Cellulose Nanofiber Hydrogel Research Articles

Structural Changes of Water in Carboxymethyl Cellulose Nanofiber Hydrogels during Vapor Swelling and Drying

Structural Changes of Water in Carboxymethyl Cellulose Nanofiber Hydrogels during Vapor Swelling and Drying

Facile Preparation of Irradiated Poly(vinyl alcohol)/Cellulose Nanofiber Hydrogels with Ultrahigh Mechanical Properties for Artificial Joint Cartilage.

In this study, Poly(vinyl alcohol)/cellulose nanofiber (PVA/CNF) hydrogels have been successfully prepared using γ-ray irradiation, annealing, and rehydration processes. In addition, the effects of CNF content and annealing methods on the hydrogel properties, including gel fraction, micromorphology, crystallinity, swelling behavior, and tensile and friction properties, are investigated. Consequently, the results show that at an absorbed dose of 30 kGy, the increase in CNF content increases the gel fraction, tensile strength, and elongation at break of irradiated PVA/CNF hydrogels, but decreases the water absorption. In addition, the cross-linking density of the PVA/CNF hydrogels is significantly increased at an annealing temperature of 80 °C, which leads to the transition of the cross-sectional micromorphology from porous networks to smooth planes. For the PVA/CNF hydrogel with a CNF content of 0.6%, the crystallinity increases from 19.9% to 25.8% after tensile annealing of 30% compared to the original composite hydrogel. The tensile strength is substantially increased from 65.5 kPa to 21.2 MPa, and the modulus of elasticity reaches 4.2 MPa. Furthermore, it shows an extremely low coefficient of friction (0.075), which suggests that it has the potential to be applied as a material for artificial joint cartilage.

Electrodeposition of cellulose nanofibers as an efficient dehydration method

Dehydration of a cellulose nanofiber (CNF)/water dispersion requires large amounts of energy and time due to the high hydrophilicities and high specific surface areas of the CNFs. Various dehydration methods have been proposed for CNF/water dispersions; however, an efficient dehydration method for individually dispersed CNFs is needed. Here, electrodeposition of CNFs was evaluated as a dehydration method. Electrodeposition at a DC voltage of 10 V on a 0.2 wt% CNF/water dispersion resulted in a concentration of ∼1.58 wt% in 1 h. The dehydration energy efficiency was ∼300 times greater than that of dehydration by evaporation. The concentrated CNF hydrogels recovered after electrodeposition were redispersed with a simple neutralization process, and clear transparent films were obtained by drying after redispersion. This work provides a new method for dehydration and reuse of individually dispersed CNF/water dispersions and provides new insights into control of the hierarchical structures of CNFs by electrodeposition.

Hydrogels and aerogels of cellulose nanofiber derived from barley straw with addition of chitosan using high-intensity ultrasound and supercritical CO2 drying

In this study, cellulose-rich residue (purity of 90.2%) removed from barley straw was used to obtain cellulose nanofiber hydrogels (1–2 wt%) by high-intensity ultrasound treatments at 1200 W for 10–30 min. The highest water retention value (82.9±0.8 g/g) and fibrillation yield (62.12±0.13 wt%) of hydrogel were obtained by 1 and 2 wt% cellulose nanofibers, respectively, after ultrasound treatment at 1200 W for 20 min. Also, chitosan (1–3 wt%) was added to the cellulose nanofiber hydrogels by ultrasound treatment at 1200 W/20 min. The addition of chitosan reduced the water retention value and fibrillation yield. All hydrogels exhibited a typical elastic gel-like behavior. Then, the hydrogels were dried using supercritical CO2 to form aerogels, and their properties (bulk density, porosity, stiffness, functional groups, morphology, and thermal behavior) were determined. The lowest bulk density (0.056±0.011 g/cm3) and the highest porosity (96.50±0.17%) was achieved using 1 wt% cellulose nanofiber. The addition of chitosan at 3 wt% increased aerogel stiffness to 3200.10±8.80 g/mm.

Far-red light-triggered cargo release from liposomes bound to a photosensitizer-cellulose nanofiber hydrogel

In our research we used the anionic nanofibrillar cellulose (ANFC) as a platform for far-red light-induced release of cargo from liposomes. In contrast to previous works, where photosensitizers are usually in the liposomal bilayers, we used a cellulose-binding dye. Our phthalocyanine derivative has been shown to bind very strongly to cellulose and cellulose nanofiber hydrogels, allowing us to place it outside of the liposomes. Both the sensitizer and cationic liposomes bind strongly to the ANFC after mixing, making the system easy to fabricate. Upon light activation, the photosensitizer generates reactive oxygen species (ROS) within the ANFC hydrogel, where the reactive oxygen species oxidize unsaturated lipids in the liposomal membrane, which makes the liposomes more permeable, resulting in on-demand cargo release. We were able to achieve ca. 70 % release of model hydrophilic cargo molecule calcein from the hydrogels with a relatively low dose of light (262 J/cm2) while employing the straightforward fabrication techniques. Our system was remarkably responsive to the far-red light (730 nm), enabling deep tissue penetration. Therefore, this very promising novel cellulose-immobilized photosensitizer liposomal platform could be used as a controlled drug delivery system, which can have applications in externally activated coatings or implants.

Fractional rheology of colloidal hydrogels with cellulose nanofibers

Colloidal gels are soft solids composed of particles dispersed in a fluid phase. Their rheological behavior highly depends on the particle concentration, but establishing a relationship can be challenging. This article showcases the potential of fractional rheology to model and predict linear viscoelastic responses of colloidal hydrogels containing TEMPO-oxidized cellulose nanofibers. Cellulose nanofiber hydrogels are soft solids whose rheology is directly related to the particle concentration. Therefore, this work defined the rheological behavior of the hydrogels using a fractional order derivative analytically solved to determine rheological responses in frequency, stress relaxation, and creep. Using two parameters, it evaluated the rheology of cellulose nanofiber hydrogels and established tests that predict rheological behaviors for given particle concentrations. The findings suggested that the fractional approach could become a standard method for characterizing cellulose nanofiber hydrogels in the reported concentration regime. The two parameters of the fractional model build a comparison framework to assess the rheology of different viscoelastic materials.Graphic abstract

TEMPO-oxidized cellulose nanofiber hydrogel electrolyte for rechargeable Zn-ion batteries.

A hydrogel composed of TEMPO-oxidized cellulose and zinc perchlorate is proposed as an electrolyte for rechargeable Zn-ion battery. The non-flowable solid-like electrolyte has strong shear-thinning behavior, room temperature conductivity of ∼10-1 S cm-1, and stable Zn/electrolyte interphase. The Zn-ion gel-battery with a β-MnO2 cathode delivers over 100 mA h g-1 at 1.5 V allowing safe energy storage.

Cellulose nanofiber hydrogel with high conductivity electrolytes for high voltage flexible supercapacitors

Although flexible double layer capacitors based on hydrogels overcome the drawbacks of commercial double layer capacitors such as low safety and non-deformability, it is still considered as attractive challenges to achieve high conductivity for hydrogel electrolytes as well as high operating voltages for hydrogel flexible supercapacitors. In this paper, ion migration channels were engineered by immobilizing positive and negative charges on polymer skeleton and dispersing cellulose nanofibers in the polymerized polyelectrolyte network, providing ultra-high ionic conductivity (103 mS cm−1). In addition, K3[Fe(CN)6] was introduced through a soaking method, leading to redox reactions on the surface of carbon electrode during charging and discharging, supporting a relatively wide voltage window (1.8 V). Moreover, the specific capacitance at high current remained 55 % of the specific capacitance at low current, indicating excellent rate performance. In addition, the device displayed high cycling stability (80.05 % after 10,000 cycles). Notably, we successfully light up the red LED with only one device. Accordingly, this work provides a feasible design concept for the development of cellulose nanofibers (CNF) hydrogel-based solid-state electrolyte with high conductivity for flexible supercapacitors with wide potential window and high energy density.

Surface-Modified Carboxylated Cellulose Nanofiber Hydrogels for Prolonged Release of Polyhexamethylene Biguanide Hydrochloride (PHMB) for Antimicrobial Applications.

The surface modification of cellulose nanofibers (CNFs) using a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)/sodium bromide (NaBr)/sodium hypochlorite (NaClO) system was successful in improving their hydrophilicity. Following that, we fabricated hydrogels containing carboxylated cellulose nanofibers (c-CNFs) and loaded them with polyhexamethylene biguanide (PHMB) using a physical crosslinking method, aiming for efficient antimicrobial uses. The morphological and physicochemical properties of all hydrogel formulations were characterized, and the results revealed that the 7% c-CNFs-2 h loaded with PHMB formulation exhibited desirable characteristics such as regular shape, high porosity, good mechanical properties, suitable gel content, and a good maximum swelling degree. The successful integration of PHMB into the c-CNF matrix was confirmed by FTIR analysis. Furthermore, the 7% c-CNFs-2 h loaded with the PHMB formulation demonstrated PHMB contents exceeding 80% and exhibited a prolonged drug release pattern for up to 3 days. Moreover, this formulation displayed antibacterial activity against S. aureus and P. aeruginosa. In conclusion, the novel approach of c-CNF hydrogels loaded with PHMB through physical crosslinking shows promise as a potential system for prolonged drug release in topical drug delivery while also exhibiting excellent antibacterial activity.

Constructing triple-network cellulose nanofiber hydrogels with excellent strength, toughness and conductivity for real-time monitoring of human movements

In recent years, there has been a lot of interest in developing composite hydrogels with superior mechanical and conductive properties. In this study, triple-network (TN) cellulose nanofiber hydrogels were prepared by using cellulose nanofiber as the first network, isotropic poly(acrylamide-co-acrylic acid) as the second network, and polyvinyl alcohol as the third network via a cyclic freezing-thawing process. The strong (9.43 ± 0.14 MPa tensile strength, (445.5 ± 7.0)% elongation-at-break), tough (15.12 ± 0.14 MJ/m3 toughness), and conductive (0.0297 ± 0.00021 S/cm ionic conductivity) TN cellulose nanofiber hydrogels were effectively created after being pre-stretched in an external force field, cross-linked by Fe3+ and added Li+. The produced composite TN cellulose nanofiber hydrogels were successfully used as a flexible sensor for real-time monitoring and detecting human movements, highlighting their potential for wearable electronics, medical technology, and human-machine interaction. Chemical compounds studied in this articleAcrylamide (PubChem CID: 6579); Acrylic acid (PubChem CID: 6581); Ammonium persulfate (PubChem CID: 6579); N, N′-methylene bisacrylamide (PubChem CID: 17956053); Sodium bromide (PubChem CID: 253881); Sodium hydroxide (PubChem CID: 14798); Sodium hypochlorite (PubChem CID: 23665760); Sodium chlorite (PubChem CID: 23668197); 2,2,6,6-tetramethylpiperidinyl-1-oxide (PubChem CID: 2724126); Polyvinyl alcohol (PubChem CID: 11199); Lithium chloride (PubChem CID: 433294); Iron nitrate nonahydrate (PubChem CID: 129774236)

Highly Flexible, Self-Bonding, Self-Healing, and Conductive Soft Pressure Sensors Based on Dicarboxylic Cellulose Nanofiber Hydrogels.

Conductive hydrogels have gained a great deal of interest in the flexible electronics industry because of their remarkable inherent properties. However, a significant challenge remains for balancing hydrogel's conductivity, self-healing, and strength properties. Herein, double network ionic hydrogels were fabricated by concurrently introducing borax into dicarboxylic cellulose nanofiber (DCNFs) and polyacrylamide (PAM) hydrogels. The incorporation of borax provided a superabsorbent feature to the PAM/DCNF hydrogels (without borax) with the equilibrium water absorption rate increased from 552 to 1800% after 42 h. The compressive strength of the prepared hydrogel was 935 kPa compared to 132 kPa for the PAM hydrogel, with high cycling stability (stable after 1000 compression cycles with 50% strain). The hydrogel pressure sensor had a very sensitive response (gauge factor = 1.36) in the strain range from 10 to 80%, which made it possible to detect mechanical motion accurately and reliably. The developed hydrogels with high-performance, environmentally friendly properties are promising for use in future artificial skin and human-machine interface applications.

One-pot and one-step preparation of “living” cellulose nanofiber hydrogel with active double-bond via chemical vapor deposition

Due to the existence of water, it is still a challenge to conduct chemical modification on cellulose nanofiber (CNF) hydrogels with active double bonds. A simple one-pot and one-step method for constructing “living” CNF hydrogel with double bond was created at room temperature. The chemical vapor deposition (CVD) of methacryloyl chloride (MACl) was used to introduce physical-trapped, chemical-anchored and functional double bonds into TEMPO-oxidized cellulose nanofiber (TOCN) hydrogels. TOCN hydrogel could be fabricated within just 0.5 h, the minimum dosage of MACl could be reduced to 3.22 mg/g (MACl/TOCN hydrogel). Furthermore, the CVD methods showed high efficiency for mass production and recyclability. Moreover, the chemical “living” reactivity of the introduced double bonds were verified by the freezing and UV crosslinking, radical polymerization and thiol-ene click reaction. Compared with pure TOCN hydrogel, the obtained functionalized TOCN hydrogel exhibited remarkable improvements in mechanical properties, with enhancements of 12.34 times and 2.04 times, as well as an increase in hydrophobicity by 2.14 times and a fluorescence performance improvement of 2.93 times.

Osmotic-Enhanced-Photoelectrochemical Hydrogen Production Based on Nanofluidics

Osmotic-Enhanced-Photoelectrochemical Hydrogen Production Based on Nanofluidics

Microscopic structural changes during the freeze cross-linking reaction in carboxymethyl cellulose nanofiber hydrogels

Freeze cross-linking increases the mechanical strength of carboxymethyl cellulose nanofiber (CMCF) hydrogels. The structural changes of CMCF hydrogels during the freeze cross-linking reaction were investigated. The SEM images of CMCF hydrogels prepared with different reaction times showed that the CMCF hydrogel in the initial state of the cross-lining reaction (t ≤ 1 h) has a fibrous structure due to the original CMCF. As the reaction progressed (t ≥ 12 h), the fibrous structure was no longer present and a sheet structure with the average thickness of 1.5 ± 0.2 µm was observed. The XRD profiles indicated that the sheet consisted of a stable crystalline structure of cellulose II, in which CMCF was aligned along the (110) plane. It was also confirmed that using acidic aqueous solutions such as citric acid, DL-malic acid, lactic acid, or hydrogen chloride, as cross-linking agents yields CMCF hydrogels with the sheet structure and high compressive strength. On the other hands, when alkaline aqueous solution such as trisodium citrate, tripolyphosphate, or urea were used as cross-linking agents, brittle CMCF hydrogels with inhomogeneous fibrous structures were formed.

An Electroconductive, Thermosensitive, and Injectable Chitosan/Pluronic/Gold-Decorated Cellulose Nanofiber Hydrogel as an Efficient Carrier for Regeneration of Cardiac Tissue.

Myocardial infarction is a major cause of death worldwide and remains a social and healthcare burden. Injectable hydrogels with the ability to locally deliver drugs or cells to the damaged area can revolutionize the treatment of heart diseases. Herein, we formulate a thermo-responsive and injectable hydrogel based on conjugated chitosan/poloxamers for cardiac repair. To tailor the mechanical properties and electrical signal transmission, gold nanoparticles (AuNPs) with an average diameter of 50 nm were physically bonded to oxidized bacterial nanocellulose fibers (OBC) and added to the thermosensitive hydrogel at the ratio of 1% w/v. The prepared hydrogels have a porous structure with open pore channels in the range of 50–200 µm. Shear rate sweep measurements demonstrate a reversible phase transition from sol to gel with increasing temperature and a gelation time of 5 min. The hydrogels show a shear-thinning behavior with a shear modulus ranging from 1 to 12 kPa dependent on gold concentration. Electrical conductivity studies reveal that the conductance of the polymer matrix is 6 × 10−2 S/m at 75 mM Au. In vitro cytocompatibility assays by H9C2 cells show high biocompatibility (cell viability of >90% after 72 h incubation) with good cell adhesion. In conclusion, the developed nanocomposite hydrogel has great potential for use as an injectable biomaterial for cardiac tissue regeneration.

On the mechanism for the highly sensitive response of cellulose nanofiber hydrogels to the presence of ionic solutes

Hydrogels formed by cellulose nanofibers (CNFs) find use in a variety of applications. CNF hydrogels generally stiffen and ultimately flocculate with increasing salt concentrations. While charge repulsion explains the behavior of nanocellulose variants that have been stabilized by charged groups, it has been a puzzle why ions have such a pronounced effect also on CNFs with unmodified surfaces. We studied the effect of ionic solutes on native CNF hydrogels, and found that already at very low concentrations of around 1 mM, ions cause crowding of the hydrogels. The ionic solutes used were NaCl, Na2SO4, NaI, NaSCN, and sodium acetate. For the hydrogels, we used low densities of CNFs which lead to relatively weak gels that were highly sensitive to salts. Screening of the electrical double layer could not explain the results at such low ion concentrations. To understand cellulose-ion interactions, we used computational molecular dynamics simulations. The results provide an explanation by the effect of ions on the structure of the hydration layers of the cellulose. Understanding how and why ions affect the properties of native CNF hydrogels can help in for example manufacture of CNFs and when using CNFs as material components, substrates for enzymes, or as rheology modifiers. Ion-effects on the hydration layer of cellulose may also be important for more fundamental understanding of interfacial interactions of cellulose with water under different conditions.Graphical abstract

Thermal and Electrical Properties of Epoxy Composites Filled with 3D h‐BN/TOCNF Fillers

AbstractEpoxy resin (EP) has been widely used in electronic packaging and electrical equipment due to its excellent electrical insulating properties. However, the low thermal conductivity (TC) of EP limits its wider application and needs to be further improved. In this study, 3D hexagonal boron nitride (3D h‐BN) is successfully synthesized by utilizing TEMPO oxidated cellulose nanofiber hydrogels (TOCNF) as an interlocking skeleton, and then 3D h‐BN/TOCNF are chosen as the functional fillers to improve the TC of EP. The microstructure, TC, and electrical insulating properties of epoxy composites are systematically characterized and analyzed. The results show that epoxy composites filled with 3D h‐BN/TOCNF deliver a significantly improved TC and maintain excellent insulating properties. When the filled content of 3D h‐BN/TOCNF is 9 wt.%/21wt.%, a TC of 0.86 W (m K)−1 is obtained at 25 °C, which also demonstrates favorable electrical insulating properties with a volume resistivity of more than 1015 Ω m and breakdown strength of 186.1 kV mm−1. This work offers an efficient method to improve the thermal and electrical performances of EP for electronics and electrical engineering applications.

Antifreezing ionotronic skin based on flexible, transparent, and tunable ionic conductive nanocellulose hydrogels

Ionic hydrogels with excellent flexibility and good conductivity have great potential in diverse electric devices. However, it remains challenging to improve the biocompatibility of ionic hydrogels. Here, natural and environment-friendly cellulose nanofiber hydrogels were prepared without adding any organic active materials. The cellulose hydrogel networks with free metal ions (Li+/Ca2+/K+) were obtained by soaking in ion aqueous solution of different concentrations in order to endow tunable conductivity, thus a new kind of transparent ionic hydrogels with both excellent sensing performance obtained by a simple, low-cost and harmless process. The free metal ions locked in the negatively charged nanocellulose network through electrostatic interaction provided adjustable conductivity and sensing performance. Hydrogels doped with 4 mol L−1 lithium ions exhibited the best sensing performance with the conductivity of 4.36 × 10–4 S cm−1, and the current response value was as high as 127%. It was worth noting that the strain-sensitive performance of calcium ions was generally excellent even at low temperatures (−30 °C). The antifreezing of the hydrogel improved its service under extreme environment. This kind of hydrogel has great application prospects in artificial intelligence products, such as human healthy monitoring equipment and soft robotics at subzero temperature.

Rheological properties of cellulose nanofiber hydrogel for high-fidelity 3D printing

Optimization of the rheological properties of the matrix is ​​critical for high-fidelity matrix-assisted 3D printing (MAP), which enables the free-form fabrication of fluidic soft materials. This report describes the generic criteria observable in the printing process of cellulose nanofiber (CNF) hydrogels: the sharpness of an angled line, the cross-sectional ratio of a feature, the surface roughness of features, and the completeness of multi-line writing. The concentration and physical properties of the CNF affects the printing fidelity by changing the values of the four criteria, which are closely related to the rheological properties of the matrix. The printing fidelity can be enhanced by the optimal combination of the inks and the CNF matrix. Hydrophilic and hydrophobic inks are printed in the CNF matrix demonstrating as a universal matrix for free-form fabrication with liquid inks.

Eco-friendly Carboxymethyl Cellulose Nanofiber Hydrogels Prepared via Freeze Cross-Linking and Their Applications

We developed a cross-linking method using freeze concentration and used it to synthesize a carboxymethyl cellulose nanofiber (CMCF) hydrogel with high water content (>94%), high compressive strengt...