Cellulose nanofibers (CNFs) are a type of nanocomposites of the polysaccharide cellulose. CNFs are obtained by the mechanical treatment of the pre-treated cellulosic extract. The mechanical treatment ...processes include methods like high pressure homogenization, micro fluidization, cryocrushing, grinding, high intensity ultrasonication and electrospinning. CNFs exist in different forms like suspensions, powders, films, hydrogels and aerogels. CNFs are also subjected to various surface modifications like acetylation/esterification, silylation, TEMPO oxidation, etc. This led to an enhancement in properties of CNFs. Such modifications e.g. TEMPO oxidation of CNFs have imparted variety of excellent biomedical applications. CNFs in different forms (especially aerogels and hydrogels) and CNF composites have been studied for various biomedical applications including drug delivery, wound healing, tissue engineering, protein delivery, antibacterial activity and biosensor application. This review article discusses the sources, isolation, fabrication and recent developments in biomedical applications of CNFs.
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•Cellulose nanofibers are prepared by mechanical treatment leading to size reduction of fibres to nanoscale.•Cellulose can be chemically modified to achieve a balance between hydrophilicity and hydrophobicity.•The chemically modified cellulose nanofibers impart numerous biomedical applications.
Flexible composite film has gained increasing attention in the fields of wearable devices and portable electronic products. In this work, a novel core-shell structure of cellulose ...nanofibers/BaTiO3@TiO2 (CNF/BTO@TiO2) was synthesized with the assistant of the biological macromolecule material of cellulose nanofiber (CNF), in which the CNF can improve the stability and dispersibility of BaTiO3 (BTO) in the aqueous phase and elevate the integrity of the core-shell structure. The core-shell structure can reduce the agglomeration of fillers in polyvinylidene fluoride (PVDF) and improve the structural defects of the composite film. Meanwhile, the core-shell structure can promote the polarization of the electric dipole and the formation of β phase in PVDF due to the generated interface spatial polarization between the shell of TiO2 and the core of BTO. When the content of the core-shell structure was 5 wt%, the β phase content reaches 61.89 %, and the piezoelectric coefficient of composite film reaches 84.29 pm/V. Thus the maximum output open-circuit voltage (VOC) and short-circuit current (ISC) of the piezoelectric composite film is as high as 13.10 V and 464.3 nA. In addition, its excellent pressure sensing capability allows for its application in various flexible electronic devices.
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•A novel CNF/BTO@TiO2 core-shell structure is synthesized for the flexible PEG.•CNF can improve uniformity of BTO during the preparation of CNF/BTO@TiO2 core-shell structure.•Core-shell structure can promote polarization of electric dipole, formation of β phase and piezoelectric coefficient.•Its output voltage and current is elevated to be 13.10 V and 464.3 nA, respectively.•The flexible PEG has conspicuous strain sensing and mechanical energy harvesting performance.
In this study, the effective role of incorporation of cellulose nanofibers (CNF) and modified acetylated cellulose nanofibers (ACNF) on mechanical, physical, and biological properties of poly ...(ε-caprolactone) (PCL)/gelatin (Gel) electrospun nanofibrous scaffold was individually investigated. It was noticed that mechanical and biological properties of the scaffolds were considerably affected by the filler type and content. Although, by addition of 2 wt% ACNF, the ultimate tensile strength (UTS) of the PCL/Gel was remarkably enhanced from 2.5 ± 0.1 MPa to 4.3 ± 0.1 MPa due to homogeneous dispersion of the ACNF, however, the degradation rate of PCL/Gel scaffold was reduced about 1.66 times. Moreover, the studies on the interactions between hybrid scaffolds and fibroblast cells revealed that the incorporation of ACNF into scaffold not only showed no cytotoxic, but also promoted cell proliferation. In conclusion, PCL/Gel nanocomposite scaffolds reinforced by ACNFs show an excellent potential as a promising candidate for soft tissue engineering applications.
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•Bionanocomposites scaffolds of PCL/Gel/ACNF were successfully fabricated by electrospinning method.•ACNF incorporating significantly improved thermal and mechanical properties.•Electrospun PCL/Gel/ACNF scaffolds exhibited a degradation behavior by none-toxic, biocompatible and biodegradable materials.•Cell adhesion and proliferation of ACNF-loaded scaffolds were improved making it a candidate for soft tissue engineering.
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Hydrogel-based sensors have attracted considerable attention due to potential opportunities in human health monitoring when both mechanical flexibility and sensing ability are ...required. Therefore, the integration of excellent mechanical properties, electrical conductivity and self-healing properties into hydrogels may improve the application range and durability of hydrogel-based sensors.
A novel composite hydrogel composed of polyaniline (PANI), polyacrylic acid (PAA) and 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNFs) was designed. The viscoelastic, mechanical, conductive, self-healing and sensing properties of hydrogels were studied.
The TOCNF/PANI/PAA hydrogel exhibits a fracture strain of 982%, tensile strength of 74.98 kPa and electrical conductivity of 3.95 S m−1, as well as good mechanical and electrical self-healing properties within 6 h at ambient temperature without applying any stimuli. Furthermore, owing to the high sensitivity of the TOCNF/PANI/PAA-0.6 hydrogel-based strain sensor (gauge factor, GF = 8.0), the sensor can accurately and rapidly detect large-scale motion and subtle localized activity. The proposed composite hydrogel is as a promising material for use as soft wearable sensors for health monitoring and smart robotics applications.
Conducting polymer hydrogels (CPHs) have emerged as a fascinating class of smart soft matters important for various advanced applications. However, achieving the synergistic characteristics of ...conductivity, self-healing ability, biocompatibility, viscoelasticity, and high mechanical performance still remains a critical challenge. Here, we develop for the first time a type of multifunctional hybrid CPHs based on a viscoelastic polyvinyl alcohol (PVA)–borax (PB) gel matrix and nanostructured CNFs–PPy (cellulose nanofibers–polypyrrole) complexes that synergizes the biotemplate role of CNFs and the conductive nature of PPy. The CNF–PPy complexes are synthesized through in situ oxidative polymerization of pyrrole on the surface of CNF templates, which are further well-dispersed into the PB matrix to synthesize homogeneous CNF–PPy/PB hybrid hydrogels. The CNF–PPy complexes not only tangle with PVA chains though hydrogen bonds, but also form reversibly cross-linked complexes with borate ions. The multi-complexation between each component leads to the formation of a hierarchical three-dimensional network. The CNF–PPy/PB-3 hydrogel prepared by 2.0 wt % of PVA, 0.4 wt % of borax, and CNF–PPy complexes with a mass ratio of 3.75/1 exhibits the highest viscoelasticity and mechanical strength. Because of a combined reinforcing and conductive network inside the hydrogel, its maximum storage modulus (∼0.1 MPa) and nominal compression stress (∼22 MPa) are 60 and 2240 times higher than those of pure CNF/PB hydrogel, respectively. The CNF–PPy/PB-3 electrode with a conductivity of 3.65 ± 0.08 S m–1 has a maximum specific capacitance of 236.9 F g–1, and its specific capacitance degradation is less than 14% after 1500 cycles. The CNF–PPy/PB hybrid hydrogels also demonstrate attractive characteristics, including high water content (∼94%), low density (∼1.2 g cm–3), excellent biocompatibility, plasticity, pH sensitivity, and rapid self-healing ability without additional external stimuli. Taken together, the combination of such unique properties endows the newly developed CPHs with potential applications in flexible bioelectronics and provides a practical platform to design multifunctional smart soft materials.
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•Anisotropic CNF/CS aerogel are prepared via directional freeze-casting.•The composite aerogel is lightweight, porous and compressible.•The aerogel exhibits anisotropic thermal ...management properties.•The composite aerogel shows high absorption capacity for various solvents.
Attributed to low cost, renewable, and high availability, cellulose-based aerogels are desirable materials for various applications. However, mechanical robustness and functionalization remain huge challenges. Herein, we synthesized a recoverable, anisotropic cellulose nanofiber (CNF) / chitosan (CS) aerogel via directional freeze casting and chemical cross-link process. The chitosan was performed as strength polymers to prohibits the shrinkage and retains the structural stability of 3D cellulose nanofiber skeleton, endowing the composite aerogel with satisfactory deformation recovery ability (without loss under 60 % stress cycled 100 times). The CNF/CS composite aerogel has ultralow density (∼8.4 mg/cm3), high temperature-invariant (above 300 °C) and high porosity (98 %). The CNF/CS aerogel demonstrates anisotropic thermal insulation properties with low thermal conductivity (28 mWm−1 K−1 in rational direction and 36 mW m−1 K−1 in the axial direction). Moreover, the composite aerogel (water contact angle ∼148°) exhibited outstanding oil/water selectivity and high absorption capacity (82–253 g/g) for various oils and organic solvents. Therefore, the multifunctional CNF/CS composite aerogels are potential materials for thermal management and oil absorption applications.
•Recent developments in production of cellulose nanofibrils (CNF) were reviewed.•Mechanical disintegration processes and biological/chemical pretreatments were discussed.•Issues of CNF fractionation ...and quantification of the extent of fibrillation were addressed.•An overview of various CNF products, e.g., powders, films, hydrogels and aerogels was proposed.
This review describes the recent advances in production of cellulose nanofibrils (CNF), otherwise known as nanofibrillated cellulose (NFC), microfibrillated cellulose (MFC) or cellulose nanofibers, a material with significant barrier, mechanical and colloidal properties, low density, renewable and biodegradable character. The above properties make CNF promising for applications in such fields as papermaking, composites, packaging, coatings, biomedicine and automotive. In this review, CNF production methods are summarized, covering raw materials selection, structural and chemical aspects necessary for understanding the nanofibril extraction process, conventional and novel mechanical disintegration techniques, as well as biological and chemical pretreatments aimed at facilitating nanofibril isolation. The issues of fractionation, performed with the objective of retrieving the residual microscopic fiber fragments from CNF suspensions, are addressed. Additionally, the preparation of CNF in various forms, such as suspensions, water-redispersible powders, films or nanopapers, hydrogels and aerogels, is discussed.
ZIF-8@cellulose nanofiber (ZIF-8@CNF) composite membranes were prepared via in-situ growing ZIF-8 crystals on cellulose nanofibers (CNFs) and vacuum filtration. Owning to the electrostatic forces ...between –COO- of CNFs and Zn2+ of ZIF-8, ZIF-8 crystals were anchored homogenously on CNFs. With ZIF-8 loading increased to sufficiently high, the intrinsic selectivity of ZIF-8 played an important role for gas separation. As a result, the optimum separation performance is achieved over ZIF-8@CNF-70 composite membrane with CO2 permeability of 550 Barrer and CO2/N2 and CO2/CH4 ideal selectivity of 45.5 and 36.2, respectively.
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•ZIF-8@CNF composite was prepared via in-situ growing ZIF-8 crystals on CNFs.•ZIF-8 crystals anchored homogenously in CNFs matrix with the electrostatic forces.•ZIF-8 loading was increased to sufficiently high in composite membrane.•The intrinsic selectivity of ZIF-8 played an important role for gas separation.
Nanocellulose, a versatile and sustainable nanomaterial derived from cellulose fibers, has attracted considerable attention in various fields due to its unique properties. Similar to dietary fibers, ...nanocellulose is difficult to digest in the human gastrointestinal tract. The indigestible nanocellulose is fermented by gut microbiota, producing metabolites and potentially exhibiting prebiotic activity in intestinal diseases. Additionally, nanocellulose can serve as a matrix material for probiotic protection and show promising prospects for probiotic delivery. In this review, we summarize the classification of nanocellulose, including cellulose nanocrystals (CNC), cellulose nanofibers (CNF), and bacterial nanocellulose (BNC), highlighting their distinct characteristics and applications. We discuss the metabolism-related characteristics of nanocellulose from oral ingestion to colon fermentation and introduce the prebiotic activity of nanocellulose in intestinal diseases. Furthermore, we provide an overview of commonly used nanocellulose-based encapsulation techniques, such as emulsification, extrusion, freeze drying, and spray drying, as well as the delivery systems employing nanocellulose matrix materials, including microcapsules, emulsions, and hydrogels. Finally, we discuss the challenges associated with nanocellulose metabolism, prebiotic functionality, encapsulation techniques, and delivery systems using nanocellulose matrix material for probiotics. This review will provide new insight into the application of nanocellulose in the treatment of intestinal diseases and probiotic delivery.
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•Aerogel Beads had higher adsorption capacity in comparison to monolithic aerogels.•The aerogels could be used effectively up to 20 times.•Coordination bonding and electrostatic ...interactions were the main adsorption mechanisms.
Heavy metals pose a significant threat to human health and ecological security due to their high toxicity, mobility, and persistence in the environment. Herein, the synthesis of a novel cellulose nanofiber-based aerogel using non-toxic biopolymers such as sodium alginate and polyglutamic acid to eradicate lead, zinc, and copper from water is described. The physical characterisation and the adsorption performance of the aerogels were evaluated in both monolithic and bead configurations. The study revealed superior adsorption performance for the aerogel beads compared to the monolithic configuration. The aerogel beads achieved a maximum adsorption capacity of 171.7 mg/g, 100.0 mg/g, and 142.0 mg/g for lead, zinc, and copper respectively. The aerogel beads exhibited a higher specific surface area compared to the monolithic aerogels. The presence of functional groups including carboxyl, amino, and hydroxyl groups on the aerogels likely facilitated the adsorption through coordinate bond formation and electrostatic interactions. Density Functional Theory calculations supported the role of oxygen and nitrogen containing groups on the aerogel in capturing heavy metal ions. The aerogels displayed a remarkable regeneration ability and were reused 20 times, without any significant reduction in the adsorption performance indicating its potential as a sustainable adsorbent for heavy metals removal from water.
