Dual crosslinked carboxymethyl cellulose/polyacrylamide interpenetrating hydrogels with highly enhanced mechanical strength and superabsorbent properties

Fabrication of liquid-free ionic conductive elastomer (ICE) from cellulose-rosin derived poly(esterimide) towards temperature-tolerant and solvent-resistant UV shadowless adhesive and sensor

Recently, the utilization of the cellulose to fabricate the multifunctional materials with aim to replace the petroleum-based product, is receiving significant attentions. However, the development of cellulose-based multifunctional materials with high mechanical strength and temperature resistance is still a challenge. Herein, the intrinsic feature and property of cellulose and rosin were creatively employed to fabricate a novel cellulose-rosin based poly(esterimide) (PEI) by esterification reaction and imidization reaction, and the obtained cellulose-rosin derived PEI exhibits superior thermal stability. Then the as-prepared cellulose-rosin derived PEI was dissolved in polymerizable deep eutectic solvents (PDES) and in-situ formed the ionic conductive elastomer (ICE) with via UV-induced polymerization. These cellulose-rosin based ICE exhibited excellent mechanical properties, solvent resistance, and temperature tolerance. By adjusting the mass ratio of cellulose-rosin derived PEI and PDES, the as-prepared liquid-free ICE functions as UV shadowless adhesive and wearable sensors. The bonding strength of UV shadowless adhesive could 1.52 MPa, which could be applied to fix the broken glass toy models. Furthermore, wearable sensors based those ICE could monitor the large and subtle movements even under extreme environmental condition, such as being soaked in organic solvent (such as tetrahydrofuran) or at low/high temperature (-25 °C or 80 °C). This work opens a new avenue for the next-generation of multifunctional ICE.

Leaching behavior of microplastics during sludge mechanical dewatering and its effect on activated sludge

Dewatering is an indispensable link in sludge treatment, but its effect on the microplastics (MPs) remains inadequately understood. This study investigated the physicochemical changes and leaching behavior of MPs during the mechanical dewatering of sludge, as well as the impact of MP leachates on activated sludge (AS). After sludge dewatering, MPs exhibit rougher surfaces, decreased sizes and altered functional groups due to the addition of dewatering agents and the application of mechanical force. Meanwhile, plastic additives, depolymerization products, and derivatives of their interactions are leached from MPs during sludge dewatering process. The concentration of MP-based leachates in sludge is 2-25 times higher than that in water. The enhancement of pH and ionic strength caused by dewatering agents induces the release of MP leachates enriched with protein-like, fulvic acid-like, and soluble microbial by-product-like substances. The reflux of MP leachates in sludge dewatering liquor to the wastewater treatment system negatively impacts AS, leading to a decrease in COD removal rate and inhibition of the extracellular polymeric substances secretion. More importantly, MP leachates cause oxidative stress to microbial cells and alter the microbial community structure of AS at the phylum and genus levels. These findings confirm that MPs undergo aging and leaching during sludge dewatering process, and MP leachates may negatively affect the wastewater treatment system.

The role of glycerol in manufacturing freeze-dried chitosan and cellulose foams for mechanically stable scaffolds in skin tissue engineering

Various strategies have extensively explored enhancing the physical and biological properties of chitosan and cellulose scaffolds for skin tissue engineering. This study presents a straightforward method involving the addition of glycerol into highly porous structures of two polysaccharide complexes: chitosan/carboxymethyl cellulose (Chit/CMC) and chitosan/oxidized cellulose (Chit/OC); during a one-step freeze-drying process. Adding glycerol, especially to Chit/CMC, significantly increased stability, prevented degradation, and improved mechanical strength by nearly 50%. Importantly, after 21 days of incubation in enzymatic medium Chit/CMC scaffold has almost completely decomposed, while foams reinforced with glycerol exhibited only 40% mass loss. It is possible due to differences in multivalent cations and polymer chain contraction, resulting in varied hydrogen bonding and, consequently, distinct physicochemical outcomes. Additionally, the scaffolds with glycerol improved the cellular activities resulting in over 40% higher proliferation of fibroblast after 21 days of incubation. It was achieved by imparting water resistance to the highly absorbent material and aiding in achieving a balance between hydrophilic and hydrophobic properties. This study clearly indicates the possible elimination of additional crosslinkers and multiple fabrication steps that can reduce the cost of scaffold production for skin tissue engineering applications while tailoring mechanical strength and degradation.

Recent Advances in Environmentally Friendly Dual-crosslinking Polymer Networks

Environmentally friendly crosslinked polymer networks feature degradable covalent or non-covalent bonds, with many of them manifesting dynamic characteristics. These attributes enable convenient degradation, facile reprocessibility, and self-healing capabilities. However, the inherent instability of these crosslinking bonds often compromises the mechanical properties of polymer networks, limiting their practical applications. In this context, environmentally friendly dual-crosslinking polymer networks (denoted EF-DCPNs) have emerged as promising alternatives to address this challenge. These materials effectively balance the need for high mechanical properties with the ability to degrade, recycle, and/or self-heal. Despite their promising potential, investigations into EF-DCPNs remain in their nascent stages, and several gaps and limitations persist. This Review provides a comprehensive overview of the synthesis, properties, and applications of recent progress in EF-DCPNs. Firstly, synthetic routes to a rich variety of EF-DCPNs possessing two distinct types of dynamic bonds (i.e., imine, disulfide, ester, hydrogen bond, coordination bond, and other bonds) are introduced. Subsequently, complex structure- and dynamic nature-dependent mechanical, thermal, and electrical properties of EF-DCPNs are discussed, followed by their exemplary applications in electronics and biotechnology. Finally, future research directions in this rapidly evolving field are outlined.

Zeolite-Loaded Hydrogels as Wound pH-Modulating Dressings for Diabetic Wound Healing

Wound pH has emerged as a promising therapeutic target in diabetic foot ulcers (DFU). Here, we aimed to develop a microparticle-loaded hydrogel for pH modulation in wound fluid. In a screen of polymeric and inorganic microparticles, zeolites were identified as pH-modulating microparticles. Zeolites were encapsulated in a calcium cross-linked alginate hydrogel, a biocompatible matrix clinically used as a wound dressing. This hydrogel potently neutralized hydroxide ions in serum-containing simulated wound fluid. These findings encourage a further development of this pH-modulating device as a molecular therapeutic system for DFUs.

Preparation of CMC-poly(N-isopropylacrylamide) semi-interpenetrating hydrogel with temperature-sensitivity for water retention

The CMC-PNIPAM hydrogel with semi-interpenetrating structure and temperature-sensitivity was prepared by in-situ polymerization of N-isopropylacrylamide (NIPAM) in sodium carboxymethylcellulose (CMC) solution at room temperature. The mass ratio of CMC to NIPAM was a key factor influencing the network structure and property of CMC-PNIPAM hydrogel. The low critical phase transition temperature (LCST) of CMC-PNIPAM hydrogels increased from 34.4 °C to 35.8 °C with the mass ratio of CMC to NIPAM rising from 0 to 1.2. The maximum compressive stress of CMC-PNIPAM hydrogel reached to 26.7 kPa and the relaxation elasticity was 52 % at strain of 60 %. The viscoelasticity of CMC-PNIPAM hydrogel was consistent with the generalized Maxwell model. The maximum swelling ratio in deionized water was 170.25 g·g-1 (dried hydrogel) with swelling rate of 2.57 g·g-1·min-1 at 25 °C. CMC-PNIPAM hydrogel hardly absorbed water above LCST, but the swollen hydrogel could release water at the rate of 0.36 g·g-1·min-1 once exceeding LCST. The test of water retention showed that soil mixed with 2 wt% dried CMC-PNIPAM hydrogel could retain 13.08 wt% water after 30 days at 25 °C that was 4.4 times than that of controlled soil without CMC-PNIPAM hydrogel. The semi-interpenetrating CMC-PNIPAM hydrogel showed a potential to conserve water responding to temperature.

Evaluation of physiochemical and biomedical properties of psyllium-poly(vinyl phosphonic acid-co-acrylamide)-cl-N,N-methylene bis acrylamide based hydrogels

Present investigation deals with the synthesis of psyllium based copolymeric hydrogels and evaluation of their physiochemical and biomedical properties. These copolymers have been prepared by grafting of poly(vinyl phosphonic acid) (poly (VPA)) and poly(acrylamide) (poly(AAm)) onto psyllium in the presence of crosslinker N,N-methylene bis acrylamide (NNMBA). These copolymers [psyllium-poly(VPA-co-AAm)-cl-NNMBA] were characterized by field emission-scanning electron micrographs (FE-SEM), electron dispersion X-ray analysis (EDAX), Atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), 13C-nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA)- differential thermal analysis (DTG). FESEM, AFM and XRD demonstrated heterogeneous morphology with a rough surface and an amorphous nature. Diffusion of ornidazole occurred with a non-Fickian diffusion mechanism, and the release profile data was fitted in the Korsemeyer-Peppas kinetic model. Biochemical analysis of hydrogel properties confirmed the blood-compatible nature during blood-polymer interactions and revealed haemolysis value 3.95 ± 0.05 %. The hydrogels exhibited mucoadhesive character during biomembrane-polymer interactions and demonstrated detachment force = 99.0 ± 0.016 mN. During 2,2-diphenyl-1-picrylhydrazyl reagent (DPPH) assay, free radical scavenging was observed 37.83 ± 3.64 % which illustrated antioxidant properties of hydrogels. Physiological and biomedical properties revealed that these hydrogels could be explored for drug delivery uses.

Enhancing protein delivery for tissue regeneration: Development of AGR2-loaded hydrogels with controlled release properties

The growth factor Anterior Gradient 2 (AGR2) has been shown to have an effective role in tissue regeneration, but remained largely unexplored in localized tissue engineering applications. Alginate beads have been proven as safe carriers for protein encapsulation, but they suffer from fragility and uncontrolled protein release. For such alginate systems, little is known about how changes in concentrations and ion-crosslinking affect protein release and accumulation in 3-D matrices. To address these questions, an engineered interpenetrating polymer network (IPN) has been used to synthesize a novel hybrid system consisting of AGR2 loaded beads composed of calcium-crosslinked sodium alginate (SA) and carboxymethyl cellulose (CMC). These beads are embedded in films consisting of SA and polyvinyl alcohol (PVA), using a simple ion gelation technique. We assess protein release kinetics and accumulation within the hybrid system by varying polymer concentrations and cross-linking parameters. The IPN hybrid system maintains controlled release over two weeks, without an initial burst period. Through this approach efficicnt delivery of AGR2 is achieved which in turn effectively mediates cell migration and proliferation, resulting in excellent cell viability and complete wound closure. The described release system opens new perspectives in tissue engineering.

The influence of different gums compared with surfactants as encapsulating stabilizers on the thermal, storage, and low-pH stability of chlorophyllin

Sodium copper chlorophyllin (SCC), with a higher stability and water solubility than chlorophyll, has limited applications in acidic products due to precipitation. We investigated the effect of pectin (PE), carboxymethyl cellulose (CMC), xanthan gum (XG), carrageenan gum (CG), gellan gum (GG), tragacanth gum (TG), gum Arabic (GA), and polysorbate 80 (PS80) on SCC stability in acidic model solutions (pH = 3.5). These stabilizers led to a significant reduction in particle size and zeta-potential compared to control sample. GA (33.3:1), PE (8:1), CMC (4:1), XG (1.33:1), and PS80 (0.67:1) stabilized SCC in acidic systems for 28 days. The FTIR analysis showed that mainly electrostatic and hydrogen bonds between SCC and stabilizers led to a substantial decline in particle size, improving SCC distribution and stability within acidic environment. Thus, XG and CMC could be effectively used for SCC stabilization under acidic solutions where applying PS80 surfactant is a health concern.

Engineering of PVA/PVP Hydrogels for Agricultural Applications

Hydrogels have gained significant popularity in agricultural applications in terms of minimizing waste and mitigating the negative environmental impact of agrochemicals. This review specifically examines the utilization of environmentally friendly, shapable hydrogels composed of polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) in various casings for crop protection against different pests, fertilizing, and watering. To activate their effectiveness, PVA/PVP hydrogels were loaded with both hydrophilic and hydrophobic environmentally friendly pesticides, namely hydrogen peroxide (HP), the essential oil thymol, and urea as a fertilizer, either separately or in combination. This review covers various physical and chemical approaches used for loading, shaping, and controlling the release profiles of pesticides and fertilizers. Additionally, it explores the evaluation of the chemical composition, structure, classification, rheology, and morphology of the hydrogels as well as their impact on the thermal stability of the encapsulated pesticides and fertilizer, followed by biological tests. These hydrogels significantly contribute to the stabilization and controlled release of essential nutrients and biocides for plants, while maintaining excellent biocidal and fertilizing properties as well as sustainability characteristics. By shedding light on the latest insights into the concepts, applications, and results of these hydrogels, this review demonstrates their immense potential for widespread future use in agriculture.

Enhanced Water Absorbency and Water Retention Rate for Superabsorbent Polymer via Porous Calcium Carbonate Crosslinking

To improve the water absorbency and water-retention rate of superabsorbent materials, a porous calcium carbonate composite superabsorbent polymer (PCC/PAA) was prepared by copolymerization of acrylic acid and porous calcium carbonate prepared from ground calcium carbonate. The results showed that the binding energies of C-O and C=O in the O 1s profile of PCC/PAA had 0.2 eV and 0.1-0.7 eV redshifts, respectively, and the bonding of -COO- groups on the surface of the porous calcium carbonate led to an increase in the binding energy of O 1s. Furthermore, the porous calcium carbonate chelates with the -COO- group in acrylic acid through the surface Ca2+ site to form multidirectional crosslinking points, which would increase the flexibility of the crosslinking network and promote the formation of pores inside the PCC/PAA to improve the water storage space. The water absorbency of PCC/PAA with 2 wt% porous calcium carbonate in deionized water and 0.9 wt% NaCl water solution increased from 540 g/g and 60 g/g to 935 g/g and 80 g/g, respectively. In addition, since the chemical crosslinker N,N'-methylene bisacrylamide is used in the polymerization process of PCC/PAA, N,N'-methylene bisacrylamide and porous calcium carbonate enhance the stability of the PCC/PAA crosslinking network by double-crosslinking with a polyacrylic acid chain, resulting in the crosslinking network of PCC/PAA not being destroyed after water absorption saturation. Therefore, PCC/PAA with 2 wt% porous calcium carbonate improved the water-retention rate by 244% after 5 h at 60 °C, and the compressive strength was approximately five-times that of the superabsorbent without porous calcium carbonate.

Muscle-inspired anisotropic carboxymethyl cellulose-based double-network conductive hydrogels for flexible strain sensors

Conductive hydrogels are considered one of the most promising materials for preparing flexible sensors due to their flexible and extensible properties. However, conventional hydrogels' weak mechanical and isotropic properties are greatly limited in practical applications. Here, the internal structure of the hydrogel was regulated by pre-stretching synergistic ion crosslinking to construct a carboxymethyl cellulose-based double network-oriented hydrogel similar to muscle. The introduction of pre-stretching increased the tensile strength of the double-network hydrogel from 1.45 MPa to 4.32 MPa, and its light transmittance increased from 67.3 % to 84.5 %. In addition, the hydrogel's thermal stability and electrical conductivity were improved to a certain extent. Its good mechanical properties and conductive properties can be converted into stable electrical signal output during deformation. The carboxymethyl cellulose-based double network oriented hydrogels were further assembled as flexible substrates into flexible sensor devices. The hydrogel sensors can monitor simple joint movements as well as complex spatial movements, which makes them have potential application value in the research field of intelligent response electronic devices such as flexible wearables, intelligent strain sensing, and soft robots.

Studies on Agrochemical Controlled Release Behavior of Copolymer Hydrogel with PVA Blends of Natural Polymers and Their Water-Retention Capabilities in Agricultural Soil

Agricultural technical development relies exclusively on the effective delivery of agrochemicals and water to plants and on reducing the harmful effects of agrochemicals on useful organisms in the soil. In this study, super-absorbent hydrogels were prepared in the form of microspheres using gum Arabic (GA), which was copolymerized once with chitosan (CS) and once with poly (vinyl alcohol) (PVA). To impart mechanical strength to the hydrogel microspheres, a covalent cross-linker (N,N'-methylenebisacrylamide (MBA)) was used for the PVA/GA hydrogel, and an ionic cross-linker (sodium hexametaphosphate (SHMP)) was used for the CS/GA hydrogel. The prepared PVA/GA-CH and CS/GA-PH hydrogel microspheres showed different degrees of swelling (DSs) in the following solution media: deionized water (DW), river water (RW), and buffered solutions (pH 4; pH 9). The PVA/GA-CH hydrogel microspheres showed a maximum DS of 84 g/g in the RW, while the CS/GA-PH hydrogel microspheres showed a maximum DS of 63 g/g in the buffered solution at a pH 9. The water-retention capabilities of the hydrogels were studied using a mixture of 0.5% (w/w) hydrogel microspheres in agricultural soil; the composite showed an additional 20 days of water retention in comparison with a control sample consisting of soil alone. The hydrogels were loaded with urea, which is an important fertilizer in the field of agriculture. The PVA/GA-CH hydrogel microspheres showed a maximum loading percentage (Lmax%) of 89% (w/w), while the CS/GA-PH hydrogel microspheres showed an Lmax% = 79.75% (w/w) for urea. The urea-release behaviors of the hydrogel microspheres were studied under different release media and temperature conditions. In practice, the PVA/GA-CH hydrogel microspheres showed a better release profile in the RW at 10 °C, while the CS/GA-PH hydrogel microspheres showed a more controlled release in media at a pH 9 and at 30 °C. The urea-loaded microspheres, aside from those following the release, were characterized via FTIR and SEM. In contrast, virgin microspheres were characterized using XRD,1H NMR, (TGA and DSC), and the maximum degree of swelling, in addition to being subjected to SEM and FTIR analyses.

The influence of molecular weight of cellulose on the properties of carboxylic acid crosslinked cellulose hydrogels for biomedical and environmental applications

Hydrogels a three-dimensional network structure of hydrophilic polymers have gained significant interest in the field of biomedicine due to its high-water absorption properties and its resemblance to native extracellular matrix. However, the hydrogel's physicochemical properties are important in its ability to serve as a matrix in biomedical applications. The variations on the molecular weight of polymers on the preparation of crosslinked hydrogels may alter the properties. Different molecular weight carboxymethyl cellulose polymers were employed in this work to determine the effect of molecular weight on the physicochemical parameters of the hydrogel's crosslinking reaction. For this study, two distinct molecular weight carboxymethyl cellulose (CMC) polymers (M_w, 250,000 and 700,000) and various concentrations of crosslinker solution were used. The hydrogels were prepared through a chemical crosslinking reaction combining CMC and citric acid, which results in the formation of an ester bond between the two polymer chains. The crosslinking reaction is confirmed by Fourier transform infrared spectroscopy and total carboxyl content analysis. According to the physicochemical, thermal, and mechanical analysis, we have identified that 7 %, 9 % and 10 % citric acid showed the most promising hydrogels and found 7CMC hydrogel had superior quality. In vitro results demonstrated that the citric acid crosslinked CMC had excellent hemocompatibility and cytocompatibility.

Superabsorbent Polymer Sponge for Saliva Absorption Pad

Aim:

Saliva is a significant hindrance to most dental procedures (e.g., root canal treatment) as the flow of saliva increases in patients undergoing dental treatment due to anxiety. Saliva absorption pads based on superabsorbent polymers can provide a dry oral environment to ease the dental treatment procedure and reduce the swallowing reflexes common during cotton use. This study focused on developing an indigenous saliva absorption pad using biodegradable superabsorbent polymer (BSAP) sponges.

Materials and Methods:

BSAP sponges were synthesized using carboxymethyl cellulose (CMC) as the base matrix. Different crosslinking mechanisms were implemented to prepare BSAP sponges, such as ionic crosslinking using aluminum ammonium sulfate (AlAS) and chemical crosslinking using methylene bisacrylamide. Three different BSAP sponges (Sap-2, SAP-PAA-1, and SAP-PAA-2) were characterized for their free swell capacity and thermal degradation kinetics along with other characterization techniques to optimize the composition for saliva absorption pad. One-way ANOVA was used for statistical evaluation.

Results:

SAP-2, synthesized using 10 wt.% AlAS showed the highest free swell capacity in water and saline (83.21 ± 3.8 g/g and 40.7 ± 3.4 g/g, respectively). However, the moisture content of the particular BSAP sponge was higher (~13%) compared to the standard limit (ISO 17190-4:2001(E)). It was observed that as the crosslinking density increases free swell capacity increases to a threshold point and decreases thereafter. As reported earlier, percentage swelling was controlled by multiple factors including crosslinking that opposes swelling and polymer/water interaction and Donnan pressure that promotes swelling.

Conclusion:

BSAP sponge based on crosslinked CMC matrix is highly advantageous in developing saliva absorption pad. Hydrophobic surface modification is recommended to reduce the moisture content to improve the storage stability of BSAP sponges.

Injectable multifunctional hydrogel based on carboxymethylcellulose/polyacrylamide/polydopamine containing vitamin C and curcumin promoted full-thickness burn regeneration

Burn injuries are a major global problem, with a high risk of infection and mortality. This study aimed to develop an injectable hydrogel for wound dressings, composed of sodium carboxymethylcellulose/polyacrylamide/polydopamine containing vitamin C (CMC/PAAm/PDA ^VitC) for its antioxidant and antibacterial properties. Simultaneously, silk fibroin/alginate nanoparticles (SF/SANPs) loaded with curcumin (SF/SANPs ^CUR) were incorporated into the hydrogel to enhance wound regeneration and reduce bacterial infection. The hydrogels were fully characterized and tested in vitro and in preclinical rat models for biocompatibility, drug release, and wound healing efficacy. Results showed stable rheological properties, appropriate swelling and degradation ratios, gelation time, porosity, and free radical scavenging capacity. Biocompatibility was confirmed through MTT, lactate dehydrogenase, and apoptosis evaluations. Hydrogels containing curcumin demonstrated antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). In the preclinical study, hydrogels containing both drugs showed superior support for full-thickness burn regeneration, with improved wound closure, re-epithelialization, and collagen expression. The hydrogels also showed neovascularization and anti-inflammatory effects, as confirmed by CD31 and TNF-α markers. In conclusion, these dual drug-delivery hydrogels showed significant potential as wound dressings for full-thickness wounds.

Multi-strand Fibers with Hierarchical Helical Structures Driven by Water or Moisture for Soft Actuators

Smart actuators that combine excellent mechanical properties and responsive actuating performance like biological muscles have attracted considerable attention. In this study, a water/humidity responsive actuator, consisting of multi-strand carboxyl methyl cellulose (CMC) fibers with helical structures, was prepared using wet-spinning and twisting methods. The results showed that owing to the multi-strand structure, the actuator consisted of one-, two-, three-, and four-strand helical fibers, thus achieving a combination of high strength (∼27 MPa), high toughness (>10.34 MJ/m³), and large load limit (>0.30 N), which enable the actuator to theoretically withstand a weight that is at least 20,000 times its weight. Meanwhile, owing to the excellent moisture-responsive ability of CMC, the actuator, with a 5 g load, could achieve untwisting motion. Additionally, its maximum speed was approximately 2158 ± 233 rpm/m under water stimulation, whereas the recovery speed could reach 804 ± 44 rpm/m. Moreover, this untwisting-recovery reversible process was cyclic, whereas the shape and the actuating speed of the actuator remained stable after more than 150 cycles. The actuator improved the load limit that the fiber could withstand when driving under stimulation, thereby enabling the actuator to lift or move heavy objects like human muscles when executing spontaneously under external stimuli. This result shows considerable potential applications in artificial muscles and biomimetic robots.

Double-Network Hydrogel Films Based on Cellulose Derivatives and κ-Carrageenan with Enhanced Mechanical Strength and Superabsorbent Properties

Covalently crosslinked sodium carboxymethyl cellulose (CMC)-hydroxyethyl cellulose (HEC) hydrogel films were prepared using citric acid (CA) as the crosslinking agent. Thereafter, the physically crosslinked κ-carrageenan (κ-CG) polymer was introduced into the CMC-HEC hydrogel structure, yielding κ-CG/CMC-HEC double network (DN) hydrogels. The κ-CG physical network provided sacrificial bonding, which effectively dissipated the stretching energy, resulting in an increase in the tensile modulus, tensile strength, and fracture energy of the DN hydrogels by 459%, 305%, and 398%, respectively, compared with those of the CMC-HEC single network (SN) hydrogel. The dried hydrogels exhibited excellent water absorbency with a maximum water-absorption capacity of 66 g/g in distilled water. Compared with the dried covalent SN gel, the dried DN hydrogels exhibited enhanced absorbency under load, attributed to their improved mechanical properties. The water-absorption capacities and kinetics were dependent on the size of the dried gel and the pH of the water.

Gallic Acid-Loaded Sodium Alginate-Based (Polyvinyl Alcohol-Co-Acrylic Acid) Hydrogel Membranes for Cutaneous Wound Healing: Synthesis and Characterization

Traditional wound dressings often cannot treat wounds caused by bacterial infections or other wound types that are insensitive to these wound treatments. Therefore, a biodegradable, bioactive hydrogel wound dressing could be an effective alternative option. The purpose of this study was to develop a hydrogel membrane comprised of sodium alginate, polyvinyl alcohol, acrylic acid, and gallic acid for treating skin wounds. The newly developed membranes were analyzed using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), sol-gel fraction, porosity, mechanical strength, swelling, drug release and data modelling, polymeric network parameters, biodegradation, and antioxidation (DPPH and ABTS) and antimicrobial activity against Gram-positive and negative bacteria. The results revealed that hydrogel membranes were crosslinked successfully and had excellent thermal stability, high drug loading, greater mechanical strength, and exhibited excellent biodegradation. Additionally, the swelling ability and the porosity of the surface facilitated a controlled release of the encapsulated drug (gallic acid), with 70.34% release observed at pH 1.2, 70.10% at pH 5.5 (normal skin pH), and 86.24% at pH 7.4 (wounds pH) in 48 h. The gallic acid-loaded hydrogel membranes showed a greater area of inhibition against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli bacteria as well as demonstrated excellent antioxidant properties. Based on Franz cell analyses, the permeation flux of the drug from optimized formulations through mice skin was 92 (pH 5.5) and 110 (pH 7.4) μg/cm²·h^-1. Moreover, hydrogel membranes retained significant amounts of drug in the skin for 24 h, such as 2371 (pH 5.5) and 3300 µg/cm² (pH 7.4). Acute dermal irritation tests in rats showed that hydrogel membranes were nonirritating. Hydrogel membranes containing gallic acid could be an effective option for improving wound healing and could result in faster wound healing.

Self-Propelled Structural Color Cylindrical Micromotors for Heavy Metal Ions Adsorption and Screening

Water contamination resulting from heavy metal ions (HMIs) poses a severe threat to public health and the ecosystem. Attempts are tending to develop functional materials to realize efficient and intelligent adsorption of HMIs. Herein, self-propelled structural color cylindrical micromotors (SCCMs) with reversible HMIs adsorption capacity and self-reporting property are presented. The SCCMs are fabricated by using platinum nanoparticles (Pt NPs) tagged responsive hydrogel of carboxymethyl chitosan (CMC) and polyacrylamide (PAM) to asymmetrically replicate tubular colloidal crystal templates (TCCTs). Owing to the self-propelled motion of the SCCMs, the enhancive ion-motor interactions bring significantly improved decontamination efficiency. Moreover, it is demonstrated that the SCCMs can realize quick and naked-eye-visible self-reporting during the adsorption/desorption process based on their responsive structure color variation and superior adsorption capacity. Thus, it is anticipated that such intelligent SCCMs can significantly facilitate the evolution of sensing assays and diverse environmental fields.

Covalent Crosslinking of Colloidal Cellulose Nanocrystals for Multifunctional Nanostructured Hydrogels with Tunable Physicochemical Properties

Cellulose nanocrystals (CNCs) have shown promise for the development of multifunctional materials for many research communities, ranging from bioresource engineering and biomedical engineering to materials science and engineering. However, accessible hydroxyl (OH) groups on the surface of colloidal CNCs at the (11̅0)β/(100)α and (110)β/(010)α facets and the intermolecular hydrogen bonding (H-bonds) between these OH groups account for the instability of self-assembled CNC structures in moist environments, limiting their practical uses to dry media. In this work, accessible OH groups of CNCs were crosslinked using two crosslinkers, that is, glutaraldehyde (GA) and epichlorohydrin (EC), to form nanoparticle-based hydrogels with tunable physicochemical properties. The intensity of the intermolecular H-bonds was controlled by the type and concentration of crosslinkers as well as the CNC concentration. Rheological analyses through the loss tangent were used to determine the degree of crosslinking with maximal values beyond 90%. Fourier-transform infrared spectroscopy demonstrated that H-bond intensity was inversely proportional to the degree of crosslinking for both GA and EC, indicating a dissimilar crosslinking mechanism for GA and EC in acidic and alkaline pH conditions, respectively. Atomic force microscopy and wettability analyses showed a significant increase in the surface roughness from 3.2 ± 0.41 nm (pure CNC) to 31.5 ± 1.08 nm (CNCs crosslinked by GA) and 23.8 ± 0.14 nm (CNCs crosslinked by EC) and water contact angle from 13° (pure CNC) to 108° (CNCs crosslinked by GA) and 104° (CNCs crosslinked by EC). Moreover, optimum water absorption values were found at 157.67 ± 2.01 g and 173.59 ± 1.26 g of water for 1 g of freeze-dried hydrogels for 10% GA and 1% EC, respectively. The results aligned with reaction conditions that led to maximal degrees of crosslinking and indicated the transformation of surface chemistry from a hydrophilic to a hydrophobic network as well as tunable topology and aqueous stability of self-assembled structures made from crosslinked CNCs. This technology demonstrated the potential of crosslinked CNCs with tunable physicochemical properties for use as advanced building blocks to produce 2D and 3D structures for their related functions.

Triblock Superabsorbent Polymer Nanocomposites with Enhanced Water Retention Capacities and Rheological Characteristics

Superabsorbent polymers (SAPs) are useful polymers in a wide range of application fields ranging from the hygiene industry to construction and agriculture. As versatility and high water absorption capacity are their important merits, SAPs usually suffer from low water retention capacity (fast release) and weak mechanical properties. To address these drawbacks, a set of new superabsorbent polymer-Halloysite nanotube (HNT) nanocomposites was synthesized via free radical polymerization of acrylamide, 2-acrylamido-2-methylpropane-1-sulfonic acid, and acrylic acid in the presence of vinyltrimethoxysilane (VTMS) as the crosslinker. FTIR and TGA characterizations confirm the polymerization of SAP and successful incorporation of HNTs into the SAP polymer matrix. The effect of the HNT nanofiller amount in the nanocomposite polymer matrix was investigated with swelling-release performance tests, crosslink density calculations, and rheology measurements. It was found that equilibrium swelling ratios are correlated and therefore can be tuned via the crosslink densities of nanocomposites, while water retention capacities are governed by storage moduli. A maximum swelling of 537 g/g was observed when 5 wt % HNT was incorporated, in which the crosslink density is the lowest. Among the SAP nanocomposites prepared, the highest storage modulus was observed when 1 wt % of nanofiller was incorporated, which coincides with the nanocomposite with the longest water retention. The water release duration of SAPs was prolonged up to 27 days with 1% HNT addition in parallel with the achieved maximum storage modulus. Finally, three different incorporation mechanisms of the HNT nanofiller into the SAP nanocomposite structure were proposed and confirmed with rheology measurements. This study provides a rapid synthesis method for SAP nanocomposites with enhanced water retention capacities and explains the relationship between swelling and crosslink density and water retention and mechanical properties of SAP nanocomposites.

Rational Design of Photothermal and Anti-Bacterial Foam With Macroporous Structure for Efficient Desalination of Water

With the environmental deterioration and the rise in demand for sustainability, the lack of freshwater resources has emerged as a global concern. To address this issue, the desalination of water using solar evaporation is centered on as a promising approach. In this study, we designed a light and photothermal liquefied-chitin-based polyurethane foam to achieve efficient water evaporation benefiting from their powerful solar spectral absorption, low thermal conductivity, quick transportation of water, hierarchically porous structures, and anti-biofouling natures. Moreover, because of the introduction of nano-silver, the newly developed foam exhibits considerable antibacterial ability and improved photothermal performance. Notably, the low thermal conductivity of the foam can reduce the loss of absorbed solar heat, whereas its large porous structure provides a smooth water transport channel. More importantly, with the assistance of heat, polyacrylamide hydrogels adhering along with the pores rapidly absorb and desorb water molecules, promoting the evaporation of water and improving solar energy conversion efficiency. Ultimately, under irradiation by one sunlight, the proposed material demonstrated a water evaporation rate and solar photothermal conversion efficiency of 2.44 kg m-2 h-1 and 153.2%, respectively.

Freeze-Tolerant Hydrogel Electrolyte with High Strength for Stable Operation of Flexible Zinc-Ion Hybrid Supercapacitors

Constructing ionic conductive hydrogels with diversified properties is crucial for portable zinc-ion hybrid supercapacitors (ZHSCs). Herein, a freeze-tolerant hydrogel electrolyte (AF PVA-CMC/Zn(CF₃ SO₃ )₂ ) is developed by forming a semi-interpenetrating anti-freezing polyvinyl alcohol-carboxymethyl cellulose (AF PVA-CMC) network filled with the ethylene glycol (EG)-containing Zn(CF₃ SO₃ )₂ aqueous solution. The semi-interpenetrating AF PVA-CMC/Zn(CF₃ SO₃ )₂ possesses enhanced mechanical properties, realizes the uniform zinc deposition, and impedes the dendrite growth. Notably, the interaction between PVA and EG suppresses the ice crystal formation and prevents freezing at -20 °C. Due to these advantages, the designed hydrogel owns high ionic conductivity of 1.73/0.75 S m^-1 at 20/-20 °C with excellent tensile/compression strength at 20 °C. Impressively, the flexible AF quasi-solid-state ZHSC employing the hydrogel electrolyte achieves a superior energy density at 20/-20 °C (87.9/60.7 Wh kg^-1 ). It maintains nearly 84.8% of the initial capacity after 10 000 cycles and a low self-discharge rate (1.77 mV h^-1 ) at 20 °C, together with great tolerance to corrosion. Moreover, this device demonstrates a stable electrochemical performance at -20 °C under deformation. The obtained results provide valuable insights for constructing durable hydrogel electrolytes in cold environments.

Sustained delivery of gemcitabine via in situ injectable mussel-inspired hydrogel for local therapy of pancreatic cancer

The issue on pervasively enhanced drug resistance of pancreatic cancer is fundamental to better understanding of gemcitabine-based chemotherapy. Currently available treatment plans containing injectable therapeutics are mainly engineered to improve...

pH-Responsive Succinoglycan-Carboxymethyl Cellulose Hydrogels with Highly Improved Mechanical Strength for Controlled Drug Delivery Systems

Carboxymethyl cellulose (CMC)-based hydrogels are generally superabsorbent and biocompatible, but their low mechanical strength limits their application. To overcome these drawbacks, we used bacterial succinoglycan (SG), a biocompatible natural polysaccharide, as a double crosslinking strategy to produce novel interpenetrating polymer network (IPN) hydrogels in a non-bead form. These new SG/CMC-based IPN hydrogels significantly increased the mechanical strength while maintaining the characteristic superabsorbent property of CMC-based hydrogels. The SG/CMC gels exhibited an 8.5-fold improvement in compressive stress and up to a 6.5-fold higher storage modulus (G') at the same strain compared to the CMC alone gels. Furthermore, SG/CMC gels not only showed pH-controlled drug release for 5-fluorouracil but also did not show any cytotoxicity to HEK-293 cells. This suggests that SG/CMC hydrogels could be used as future biomedical biomaterials for drug delivery.

Superabsorbent Hydrogels Based to Polyacrylamide/Cashew Tree Gum for the Controlled Release of Water and Plant Nutrients

Agricultural production is influenced by the water content in the soil and availability of fertilizers. Thus, superabsorbent hydrogels, based on polyacrylamide, natural cashew tree gum (CG) and potassium hydrogen phosphate (PHP), as fertilizer and water releaser were developed. The structure, morphology, thermal stability and chemical composition of samples of polyacrylamide and cashew tree gum hydrogels with the presence of fertilizer (HCGP) and without fertilizer (HCG) were investigated, using X-ray diffractometry (XRD), Fourier Transformed Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA/DTG) and Energy Dispersive Spectroscopy (EDS). Swelling/reswelling tests, textural analysis, effect of pH, release of nutrients and kinetics were determined; the ecotoxicity of the hydrogels was investigated by the Artemia salina test. The results showed that PHP incorporation in the hydrogel favored the crosslinking of chains. This increased the thermal stability in HCGP but decreased the hardness and adhesion properties. The HCGP demonstrated good swelling capacity (~15,000 times) and an excellent potential for reuse after fifty-five consecutive cycles. The swelling was favored in an alkaline pH due to the ionization of hydrophilic groups. The sustained release of phosphorus in HCGP was described by the Korsmeyer-Peppas model, and Fickian diffusion is the main fertilizer release mechanism. Finally, the hydrogels do not demonstrate toxicity, and HCGP has potential for application in agriculture.

Multiresponsive Cellulose Nanocrystal Cross-Linked Copolymer Hydrogels for the Controlled Release of Dyes and Drugs

Multiresponsive hydrogels have attracted tremendous interest due to their promising applications in tissue engineering, wearable devices, and flexible electronics. In this work, we report a multiresponsive upper critical solution temperature (UCST) composite hydrogel based on poly (acrylic acid-co-acrylamide), PAAc-co-PAAm, sequentially cross-linked by acid-hydrolysis cellulose nanocrystals (CNCs). Scanning electron microscopy (SEM) observations demonstrated that the hydrogels are formed by densely cross-linked porous structures. The PAAc/PAAm/CNC hybrid hydrogels exhibit swelling and shrinking properties that can be induced by multiple stimuli, including temperature, pH, and salt concentration. The driving force of the volume transition is the formation and dissociation of hydrogen bonds in the hydrogels. A certain content of CNCs can greatly enhance the shrinkage capability and mechanical strength of the hybrid hydrogels, but an excess addition may impair the contractility of the hydrogel. Furthermore, the hydrogels can be used as a matrix to adsorb dyes, such as methylene blue (MB), for water purification. MB may be partly discharged from hydrogels by saline solutions, especially by those with high ionic strength. Notably, through temperature-controlled hydrogel swelling and shrinking, doxorubicin hydrochloride (DOX-HCl) can be controllably adsorbed and released from the prepared hydrogels.

Fabrication and Characterization of Polysaccharide Metallohydrogel Obtained from Succinoglycan and Trivalent Chromium

In the present study, a polysaccharide metallohydrogel was successfully fabricated using succinoglycan and trivalent chromium and was verified via Fourier transform infrared spectroscopy, differential scanning calorimetry analysis, thermogravimetric analysis (TGA), field emission scanning electron microscopy, and rheological measurements. Thermal behavior analysis via TGA indicated that the final mass loss of pure succinoglycan was 87.8% although it was reduced to 65.8% by forming a hydrogel with trivalent chromium cations. Moreover, succinoglycan-based metallohydrogels exhibited improved mechanical properties based on the added concentration of Cr³⁺ and displayed a 10 times higher compressive stress and enhanced storage modulus (G′) of 230% at the same strain. In addition, the pore size of the obtained SCx could be adjusted by changing the concentration of Cr³⁺. Gelation can also be adjusted based on the initial pH of the metallohydrogel formulation. This was attributed to crosslinking between chromium trivalent ions and hydroxyl/carboxyl groups of succinoglycan, each of which exhibits a specific pH-dependent behavior in aqueous solutions. It could be used as a soft sensor to detect Cr³⁺ in certain biological systems, or as a soft matrix for bioseparation that allows control of pore size and mechanical strength by tuning the Cr³⁺ concentration.