Cellulose Nanofiber Network Research Articles

Enrichment of bovine milk-derived extracellular vesicles using surface-functionalized cellulose nanofibers

The isolation of extracellular vesicles (EVs) from milk, a complex mixture of colloidal structures having a comparable size to EVs, is challenging. Although ultracentrifugation (UC) has been widely used for EV isolation, this has significant limitations, including a long processing time at high g-force conditions and large sample volume requirements. We introduced a new approach based on nature nanoentities cellulose nanofibers (CNFs) and short time and low g-force centrifugation to isolate EVs from various milk fractions. The flexible and entangled network of CNFs forms nanoporous, which entraps the EVs. Further, positively charged CNFs interact with anionic EVs through an electrostatic attraction, promoting their isolation with efficiency comparable with UC. The functionality and toxicity of isolated milk EVs were tested in Caco2 cells. Overall, the newly developed approach provides straightforward isolation and biocompatibility and preserves the natural properties of the isolated EVs, enabling further applications.

Atmosphere‐free activation methodology for holey graphene/cellulose nanofiber‐based film electrode with highly efficient capacitance performance

AbstractAn efficient chamber‐induced activation method was applied for the preparation of holey graphene/cellulose nanofiber‐based film with high specific surface area (SSA) and multiple channels through the graphene nanosheets. With the cellulose nanofiber (CNF) simultaneously serving as “dispersing agent,” “spacer,” and “activating agent,” the graphene oxide (GO) nanosheets are perforated by the pyrolysis gas from CNF in the confined space inside the hybrid films, uniformly dispersed, and sandwiched between CNF networks with less agglomeration and restacking. Additionally, we have proved that H2O and H2 are primarily responsible for the activation and etching of GO/CNF film. As the CNF content increases, the mesoporosity of the activated reduced GO/CNF (A‐RGO/CNF) film increases, and the graphene nanosheets show more nanopore perforations. Benefitting from the high SSA, high density, moderate mesoporosity, and abundant channels for ion diffusion through the graphene nanosheets, the A‐RGO/CNF film exhibits the highest specific capacitance of 323 (236) F g−1 (F cm−3) at 1 A g−1. For the A‐RGO5/CNF5 film containing half CNF and half GO, an excellent comprehensive electrochemical performance including superior rate performance (208 (160) F g−1 (F cm−3) at 60 A g−1) is exhibited. Moreover, the A‐RGO5/CNF5 electrode in an all‐solid‐state flexible symmetric supercapacitor delivers a high specific capacitance of 250 (193) F g−1 (F cm−3) at 1 A g−1. This study provides a novel idea for the preparation of holey graphene‐based film for supercapacitor electrodes. The strategy of simultaneously employing CNF as “dispersing agent,” “spacer,” and “activating agent” also offers a new vision for the assembly of homogeneous nanohybrid material and the utilization of pyrolysis gas.

Remarkable toughness reinforcement of elastomer with cellulose microgel: Employing polymer matrix and cellulose nanofiber network as the continuous phase and energy dissipation agent

Double-network reinforcement strategy has been widely used to improve hydrogels' toughness but is rarely applied in bulk polymer. The key to this strategy is introducing sacrificial bonds to improve strength and maintain the integrity of the polymer matrix at high elongation, dissipating applied energy as much as possible. In this study, a micron-sized microgel was employed as a sacrificial agent to reinforce polymer matrix. A simple and versatile process was introduced for the fabrication of cellulose microgel/ poly(butyl acrylate(BA)-co-methyl methacrylate(MMA)) nanocomposites by in situ free-radical polymerizations of BA and MMA complex monomer solution contained with well-dispersed cellulose microgels. After polymerization, the microgels were found homogeneously distributed within the polymer matrix. The organic-phase bacterial cellulose microgels (OB-microgel) reinforced polymer exhibited marvelous performance in the tensile test. The ultimate strength, Young's modulus, and toughness of P(BA-co-MMA) reinforced with 1.0 wt% OB-microgel were 1.13 MPa, 1.09 MPa, and 1.11 KJ m−3, about 2–3 times higher than neat P(BA-co-MMA) respectively. Moreover, a high strain to failure similar to the neat P(BA-co-MMA) was maintained. This reinforcement was mainly attributed to the sacrificing effect of microgel, not the formation of a percolation network, which was also supported by DMA test. Hence, cellulose microgel consisting of cellulose nanofiber network was demonstrated to be an efficient energy dissipation agent for the continuous phase of the polymer matrix to acquire high strain to failure and high tensile strength.

Nanofiltration performance of glutaraldehyde crosslinked graphene oxide-cellulose nanofiber membrane

Cellulose nanofibers have been widely used in membrane fabrication due to their unique structure, hydrophilicity, sustainability, facile surface modification, and low cost. In this study, the efficient combination of the precise molecular sieving characteristics of graphene oxide (GO) and the high permeability of the cellulose nanofibers (CNFs) network is demonstrated. GO nanosheets were incorporated into the CNF matrix using a facile vacuum filtration technique followed by chemical cross-linking. Cross-linking with glutaraldehyde not only resisted membrane swelling but also improved molecular selectivity. The nanofiltration performance of prepared membranes was evaluated in both aqueous and organic solutions. The optimized crosslinked membranes exhibited a pure solvent flux of 13.9 ± 1.9 Lm−2h−1bar−1 and 4.1 ± 0.35 Lm−2h−1bar−1 for water and ethanol respectively, while maintaining a rejection above 90% for Rose Bengal and Brilliant Blue dyes.

Thermal Conductivity of Cellulose Fibers in Different Size Scales and Densities.

Considering the growing use of cellulose in various applications, knowledge and understanding of its physical properties become increasingly important. Thermal conductivity is a key property, but its variation with porosity and density is unknown, and it is not known if such a variation is affected by fiber size and temperature. Here, we determine the relationships by measurements of the thermal conductivity of cellulose fibers (CFs) and cellulose nanofibers (CNFs) derived from commercial birch pulp as a function of pressure and temperature. The results show that the thermal conductivity varies relatively weakly with density (ρsample = 1340–1560 kg m–3) and that its temperature dependence is independent of density, porosity, and fiber size for temperatures in the range 80–380 K. The universal temperature and density dependencies of the thermal conductivity of a random network of CNFs are described by a third-order polynomial function (SI-units): κCNF = (0.0787 + 2.73 × 10–3·T – 7.6749 × 10–6·T2 + 8.4637 × 10–9·T3)·(ρsample/ρ0)2, where ρ0 = 1340 kg m–3 and κCF = 1.065·κCNF. Despite a relatively high degree of crystallinity, both CF and CNF samples show amorphous-like thermal conductivity, that is, it increases with increasing temperature. This appears to be due to the nano-sized elementary fibrils of cellulose, which explains that the thermal conductivity of CNFs and CFs shows identical behavior and differs by only ca. 6%. The nano-sized fibrils effectively limit the phonon mean free path to a few nanometers for heat conduction across fibers, and it is only significantly longer for highly directed heat conduction along fibers. This feature of cellulose makes it easier to apply in applications that require low thermal conductivity combined with high strength; the weak density dependence of the thermal conductivity is a particularly useful property when the material is subjected to high loads. The results for thermal conductivity also suggest that the crystalline structures of cellulose remain stable up to at least 0.7 GPa.

Preparation of cellulose microparticles having hierarchical internal structures from multiple emulsion templates

Microparticles having porous walls composed of nanofibers of cellulose were prepared from water-in-oil emulsion templates. This was achieved by emulsifying hot solutions of cellulose in a saturated aqueous solution of Ca(SCN)2 in decane in the presence of sorbitan monooleate as an emulsifier. Cooling the emulsion induced micro-phase separation within droplets of the cellulose solution, during which a three-dimensional network of cellulose nanofibers was formed and solidified the droplets. The particles size could be controlled by changing emulsification conditions such as stirring rate, the amount of emulsifier, and the volume ratio between the cellulose solution and decane. We found multiple emulsions (O/W/O and W/O/W/O emulsions) were formed when high amounts (>40 vol%) of the cellulose solution were emulsified. Particles obtained from the multiple emulsions had unique hierarchical internal structures, including a hollow particle with nanofibrous walls and particles-in-particle type structures where multiple porous particles are contained within a particle.

Highly stretchable and sensitive strain sensor based on polypyrrole coated bacterial cellulose fibrous network for human motion detection

Recently, wearable strain sensors based on elastomeric conductive composites have attracted tremendous attention in human motions and physical signals detection. However, it is still challenging to achieve good conjunction between broad strain range and high sensitivity performance for a wide range of applications. Here, we construct a highly stretchable and sensitive natural rubber (NR) based strain sensor from polypyrrole modified bacterial cellulose nanofiber (cPPy/BCNF) network. Due to the large aspect ratio and strong interfacial interaction of BCNF templates, cPPy/BCNF could form continuous conductive pathways in NR matrix with an extremely low loading, thus greatly reducing the permeability threshold of the elastomer. Consequently, our strain sensor performs remarkable sensitivity over a broad strain range (0–388%) and long-term reliability (3000 cycles at 60% and 180% strain). Particularly, a high gauge factor of 355.3 recorded in the strain range of 279–388% has been achieved, outperforming most reported NR-based stretchable strain sensor. Meanwhile, the sensor also exhibits stable strain sensing behavior under different amplitude of human motions such as finger, wrist, elbow, and knee joint bending. Our work provides more opportunities for the design of effective elastomeric conductors in the application of wearable electronic devices.

Water Lubricating and Biocompatible Films of Bacterial Cellulose Nanofibers Surface-Modified with Densely Grafted, Concentrated Polymer Brushes

Here, an articular cartilage-inspired system was developed using a densely grafted, concentrated polymer brush (CPB) for lubrication and bioinertness and a cellulose nanofiber (CNF) network for mec...

Plasmonic gold-cellulose nanofiber aerogels.

Assembly of plasmonic nanomaterials into a low refractive index medium, such as an aerogel, holds a great promise for optical metamaterials, optical sensors, and photothermal energy converters. However, conventional plasmonic aerogels are opaque and optically isotropic composites, impeding them from being used as low-loss or polarization-dependent optical materials. Here we demonstrate a plasmonic-cellulose nanofiber composite aerogel that comprises of well-dispersed gold nanorods within a cellulose nanofiber network. The cellulose aerogel host is highly transparent owing to the small scattering cross-section of the nanofibers and forms a nematic liquid crystalline medium with strong optical birefringence. We find that the longitudinal surface plasmon resonance peak of gold nanorods shows a dramatic shift when probed for the cellulose aerogel compared with the wet gels. Simulations reveal the shift of surface plasmon resonance peak with gel drying can be attributed to the change of the effective refractive index of the gels. This composite material may provide a platform for three- dimensional plasmonic devices ranging from optical sensors to metamaterials.

Hydrophobic Shape-Memory Biocomposites from Tung-Oil-Based Bioresin and Onion-Skin-Derived Nanocellulose Networks.

The fabrication of smart biocomposites from sustainable resources that could replace today’s petroleum-derived polymer materials is a growing field of research. Here, we report preparation of novel biocomposites using nanocellulose networks extracted from food residue (onion skin) and a vegetable oil-based bioresin. The resin was synthesized via the Diels-Alder reaction between furfuryl methacrylate and tung oil at various ratios of the components. The onion-skin-extracted cellulose nanofiber and cellulose nanocrystal networks were then impregnated with the resins yielding biocomposites that exhibited improved mechanical strength and higher storage modulus values. The properties of the resins, as well as biocomposites, were affected by the resin compositions. A 190–240-fold increase in mechanical strength was observed in the cellulose nanofiber (CNF) and cellulose nanocrystal (CNC)-reinforced biocomposites with low furfuryl methacrylate content. The biocomposites exhibited interesting shape-memory behavior with 80–96% shape recovery being observed after 7 creep cycles.

Partial Amorphization of Cellulose through Zinc Chloride Treatment: A Facile and Sustainable Pathway to Functional Cellulose Nanofibers with Flame-Retardant and Catalytic Properties

This work established an energy-saving and straightforward treatment of cellulosic pulp to obtain functional cellulose nanofibers equipping them at the same time with catalytic activity and flame-retardant properties. For this purpose, dried cellulose pulp was mixed with a recyclable swelling agent, ZnCl2 hydrate, at room temperature. The mild treatment affected the crystal structure through a partial amorphization, yielding a mix of native cellulose I and regenerated cellulose II. This treatment tremendously facilitated the fibrillation into a cellulose nanofiber (CNF) network. In comparison to fibrillated cellulose from nontreated pulp, the ZnCl2-treated counterpart featured higher viscosity, film transparency, better mechanical properties, and higher heat stability. Films produced from these nanofibers showed flame-retardant properties without any further modification. The ZnCl2–CNF showed also high reactivity in fiber surface acetylation and allowed a fast and efficient reaction while using very mild conditions. All in all, we propose a simple and resource-efficient cellulose treatment to obtain a nanostructured cellulose. These nanofibrils are decorated with ZnCl2 which imposes flame-retardant properties and confined catalytic activity at the fibril surface.

Cellulose-reinforced bioglass composite as flexible bioactive bandage to enhance bone healing

Low mechanical strength of cellulose nanofiber (CNF) and its lack of osseoconductivity in physiological media limit its application for bone tissue regeneration. To resolve these limitations, the densely packed cellulosic layers with thickness of ~50 μm impregnated by 58S bioglass (BG) nanoparticles was made-up (via the simple method of vacuum filtration) in this study. The developed fabrics showed uniform distribution of BG nanoparticles and effectively wrapped between CNF layers which caused sustained ion release into the SBF × 5 solution. The FTIR spectrum of the fabric after the SBF test was illustrated the presence of newly formed HA on the fabric. Also, no significant difference in the hydrophilicity of pure CNF and the developed fabric was presented by AFM results. Alkaline phosphatase activity (ALP) and cytotoxicity evaluation were performed to investigate cell treatment of the fabric which indicated its superior osteogenic potential of developed fabric compared with pure CNF. The increase in osseoconductivity of the developed fabric caused better cell attachment thanks to the interconnected CNFs network. Effective integration of BG nanoparticles between CNF interlayers increased Young's modulus of the developed fabric by 50% that mitigated swelling and enhanced structural stability of CNFs in the SBF × 5 solution. Thus, developed fabric could be considered as an appropriate biomaterial such as a bandage around cracked bone before metallic implantation with good mechanical integrity of the layered constructs obtained as well as strength and swelling.

Ultra-Strong, Ultra-Tough, Transparent, and Sustainable Nanocomposite Films for Plastic Substitute

Summary Plastics play a critical role in daily life but possess a considerably increasing negative impact on the environment and human health. Fabrication of biodegradable and eco-friendly alternatives with competitive properties for plastic substitute is urgently needed. Here, inspired by the hierarchical structure of nacre, we firstly developed a high-performance nacre-inspired composite with high transmittance (83.4% at 550 nm) and high haze (88.8% at 550 nm) via an aerosol-assisted biosynthesis process combined with the hot-press technique. The nacre-inspired composite film combines higher strength (482 MPa) and toughness (17.71 MJ m−3) than most other nacre-inspired films, and can be folded into various shapes without visible failure after unfolding. Moreover, compared with most commercial plastic films, it exhibits a lower thermal expansion coefficient (∼3 ppm K−1) and higher maximum service temperature besides better mechanical properties, which makes it a promising alternative to plastics in many technical fields.

The reinforcement effect of cellulose nanofiber on Young’s modulus of polyvinyl alcohol gel produced through the freeze/thaw method

Cellulose nanofiber (CNF) is the most effective reinforcement fiber for enhancing the physical properties of water-soluble polymers. Here, effect of CNF on the Young’s modulus of a polyvinyl alcohol (PVA) hydrogel produced through the freeze/thaw method is examined. PVA/CNF composite gels with different contents of CNF and PVA were produced without significant aggregation of CNFs during the freeze/thaw process. The Young’s modulus of the produced PVA/CNF gel gradually increased as the CNF content increased, and it was confirmed that CNF had a marked reinforcement effect. In gel with PVA = 7 vol%, percolation networks formed at CNF ≥ 0.6 vol%. Furthermore, adding ca. CNF = 1.5 vol% resulted in a 250% increase in the gel’s Young’s modulus. In addition, mechanical interaction was observed between the PVA and CNF networks. It was suggested that, similarly to CNF networks, PVA networks also limit the deformation of CNF networks.

Rapid Preparation of Cellulose Nanofibers from Energy Cane Bagasse and Their Application as Stabilizer and Rheological Modifiers in Magnetorheological Fluid

Magnetorheological fluids (MRFs) are smart fluids made of magnetic particles in a viscous carrier fluid, and their rheological properties are controllable by an external magnetic field. However, MRFs suffer from serious sedimentation and redispersibility problems, which limit their effectiveness and feasibility in a wide variety of applications. Herein, we present a novel strategy to improve magnetorheological property and stability of MRFs using cellulose nanofibers (CNFs), rapidly prepared from energy cane bagasse using microwave-assisted alkali-H2O2 and ultrasonic treatment. High delignification rate of 94.3% was achieved by the microwave treatment for 15 min. Chemical structure analysis revealed that the removal of lignin and carboxylation of cellulose occurred simultaneously. The obtained CNFs exhibited a highly entangled network structure, and their suspension showed the gel-like viscoelastic behavior. In CNF-MRF, the magnetic particles were entrapped and suspended by the entangled network of CNFs, which is due to the physical entanglement and the electrostatic repulsion force between Fe3O4 and CNFs. CNFs helped suspend magnetic particles in CNF-MRFs, leading to improved stability and magnetorheological properties (i.e., viscosity stability after cycling, reversible rate of 95.57% after 100 cycles). This work demonstrates a new path for the production of CNFs from energy cane bagasse wastes and their value-added utilization in MRFs.

A Synthetic Hydrogel Composite with the Mechanical Behavior and Durability of Cartilage

AbstractThis article reports the first hydrogel with the strength and modulus of cartilage in both tension and compression, and the first to exhibit cartilage‐equivalent tensile fatigue strength at 100 000 cycles. These properties are achieved by infiltrating a bacterial cellulose (BC) nanofiber network with a poly(vinyl alcohol) (PVA)–poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid sodium salt) (PAMPS) double network hydrogel. The BC provides tensile strength in a manner analogous to collagen in cartilage, while the PAMPS provides a fixed negative charge and osmotic restoring force similar to the role of aggrecan in cartilage. The hydrogel has the same aggregate modulus and permeability as cartilage, resulting in the same time‐dependent deformation under confined compression. The hydrogel is not cytotoxic, has a coefficient of friction 45% lower than cartilage, and is 4.4 times more wear‐resistant than a PVA hydrogel. The properties of this hydrogel make it an excellent candidate material for replacement of damaged cartilage.

Surfactin-Loaded ĸ-Carrageenan Oligosaccharides Entangled Cellulose Nanofibers as a Versatile Vehicle Against Periodontal Pathogens.

PurposePeriodontitis is a chronic inflammatory disease associated with microbial accumulation. The purpose of this study was to reuse the agricultural waste to produce cellulose nanofibers (CNF) and further modification of the CNF with κ-carrageenan oligosaccharides (CO) for drug delivery. In addition, this study is focused on the antimicrobial activity of surfactin-loaded CO-CNF towards periodontal pathogens.Materials and MethodsA chemo-mechanical method was used to extract the CNF and the modification was done by using CO. The studies were further proceeded by adding different quantities of surfactin [50 mg (50 SNPs), 100 mg (100 SNPs), 200 mg (200 SNPs)] into the carrier (CO-CNF). The obtained materials were characterized, and the antimicrobial activity of surfactin-loaded CO-CNF was evaluated.ResultsThe obtained average size of CNF and CO-CNF after ultrasonication was 263 nm and 330 nm, respectively. Microscopic studies suggested that the CNF has a short diameter with long length and CO became cross-linked to form as beads within the CNF network. The addition of CO improved the degradation temperature, crystallinity, and swelling property of CNF. The material has a controlled drug release, and the entrapment efficiency and loading capacity of the drug were 53.15 ± 2.36% and 36.72 ± 1.24%, respectively. It has antioxidant activity and inhibited the growth of periodontal pathogens such as Streptococcus mutans and Porphyromonas gingivalis by preventing the biofilm formation, reducing the metabolic activity, and promoting the oxidative stress.ConclusionThe study showed the successful extraction of CNF and modification with CO improved the physical parameters of the CNF. In addition, surfactin-loaded CO-CNF has potential antimicrobial activity against periodontal pathogens. The obtained biomaterial is economically valuable and has great potential for biomedical applications.

Robust Silica-Cellulose Composite Aerogels with a Nanoscale Interpenetrating Network Structure Prepared Using a Streamlined Process.

Silica aerogels can be strengthened by forming a nanoscale interpenetrating network (IPN) comprising a silica gel skeleton and a cellulose nanofiber network. Previous studies have demonstrated the effectiveness of this method for improving the mechanical properties and drying of aerogels. However, the preparation process is generally tedious and time-consuming. This study aims to streamline the preparation process of these composite aerogels. Silica alcosols were directly diffused into cellulose wet gels with loose, web-like microstructures, and an IPN structure was gradually formed by regulating the gelation rate. Supercritical CO2 drying followed to obtain composite aerogels. The mechanical properties were further enhanced by a simple secondary regulation process that increased the quantity of bacterial cellulose (BC) nanofibers per unit volume of the matrix. This led to the production of aerogels with excellent bendability and a high tensile strength. A maximum breaking stress and tensile modulus of 3.06 MPa and 46.07 MPa, respectively, were achieved. This method can be implemented to produce robust and bendable silica-based composite aerogels (CAs).

Wood‐Derived Lightweight and Elastic Carbon Aerogel for Pressure Sensing and Energy Storage

AbstractLightweight and elastic carbon materials have attracted great interest in pressure sensing and energy storage for wearable devices and electronic skins. Wood is the most abundant renewable resource and offers green and sustainable raw materials for fabricating lightweight carbon materials. Herein, a facile and sustainable strategy is proposed to fabricate a wood‐derived elastic carbon aerogel with tracheid‐like texture from cellulose nanofibers (CNFs) and lignin. The flexible CNFs entangle and assemble into an interconnected framework, while lignin with high thermal stability and favorable stiffness prevents the framework from severe structural shrinkage during annealing. This strategy leads to an ordered tracheid‐like structure and significantly reduces the thermal deformation of the CNFs network, producing a lightweight and elastic carbon aerogel. The wood‐derived carbon aerogel exhibits excellent mechanical performance, including high compressibility (up to 95% strain) and fatigue resistance. It also reveals high sensitivity at a wide working pressure range of 0–16.89 kPa and can detect human biosignals accurately. Moreover, the carbon aerogel can be assembled into a flexible and free‐standing all‐solid‐state symmetric supercapacitor that reveals satisfactory electrochemical performance and mechanical flexibility. These features make the wood‐derived carbon aerogel highly attractive for pressure sensor and flexible electrode applications.

Zeolitic imidazolate framework-cellulose nanofiber hybrid membrane as Li-Ion battery separator: Basic membrane property and battery performance

Zeolitic imidazolate framework-8 (ZIF8) concept was introduced in the fabrication of li-ion battery (LIB) separator for the first time. The ZIF8 crystals were synthesized on the surface of cellulose nanofibers (CNFs) by mixing 2-methylimidazole (Hmim) with zinc nitrate hexahydrate (Zn) in methanol. ZIF8- or Zn (mim)2-CNF composite membrane was fabricated and the effect of ZIF8 on the pore structure of CNF network was investigated. The pores of the ZIF8-CNF membrane distributed more homogeneously than that of the pure CNF membrane. The porosity increased from 42% (pure CNF membrane) to 55% (composite membrane). The successful synthesis of ZIF8 crystals on CNF surface was confirmed through elemental composition and crystalline structure analysis of the composite. Compared with polymer based separator, the ZIF8-2-CNF membrane exhibited better thermal stability, mechanical property (isotropic vs. anisotropic), thermal expansion behavior (15.53 vs. 178.90 ppm/k), and surface wettability (13.31° vs. 96.18°). The LIB fabricated with ZIF8-CNF membrane had a comparable cycling stability and a better discharge retention stability (88.3% vs 80.2%) in comparison with these of a tri-layer commercial polymer membrane. The environmentally friendly ZIF8-CNF nanocomposite membrane can be considered as a good alternative for manufacturing LIBs.