Regular Linking of Cellulose Nanocrystals via Click Chemistry: Synthesis and Formation of Cellulose Nanoplatelet Gels

Functionalization of cellulose nanocrystals with a potent antimalarial compound: Synthesis, characterization, and biological studies

Cellulosic materials, such as cellulose nanocrystals (CNCs), are biocompatible, biodegradable and have unique and fascinating biomedical applications. Calxinin (CXN), a potent multistage antimalarial compound was functionalised with CNCs to improve biocompatibility and enhance the bioactivity of the resulting CNC-CXN nano-conjugate. Elemental analysis, powder X-ray, SEM, AFM, Infrared, and solid-state NMR spectroscopic techniques confirmed the composition of novel CNC-CXN nano-conjugate. Next, CNC-CXN nano-conjugate did not exhibit apparent cytotoxic effects on the sensitive Vero E6 cell line up to a concentration of 4.66 μg/μl. The CNC-CXN nano-conjugate was also evaluated for its preliminary efficacy on Plasmodium falciparum (3D7) malaria parasite and showed a 50 % inhibitory concentration value of 0.02 μg/μl. Overall, the selectivity index (SI) of the CNC-CXN nano-conjugate significantly improved to 233, indicating its suitability for further validation studies in animal models.

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.

Modification and characterization of a novel and fluorine-free cellulose nanofiber with hydrophobic and oleophobic properties

In this study, a brand-new, easy, and environmentally friendly approach for chemically functionalizing 2,2,6,6-tetramethylpiperidinyloxyl radical (TEMPO)-oxidized cellulose nanofiber (TOCNF) to produce modified cellulose nanofiber (octadecylamine-citric acid-CNF) was proposed. Effects of octadecylamine (ODA)/TOCNF mass ratio on the chemical structure, morphology, surface hydrophobicity and oleophobicity were studied. According to Fourier transform infrared spectroscopy (FTIR) analysis, ODA was successfully grafted onto the TOCNF by simple citric acid (CA) esterification and amidation reactions. Scanning electron microscopy (SEM) showed that a new rough structure was formed on the ODA-CA-CNF surface. The water contact angle (WCA) and the castor oil contact angle (OCA) of the ODA-CA-CNF reached 139.6° and 130.6°, respectively. The high-grafting-amount ODA-CA-CNF was sprayed onto paper, and the OCA reached 118.4°, which indicated good oil-resistance performance. The low-grafting-amount ODA-CNF was applied in a pH-responsive indicator film, exhibiting a colour change in response to the pH level, which can be applied in smart food packaging. The ODA-CA-CNF with excellent water/oil-resistance properties and fluorine-free properties can replace petrochemical materials and can be used in the fields of fluorine-free oil-proof paper.

Controllable Drug-Release Ratio and Rate of Doxorubicin-Loaded Natural Composite Films Based on Polysaccharides: Evaluation of Transdermal Permeability Potential

In drug delivery systems, it is crucial to develop a drug carrier capable of regulating both the drug-release rate and the drug-release ratio. This study proposes a method for controlling the drug-release ratio/rate using doxorubicin-loaded natural composite films composed of polysaccharides (cellulose, chitin, chitosan, or cellulose nanocrystal) and mineral substances (MMT: montmorillonite). We succeeded in controlling the doxorubicin release ratio from 25 to 88% depending on the natural polysaccharide. Likewise, the reduction rate differed depending on the type of natural polysaccharide, whereas the reduction in release was achieved by mixing MMT. Cellulose had the largest reduction in the drug release ratio, approximately 30%, and cellulose nanocrystals showed little change. Furthermore, we conducted a skin permeation test on the natural polysaccharide film with the highest release rate to confirm its transdermal permeability potential. The polysaccharide doxorubicin-loaded film sustainably released doxorubicin for 2 days, which indicated the potential of a carrier for DDS applications.

Low-temperature, ultra-fast, and recyclable self-healing nanocomposites reinforced with non-solvent silylated modified cellulose nanocrystals

Developing polymeric materials with remarkable mechanical properties and fast self-healing performance even at low temperatures is challenging. Herein, the polymeric nanocomposites containing silane-treated cellulose nanocrystals (SCNC) with ultrafast self-healing and exceptional mechanical characteristics were developed even at low temperatures. First, CNC is modified with a cyclic silane coupling agent using an eco-friendly chemical vapor deposition method. The nanocomposite was then fabricated by blending SCNC with matrix prepolymer, prepared from monomers that possess lower critical solution temperature, followed by the inclusion of dibutyltin dilaurate and hexamethylene diisocyanate. The self-healing capability of the novel SCNC/polymer nanocomposites was enhanced remarkably by increasing the content of SCNC (0-3 wt%) and reaching (≥99 %) at temperatures (5 & 25 °C) within <20 min. Moreover, SCNC-3 showed a toughness of (2498 MJ/m3) and SCNC-5 displayed a robust tensile strength of (22.94 ± 0.4 MPa) whereas SCNC-0 exhibited a lower tensile strength (7.4 ± 03 MPa) and toughness of (958 MJ/m3). Additionally, the nanocomposites retain their original mechanical properties after healing at temperatures (5 & 25 °C) owing to the formation of hydrogen bonds via incorporation of the SCNC. These novel SCNC-based self-healable nanocomposites with tunable mechanical properties offer novel insight into preparing damage and temperature-responsive flexible and wearable devices.

Graft onto approaches for nanocellulose-based advanced functional materials

The resurgence of cellulose as nano-dimensional 'nanocellulose' has unlocked a sustainable bioeconomy for the development of advanced functional biomaterials. Bestowed with multifunctional attributes, such as renewability and abundance of its source, biodegradability, biocompatibility, superior mechanical, optical, and rheological properties, tunable self-assembly and surface chemistry, nanocellulose presents exclusive opportunities for a wide range of novel applications. However, to alleviate its intrinsic hydrophilicity-related constraints surface functionalization is inevitably needed to foster various targeted applications. The abundant surface hydroxyl groups on nanocellulose offer opportunities for grafting small molecules or macromolecular entities using either a 'graft onto' or 'graft from' approach, resulting in materials with distinctive functionalities. Most of the reviews published to date extensively discussed 'graft from' modification approaches, however 'graft onto' approaches are not well discussed. Hence, this review aims to provide a comprehensive summary of 'graft onto' approaches. Furthermore, insight into some of the recently emerging applications of this grafted nanocellulose including advanced nanocomposite formulation, stimuli-responsive materials, bioimaging, sensing, biomedicine, packaging, and wastewater treatment has also been reviewed.

Solution-state nuclear magnetic resonance spectroscopy of crystalline cellulosic materials using a direct dissolution ionic liquid electrolyte

Owing to its high sustainable production capacity, cellulose represents a valuable feedstock for the development of more sustainable alternatives to currently used fossil fuel-based materials. Chemical analysis of cellulose remains challenging, and analytical techniques have not advanced as fast as the development of the proposed materials science applications. Crystalline cellulosic materials are insoluble in most solvents, which restricts direct analytical techniques to lower-resolution solid-state spectroscopy, destructive indirect procedures or to 'old-school' derivatization protocols. While investigating their use for biomass valorization, tetralkylphosphonium ionic liquids (ILs) exhibited advantageous properties for direct solution-state nuclear magnetic resonance (NMR) analysis of crystalline cellulose. After screening and optimization, the IL tetra-n-butylphosphonium acetate [P₄₄₄₄][OAc], diluted with dimethyl sulfoxide-d₆, was found to be the most promising partly deuterated solvent system for high-resolution solution-state NMR. The solvent system has been used for the measurement of both 1D and 2D experiments for a wide substrate scope, with excellent spectral quality and signal-to-noise, all with modest collection times. The procedure initially describes the scalable syntheses of an IL, in 24-72 h, of sufficient purity, yielding a stock electrolyte solution. The dissolution of cellulosic materials and preparation of NMR samples is presented, with pretreatment, concentration and dissolution time recommendations for different sample types. Also included is a set of recommended 1D and 2D NMR experiments with parameters optimized for an in-depth structural characterization of cellulosic materials. The time required for full characterization varies between a few hours and several days.

High-Flux Nanofibrous Composite Reverse Osmosis Membrane Containing Interfacial Water Channels for Desalination

A nanofibrous composite reverse osmosis (RO) membrane with a polyamide barrier layer containing interfacial water channels was fabricated on an electrospun nanofibrous substrate via an interfacial polymerization process. The RO membrane was employed for desalination of brackish water and exhibited enhanced permeation flux as well as rejection ratio. Nanocellulose was prepared by sequential oxidations of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and sodium periodate systems and surface grafting with different alkyl groups including octyl, decanyl, dodecanyl, tetradecanyl, cetyl, and octadecanyl groups. The chemical structure of the modified nanocellulose was verified subsequently by Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), and solid NMR measurements. Two monomers, trimesoyl chloride (TMC) and m-phenylenediamine (MPD), were employed to prepare a cross-linked polyamide matrix, i.e., the barrier layer of the RO membrane, which integrated with the alkyl groups-grafted nanocellulose to build up interfacial water channels via interfacial polymerization. The top and cross-sectional morphologies of the composite barrier layer were observed by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) to verify the integration structure of the nanofibrous composite containing water channels. The aggregation and distribution of water molecules in the nanofibrous composite RO membrane verified the existence of water channels, demonstrated by molecular dynamics (MD) simulations. The desalination performance of the nanofibrous composite RO membrane was conducted and compared with that of commercially available RO membranes in the processing of brackish water, where 3 times higher permeation flux and 99.1% rejection ratio against NaCl were accomplished. This indicated that the engineering of interfacial water channels in the barrier layer could substantially increase the permeation flux of the nanofibrous composite membrane while retaining the high rejection ratio as well, i.e., to break through the trade-off between permeation flux and rejection ratio. Antifouling properties, chlorine resistance, and long-term desalination performance were also demonstrated to evaluate the potential applications of the nanofibrous composite RO membrane; remarkable durability and robustness were achieved in addition to 3 times higher permeation flux and a higher rejection ratio against commercial RO membranes in brackish water desalination.

Nanocellulose-based drug carriers: Functional design, controllable synthesis, and therapeutic applications

With rising living standards and environmental awareness, materials-oriented chemical engineering has increasingly transitioned from traditional rough models to more resource-saving and eco-friendly models, providing an avenue for bio-based materials in the drug carrier field. Because of its excellent physical and chemical properties, including high specific surface area, abundant accessible hydroxyl groups, biocompatibility, and degradability, nanocellulose (NC) is an emerging bio-based material that has been widely exploited as biomedical materials. The modification techniques of NC, as well as advancements in the design and applications of drug carriers, were primarily discussed in this study. First, the NC modification methods are described; second, the applications of NC and its derivatives as drug carriers are summarized, focusing on NC-based carrier models, types of loaded therapeutic agents, and controlled release stimulators; and finally, the current challenges of NC in the drug carrier field and the directions of future research are also discussed.

Click Chemistry: A Promising Tool for Building Hierarchical Structures

The hierarchical structures are utilized at different levels in nature. Moreover, a wide spectrum of nature’s properties (e.g., mechanical, physical and biological properties) has been attributed to this hierarchy. Different reviews have been published to cover the use of click chemistry in building hierarchical structures. However, each one of those reviews focused on a narrow area on this topic, i.e., specific chemical reaction, such as in thiol-ene chemistry, or a specific molecule or compound such as polyhedral oligomeric silsesquioxane, or a certain range of hierarchical structures between the nano to micro range, e.g., nanocrystals. In this review, a frame to connect the dots between the different published works has been demonstrated. This article will not attempt to give an exhaustive review of all the published work in the field, instead the potential of click chemistry to build hierarchical structures of different levels using building blocks of different length scales has been shown through two main approaches. The first is a one-step direct formation of 3D micro/macrometer dimensions structures from Pico dimensions structures (molecules, monomers, etc.). The second approach includes several steps Pico ➔ 0D nano ➔ 1D nano ➔ 2D nano ➔ 3D nano/micro/macro dimensions structures. Another purpose of this review article is to connect between (a) the atomic theory, which covers the atoms and molecules in the picometer dimensions (picoscopic chemistry set); (b) “nano-periodic system” model, which covers different nanobuilding blocks in the nanometers range such as nanoparticles, dendrimers, buckyball, etc. which was developed by Tomalia; and (c) the micro/macrometer dimensions level.

Chitosan-Gelatin Films Cross-Linked with Dialdehyde Cellulose Nanocrystals as Potential Materials for Wound Dressings

In this study, thin chitosan-gelatin biofilms cross-linked with dialdehyde cellulose nanocrystals for dressing materials were received. Two types of dialdehyde cellulose nanocrystals from fiber (DNCL) and microcrystalline cellulose (DAMC) were obtained by periodate oxidation. An ATR-FTIR analysis confirmed the selective oxidation of cellulose nanocrystals with the creation of a carbonyl group at 1724 cm-1. A higher degree of cross-linking was obtained in chitosan-gelatin biofilms with DNCL than with DAMC. An increasing amount of added cross-linkers resulted in a decrease in the apparent density value. The chitosan-gelatin biofilms cross-linked with DNCL exhibited a higher value of roughness parameters and antioxidant activity compared with materials cross-linked with DAMC. The cross-linking process improved the oxygen permeability and anti-inflammatory properties of both measurement series. Two samples cross-linked with DNCL achieved an ideal water vapor transition rate for wound dressings, CS-Gel with 10% and 15% addition of DNCL-8.60 and 9.60 mg/cm2/h, respectively. The swelling ability and interaction with human serum albumin (HSA) were improved for biofilms cross-linked with DAMC and DNCL. Significantly, the films cross-linked with DAMC were characterized by lower toxicity. These results confirmed that chitosan-gelatin biofilms cross-linked with DNCL and DAMC had improved properties for possible use in wound dressings.

Hollow Filaments Synthesized by Dry-Jet Wet Spinning of Cellulose Nanofibrils: Structural Properties and Thermoregulation with Phase-Change Infills

We use dry-jet wet spinning in a coaxial configuration by extruding an aqueous colloidal suspension of oxidized nanocellulose (hydrogel shell) combined with airflow in the core. The coagulation of the hydrogel in a water bath results in hollow filaments (HF) that are drawn continuously at relatively high rates. Small-angle and wide-angle X-ray scattering (SAXS/WAXS) reveals the orientation and order of the cellulose sheath, depending on the applied shear flow and drying method (free-drying and drying under tension). The obtained dry HF show Young's modulus and tensile strength of up to 9 GPa and 66 MPa, respectively. Two types of phase-change materials (PCM), polyethylene glycol (PEG) and paraffin (PA), are used as infills to enable filaments for energy regulation. An increased strain (9%) is observed in the PCM-filled filaments (HF-PEG and HF-PA). The filaments display similar thermal behavior (dynamic scanning calorimetry) compared to the neat infill, PEG, or paraffin, reaching a maximum latent heat capacity of 170 J·g-1 (48-55 °C) and 169 J·g-1 (52-54 °C), respectively. Overall, this study demonstrates the facile and scalable production of two-component core-shell filaments that combine structural integrity, heat storage, and thermoregulation properties.

Nanocomposite-enhanced hydrophobicity effect in biosourced polyurethane with low volume fraction of organophilic CNC: towards solvent-absorbent and porous membranes

Herein, we focus on the development of new nanocomposite porous membranes based on castor oil-derived polyurethane (PUBCO) and octadecylamine-functionalized cellulose nanocrystals (CNC-ODA) as compatible nanoreinforcements.

Enhancing Removal of Cr(VI), Pb2+, and Cu2+ from Aqueous Solutions Using Amino-Functionalized Cellulose Nanocrystal

In this work, the amino-functionalized cellulose nanocrystal (ACNC) was prepared using a green route and applied as a biosorbent for adsorption of Cr(VI), Pb²⁺, and Cu²⁺ from aqueous solutions. CNC was firstly oxidized by sodium periodate to yield the dialdehyde nanocellulose (DACNC). Then, DACNC reacted with diethylenetriamine (DETA) to obtain amino-functionalized nanocellulose (ACNC) through a Schiff base reaction. The properties of DACNC and ACNC were characterized by using elemental analysis, Fourier transform infrared spectroscopy (FT-IR), Kaiser test, atomic force microscopy (AFM), X-ray diffraction (XRD), and zeta potential measurement. The presence of free amino groups was evidenced by the FT-IR results and Kaiser test. ACNCs exhibited an amphoteric nature with isoelectric points between pH 8 and 9. After the chemical modification, the cellulose I polymorph of nanocellulose remained, while the crystallinity decreased. The adsorption behavior of ACNC was investigated for the removal of Cr(VI), Pb²⁺, and Cu²⁺ in aqueous solutions. The maximum adsorption capacities were obtained at pH 2 for Cr(VI) and pH 6 for Cu²⁺ and Pb²⁺, respectively. The adsorption all followed pseudo second-order kinetics and Sips adsorption isotherms. The estimated adsorption capacities for Cr(VI), Pb²⁺, and Cu²⁺ were 70.503, 54.115, and 49.600 mg/g, respectively.

Mechanics Design in Cellulose-Enabled High-Performance Functional Materials

The abundance of cellulose found in natural resources such as wood, and the wide spectrum of structural diversity of cellulose nanomaterials in the form of micro-nano-sized particles and fibers, have sparked a tremendous interest to utilize cellulose's intriguing mechanical properties in designing high-performance functional materials, where cellulose's structure-mechanics relationships are pivotal. In this progress report, multiscale mechanics understanding of cellulose, including the key role of hydrogen bonding, the dependence of structural interfaces on the spatial hydrogen bond density, the effect of nanofiber size and orientation on the fracture toughness, are discussed along with recent development on enabling experimental design techniques such as structural alteration, manipulation of anisotropy, interface and topology engineering. Progress in these fronts renders cellulose a prospect of being effectuated in an array of emerging sustainable applications and being fabricated into high-performance structural materials that are both strong and tough.

Cu(I)-Catalyzed Click Chemistry in Glycoscience and Their Diverse Applications

Copper(I)-catalyzed 1,3-dipolar cycloaddition between organic azides and terminal alkynes, commonly known as CuAAC or click chemistry, has been identified as one of the most successful, versatile, reliable, and modular strategies for the rapid and regioselective construction of 1,4-disubstituted 1,2,3-triazoles as diversely functionalized molecules. Carbohydrates, an integral part of living cells, have several fascinating features, including their structural diversity, biocompatibility, bioavailability, hydrophilicity, and superior ADME properties with minimal toxicity, which support increased demand to explore them as versatile scaffolds for easy access to diverse glycohybrids and well-defined glycoconjugates for complete chemical, biochemical, and pharmacological investigations. This review highlights the successful development of CuAAC or click chemistry in emerging areas of glycoscience, including the synthesis of triazole appended carbohydrate-containing molecular architectures (mainly glycohybrids, glycoconjugates, glycopolymers, glycopeptides, glycoproteins, glycolipids, glycoclusters, and glycodendrimers through regioselective triazole forming modular and bio-orthogonal coupling protocols). It discusses the widespread applications of these glycoproducts as enzyme inhibitors in drug discovery and development, sensing, gelation, chelation, glycosylation, and catalysis. This review also covers the impact of click chemistry and provides future perspectives on its role in various emerging disciplines of science and technology.

Preparation and Surface Functionalization of Carboxylated Cellulose Nanocrystals

In recent years, cellulose nanocrystals (CNCs) have emerged as a leading biomass-based nanomaterial owing to their unique functional properties and sustainable resourcing. Sulfated cellulose nanocrystals (sCNCs), produced by sulfuric acid-assisted hydrolysis of cellulose, is currently the predominant form of this class of nanomaterial; its utilization leads the way in terms of CNC commercialization activities and industrial applications. The functional properties, including high crystallinity, colloidal stability, and uniform nanoscale dimensions, can also be attained through carboxylated cellulose nanocrystals (cCNCs). Herein, we review recent progress in methods and feedstock materials for producing cCNCs, describe their functional properties, and discuss the initial successes in their applications. Comparisons are made to sCNCs to highlight some of the inherent advantages that cCNCs may possess in similar applications.

Bioorthogonal hydroxyethyl cellulose-based scaffold crosslinked via click chemistry for cartilage tissue engineering applications

In this study, azide and alkyne moieties were introduced to the structure of citric acid-modified hydroxyethyl cellulose (HEC) and then through a bioorthogonal click chemistry method: Strain-promoted azide-alkyne cycloaddition, a novel crosslinked HEC scaffold (click sample) was obtained. Chemical modifications and successful crosslinking of the samples were assessed with FTIR and ¹H NMR spectroscopy. Lyophilized samples exhibited a porous interconnected microarchitecture with desirable features for commensurate cartilage tissue engineering applications. As the stability of scaffolds improved upon crosslinking, considerable water uptake and swelling degree of ~650% could still be measured for the click sample. Offering Young's modulus of ~10 MPa and tensile strength of ~0.43 MPa, the mechanical characteristics of click sample were comparable with those of normal cartilage tissue. Various in vitro biological assays, including MTT analysis, cellular attachment, histological staining with safranin O, and real-time PCR decisively approved significant biocompatibility, chondrogenic ability, and bioorthogonal features of click sample.

Nanocellulose: Recent Fundamental Advances and Emerging Biological and Biomimicking Applications

In the effort toward sustainable advanced functional materials, nanocelluloses have attracted extensive recent attention. Nanocelluloses range from rod-like highly crystalline cellulose nanocrystals to longer and more entangled cellulose nanofibers, earlier denoted also as microfibrillated celluloses and bacterial cellulose. In recent years, they have spurred research toward a wide range of applications, ranging from nanocomposites, viscosity modifiers, films, barrier layers, fibers, structural color, gels, aerogels and foams, and energy applications, until filtering membranes, to name a few. Still, nanocelluloses continue to show surprisingly high challenges to master their interactions and tailorability to allow well-controlled assemblies for functional materials. Rather than trying to review the already extensive nanocellulose literature at large, here selected aspects of the recent progress are the focus. Water interactions, which are central for processing for the functional properties, are discussed first. Then advanced hybrid gels toward (multi)stimuli responses, shape-memory materials, self-healing, adhesion and gluing, biological scaffolding, and forensic applications are discussed. Finally, composite fibers are discussed, as well as nanocellulose as a strategy for improvement of photosynthesis-based chemicals production. In summary, selected perspectives toward new directions for sustainable high-tech functional materials science based on nanocelluloses are described.

Grafting Nature-Inspired and Bio-Based Phenolic Esters onto Cellulose Nanocrystals Gives Biomaterials with Photostable Anti-UV Properties

New nature-inspired and plant-derived p-hydroxycinnamate esters and p-hydroxycinnamate diesters provide excellent protection against UV radiation when incorporated into a matrix. Herein, an efficient and sustainable pathway is reported to graft these phenolic compounds onto cellulose nanocrystals (CNCs) via click-type copper-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The successful grafting of the phenolic esters on CNC surface was evidenced by a range of chemical analyses, and the degrees of substitution (DS) of the CNC were found to depend on the structure of the phenolic ester grafted. Moreover, aqueous suspensions of the phenolic ester-grafted CNCs not only strongly absorb in both the UVA and UVB regions, but they also exhibit average to very high photostability. Their wide spectrum UV-absorbing properties and their stability upon exposure to UV are highly influenced by the structure of the phenolic ester, particularly by the extra ester group in p-hydroxycinnamate diesters. These findings demonstrate that cellulose nanocrystals decorated with such plant-derived and nature-inspired phenolic esters are promising sustainable nanomaterials for anti-UV applications.

Grafting Diels-Alder moieties on cellulose nanocrystals through carbamation

The Diels-Alder reaction is a promising click chemistry for the design of advanced materials from cellulose nanocrystals (CNCs). Transferring such chemistry to cellulose nanocrystals requires the precise grafting of reactive Diels-Alder moeities under heterogeneous conditions without compromising the nanocrystals morphology. In this study toluene diisocyanate is used as a spacer to graft Diels-Alder moieties viz the furyl and protected maleimido moieties onto cellulose nanocrystals. A factorial experimental design reveals that reaction time and reactant molar ratio positively affect the grafting efficiency, as evidenced by FTIR and CHNS elemental analysis. The surface degree of substitution was analyzed via CHNS elemental analysis and XPS and found to range between 0.05 to 0.30, with a good agreement between the two techniques. ¹³C CP/MAS NMR confirmed that the grafted moieties and CNCs are intact after reaction. Side reactions were also observed and their impact on performing controllable click chemistry between cellulose nanocrystals is discussed.

Surface-Initiated Controlled Radical Polymerization Approach to In Situ Cross-Link Cellulose Nanofibrils with Inorganic Nanoparticles

This paper investigates a strategy to convert hydrophilic cellulose nanofibrils (CNF) into a hydrophobic highly cross-linked network made of cellulose nanofibrils and inorganic nanoparticles. First, the cellulose nanofibrils were chemically modified through an esterification reaction to produce a nanocellulose-based macroinitiator. Barium titanate (BaTiO₃, BTO) nanoparticles were surface-modified by introducing a specific monomer on their outer-shell surface. Finally, we studied the ability of the nanocellulose-based macroinitiator to initiate a single electron transfer living radical polymerization of stearyl acrylate (SA) in the presence of the surface-modified nanoparticles. The BTO nanoparticles will transfer new properties to the nanocellulose network and act as a cross-linking agent between the nanocellulose fibrils, while the monomer (SA) directly influences the hydrophilic-lipophilic balance. The pristine CNF and the nanoparticle cross-linked CNF are characterized by FTIR, SEM, and solid-state ¹³C NMR. Rheological and dynamic mechanical analyses revealed a high dregee of cross-linking.

Electroactive γ-Phase, Enhanced Thermal and Mechanical Properties and High Ionic Conductivity Response of Poly (Vinylidene Fluoride)/Cellulose Nanocrystal Hybrid Nanocomposites

Cellulose nanocrystals (CNCs) were incorporated into poly (vinylidene fluoride) (PVDF) to tailor the mechanical and dielectric properties of this electroactive polymer. PVDF/CNC nanocomposites with concentrations up to 15 wt.% were prepared by solvent-casting followed by quick vacuum drying in order to ensure the formation of the electroactive γ-phase. The changes induced by the presence of CNCs on the morphology of PVDF and its crystalline structure, thermal properties, mechanical performance and dielectric behavior are explored. The results suggest a relevant role of the CNC surface -OH groups, which interact with PVDF fluorine atoms. The real dielectric constant ε' of nanocomposites at 200 Hz was found to increase by 3.6 times up to 47 for the 15 wt.% CNC nanocomposite due to an enhanced ionic conductivity provided by CNCs. The approach reported here in order to boost the formation of the γ-phase of PVDF upon the incorporation of CNCs serves to further develop cellulose-based multifunctional materials.

Emerging challenges in the thermal management of cellulose nanofibril-based supercapacitors, lithium-ion batteries and solar cells: A review

In recent years, extensive efforts have been devoted to electronic miniaturization and integration. Accordingly, heating up of electronics has become a critical problem that needs to be urgently solved by efficient and reliable thermal management. Electronic device substrates made of cellulose nanofibrils (CNFs) exhibit outstanding flexibility, mechanical properties, and optical properties. Combining CNFs with high-thermal-conductivly fillers is an effective thermal management technique. This paper focuses on the thermal management of electronic devices and highlights the potential of CNF-based materials for efficient thermal management of energy storage electronic such as supercapacitors, lithium-ion batteries and solar cells. A high-thermal-conductivity composite material for electronic devices can be obtained by combining CNFs as the framework material with carbon nanotubes, graphene, and inorganic nitrides. Moreover, The research progress in the application of CNFs-based materials for supercapacitors, lithium-ion batteries and solar cells is highlighted, and the emerging challenges of different CNFs-based energy storage devices are discussed.

Coaxial Spinning of All-Cellulose Systems for Enhanced Toughness: Filaments of Oxidized Nanofibrils Sheathed in Cellulose II Regenerated from a Protic Ionic Liquid

Hydrogels of TEMPO-oxidized nanocellulose were stabilized for dry-jet wet spinning using a shell of cellulose dissolved in 1,5-diazabicyclo[4.3.0]non-5-enium propionate ([DBNH][CO₂Et]), a protic ionic liquid (PIL). Coagulation in an acidic water bath resulted in continuous core-shell filaments (CSFs) that were tough and flexible with an average dry (and wet) toughness of ∼11 (2) MJ·m^-3 and elongation of ∼9 (14) %. The CSF morphology, chemical composition, thermal stability, crystallinity, and bacterial activity were assessed using scanning electron microscopy with energy-dispersive X-ray spectroscopy, liquid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermogravimetric analysis, pyrolysis gas chromatography-mass spectrometry, wide-angle X-ray scattering, and bacterial cell culturing, respectively. The coaxial wet spinning yields PIL-free systems carrying on the surface the cellulose II polymorph, which not only enhances the toughness of the filaments but facilities their functionalization.

Nanocellulose, a Versatile Green Platform: From Biosources to Materials and Their Applications

With increasing environmental and ecological concerns due to the use of petroleum-based chemicals and products, the synthesis of fine chemicals and functional materials from natural resources is of great public value. Nanocellulose may prove to be one of the most promising green materials of modern times due to its intrinsic properties, renewability, and abundance. In this review, we present nanocellulose-based materials from sourcing, synthesis, and surface modification of nanocellulose, to materials formation and applications. Nanocellulose can be sourced from biomass, plants, or bacteria, relying on fairly simple, scalable, and efficient isolation techniques. Mechanical, chemical, and enzymatic treatments, or a combination of these, can be used to extract nanocellulose from natural sources. The properties of nanocellulose are dependent on the source, the isolation technique, and potential subsequent surface transformations. Nanocellulose surface modification techniques are typically used to introduce either charged or hydrophobic moieties, and include amidation, esterification, etherification, silylation, polymerization, urethanization, sulfonation, and phosphorylation. Nanocellulose has excellent strength, high Young's modulus, biocompatibility, and tunable self-assembly, thixotropic, and photonic properties, which are essential for the applications of this material. Nanocellulose participates in the fabrication of a large range of nanomaterials and nanocomposites, including those based on polymers, metals, metal oxides, and carbon. In particular, nanocellulose complements organic-based materials, where it imparts its mechanical properties to the composite. Nanocellulose is a promising material whenever material strength, flexibility, and/or specific nanostructuration are required. Applications include functional paper, optoelectronics, and antibacterial coatings, packaging, mechanically reinforced polymer composites, tissue scaffolds, drug delivery, biosensors, energy storage, catalysis, environmental remediation, and electrochemically controlled separation. Phosphorylated nanocellulose is a particularly interesting material, spanning a surprising set of applications in various dimensions including bone scaffolds, adsorbents, and flame retardants and as a support for the heterogenization of homogeneous catalysts.

Current characterization methods for cellulose nanomaterials

A new family of materials comprised of cellulose, cellulose nanomaterials (CNMs), having properties and functionalities distinct from molecular cellulose and wood pulp, is being developed for applications that were once thought impossible for cellulosic materials. Commercialization, paralleled by research in this field, is fueled by the unique combination of characteristics, such as high on-axis stiffness, sustainability, scalability, and mechanical reinforcement of a wide variety of materials, leading to their utility across a broad spectrum of high-performance material applications. However, with this exponential growth in interest/activity, the development of measurement protocols necessary for consistent, reliable and accurate materials characterization has been outpaced. These protocols, developed in the broader research community, are critical for the advancement in understanding, process optimization, and utilization of CNMs in materials development. This review establishes detailed best practices, methods and techniques for characterizing CNM particle morphology, surface chemistry, surface charge, purity, crystallinity, rheological properties, mechanical properties, and toxicity for two distinct forms of CNMs: cellulose nanocrystals and cellulose nanofibrils.

Ensemble and Single Particle Fluorescence Characterization of Dye-Labeled Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) have been covalently labeled with both fluorescein and rhodamine and studied by a combination of UV-vis absorption spectroscopy and ensemble and single molecule fluorescence spectroscopy. For all samples, the fluorescence anisotropy and lifetimes were consistent with effects expected for covalently bound dye molecules. Low dye loading levels (∼0.1 dye/particle) were estimated for the fluorescein-labeled CNC which coupled with the strong pH dependence make this a less suitable fluorophore for most applications. Rhodamine-labeled CNCs were prepared from both sulfated and carboxylated CNCs and had loading levels that varied from 0.25 to ∼15 dye molecules/CNC. For the sulfated samples, the absorption due to (nonfluorescent) dimeric dye increased with dye loading; in contrast, the carboxylated sample, which had the highest rhodamine content, had a low dimer yield. Single particle fluorescence studies for two of the rhodamine-labeled CNCs demonstrated that individual particles are readily detected by their stepwise blinking/bleaching behavior and by polarization effects. Overall, the results indicate the importance of understanding the effects of loading on dye photophysics to select an optimal dye concentration to maximize sensitivity while minimizing the effect of the dye on the CNC behavior. The results also demonstrate that CNCs with relatively low dye loadings (e.g., ∼1 dye/particle) are readily detectable by fluorescence and should be adequate for use in fluorescence-based biological assays or to probe the distribution of CNCs in composite materials.

Photoluminescent Hybrids of Cellulose Nanocrystals and Carbon Quantum Dots as Cytocompatible Probes for in Vitro Bioimaging

We present an approach to construct biocompatible and photoluminescent hybrid materials comprised of carbon quantum dots (CQDs) and TEMPO-oxidized cellulose nanocrystals (TO-CNCs). First, the amino-functionalized carbon quantum dots (NH₂-CQDs) were synthesized using a simple microwave method, and the TO-CNCs were prepared by hydrochloric acid (HCl) hydrolysis followed by TEMPO-mediated oxidation. The conjugation of NH₂-CQDs and TO-CNCs was conducted via carbodiimide-assisted coupling chemistry. The synthesized TO-CNC@CQD hybrid nanomaterials were characterized using X-ray photoelectron spectroscopy, cryo-transmittance electron microscopy, confocal microscopy, and fluorescence spectroscopy. Finally, the interactions of TO-CNC@CQD hybrids with HeLa and RAW 264.7 macrophage cells were investigated in vitro. Cell viability tests suggest the surface conjugation with NH₂-CQDs not only improved the cytocompatibility of TO-CNCs, but also enhanced their cellular association and internalization on both HeLa and RAW 264.7 cells after 4 and 24 h incubation.

Complexes of Magnetic Nanoparticles with Cellulose Nanocrystals as Regenerable, Highly Efficient, and Selective Platform for Protein Separation

We present an efficient approach to develop cellulose nanocrystal (CNC) hybrids with magnetically responsive Fe₃O₄ nanoparticles that were synthesized using the (Fe³⁺/Fe²⁺) coprecipitation. After 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-catalyzed oxidation of CNC, carbodiimide (EDC/NHS) was used for coupling amine-containing iron oxide nanoparticles that were achieved by dopamine ligand exchange (NH₂-Fe₃O₄ NPs). The as-prepared hybrids (Fe₃O₄@CNC) were further complexed with Cu(II) ions to produce specific protein binding sites. The performance of magnetically responsive Cu-Fe₃O₄@CNC hybrids was assessed by selectively separating lysozyme from aqueous media. The hybrid system displayed a remarkable binding capacity with lysozyme of 860.6 ± 14.6 mg/g while near full protein recovery (∼98%) was achieved by simple elution. Moreover, the regeneration of Fe₃O₄@CNC hybrids and efficient reutilization for protein separation was demonstrated. Finally, lysozyme separation from matrices containing egg white was achieved, thus revealing the specificity and potential of the presented method.

Enhancement of photobactericidal activity of chlorin-e6-cellulose nanocrystals by covalent attachment of polymyxin B

Following light irradiation, a new nanomaterial, elaborated from CNCs, chlorin-e6 and polymyxin B, demonstrated efficiency against Gram-negative bacteria (Escherichia coli,Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus,Staphylococcus epidermidis).