Gels are transversal materials with key applications in multiple scientific and technological sectors, including the preservation of Cultural Heritage that is a fundamental drive for socioeconomic resilience. Recently, the new class of twin-chain (TC) polymer gel networks was developed, using freeze-thaw (FT) cycles on solutions of polyvinyl alcohol (PVA) with two different hydrolysis degree and molar mass. Taking advantage of polymerpolymer phase separation in the pre-gel solutions, a sponge-like, interconnected porosity is templated in the hydrogels during FT, which concurs to boost the cleaning capability of the gels versus soil and aged coatings that jeopardize paintings and other iconic artworks. This review covers the latest developments in this new class of gels, and their use in the conservation of works of art. The TC gels allowed time-effective restoration of masterpieces (paintings by Picasso, Pollock, Lichtenstein), which would have been risky and time-consuming with conventional restoration materials in wet cleaning. The review discusses gelation mechanisms, the partial replacement or decoration of PVA with non-toxic synthetic or bio-based polymers, the counterintuitive role of gels' tortuosity in the cleaning process, and the upload of these gels with nanostructured cleaning fluids (microemulsions, micelles). Overall, the TC PVA hydrogels constitute an advanced tool to preserve Cultural Heritage and transfer it to future generations; moreover, they represent a class of sustainable soft matter materials with potential impact in several fields, spanning from detergency to the cosmetic, pharmaceutical and food industries, tissue engineering, and others.

Fogged surfaces, such as bathroom mirrors, quickly become a nuisance in everyday life, but are particularly problematic in safety-relevant and medical areas. Present approaches are often based on hydrophilic coatings, which can prevent fogging, but are not very durable. Surface-attached polymer networks that can be quickly and easily prepared from thin films of prepolymers by photochemical activation using brief irradiation with ambient light are presented. This novel photoreactive copolymer contains ionic, hydrophilic repeating units and hydrophilic nitro-substituted phenyl diazo ester moieties. The diazo groups in the prepolymer films form carbenes after excitation, which then bind to adjacent chains and to the substrate by C,H insertion cross-linking (CHic). The resulting surfaces exhibit excellent anti-fogging properties as they allow water to condense into a uniform thin film. The substrates remain highly transparent, even after frequent washing. In addition, the polymers can also be easily applied to previously damaged coatings by soiling in order to fully restore the anti-fog properties. Due to the solubility of the prepolymers in water, the easy cross-linking in sunlight, the durability of the coating, and the possibility of damage repair, the polymers are suitable for easy-use scenarios by non-professionals, which offers great potential for such an approach.

Superabsorbent nanocomposite hydrogels based on polyacrylamide (PAAm), cashew tree gum (CG), and laponite (LAP) were synthesized in different concentrations to investigate swelling, thermal, morphological and rheological properties. Vibrational modes confirmed the formation of hydrogels, while X-ray diffraction patterns reveal the semi-crystalline structure of the hydrogels. Thermal analysis showed that higher LAP content and CGLAP interactions improved the thermal stability of the hydrogels. Morphology analysis presented porous structures in CG-based hydrogels, contrasting with irregular plate-like structures in those without CG. The swelling capacity had better results in hydrogels with CG that were subjected to alkaline hydrolysis, mainly in a buffer solution with a pH > 4, due to the ionization of the hydrophilic groups. Hydrogels containing LAP maintained swelling degree stability at pH 10 and 12. In rheological tests, the addition of LAP increased the viscosity of the hydrogels, significantly improving the mechanical resistance of the hydrogels. Rheological parameters, such as the storage modulus (G ') and loss modulus (G ''), indicated that the materials exhibited predominantly solid behavior, particularly in CG-LAP-rich hydrogels. Low mortality of Artemia salina nauplii in toxicity tests confirmed material safety. The results indicate that CG-LAP hydrogels are promising for agricultural applications, offering optimized swelling properties, thermal stability, and mechanical strength.

Biodegradability and eco-friendliness are the most importance topic to consider in the development of new products. Commercial hydrogels for agriculture applications are made from fully synthetic polymers, which is non-biodegradable and harmful to environment. The utilization of polysaccharide in hydrogels production has sparked the rise of biodegradable hydrogels (BHs). However, using it alone results in poor mechanical properties and very fast degradation. Therefore, combining it with other materials as a composite is necessary. This article reviewed the development of BHs in the last 5 years. Classifications, materials resources, preparation methods, biodegradability of BHs, seeds germination and plant growth performance are critically investigated. Fundamental concepts such as definitions and application methods of BHs are described. Finally, important conclusions and outlook have been mentioned at the end of this article.

Hydrogel is a three-dimensional polymer that can absorb large amounts of reagents while maintaining structural integrity. This material has been applied in many fields especially in smart agriculture. To improve the economic viability, the reusability of hydrogels in agricultural engineering over multiple cycles of adsorption and desorption is an urgent requirement. This can be solved if the crosslinker is used properly. Therefore, in this work, a series of porous semi-interpenetrating polymer network (IPN) hydrogels based on linear polyacrylamide, acrylamide, maleic acid, and N,N'-methylenebisacrylamide (MBA) were synthesized. The hydrogels were evaluated for the impact of MBA content on the characteristics and applicability as a urea fertilizer carrier. The chemical composition, morphology, mechanical, and rheological properties, swelling behavior, urea absorption, and desorption of hydrogels with crosslinker content in the range of 0.5%-2.0% were investigated. The porous structure was confirmed by scanning electron microscopy images. Changing the MBA content significantly affected all characteristics of the hydrogels. In particular, increasing the MBA content decreased the equilibrium swelling ratios in all investigated environments. The maximum amount of urea loaded into the hydrogel was also reduced from 435.88 to 188.50 mg/g. This increase also changed the swelling mechanism from non-Fickian to Fickian, whereas the urea release mechanism changed from Fickian to non-Fickian. Finally, the hydrogels demonstrated stability in soil over multiple cycles of water absorption and release. This study provides valuable insights into designing a semi-IPN hydrogel with desired properties that meet the application requirements of modern farming techniques.

Agricultural production is facing challenges such as water scarcity, declining soil quality, and excessive use of chemical fertilisers and pesticides, and there is an urgent need to find sustainable solutions. Hydrogel, as a novel functional polymer material, is considered as a potential agro-material to solve these problems due to its excellent water retention, swelling, slow release, biocompatibility and biodegradability. However, there are still challenges in designing efficient agrohydrogels, such as sustainability of the materials, environmental impacts of cross-linking methods, adaptability of the network structure to the crop growing environment, as well as the cost of the materials and the effectiveness of the practical applications. Therefore, a systematic review of the design, properties and applications of agrohydrogels is of great theoretical and practical significance. This paper reviews the design methods of agricultural hydrogels, including network structure design, material source selection, crosslinking technology and its mechanism research. Then, the key properties of agricultural hydrogels, such as water retention, swelling, slow release, biocompatibility and biodegradability, are discussed in detail. Finally, the applications of hydrogels in the fields of soilless cultivation, soil improvement and smart agriculture are presented. This paper concludes that with the continuous progress of technology, agricultural hydrogels will play an important role in future agricultural production.

The paper reports new hydrogels based on quaternary ammonium salts of chitosan designed as biocidal products. The chitosan derivative was crosslinked with salicylaldehyde via reversible imine bonds and supramolecular selfassemble to give dynamic hydrogels which respond to environmental stimuli. The crosslinking mechanism was demonstrated by 1H NMR and FTIR spectroscopy, and X-ray diffraction and polarized light microscopy. The hydrogel nature, self-healing and thixotropy were proved by rheological investigation and visual observation, and their morphology was assessed by scanning electron microscopy. The relevant properties for application as biocidal products, such as swelling, dissolution, bioadhesiveness, antimicrobial activity and ex-vivo hemocompatibility and in vivo local toxicity and biocompatibility on experimental mice were measured and analyzed in relationship with the imination degree and the influence of each component. It was found that the hydrogels are superabsorbent, have good adhesivity to skin and various surfaces and antimicrobial activity against relevant gram-positive and gram-negative bacteria, while being hemocompatible and biocompatible. Besides, the hydrogels are easily biodegraded in soil. All these properties recommend the studied hydrogels as ecofriendly biocidal agents for living tissues and surfaces, but also open the perspectives of their use as platform for in vivo applications in tissue engineering, wound healing, or drug delivery systems.

Lead (Pb) contamination in agricultural soils poses a significant threat to both ecosystems and human health. While nano-Fe3O4 exhibits promising potential for Pb remediation, its practical application in the soil is hindered by its' biotoxicity, easy aggregation, and the risk of secondary pollution. Thus, this study presents a novel approach wherein Fe3O4 was incorporated into hydrogel via a one-pot synthetic strategy (Fe3O4@LH). This incorporation enhanced the mechanical properties and environmental stability of the hydrogel composites. Based on the mechanical properties, environmental stability, and single-point adsorption results for Pb, we selected Fe3O4@LH-4 for further research. The removal mechanism and the feasibility of employing Fe3O4@LH-4 for Pb removal from paddy soil were investigated through batch adsorption experiments and soil culture studies. Results showed that the adsorption process was primarily governed by swelling adsorption, electrostatic adsorption, ion exchange, precipitation, nanometer effect, and complexation mechanisms. The application of Fe3O4@LH-4 significantly led to the reduction of 16.7 %-25.4 % in soil Pb content, with removal rates escalating alongside increased dosage and application periods of Fe3O4@LH-4. Fitting results of the prediction model indicated that the Pb content in mildly Pb-contaminated soil (186.55 mg/kg) would decrease to be below the risk control standard for soil contamination of agricultural land in China (140 mg/kg) after 112 days of continuous application. Concurrently, cadmium and arsenic contents in the soil decreased by 5.2 %-10.8 % and 7.1 %-16.7 %, respectively. Moreover, the application of Fe3O4@LH-4 positively influenced soil nutrient levels, with total nitrogen and soil organic matter content significant increments of 13.6 %-41.0 % and 4.6 %-16.1 %, respectively. Furthermore, Fe3O4@LH-4 recovery exceeded 88.3 % after a 90-day application period. These findings underscore the potential of Fe3O4 incorporated hydrogel as a promising agent for the sustained removal of heavy metal Pb from paddy soil.

In this research, we prepared novel hydrogels from enzymatically synthesized alpha-1,3-glucan and its carboxymethyl derivative by crosslinking with ethylene glycol diglycidyl ether. The resulting hydrogels were highly swellable and pH-sensitive with an enhanced, highly developed structure, and showed excellent protein/dye adsorption performances. Furthermore, the hydrogels had good biodegradability and could be degraded in soil extract solution. The prepared hydrogels have potential applications as green and environmentally-friendly adsorbents for the effective removal of organic dyes in printing and dyeing wastewater. Graphical Abstract Enzymatic synthesized alpha-1,3-glucan was converted into carboxymethyl glucan and subsequently crosslinked with ethylene glycol diglycidyl ether to form hydrogels. We evaluated the protein and dye adsorption capacity of the hydrogels and analyzed the absorption mechanism. Furthermore, the hydrogels' notable biodegradability, evidenced by their decomposition in soil extracts, underscores their potential as environmentally-friendly adsorbents for environmental remediation.

Cellulosic hydrogels are widely used in various applications, as they are natural raw materials and have excellent degradability. However, their poor mechanical properties restrict their practical application. This study presents a facile approach for fabricating cellulosic hydrogels with high strength by synergistically utilizing salting-out and ionic coordination, thereby inducing the collapse and aggregation of cellulose chains to form a crosslinked network structure. Cellulosic hydrogels are prepared by soaking cellulose in an Al2(SO4)3 solution, which is both strong (compressive strength of up to 16.99 MPa) and tough (compressive toughness of up to 2.86 MJ/m3). The prepared cellulosic hydrogels exhibit resistance to swelling in different solutions and good biodegradability in soil. The cellulosic hydrogels are incorporated into strain sensors for human-motion monitoring by introducing AgNWs. Thus, the study offers a promising, simple, and scalable approach for preparing strong, degradable, and anti-swelling hydrogels using common biomass resources with considerable potential for various applications.