Search Results (143)

Prolonged drought and soil degradation severely affect soil fertility and limit crop productivity. Superabsorbent hydrogels offer an effective solution for improving water retention in soil and supporting plant growth. In this work, we examined the performance of superabsorbent hydrogels based on sodium alginate, acrylic acid (AA), and poly (ethylene oxide) (PEO) cross-linked with 12.5 kGy using e-beam irradiation. The hydrogels were assessed in various aqueous environments by examining network characteristics, swelling capacity, and swelling kinetics to evaluate the impact of water’s electrical conductivity (which ranges from 0.05 to 321 μS/cm). Morphological and chemical structure changes were evaluated using SEM and FTIR techniques. The results demonstrated that water conductivity significantly affected the physicochemical properties of the hydrogels. Swelling behavior showed notable sensitivity to electrical conductivity variations, with swelling degrees reaching 28,400% at 5 μS/cm and 14,000% at 321 μS/cm, following first-order and second-order kinetics. FTIR analysis confirmed that structural modifications correlated with water conductivity, particularly affecting the O–H, C–H, and COOH groups sensitive to the ionic environment. SEM characterization revealed a porous morphology with an interconnected microporous network that facilitates efficient water diffusion. These hydrogels show exceptional swelling capacity and are promising candidates for sustainable agriculture applications. Full article

Poly(acrylic acid) (PAA) and hydroxypropylcellulose (HPC) hydrogels were synthesized in the absence of a crosslinker. Chemical crosslinking between PAA and HPC was demonstrated through free radical polymerization by a precipitation reaction in acetone as the solvent. These hydrogels exhibited smaller swelling ratios (1 to 5 g H₂O/g) than homo PAA hydrogels synthesized in water as the solvent. They were swollen in a 0.1 M NaOH solution and subsequently used to remove Ni²⁺ ions from aqueous solutions with concentrations ranging from 1000 to 4000 ppm. The absorption capacity of these hydrogels ranged from 91 to 340 mg of Ni²⁺/g in a rapid 1 h process, and from 122 to 435 mg of Ni²⁺/g in a 24 h process, demonstrating an improvement in Ni²⁺ absorption compared to previously reported hydrogels. The colored 1000 and 2000 ppm Ni²⁺ solutions became clear after treatment, while the PAA-HPC hydrogels turned green due to the uptake of Ni²⁺ ions, which were partially chelated by carboxylate groups as nickel polyacrylate and partially precipitated as Ni(OH)₂, resulting in an average absorption efficiency of 80%. The hydrogel was able to release the absorbed Ni²⁺ upon immersion in an HCl solution, with an average release percentage of 76.4%, indicating its potential for reuse. These findings support the use of PAA-HPC hydrogels for cleaning Ni²⁺-polluted water. The cost of producing 1 g of these hydrogels in laboratory conditions is approximately 0.2 USD. Full article

Hydrogels are three-dimensional polymeric systems, being able to accommodate different categories of bioactive agents and act as promising drug delivery systems in many different biomedical applications. Due to their extended 3D network, hydrogels exhibit many advantages, such as extensive loading capacity and controlled drug release profiles, combined with characteristics such as biocompatibility and biodegradability, due to their constructive polymeric biomaterials. Moreover, hydrogels are capable of being administered via different routes of administration, including systemic and topical ones, due to their tunable characteristics. Stimuli-responsive hydrogels are characterized as smart biomaterials, while environmental stimuli, such as pH, can be employed to trigger on-demand drug release from the hydrogels via the provocation of conformational changes. In the present study, an emphasis on the pH-responsive hydrogels is taking place through various literature cases in drug delivery, wound healing, and some alternative applications, including implantation, oral administration, etc., wherein many different polymeric derivatives have been utilized. Moreover, the role of each used polymer or polymeric combination with other functional biomaterials, their mode of structure formation (for example, crosslinking), and their content release mechanism are highlighted, as well as the therapeutic effect of the hydrogels on different pathological conditions, as promising candidates for pharmaceutical applications. Full article

In addition to protection against microorganisms and hemostasis, wound dressings are now expected to actively promote healing. A water-absorbing complex of poly(acrylic acid) (PAA) and polyvinylpyrrolidone (PVP) was developed by mixing the polymers under specific conditions. This complex swells in water and adheres strongly to biological tissues. Upon application to a wound, it absorbs blood, swells, and adheres firmly, providing coverage. During this process, blood cells that infiltrate the gel secrete growth factors and other bioactive molecules, which are retained and gradually released toward the wound, promoting healing. In the present study, the mechanical properties of the PAA/PVP complexes were analyzed, and their healing-promoting effects were examined. In a diabetic mouse skin wound model, untreated wounds remained over 95% of their original size after 4 days. In contrast, wounds treated with the PAA/PVP complex shrank to 70–75% of their original size by day 4, and further reduced to 17–23% by day 11. Histological analysis on day 11 showed complete or nearly complete re-epithelialization in PAA/PVP-treated wounds, while untreated wounds exhibited incomplete tissue regeneration. These results suggest that the PAA/PVP complex not only provides physical protection, but also facilitates tissue repair, demonstrating its potential as a next-generation wound dressing. Full article

Drug-loaded hydrogels are promising for modern medicine due to their physical modifiability. However, most hydrogels suffer from poor swelling, which limits their drug encapsulation and release capabilities. In this study, Poly (N-(2-hydroxyethyl) acrylamide-co-acrylic acid) (Poly (HEAA-co-AA)) hydrogels with high swelling properties are synthesized via free radical polymerization of neutralized acrylic monomers. The effects of the material ratio and acrylic acid neutralization degree on the swelling properties of hydrogels in water are investigated, and the swelling properties of hydrogels prepared with different monomer ratios in different pH buffer solutions are systematically studied. The results show that the swelling degree is sensitive to the monomer ratio and pH. The maximum equilibrium swelling degree of the hydrogels occurs at an HEAA to AA molar ratio of 2:2, with values of 11.36 g g⁻¹ at pH 1.68 and 112.79 g g⁻¹ at pH 9.18. Finally, the mechanical properties of PHA hydrogels under different HEAA/AA molar ratios are investigated, showing that the mechanical properties of PHA improved compared to those of PAA. The mechanical properties of the hydrogels are best and show good stability in rheological tests when the molar ratio of HEAA to AA is 2:2. This work has major potential applications in drug carrier systems. Full article

Global challenges in agriculture, in terms of water and nutrient loss control, require new approaches to maintaining or even increasing crop production. Promising materials, such as superabsorbent hydrogels of hybrid types obtained from natural polymers grafted with synthetic polymers, represent a viable solution to solve these problems and maintain a clean environment. In view of this, two types of hydrogels based on sodium alginate, acrylic acid and polyethylene oxide obtained using 5.5 MeV electron-beam irradiation were subjected to degradation through burial in the soil. Swollen hydrogels in two types of water (distilled and tap) and two types of nutrient solutions (synthetic nutrient solution and 100% natural organic nutrient solution), with different pHs of 5.40, 6.05, 7.45 and 7.66, were buried in soil for 30 and 60 days and then extracted and analyzed in terms of their mass loss, swelling behavior and cross-linking structure. The highest mass losses after both 30 and 60 days were recorded for the hydrogels buried in soils whose humidity was maintained by watering them with the basic solutions (tap water and the organic nutrient solution). Structural modifications associated with the degradation process were highlighted by decreases in the cross-link densities and increases in the mesh sizes and swelling. These results were confirmed using FTIR and SEM techniques. Full article

The effect of the presence of guar gum (0–0.75 wt%) in a thermo-responsive triple-network (TN) PVA/TA/PVA-MA-g-PNIPAAm hydrogel (PVA: polyvinyl alcohol; MA: methacrylate, PNIPAAm: poly-N-isopropyl acryl amide; TA: tannic acid) with respect to the structural, mechanical, and viscoelastic properties was mapped. A comprehensive analysis, using large-amplitude oscillatory shear (LAOS), SEM imaging, XRD, and mechanical analysis revealed that guar enhances hydrogel crystallinity (up to 30% at 0.75 wt%), which goes along with a strain hardening. The hydrogel achieved superior mechanical performance at a gum concentration of 0.5 wt% with a 40% increase in shear-thickening, an enhanced strain tolerance in nonlinear regimes, and a good mechanical robustness (maximum elongation to break of 500% and stress of 620 kPa). The hydrogel with 0.5 wt% guar exhibited also a good thermal response (equilibrium swelling ratio changed from 8.4 at 5 °C to 2.5 at 50 °C) and an excellent thermal cycling dimensional stability. Higher guar concentrations reduce structural resilience, leading to brittle hydrogels with lower extensibility and viscoelastic stability. Full article

Superabsorbent hydrogels used in products like diapers, hygiene items, and medical patches depend on their swelling ratio. However, improving the swelling performance across hydrogel assemblies remains challenging. This study identifies a decline in the water absorption capacity in hydrogel assemblies with high swelling ratios, as confirmed through MRI analysis, and introduces a solution using a branched crosslinker to address this issue. The branched crosslinker was synthesized by grafting acrylate groups onto poly(aspartic acid)s. This branched poly(aspartic acid) crosslinker was incorporated into hydrogels with the same number of acrylate groups as PEGDA575, a conventional linear crosslinker, and their absorption performance and behavior were compared. The results showed that hydrogels with the branched crosslinker exhibited a swelling ratio twice as high as the PEGDA575 group, with a slower initial absorption rate, demonstrating a more gradual swelling behavior. Additionally, while the initial absorption rate was approximately 30% slower than the PEGDA575 group, the absorption rate showed a gradual decrease of less than 15% within the first 30 min, indicating sustained absorption behavior. Overall, the new strategy presented in this study of introducing a branched crosslinker into hydrogels is expected to be a useful application for existing industries by enhancing swelling ratios and promoting continuous absorption. Full article

Hydrogels are extensively utilized in biomedical fields because of their remarkable properties, including biocompatibility, high water content, flexibility, and elasticity. However, despite substantial progress in hydrogel research, creating a hydrogel adhesive that integrates high stretchability, fatigue resistance, and reversible adhesion continues to pose significant challenges. In this study, we aimed to address these challenges by preparing hydrogels using a combination of acrylic acid, acrylamide, carboxymethylcellulose methacrylate, thiol-functionalized polyhedral oligomeric silsesquioxane, and poly(ethylene glycol) dimethacrylate (PEGDM). By systematically varying the molecular weight of PEG, we were able to precisely adjust the mechanical and adhesive properties of the hydrogels. Our research revealed that a PEG molecular weight of 2000 (resulting in P1 hydrogel) provided a notable adhesive strength of 717.2 kPa on glass surfaces. This performance is particularly impressive given the challenges associated with achieving high adhesive strength while maintaining other desirable hydrogel properties. Beyond its strong adhesive capabilities, the P1 hydrogel also demonstrated exceptional stretchability, support, and fatigue resistance. These characteristics are crucial for applications where the adhesive needs to endure repeated stress and deformation without losing effectiveness. The successful development of P1 hydrogel underscores its potential as a multifunctional adhesive material with a broad range of applications. The ability to tailor the properties of hydrogels through molecular weight adjustments offers a promising approach to creating advanced adhesive solutions that meet the demanding requirements of modern biomedical and industrial applications. Full article

In this work, cellulose nanocrystals (CNCs) were obtained from the wood of Acacia farnesiana L. Willd (Huizache) via acid hydrolysis; then, they were used to reinforce polyacrylic acid–co-acrylamide (AAc/AAm) hydrogels synthesized in a solution process via in situ free radical photopolymerization. The nanomaterials were characterized using atomic force microscopy, dynamic light scattering (DLS), and the residual charge on the CNCs; the nanohydrogels were characterized using infrared spectroscopy, scanning electron microscopy, swelling kinetics, and Young’s modulus. Soluble-grade cellulose presented 94.6% α-cellulose, 0.5% β-cellulose, and 2.7% γ-cellulose, as well as a viscosity of 8.25 cp and a degree of polymerization (DP) of 706. The CNCs averaged 180 nm in length and 20 nm in width. In the nanohydrogels, it was observed that the swelling kinetic behavior followed the Schott kinetic model, at times lower than 500 h; after that, it became linear. The results show that the hydrogel swelling capacity depended on the crosslinking agent and CNC concentration, as well as the CNC chemical and morphological properties, rather than the CNC source. The hydrogels with CNCs exhibited a decreased swelling degree compared to the hydrogels without CNCs. Young’s modulus increased with CNC presence and depended on the concentration and characteristics of the CNC as a crosslinking agent. Full article

Polymeric hydrogel materials have excellent electrical conductivity and mechanical properties and will be potentially used in wearable electronic devices, soft robotics, and medical treatment. In this paper, a PAA-Fe³⁺-IL ionohydrogel (poly(acrylic acid)-Fe³⁺-ionic liquid ionohydrogel) with excellent mechanical and conductive properties is prepared by simple free radical polymerization. The presence of metal-ligand crosslinking within the ionohydrogel improves the mechanical properties of the hydrogel. When the IL content is 10 wt%, it has the maximum tensile strength and strain. When the ferric ion concentration is 0.3 mol%, the maximum tensile strength is 495.09 kPa. When the ferric ion concentration is 0.1 mol%, the maximum strain is 1151.35%. The tensile behavior of the ionohydrogels is quantitatively analyzed by the viscoelastic model. In addition, free metal ions and anions and cations in IL endowed the hydrogel with a conductivity of 1.48 S/m and a strain sensitivity of 8.04. Thus, the PAA-Fe³⁺-IL ionohydrogel can be successfully used as a humidity sensor due to the hydrophilic ionic liquid, which can increase the conductivity of the hydrogel by absorbing water. The physical crosslinking density inside the hydrogel is much higher than the chemical crosslinking density, which causes hydrogel dissolution in deionized water by swelling and is conducive to the recycling of the hydrogel. This is a promising material for use in intelligent wearable electronics and as a humidity sensor. Full article

Paper-based artworks are prone to natural aging processes driven by chemical and biological processes. Numerous treatments have been developed to mitigate deterioration and prevent irreversible damage. In this study, we investigated the use of poly(acrylic acid)/TiO₂ composite hydrogels, combining their cleaning and protective functions in a minimally invasive treatment. Hydrogels allow for controlled water flow and photocatalytic TiO₂ nanoparticles enhance the hydrogel’s efficacy by enabling the removal of oxidation products and inactivating biological contaminants. Furthermore, this innovative material can act as a protective coating against UV-induced aging, preserving both color and stability of the paper. Raman spectroscopy and confocal laser scanning microscopy imaging techniques were employed to evaluate the treatments, allowing for us to differentiate between hydrolytic and oxidative aging processes. Our findings demonstrate that papers coated with poly(acrylic acid)/TiO₂ composite hydrogels exhibit significant reductions in oxidative markers, an enhanced color stability, and an overall improved resistance to degradation compared to uncoated samples. Full article

In this article, we report on the alginate heterografted by Poly(N-isopropyl acrylamide-co-N-tert-butyl acrylamide) and Poly(N-isopropyl acrylamide) (ALG-g-P(NIPAM86-co-NtBAM14)-g-PNIPAM) copolymer thermoresponsive hydrogel, reinforced by substituting part of the 5 wt% aqueous formulation by small amounts of Poly(acrylic acid)-g-P(boc-L-Lysine) (PAA-g-P(b-LL)) graft copolymer (up to 1 wt%). The resulting complex hydrogels were explored by oscillatory and steady-state shear rheology. The thermoresponsive profile of the formulations were affected remarkably by increasing the PAA-g-P(b-LL) component of the polymer blend. Especially, the sol-gel behavior altered to soft gel–strong gel behavior due to the formation of a semi-interpenetrating network based on the hydrophobic self-organization of the PAA-g-P(b-LL). In addition, the critical characteristics, namely T_{c,thermothickening} (temperature above which the viscosity increases steeply) and ΔT (transition temperature window), shifted and broadened to lower temperatures, respectively, due to the influence of the hydrophobic side chains P(b-LL) on the LCST of the PNIPAM-based grafted chains of the alginate. The effect of ionic strength was also examined, showing that this is another important factor affecting the thermoresponsiveness of the hydrogel. Again, the thermoresponsive profile of the hydrogel was changed significantly by the presence of salt. All the formulations showed self-healing capability and tolerance injectability, suitable for potential bioapplications in living bodies. Full article

In this study, a novel polyacrylate-co-vinyl imidazole hydrogel-supported palladium (Pd) catalyst (P(AA-co-VI)@Pd) was prepared through heat-initiated polymerization, starting with the formation of a complex between vinyl imidazole and palladium chloride, followed by the addition of 75% neutralized acrylic acid (AA), crosslinking agent, and initiator. The structure and morphology of the catalyst were characterized using ICP-OES, SEM, EDX, Mapping, FT-IR, TGA, XRD, XPS and TEM techniques. It was confirmed that the catalyst exhibited excellent compatibility with water solvent and uniform distribution of Pd. The P(AA-co-VI)@Pd hydrogel catalyst demonstrated remarkable catalytic activity and ease of separation. Notably, in a Tsuji–Trost reaction, employing water as the solvent, it achieved a conversion rate as high as 94% at very low catalyst dosages, indicating its superior catalytic performance. Moreover, after six consecutive cycles, the catalyst maintained good activity and structural stability, highlighting its exceptional reusability and environmental friendliness. Furthermore, the outstanding efficiency of the catalyst was also observed in a Suzuki coupling reaction where both conversion rate and yield reached 100% and 99%, respectively, within just one hour reaction time, thus further validating its universality and efficacy across various chemical reactions. Full article

This study describes the physicochemical characterisation of interpenetrating hydrogel networks (IHNs) composed of either poly(hydroxyethylmethacrylate, p(HEMA)) or poly(methacrylic acid, p(MAA)), and Pluronic block copolymers (grades F127, P123 and L121). IHNs were prepared by mixing the acrylate monomer with Pluronic block copolymers followed by free radical polymerisation. p(HEMA)–Pluronic blends were immiscible, evident from a lack of interaction between the two components (Raman spectroscopy) and the presence of the glass transitions (differential scanning calorimetry, DSC) of the two components. Conversely, IHNs of p(MAA) and each Pluronic were miscible, displaying a single glass transition and secondary bonding between the carbonyl group of p(MAA) and the ether groups in the Pluronic block copolymers (Raman and ATR-FTIR spectroscopy). The effect of storage of the IHNs in Tris buffer on the physical state of each Pluronic and on the loss of Pluronic from the IHNs were studied using DSC and gravimetric analysis, respectively. Pluronic loss from the IHNs was dependent on the grade of Pluronic, time of immersion in Tris buffer, and the nature of the IHN (p(HEMA) or p(MAA)). At equilibrium, the loss was greater from p(HEMA) than from p(MAA) IHNs, whereas increasing ratio of poly(propylene oxide) to poly(ethylene oxide) decreased Pluronic loss. The retention of each Pluronic grade was shown to be primarily due to its micellization; however, hydrogen bonding between Pluronic and p(MAA) (but not p(HEMA)) IHNs contributed to their retention. Full article