroptical sensing with real-time colorimetrical detection has been emerged as quantifiable properties, enantioselective responsiveness, and optical manipulation in environmental monitoring, food safety and other trace identification fields. However, the sensitivity of chiroptical sensing materials remains an immense challenge. Here, we report a dynamically crosslinking strategy to facilitate highly sensitive chiroptical sensing material. Chiral nematic cellulose nanocrystals (CNC) were co-assembled with amino acid by a two-step esterification, of which a precisely tunable helical pitch, a unique spiral conformation with hierarchical and numerous active sites in sensing performance could be trigged by dynamic covalent bond on amines. Such a CNC/amino acid chiral optics features an ultra-trace amount of 0.08 mg/m3 and a high sensitivity of 60 nm/(mg/m3) for formaldehyde gas at a molecule level detection, which is due to the three synergistic adsorption enhancement of dynamic covalent bonded interaction, hydrogen bonded interaction and van der Waals interaction. Meanwhile, an enhancement hierarchical adsorption of CNC/amino acid chiral materials can be readily representative to the precise helical pitch and colorimetrical switch for sensitive visualization reorganization.

Bonding strength performance of bamboo-based composite materials: An in-depth insight for sustainable construction applications

This review systematically examines the multitude of factors influencing bonding strength in bamboo-based composite materials, given the rising prominence of bamboo as a green building material. With bamboo's inherent variability in mechanical properties and structure, engineered bamboo products have emerged to address challenges related to connections and joints. Such advancements have necessitated a detailed exploration of adhesive systems, a significant cost determinant in bamboo production. The adhesive bonding mechanism in bamboo, akin to wood, involves intricate processes including adhesive spreading, penetration, and solidification, influenced by the unique chemical composition of bamboo. The interfacial bond quality plays a pivotal role in determining the durability and performance of the final products, with numerous factors such as bamboo species, layered structure, adhesive type, and treatment types impacting the mechanical properties. Particular attention is given to the disparities in physical and mechanical properties between the bamboo culm's core and shell layers, attributing complexities to the gluing process. Examining shear failure strength reveals its criticality in mechanical investigations, with variations in bonding strength affecting the outcome. The review underscores the need for consistent quality control and adept manipulation of these influential factors for the successful manufacture of bamboo-based products. A comprehensive discussion ensues on the variables controlling the bonding properties of the developed bamboo products, aiming to evaluate and highlight the optimal parameters and procedures essential for enhancing the quality and reliability of bamboo-based composite materials for sustainable construction applications.

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.

TiO2 Films with Macroscopic Chiral Nematic-Like Structure Stabilized by Copper Promoting Light-Harvesting Capability for Hydrogen Generation

Cellulose nanocrystals (CNCs) have inspired the synthesis of various advanced nanomaterials, opening opportunities for different applications. However, a simple and robust approach for transferring the long-range chiral nematic nanostructures into TiO2 photocatalyst is still fancy. Herein, a successful fabrication of freestanding TiO2 films maintaining their macroscopic chiral nematic structures after removing the CNCs biotemplate is reported. It is demonstrated that including copper acetate in the sol avoids the epitaxial growth of the lamellar-like structure of TiO2 and stabilizes the chiral nematic structure instead. The experimental results and optical simulation demonstrate an enhancement at the blue and red edges of the Fabry-Pérot reflectance peak located in the visible range. This enhancement arises from the light scattering effect induced by the formation of the chiral nematic structure. The nanostructured films showed 5.3 times higher performance in the photocatalytic hydrogen generation, compared to lamellar TiO2, and benefited from the presence of copper species for charge carriers' separation. This work is therefore anticipated to provide a simple approach for the design of chiral nematic photocatalysts and also offers insights into the electron transfer mechanisms on TiO2/CuxO with variable oxidation states for photocatalytic hydrogen generation.

Mechanically Tunable Circularly Polarized Luminescence of Liquid Crystal-Templated Chiral Perovskite Quantum Dots

Endowing perovskite quantum dots (PQDs) with circularly polarized luminescence (CPL) offers great promise for innovative chiroptical applications, but the existing strategies are inefficient in acquiring stimuli-responsive flexible chiral perovskite films with large, tunable dissymmetry factor (glum) and long-term stability. Here, we report a strategy for the design and synthesis of luminescent cholesteric liquid crystal elastomer (Lumin-CLCE) films with mechanically tunable CPL, which is enabled by liquid crystal-templated chiral self-assembly and in situ covalent cross-linking of judiciously designed photopolymerizable CsPbX3 (X=Cl, Br, I) PQD nanomonomers into the elastic polymer networks. The resulting Lumin-CLCE films showcase circularly polarized structural color in natural light and noticeable CPL with a maximum glum value of up to 1.5 under UV light. The manipulation of CPL intensity and rotation direction is achieved by controlling the self-assembled helicoidal nanostructure and the handedness of soft helices. A significant breakthrough lies in the achievement of a reversible, mechanically tunable perovskite-based CPL switch activated by biaxial stretching, which enables flexible, dynamic anti-counterfeiting labels capable of decrypting preset information in specific polarization states. This work can provide new insights for the development of advanced chiral perovskite materials and their emerging applications in information encryption, flexible 3D displays, and beyond.

Omnidirectional color wavelength tuning of stretchable chiral liquid crystal elastomers

Wavelength-tunable structural colors using stimuli-responsive materials, such as chiral liquid crystals (CLCs), have attracted increasing attention owing to their high functionality in various tunable photonic applications. Ideally, on-demand omnidirectional wavelength control is highly desirable from the perspective of wavelength-tuning freedom. However, despite numerous previous research efforts on tunable CLC structural colors, only mono-directional wavelength tuning toward shorter wavelengths has been employed in most studies to date. In this study, we report the ideally desired omnidirectional wavelength control toward longer and shorter wavelengths with significantly improved tunability over a broadband wavelength range. By using areal expanding and contractive strain control of dielectric elastomer actuators (DEAs) with chiral liquid crystal elastomers (CLCEs), simultaneous and omnidirectional structural color-tuning control was achieved. This breakthrough in omnidirectional wavelength control enhances the achievable tuning freedom and versatility, making it applicable to a broad range of high-functional photonic applications.

On rheological properties of disc-shaped cellulose nanocrystals

The rheological properties of a substance depend greatly on its morphology, and rod-shaped cellulose nanocrystals (RCNCs) and cellulose nanofibrils (CNFs) have been extensively studied for their rheological properties. Nevertheless, the rheological properties of disc-shaped cellulose nanocrystals (DCNCs) with crystalline allomorph II derived from mercerized cellulose remain unknown yet. This work investigated the DCNCs' rheological properties in depth using steady-shear and oscillation measurements. At the same concentration, DCNC's suspension viscosity is lower than that of RCNC; RCNC has an instinct viscosity of 258.2, while DCNC has 187.9. Comparing RCNC suspensions with cellulose nanorods, DCNC has a lower aspect ratio and exhibits a distinct steady shear behavior. Under polarized film, DCNC suspension cannot self-assemble into chiral or liquid crystal phases, and with increasing concentrations, the system transitions from an isotropic phase to a gel phase. Oscillation sweeps demonstrate that the gel transition occurs at 7 %-8 %. Based on thixotropic recovery sweep outcomes, the high-stress oscillations enhance the network structure of DCNC suspensions, which is significantly different from that of RCNC suspensions. Results demonstrate the unique properties of DCNC, highlighting its application as a rheological modifier.

Sidewinder-Inspired Self-Adjusting, Lateral-Rolling Soft Robots for Autonomous Terrain Exploration

Helical structures of liquid crystal elastomers (LCEs) hold promise in soft robotics for self-regulated rolling motions. The understanding of their motion paths and potentials for terrain exploration remains limited. This study introduces a self-adjusting, lateral-rolling soft robot inspired by sidewinder snakes. The spring-like LCE helical filaments (HFs) autonomously respond to thermal cues, demonstrating dynamic and sustainable locomotion with adaptive rolling along non-linear paths. By fine-tuning the diameter, pitch, and modulus of the LCE HFs, and the environmental temperature, the movements of the LCE HFs, allowing for exploration of diverse terrains over a 600 cm2 area within a few minutes, can be programmed. LCE HFs are showcased to navigate through over nine obstacles, including maze escaping, terrain exploration, target hunting, and successfully surmounting staircases through adaptable rolling.

Chirality Supramolecular Systems: Helical Assemblies, Structure Designs, and Functions

Chirality, as one of the most striking characteristics, exists at various scales in nature. Originating from the interactions of host and guest molecules, supramolecular chirality possesses huge potential in the design of functional materials. Here, an overview of the recent progress in structure designs and functions of chiral supramolecular materials is present. First, three design routes of the chiral supramolecular structure are summarized. Compared with the template-induced and chemical synthesis strategies that depend on accurate molecular identification, the twisted-assembly technique creates chiral materials through the ordered stacking of the nanowire or films. Next, chirality inversion and amplification are reviewed to explain the chirality transfer from the molecular level to the macroscopic scale, where the available external stimuli on the chirality inversion are also given. Lastly, owing to the optical activity and the characteristics of the layer-by-layer stacking structure, the supramolecular chirality materials display various excellent performances, including smart response, shape-memorization, superior mechanical performance, and applications in biomedical fields. To sum up, this work provides a systematic review of the helical assemblies, structure design, and applications of supramolecular chirality systems.

Recent Advances in Flexible CNC-Based Chiral Nematic Film Materials

Cellulose nanocrystal (CNC) is a renewable resource derived from lignocellulosic materials, known for its optical permeability, biocompatibility, and unique self-assembly properties. Recent years have seen great progresses in cellulose nanocrystal-based chiral photonic materials. However, due to its inherent brittleness, cellulose nanocrystal shows limitations in the fields of flexible materials, optical sensors and food freshness testing. In order to solve the above limitations, attempts have been made to improve the flexibility of cellulose nanocrystal materials without destroying their structural color. Despite these progresses, a systematic review on them is lacking. This review aims to fill this gap by providing an overview of the main strategies and the latest research findings on the flexibilization of cellulose nanocrystal-based chiral nematic film materials (FCNM). Specifically, typical substances and methods used for their preparation are summarized. Moreover, different kinds of cellulose nanocrystal-based composites are compared in terms of flexibility. Finally, potential applications and future challenges of flexible cellulose nanocrystal-based chiral nematic materials are discussed, inspiring further research in this field.

Cellulose nanocrystals in the development of biodegradable materials: A review on CNC resources, modification, and their hybridization

The escalating demand for sustainable materials has propelled cellulose into the spotlight as a promising alternative to petroleum-based products. As the most abundant organic polymer on Earth, cellulose is ubiquitous, found in plants, bacteria, and even a unique marine animal-the tunicate. Cellulose polymers naturally give rise to microscale semi-crystalline fibers and nanoscale crystalline regions known as cellulose nanocrystals (CNCs). Exhibiting rod-like structures with widths spanning 3 to 50 nm and lengths ranging from 50 nm to several microns, CNC characteristics vary based on the cellulose source. The degree of crystallinity, crucial for CNC properties, fluctuates between 49 and 95 % depending on the source and synthesis method. CNCs, with their exceptional properties such as high aspect ratio, relatively low density (≈1.6 g cm-3), high axial elastic modulus (≈150 GPa), significant tensile strength, and birefringence, emerge as ideal candidates for biodegradable fillers in nanocomposites and functional materials. The percolation threshold, a mathematical concept defining long-range connectivity between filler and polymer, governs the effectiveness of reinforcement in nanocomposites. This threshold is intricately influenced by the aspect ratio and molecular interaction strength, impacting CNC performance in polymeric and pure nanocomposite materials. This comprehensive review explores diverse aspects of CNCs, encompassing their derivation from various sources, methods of modification (both physical and chemical), and hybridization with heterogeneous fillers. Special attention is devoted to the hybridization of CNCs derived from tunicates (TCNC) with those from wood (WCNC), leveraging the distinct advantages of each. The overarching objective is to demonstrate how this hybridization strategy mitigates the limitations of WCNC in composite materials, offering improved interaction and enhanced percolation. This, in turn, is anticipated to elevate the reinforcing effects and pave the way for the development of nanocomposites with tunable viscoelastic, physicochemical, and mechanical properties.

Structural Color from Cellulose Nanocrystals or Chitin Nanocrystals: Self-Assembly, Optics, and Applications

Widespread concerns over the impact of human activity on the environment have resulted in a desire to replace artificial functional materials with naturally derived alternatives. As such, polysaccharides are drawing increasing attention due to offering a renewable, biodegradable, and biocompatible feedstock for functional nanomaterials. In particular, nanocrystals of cellulose and chitin have emerged as versatile and sustainable building blocks for diverse applications, ranging from mechanical reinforcement to structural coloration. Much of this interest arises from the tendency of these colloidally stable nanoparticles to self-organize in water into a lyotropic cholesteric liquid crystal, which can be readily manipulated in terms of its periodicity, structure, and geometry. Importantly, this helicoidal ordering can be retained into the solid-state, offering an accessible route to complex nanostructured films, coatings, and particles. In this review, the process of forming iridescent, structurally colored films from suspensions of cellulose nanocrystals (CNCs) is summarized and the mechanisms underlying the chemical and physical phenomena at each stage in the process explored. Analogy is then drawn with chitin nanocrystals (ChNCs), allowing for key differences to be critically assessed and strategies toward structural coloration to be presented. Importantly, the progress toward translating this technology from academia to industry is summarized, with unresolved scientific and technical questions put forward as challenges to the community.

A Review of Structure Engineering of Strain-Tolerant Architectures for Stretchable Electronics

Stretchable electronics possess significant advantages over their conventional rigid counterparts and boost game-changing applications such as bioelectronics, flexible displays, wearable health monitors, etc. It is, nevertheless, a formidable task to impart stretchability to brittle electronic materials such as silicon. This review provides a concise but critical discussion of the prevailing structural engineering strategies for achieving strain-tolerant electronic devices. Not only the more commonly discussed lateral designs of structures such as island-bridge, wavy structures, fractals, and kirigami, but also the less discussed vertical architectures such as strain isolation and elastoplastic principle are reviewed. Future opportunities are envisaged at the end of the paper.

Programmable nanocomposites of cellulose nanocrystals and zwitterionic hydrogels for soft robotics

Stimuli-responsive hydrogels have garnered significant attention as a versatile class of soft actuators. Introducing anisotropic properties, and shape-change programmability to responsive hydrogels promises a host of opportunities in the development of soft robots. Herein we report the synthesis of pH-responsive hydrogel nanocomposites with predetermined microstructural anisotropy, shape-transformation, and self-healing. Our hydrogel nanocomposites are largely composed of zwitterionic monomers and asymmetric cellulose nanocrystals. While the zwitterionic nature of the network imparts both self-healing and cytocompatibility to our hydrogel nanocomposites, the shear-induced alignment of cellulose nanocrystals renders their anisotropic swelling and mechanical properties. Thanks to the self-healing properties, we utilized a cut-and-paste approach to program reversible, and complex deformation into our hydrogels. As a proof-of-concept, we demonstrated the transport of light cargo using tethered and untethered soft robots made from our hydrogels. We believe the proposed material system introduce a powerful toolbox for the development of future generations of biomedical soft robots.

Responsive Regulation of Energy Transfer in Lanthanide-Doped Nanomaterials Dispersed in Chiral Nematic Structure

The responsive control of energy transfer (ET) plays a key role in the broad applications of lanthanide-doped nanomaterials. Photonic crystals (PCs) are excellent materials for ET regulation. Among the numerous materials that can be used to fabricate PCs, chiral nematic liquid crystals are highly attractive due to their good photoelectric responsiveness and biocompatibility. Here, the mechanisms of ET and the photonic effect of chiral nematic structures on ET are introduced; the regulation methods of chiral nematic structures and the resulting changes in ET of lanthanide-doped nanomaterials are highlighted; and the challenges and promising opportunities for ET in chiral nematic structures are discussed.

Biobased Electronics: Tunable Dielectric and Piezoelectric Cellulose Nanocrystal-Protein Films

Cellulose has been a go-to material for its dielectric properties from the onset of capacitor development. The demand for an energy storage solution continues to grow, but the supply remains limited and relies too often on fossil and mined materials. This work proposes a fully sustainable and green method with which to produce dielectric thin films made of renewable and degradable materials. Cellulose nanocrystals (CNC) made an excellent matrix for the dispersion of proteins and the fabrication of robust transparent thin films with enhanced dielectric permittivity. A range of proteins sources, additives and concentrations allowed for us to control the dielectric permittivity from εr = 4 to 50. The proteins screened came from animal and plant sources. The films were formed from drying a water suspension of the CNC and proteins through evaporation-induced self-assembly. This yielded nano-layered structures with very high specific surface areas, ideal for energy storage devices. The resulting films were characterized with respect to the electrical, mechanical, piezoelectric, and optical properties to be compared. Electrically conductive (σ = 1.53 × 103 S/m) CNC films were prepared with carbon nanotubes (CNT). The fabricated films were used to make flexible, sustainable, and degradable capacitors by layering protein-based films between CNC-CNT composite films.

Bioinspired humidity-responsive liquid crystalline materials: from adaptive soft actuators to visualized sensors and detectors

Inspired by nature, humidity-responsive materials and devices have attracted significant interest from scientists in multiple disciplines, ranging from chemistry, physics and materials science to biomimetics. Owing to their superiorities, including harmless stimulus and untethered control, humidity-driven materials have been widely investigated for application in soft robots, smart sensors and detectors, biomimetic devices and anticounterfeiting labels. Especially, humidity-responsive liquid crystalline materials are particularly appealing due to the combination of programmable and adaptive liquid crystal matrix and humidity-controllability, enabling the fabrication of advanced self-adaptive robots and visualized sensors. In this review, we summarize the recent progress in humidity-driven liquid crystalline materials. First, a brief introduction of liquid crystal materials, including liquid crystalline polymers, cholesteric liquid crystals, blue-phase liquid crystals and cholesteric cellulose nanocrystals is provided. Subsequently, the mechanisms of humidity-responsiveness are presented, followed by the diverse strategies for the fabrication of humidity-responsive liquid crystalline materials. The applications of humidity-driven devices will be presented ranging from soft actuators to visualized sensors and detectors. Finally, we provide an outlook on the development of humidity-driven liquid crystalline materials.

Encryptable Electrochromic Smart Windows: Uniaxially Oriented and Polymerized Hierarchical Nanostructures Constructed by Self-Assembly of Tetrathiafulvalene-Based Reactive Mesogens

Tetrathiafulvalene (TTF)-based reactive mesogens (TTF-E and TTF-T) are synthesized, self-assembled, uniaxially oriented, and polymerized for the development of encryptable electrochromic smart windows. Electrochemical and spectroscopic experiments prove that the self-assembled TTF mixture (TTFM, TTF-E:TTF-T = 1:1) can reversibly switch the absorption wavelength of the TTF chromophore according to the redox reactions. Based on the identification of the phase transition and crystallographic structure, uniaxially oriented hierarchical nanostructures are easily constructed on the macroscopic area by simple coating and a self-assembly process. Subsequent polymerization of hierarchical nanostructures of TTFM significantly enhances thermal and mechanical stabilities and makes it possible for them to be fabricated as an electrochromic device. The angularly dependent correlation between the anisotropy of mesogens and the linearly polarized light allow us to demonstrate TTFM as smart windows capable of various optical security applications, including privacy protection and information encryption.

Mechanochromic and Conductive Chiral Nematic Nanostructured Film for Bioinspired Ionic Skins

Chameleon skin is naturally adaptive and can sense environmental changes and transform sensing into bioelectrical and optical signals by manipulating ion transduction and photonic nanostructures. The increasing interest in mimicking biological skins has considerably promoted the development of advanced photonic materials with an increasing ionic conductivity. Herein, we report the judicious design and fabrication of a bioinspired mechanochromic chiral nematic nanostructured film with good ionic conductivity by infiltrating fluorine-rich ionic liquids (FILs) into a swollen self-assembled cellulose nanocrystal (CNC) film with helical nanoarchitectures. Notably, the introduction of 2-hydroxyethyl acrylate considerably enhances the compatibility of hydrophobic FILs and hydrophilic CNCs. The resulting FIL-CNC nanostructured films exhibited excellent mechanochromism, good ionic conductivity, and outstanding optical/electrical dual-signal sensing performance when used as a bioinspired ionic skin for real-time monitoring of human motions. Owing to the integration of FILs, the underwater stability of the chiral liquid crystal nanostructures of CNCs was significantly enhanced. Notably, underwater contact/contactless sensing modes and encrypted information transmission have been achieved with the FIL-CNC nanostructured film. This study can offer great insights for the advancement of biomimetic multifunctional artificial skins and emerging interactive devices, which can find important applications in wearable iontronics, human-machine interactions, and intelligent robots.

Bioinspired Additive Manufacturing of Hierarchical Materials: From Biostructures to Functions

Throughout billions of years, biological systems have evolved sophisticated, multiscale hierarchical structures to adapt to changing environments. Biomaterials are synthesized under mild conditions through a bottom-up self-assembly process, utilizing substances from the surrounding environment, and meanwhile are regulated by genes and proteins. Additive manufacturing, which mimics this natural process, provides a promising approach to developing new materials with advantageous properties similar to natural biological materials. This review presents an overview of natural biomaterials, emphasizing their chemical and structural compositions at various scales, from the nanoscale to the macroscale, and the key mechanisms underlying their properties. Additionally, this review describes the designs, preparations, and applications of bioinspired multifunctional materials produced through additive manufacturing at different scales, including nano, micro, micro-macro, and macro levels. The review highlights the potential of bioinspired additive manufacturing to develop new functional materials and insights into future directions and prospects in this field. By summarizing the characteristics of natural biomaterials and their synthetic counterparts, this review inspires the development of new materials that can be utilized in various applications.

Engineering Dynamic Structural Color Pixels at Microscales by Inhomogeneous Strain-Induced Localized Topographic Change

Structural colors in homogeneous elastomeric materials predominantly exhibit uniform color changes under applied strains. However, juxtaposing mechanochromic pixels that exhibit distinct responses to applied strain remains challenging, especially on the microscale where the demand for miscellaneous spectral information increases. Here, we present a method to engineer microscale switchable color pixels by creating localized inhomogeneous strain fields at the level of individual microlines. Trenches produced by transfer casting from 2.5D structures into elastomers exhibit a uniform structural color in the unstretched state due to interference and scattering effects, while they show different colors under an applied uniaxial strain. This programmable topographic change resulting in color variation arises from strain mismatch between layers and trench width. We utilized this effect to achieve the encryption of text strings with Morse code. The effective and facile design principle is promising for diverse optical devices based on dynamic structures and topographic changes.

Chiro-Optoelectronic Encodable Multilevel Thin Film Electronic Elements with Active Bio-Organic Electrolyte Layer

It is suggested that chiral photonic bio-enabled integrated thin-film electronic elements can pave the base for next-generation optoelectronic processing, including quantum coding for encryption as well as integrated multi-level logic circuits. Despite recent advances, thin-film electronics for encryption applications with large-scale reconfigurable and multi-valued logic systems are not reported to date. Herein, highly secure optoelectronic encryption logic elements are demonstrated by facilitating the humidity-sensitive helicoidal organization of chiral nematic phases of cellulose nanocrystals (CNCs) as an active electrolyte layer combined with printed organic semiconducting channels. The ionic-strength controlled tunable photonic band gap facilitates distinguishable and quantized 13-bit electric signals triggered by repetitive changes of humidity, voltage, and the polarization state of the incident light. As a proof-of-concept, the integrated circuits responding to circularly polarized light and humidity are demonstrated as unique physically unclonable functional devices with high-level logic rarely achieved. The convergence between functional nanomaterials and the multi-valued logic thin-film electronic elements can provide optoelectronic counterfeiting, imaging, and information processing with multilevel logic nodes.

Hydrogen-bonding topological remodeling modulated ultra-fine bacterial cellulose nanofibril-reinforced hydrogels for sustainable bioelectronics

Bacterial cellulose (BC) with its inherent nanofibrils framework is an attractive building block for the fabrication of sustainable bioelectronics, but there still lacks an effective and green strategy to regulate the hydrogen-bonding topological structure of BC to improve its optical transparency and mechanical stretchability. Herein, we report an ultra-fine nanofibril-reinforced composite hydrogel by utilizing gelatin and glycerol as hydrogen-bonding donor/acceptor to mediate the rearrangement of the hydrogen-bonding topological structure of BC. Attributing to the hydrogen-bonding structural transition, the ultra-fine nanofibrils were extracted from the original BC nanofibrils, which reduced the light scattering and endowed the hydrogel with high transparency. Meanwhile, the extracted nanofibrils were connected with gelatin and glycerol to establish an effective energy dissipation network, leading to an increase in stretchability and toughness of hydrogels. The hydrogel also displayed tissue-adhesiveness and long-lasting water-retaining capacity, which acted as bio-electronic skin to stably acquire the electrophysiological signals and external stimuli even after the hydrogel was exposing to air condition for 30 days. Moreover, the transparent hydrogel could also serve as a smart skin dressing for optical identification of bacterial infection and on-demand antibacterial therapy after combined with phenol red and indocyanine green. This work offers a strategy to regulate the hierarchical structure of natural materials for designing skin-like bioelectronics toward green, low cost, and sustainability.

Cellulose nanocrystals-based bio-composite optical materials for reversible colorimetric responsive films and coatings

Photonic materials with a tunable chiral nematic structure that can selectively reflect light dynamically are valuable for applications in smart responsive materials. Here, we prepared potential photonic composites with a chiral nematic structure by forming cellulose nanocrystals (CNCs) and waterborne polyurethane (WPU) composites with different compositions on different substrates by evaporation-induced self-assembly. With increasing WPU content, the reflected wavelength increased from 400 to 680 nm, which was mainly caused by the increase of the chiral nematic pitch. In addition, the mechanical properties were better for higher WPU content. WPU was sensitive to small amounts of moisture in ethanol owing to the swollen WPU after absorbing water will increase the helical pitch. The reversible red shift induced by moisture was approximately 100 nm. When wood was used as the substrate, the CNCs still self-assembled to form chiral nematic structures and the adhesion forces of the composites to the wood substrate were strong. By using MgCl₂ solution as an ink, invisible patterns can be written on the coating, which can be revealed temporarily by ethanol. In addition, the invisible pattern of photonic coating is rewritable. The easily prepared environmentally friendly photonic composite has great potential in sensors, anti-counterfeiting labels and smart decorative coatings.

Flow and assembly of cellulose nanocrystals (CNC): A bottom-up perspective - A review

Cellulosic sources, such as lignocellulose-rich biomass, can be mechanically or acid degraded to produce inclusions called cellulose nanocrystals (CNCs). They have several uses in the sectors of biomedicine, photonics, and material engineering because of their biodegradability, renewability, sustainability, and mechanical qualities. The processing and design of CNC-based products are inextricably linked to the rheological behaviour of CNC suspension or in combination with other chemicals, such as surfactants or polymers; in this context, rheology offers a significant link between microstructure and macro scale flow behaviour that is intricately linked to material response in applications. The flow behaviour of CNC items must be properly specified in order to produce goods with value-added characteristics. In this review article, we provide new research on the shear rheology of CNC dispersion and CNC-based hydrogels in the linear and nonlinear regime, with storage modulus values reported to range from ~10^-3 to 10³ Pa. Applications in technology and material science are also covered simultaneously. We carefully examined the effects of charge density, aspect ratio, concentration, persistence length, alignment, liquid crystal formation, the cause of chirality in CNCs, interfacial behaviour and interfacial rheology, linear and nonlinear viscoelasticity of CNC suspension in bulk and at the interface using the currently available literature.

Self-Healable, Solvent Response Cellulose Nanocrystal/Waterborne Polyurethane Nanocomposites with Encryption Capability

Cellulose nanocrystal (CNC)-based chiral nematic structure is widely used in stimulus response and sensing. A popular area of research is enhancing the mechanical characteristics and environmental adaptability of chiral nematic materials. In this paper, a flexible photonic film with self-healing ability (FPFS) was prepared by combining waterborne polyurethane containing dynamic covalent disulfide bonds (SSWPU) with CNC. The results found that the FPFS showed excellent toughness under the action of stretching, bending, twisting, and folding. The FPFS exhibited an amazing self-healing efficiency, which can be self-healed within 2 h at room temperature. Moreover, the FPFS could respond immediately and produce reversible color change when it was soaked in typical solvents. In addition, when ethanol was used as ink to paint on the FPFS, a visible pattern only under polarized light was formed. This study offers fresh perspectives in the areas of self-healing, biological anticounterfeiting, solvent response, and flexible photonic materials.

Anisotropic cellulose nanocrystal composite hydrogel for multiple responses and information encryption

Anisotropic composites based on well-ordered cellulose nanocrystals (CNCs) have received increasing attention due to their fascinating optical properties. In this study, we fabricated a multi-functional hydrogel with nematic organization of CNC by soaking a pre-stretched polyvinyl alcohol (PVA)/CNC cyrogel in Na₂SO₄, CaCl₂ solution and DI water in sequence. The crystalline domains, water content and transmittance of the hydrogel are regulated via the Hofmeister effect and hydrophobic interactions, which makes the birefringence of the hydrogel observable by interference colors. The aligned CNC not only enhance the mechanical strength of hydrogel, but also endow it with stimuli-responsive ability to the varying environment such as ion strength (0 to 5 M NaCl solution) and external forces (pressure of 0 to 248 kPa). Moreover, the patterned hydrogels are successfully fabricated by the method of local solvent displacement. Due to the low light transmission, the pattern can be encrypted and only be observed between crossed polarizers. These optical properties made the hydrogel a promising candidate for environmental monitoring and anti-counterfeit material.

Chirality Transfer from an Innately Chiral Nanocrystal Core to a Nematic Liquid Crystal 2: Lyotropic Chromonic Liquid Crystals

The importance of and the difference between molecular versus structural core chirality of substances that form nanomaterials, and their ability to transmit and amplify their chirality to and within a surrounding condensed medium is yet to be exactly understood. Here we demonstrate that neat as well as disodium cromoglycate (DSCG) surface-modified cellulose nanocrystals (CNCs) with both molecular and morphological core chirality can induce homochirality in racemic nematic lyotropic chromonic liquid crystal (rac-N-LCLC) tactoids. In comparison to the parent chiral organic building blocks, D-glucose, endowed only with molecular chirality, both CNCs showed a superior chirality transfer ability. Here, particularly the structurally compatible DSCG-modified CNCs prove to be highly effective since the surface DSCG moieties can insert into the DSCG stacks that constitute the racemic tactoids. Overall, this presents a highly efficient pathway for chiral induction in an aqueous medium and thus for understanding the origins of biological homochirality in a suitable experimental system.

Liquid Crystalline Systems from Nature and Interaction of Living Organisms with Liquid Crystals

Biomaterials, which are substances interacting with biological systems, have been extensively explored to understand living organisms and obtain scientific inspiration (such as biomimetics). However, many aspects of biomaterials have yet to be fully understood. Because liquid crystalline phases are ubiquitously found in biomaterials (e.g., cholesterol, amphiphile, DNA, cellulose, bacteria), therefore, a wide range of research has made attempts to approach unresolved issues with the concept of liquid crystals (LCs). This review presents these studies that address the interactive correlation between biomaterials and LCs. Specifically, intrinsic LC behavior of various biomaterials such as DNA, cellulose nanocrystals, and bacteriaare first introduced. Second, the dynamics of bacteria in LC media are addressed, with focus on how bacteria interact with LCs, and how dynamics of bacteria can be controlled by exploiting the characteristics of LCs. Lastly, how the strong correlation between LCs and biomaterials has been leveraged to design a new class of biosensors with additional functionalities (e.g., self-regulated drug release) that are not available in previous systems is reviewed. Examples addressed in this review convey the message that the intersection between biomaterials and LCs offers deep insights into fundamental understanding of biomaterials, and provides resources for development of transformative technologies.

Molecular Dynamics Simulations of the Mechanical Properties of Cellulose Nanocrystals-Graphene Layered Nanocomposites

Cellulose nanocrystals (CNCs) have received a significant amount of attention due to their excellent physiochemical properties. Herein, based on bioinspired layered materials with excellent mechanical properties, a CNCs-graphene layered structure with covalent linkages (C-C bond) is constructed. The mechanical properties are systematically studied by molecular dynamics (MD) simulations in terms of the effects of temperature, strain rate and the covalent bond content. Compared to pristine CNCs, the mechanical performance of the CNCs-graphene layered structure has significantly improved. The elastic modulus of the layered structure decreases with the increase of temperature and increases with the increase of strain rate and covalent bond coverage. The results show that the covalent bonding and van der Waals force interactions at the interfaces play an important role in the interfacial adhesion and load transfer capacity of composite materials. These findings can be useful in further modeling of other graphene-based polymers at the atomic scale, which will be critical for their potential applications as functional materials.

Photoelastic Organogel with Multiple Stimuli Responses

The photoelastic effect has many uses in mechanics today, but it is usually disregarded in flexible materials. Using 2-phenoxyethyl acrylate as a monomer and 4-cyano-4'-pentylbiphenyl (5CB) as a solvent, a multiple responsive photoelastic organogel (PO) with strong birefringence but low modulus is created. 5CB is a liquid crystal molecule that does not participate in the polymerization process and is always present as tiny molecules in the polymer. It endows the PO low modulus and high birefringence, as well as the ability to drive the birefringence using an electric field. This PO not only has high sensitivity and fast response as a photoelastic strain sensor, but also has a very sensitive response to heat, especially in the range of human body temperature. It also has a high dielectric constant and a strong correlation between the interference color and the applied electric field, allowing for easy writing and erasure of encrypted data. This unique multisignal response feature and low modulus that mimics human skin bring up new opportunities in the potential applications such as multiple information encryption, anticounterfeiting, and multifunctional wearable sensors.

Naturally Derived Janus Cellulose Nanomaterials: Anisotropic Cellulose Nanomaterial Building Blocks and Their Assembly into Asymmetric Structures

Naturally derived cellulose nanomaterials (CNMs) with desirable physicochemical properties have drawn tremendous attention for their versatile applications in a broad range of fields. More recently, Janus amphiphilic cellulose nanomaterial particles with asymmetric structures (i.e., reducing and nonreducing ends and crystalline and amorphous domains) have been in the spotlight, offering a rich and sophisticated toolbox for Janus nanomaterials. With careful surface and interfacial engineering, Janus CNM particles have demonstrated great potential as surface modifiers, emulsifiers, stabilizers, compatibilizers, and dispersants in emulsions, nanocomposites, and suspensions. Naturally derived Janus CNM particles offer a fascinating opportunity for scaling up the production of self-standing Janus CNM membranes. Nevertheless, most Janus CNM membranes to date are constructed by asymmetric fabrication or asymmetric modification without considering the Janus traits of CNM particles. More future research should focus on the self-assembly of Janus CNM particles into bulk self-standing Janus CNM membranes to enable more straightforward and sustainable approaches for Janus membranes. This review explores the fabrication, structure-property relationship, and Janus configuration mechanisms of Janus CNM particles and membranes. Janus CNM membranes are highlighted for their versatile applications in liquid, thermal, and light management. This review also highlights the significant advances and future perspectives in the construction and application of sustainable Janus CNM particles and membranes.

Advanced cellulose nanocrystals (CNC) and cellulose nanofibrils (CNF) aerogels: Bottom-up assembly perspective for production of adsorbents

The most common and abundant polymer in nature is the linear polysaccharide cellulose, but processing it requires a new approach since cellulose degrades before melting and does not dissolve in ordinary organic solvents. Cellulose aerogels are exceptionally porous (>90 %), have a high specific surface area, and have low bulk density (0.0085 mg/cm³), making them suitable for a variety of sophisticated applications including but not limited to adsorbents. The production of materials with different qualities from the nanocellulose based aerogels is possible thanks to the ease with which other chemicals may be included into the structure of nanocellulose based aerogels; despite processing challenges, cellulose can nevertheless be formed into useful, value-added products using a variety of traditional and cutting-edge techniques. To improve the adsorption of these aerogels, rheology, 3-D printing, surface modification, employment of metal organic frameworks, freezing temperature, and freeze casting techniques were all investigated and included. In addition to exploring venues for creation of aerogels, their integration with CNC liquid crystal formation were also explored and examined to pursue "smart adsorbent aerogels". The objective of this endeavour is to provide a concise and in-depth evaluation of recent findings about the conception and understanding of nanocellulose aerogel employing a variety of technologies and examination of intricacies involved in enhancing adsorption properties of these aerogels.

Self-assembled liquid crystal architectures for soft matter photonics

Self-assembled architectures of soft matter have fascinated scientists for centuries due to their unique physical properties originated from controllable orientational and/or positional orders, and diverse optic and photonic applications. If one could know how to design, fabricate, and manipulate these optical microstructures in soft matter systems, such as liquid crystals (LCs), that would open new opportunities in both scientific research and practical applications, such as the interaction between light and soft matter, the intrinsic assembly of the topological patterns, and the multidimensional control of the light (polarization, phase, spatial distribution, propagation direction). Here, we summarize recent progresses in self-assembled optical architectures in typical thermotropic LCs and bio-based lyotropic LCs. After briefly introducing the basic definitions and properties of the materials, we present the manipulation schemes of various LC microstructures, especially the topological and topographic configurations. This work further illustrates external-stimuli-enabled dynamic controllability of self-assembled optical structures of these soft materials, and demonstrates several emerging applications. Lastly, we discuss the challenges and opportunities of these materials towards soft matter photonics, and envision future perspectives in this field.

Bioinspired Optical Flexible Cellulose Nanocrystal Films with Strain-Adaptive Structural Coloration

Recent advances of photonic crystals are driven to mechanical sensors and smart wearable devices; however, for chiral photonic cellulose nanocrystal (CNC) materials, vivid structural coloration and reversible mechanochromism like chameleon skin remain a big challenge. Here, we report a ternary co-assembly and post-UV-irradiation polymerization strategy to develop flexible and elastic CNC composite films, which, notably, have naked-eye-visible brilliant structural colors and stretching-induced color change covering a broad wavelength region at a moderate deformation (like skin). By adjusting the stretching, the film is designed as a smart skin to adapt to surrounding environments for camouflage. This work offers a universal strategy for constructing biomimic optically functional cellulose skins.

Chiral Liquid Crystalline Properties of Cellulose Nanocrystals: Fundamentals and Applications

By using an independent self-assembly process that is occasionally controlled by evaporation, cellulose nanocrystals (CNCs) may create films (pure or in conjunction with other materials) that have iridescent structural colors. The self-forming chiral nematic structures and environmental safety of a new class of photonic liquid crystals (LCs), referred to as CNCs and CNC-embedded materials, make them simple to make and treat. The structure of the matrix interacts with light to give structural coloring, as opposed to other dye pigments, which interact with light by adsorption and reflection. Understanding how CNC self-assembly constructs structures is vital in several fields, including physics, science, and engineering. To constructure this review, the colloidal characteristics of CNC particles and their behavior during the formation of liquid crystals and gelling were studied. Then, some of the recognized applications for these naturally occurring nanoparticles were summarized. Different factors were considered, including the CNC aspect ratio, surface chemistry, concentration, the amount of time needed to produce an anisotropic phase, and the addition of additional substances to the suspension medium. The effects of alignment and the drying process conditions on structural changes are also covered. The focus of this study however is on the optical properties of the films as well as the impact of the aforementioned factors on the final transparency, iridescent colors, and versus the overall response of these bioinspired photonic materials. Control of the examined factors was found to be necessary to produce reliable materials for optoelectronics, intelligent inks and papers, transparent flexible support for electronics, and decorative coatings and films.

Programmable Birefringent Patterns from Modulating the Localized Orientation of Cellulose Nanocrystals

Birefringence has been attracting broad attention due to its strong potential for applications in biomedicine and optics, such as biomedical diagnosis, colorimetric sensing, retardant, and polarization encoding. However, engineering architectures with precisely controllable birefringence remains a challenge due to the lack of effective modulation of the localized orientation. Here, by taking advantage of the inherently one-dimensional (1D) anisotropic structure of cellulose nanocrystals (CNCs), we demonstrate an approach to tune the alignment of CNCs with a well-controllable orientation at localized preciseness, which is in contrast to the previously reported unidirectional/radical orientation of CNC-based birefringent structures. The localized modulation of CNC orientation is facilitated by directing the 1D nanocrystals to align along the template periphery and the migrated three-phase contact line during the evaporation. The resultant CNC films exhibit birefringent extinction patterns under polarized light, in which versatile pattern designs can be obtained by employing templates with different shapes and template arrays with varied layouts. Due to the locally modulated orientation of CNCs, the films indicate "kaleidoscope-like" dynamically transformable designs of the birefringent patterns depending on the polarized angle, which has barely been observed previously. Furthermore, an N-nary encoding system for abundant information storage is demonstrated based on the sunlight-transparent CNC films, but with visible extinction patterns under polarized light, which is promising for encryptions, anticounterfeiting, and imaging, enriching the attractive research area of bio-based photonics.

Biopolymeric Nanocarriers for Nutrient Delivery and Crop Biofortification

Driven by the possibility of precise transformational change in nutrient-enrichment technology to meet global food demand, advanced nutrient delivery strategies have emerged to pave the path toward success for nutrient enrichment in edible parts of crops through bioderived nanocarriers with increased productivity. Slow and controlled release of nutrient carrier materials influences the nutrient delivery rate in soil and in the edible parts of crops with a sluggish nutrient delivery to enhance their availability in roots by minimizing nutrient loss. With a limited understanding of the nutrient delivery mechanism in soil and the edible parts of crops, it is envisaged to introduce nutrient-enrichment technology for nutrient delivery that minimizes environmental impact due to its biodegradable nature. This article attempts to analyze the possible role of the cellulose matrix for nutrient release and the role of cellulose nanocomposites and nanofibers. We have proposed a few cellulose derived biofortificant materials as nutrient carriers, such as (1) nanofibers, (2) polymer-nanocellulose-clay composites, (3) silk-fibroin derived nanocarriers, and (4) carboxymethyl cellulose. An effort is undertaken to describe the research need by linking a biopolymer derived nanocarrier for crop growth regulation and experimental nitrogen release analysis. We have finally provided a perspective on cellulose nanofibers (CNFs) for microcage based nutrient loading ability. This article aims to explain why biopolymer derived nutrient carriers are the alternative candidate for alleviating nutrient deficiency challenges which are involved in focusing the nutrient delivery profile of biopolymers and promising biofortification of crops.

Structurally Colored Cellulose Nanocrystal Films as Transreflective Radiative Coolers

Radiative cooling forms an emerging direction in which objects are passively cooled via thermal radiation to cold space. Cooling materials should provide high thermal emissivity (infrared absorptance) and low solar absorptance, making cellulose an ideal and sustainable candidate. Broadband solar-reflective or transparent coolers are not the only systems of interest, but also more pleasingly looking colored systems. However, solutions based on wavelength-selective absorption generate not only color but also heat and thereby counteract the cooling function. Intended as coatings for solar cells, we demonstrate a transreflective cellulose material with minimal solar absorption that generates color by wavelength-selective reflection, while it transmits other parts of the solar spectrum. Our solution takes advantage of the ability of cellulose nanocrystals to self-assemble into helical periodic structures, providing nonabsorptive films with structurally colored reflection. Application of violet-blue, green, and red cellulose films on silicon substrates reduced the temperature by up to 9 °C under solar illumination, as result of a combination of radiative cooling and reduced solar absorption due to the wavelength-selective reflection by the colored coating. The present work establishes self-assembled cellulose nanocrystal photonic films as a scalable photonic platform for colored radiative cooling.

Liquid crystal-templated chiral nanomaterials: from chiral plasmonics to circularly polarized luminescence

Chiral nanomaterials with intrinsic chirality or spatial asymmetry at the nanoscale are currently in the limelight of both fundamental research and diverse important technological applications due to their unprecedented physicochemical characteristics such as intense light-matter interactions, enhanced circular dichroism, and strong circularly polarized luminescence. Herein, we provide a comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials. The chiroptical properties of chiral nanomaterials are touched, and their fundamental design principles and bottom-up synthesis strategies are discussed. Different chiral functional nanomaterials based on liquid-crystalline soft templates, including chiral plasmonic nanomaterials and chiral luminescent nanomaterials, are systematically introduced, and their underlying mechanisms, properties, and potential applications are emphasized. This review concludes with a perspective on the emerging applications, challenges, and future opportunities of such fascinating chiral nanomaterials. This review can not only deepen our understanding of the fundamentals of soft-matter chirality, but also shine light on the development of advanced chiral functional nanomaterials toward their versatile applications in optics, biology, catalysis, electronics, and beyond.

Modulating the chiral nanoarchitecture of cellulose nanocrystals through interaction with salts and polymer

HYPOTHESIS

The conditions to allow self-assembly of cellulose nanocrystal (CNC) suspensions into chiral nematic structures are based on aspect ratio, surface charge density and a balance between repulsive and attractive forces between CNC particles.

EXPERIMENTS

Three types of systems were characterized in suspensions and subsequently in their solid dried films: 1) neat water dialyzed CNC, 2) CNC combined with polyethylene glycol(PEG) (CNC/PEG), and 3) CNC with added salt (CNC/Salt). All suspensions were characterized by polarized optical microscope (POM) and small angle X-ray scattering (SAXS), while the resultant dried films were analyzed by reflectance spectrometer, scanning electron microscope (SEM) and SAXS.

FINDINGS

The presence of chiral nematic (CN*) structures was not observed in dialyzed aqueous suspensions of CNC during water evaporation. By introducing salts or a non-adsorbing polymer, chirality was apparent in both suspensions and films. The interaxial angle between CNC rods increased when the suspensions of CNC/PEG and CNC/salt were dried to solid films. The angle was found to be dependent on both species of ions and ionic strength, while the inter-particle distance was only related to the salt concentration, as explained in terms of interaction energies. The CNC suspensions/film chirality can be modulated by controlling the colloidal forces.

Polymerizable Deep Eutectic Solvent-Based Skin-Like Elastomers with Dynamic Schemochrome and Self-Healing Ability

Animal skin is a huge source of inspiration when it comes to multifunctional sensing materials. Bioinspired sensors integrated with the intriguing performance of skin-like steady wide-range strain detection, real-time dynamic visual cues, and self-healing ability hold great promise for next-generation electronic skin materials. Here, inspired by the skins of a chameleon, cellulose nanocrystals (CNCs) liquid crystal skeleton is embedded into polymerizable deep eutectic solvent (PDES) via in situ polymerization to develop a skin-like elastomer. Benefiting from the elastic ionic conductive PDES matrix and dynamic interfacial hydrogen bonding, this strategy has broken through the limitations that CNCs-based cholesteric structure is fragile and its helical pitch is non-adjustable, endowing the resulting elastomer with strain-induced wide-range (0-500%) dynamic structural colors and excellent self-healing ability (78.9-90.7%). Furthermore, the resulting materials exhibit high stretch-ability (1163.7%), strain-sensing and self-adhesive abilities, which make them well-suitable for developing widely applicable and highly reliable flexible sensors. The proposed approach of constructing biomimetic skin-like materials with wide-range dynamic schemochrome is expected to extend new possibilities in diverse applications including anti-counterfeit labels, soft foldable displays, and wearable optical devices.

Anisotropic cellulose nanocrystal hydrogel with multi-stimuli response to temperature and mechanical stress

Conventional hydrogels with isotropic polymer networks usually lack selective response to external stimuli and that limits their applications in intelligent devices. Herein, hydrogels with distinctive anisotropic optical characteristics combined with thermosensitivity were prepared through in situ photopolymerization. Self-assembled cellulose nanocrystals (CNCs) with chiral nematic ordered structure were embedded in polyethylene glycol derivatives/polyacrylamide polymer networks. The arrangement of CNCs showed a strong dependence on the self-assembly angle and standing time, enabling the fabrication of hydrogels with customizable CNCs arrangements. Increasing the self-assembly angle from 0° to 90° changed the CNCs arrangement from chiral nematic to symmetrical nematic order which, together with CNCs dynamic arrangement from isotropic to annealed chiral nematic phase at longer standing time, provided versatile ways to produce CNCs hydrogels with tunable anisotropic properties. In addition, the obtained hydrogel displayed reversible temperature and compression response, showing excellent promise to be used as soft mechanical stress and temperature sensors or novel anti-counterfeiting materials.

Three-dimensional artificial chirality towards low-cost and ultra-sensitive enantioselective sensing

Artificial chiral structures have potential applications in the field of enantioselective signal sensing. Advanced nanofabrication methods enable a large diversity in geometric structures and broad selectivity of materials, which can be exploited to manufacture artificial three-dimensional chiral structures. Various chiroptical phenomena exploiting spin and orbital angular momentum at the nanoscale have been continuously exploited as a way to effectively detect enantiomers. This review introduces precisely controlled bottom-up and large-area top-down metamaterial fabrication methods to solve the limitations of high manufacturing cost and low production speed. Particle synthesis, self-assembly, glanced angled vapor deposition, and three-dimensional plasmonic nanostructure printing are introduced. Furthermore, emerging sensitive chiral sensing methods such as cavity-enhanced chirality, photothermal circular dichroism, and helical dichroism of single particles are discussed. The continuous progress of nanofabrication technology presents the strong potential for developing artificial chiral structures for applications in biomedical, pharmaceutical, nanophotonic systems.

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.