Ionization Engineering of Hydrogels Enables Highly Efficient Salt‑Impeded Solar Evaporation and Night‑Time Electricity Harvesting

Interfacial solar evaporation holds immense potential for brine desalination with low carbon footprints and high energy utilization.Hydrogels,as a tunable material platform from the molecular level to the macroscopic scale,have been considered the most promising candidate for solar evaporation.However,the simultaneous achievement of high evaporation efficiency and satisfactory tolerance to salt ions in brine remains a challenging scientific bottleneck,restricting the widespread application.Herein,we report ionization engineering,which endows polymer chains of hydrogels with electronegativity for impeding salt ions and activating water molecules,fundamentally overcoming the hydrogel salt-impeded challenge and dramatically expediting water evaporating in brine.The sodium dodecyl benzene sulfonate-modified carbon black is chosen as the solar absorbers.The hydrogel reaches a ground-breaking evaporation rate of 2.9 kg m−2 h−1 in 20 wt%brine with 95.6%efficiency under one sun irradiation,surpassing most of the reported literature.More notably,such a hydrogel-based evaporator enables extracting clean water from oversaturated salt solutions and maintains durability under different high-strength deformation or a 15-day continuous operation.Meantime,on the basis of the cation selectivity induced by the electronegativity,we first propose an all-day system that evaporates during the day and generates salinity-gradient electricity using waste-evaporated brine at night,anticipating pioneer a new opportunity for all-day resource-generating systems in fields of freshwater and electricity.

Application of Optical Hydrogels in Environmental Sensing

The ever-increasing complexity of environmental pollutants urgently warrants the development of new detection technologies.Sensors based on the optical properties of hydrogels enabling fast and easy in situ detection are attracting increasing attention.In this paper,the data from 138 papers about different optical hydrogels(OHs)are extracted for statistical analysis.The detection performance and potential of various types of OHs in different environmental pollutant detection scenarios were evaluated and compared to those obtained using the standard detection method.Based on this analysis,the target recognition and sensing mechanisms of two main types of OHs are reviewed and discussed:photonic crystal hydrogels(PCHs)and fluorescent hydrogels(FHs).For PCHs,the environmental stimulus response,target receptors,inverse opal structures,and molecular imprinting techniques related to PCHs are reviewed and summarized.Furthermore,the different types of fluorophores(i.e.,compound probes,biomacromolecules,quantum dots,and luminescent microbes)of FHs are discussed.Finally,the potential academic research directions to address the challenges of applying and developing OHs in environmental sensing are proposed,including the fusion of various OHs,introduction of the latest technologies in various fields to the construction of OHs,and development of multifunctional sensor arrays.

Fluorescent Double Network Hydrogels with Ionic Responsiveness and High Mechanical Properties for Visual Detection

We developed a fluorescent double network hydrogel with ionic responsiveness and high mechanical properties for visual detection.The nanocomposite hydrogel of laponite and polyacrylamide serves as the first network,while the ionic cross-linked hydrogel of terbium ions and sodium alginate serves as the second network.The double-network structure,the introduction of nanoparticles and the reversible ionic crosslinked interactions confer high mechanical properties to the hydrogel.Terbium ions are not only used as the ionic cross-linked points,but also used as green emitters to endow hydrogels with fluorescent properties.On the basis of the “antenna effect” of terbium ions and the ion exchange interaction,the fluorescence of the hydrogels can make selective responses to various ions(such as organic acid radical ions,transition metal ions) in aqueous solutions,which enables a convenient strategy for visual detection toward ions.Consequently,the fluorescent double network hydrogel fabricated in this study is promising for use in the field of visual sensor detection.

Nanozyme‑Engineered Hydrogels for Anti‑Inflammation and Skin Regeneration

Inflammatory skin disorders can cause chronic scarring and functional impairments,posing a significant burden on patients and the healthcare system.Conventional therapies,such as corticosteroids and nonsteroidal anti-inflammatory drugs,are limited in efficacy and associated with adverse effects.Recently,nanozyme(NZ)-based hydrogels have shown great promise in addressing these challenges.NZ-based hydrogels possess unique therapeutic abilities by combining the therapeutic benefits of redox nanomaterials with enzymatic activity and the water-retaining capacity of hydrogels.The multifaceted therapeutic effects of these hydrogels include scavenging reactive oxygen species and other inflammatory mediators modulating immune responses toward a pro-regenerative environment and enhancing regenerative potential by triggering cell migration and differentiation.This review highlights the current state of the art in NZ-engineered hydrogels(NZ@hydrogels)for anti-inflammatory and skin regeneration applications.It also discusses the underlying chemo-mechano-biological mechanisms behind their effectiveness.Additionally,the challenges and future directions in this ground,particularly their clinical translation,are addressed.The insights provided in this review can aid in the design and engineering of novel NZ-based hydrogels,offering new possibilities for targeted and personalized skin-care therapies.

Recent advances on thermosensitive hydrogels-mediated precision therapy

Precision therapy has become the preferred choice attributed to the optimal drug concentration in target sites,increased therapeutic efficacy,and reduced adverse effects.Over the past few years,sprayable or injectable thermosensitive hydrogels have exhibited high therapeutic potential.These can be applied as cell-growing scaffolds or drug-releasing reservoirs by simply mixing in a free-flowing sol phase at room temperature.Inspired by their unique properties,thermosensitive hydrogels have been widely applied as drug delivery and treatment platforms for precision medicine.In this review,the state-of-theart developments in thermosensitive hydrogels for precision therapy are investigated,which covers from the thermo-gelling mechanisms and main components to biomedical applications,including wound healing,anti-tumor activity,osteogenesis,and periodontal,sinonasal and ophthalmic diseases.The most promising applications and trends of thermosensitive hydrogels for precision therapy are also discussed in light of their unique features.

Advances in Biomedical Applications of Hydrogels from Seaweed-Derived Sulfated Polysaccharides:Carrageenan,Fucoidan,and Ulvan

Sulfated polysaccharides extracted from seaweeds,including Carrageenan,Fucoidan and Ulvan,are crucial bioactive compounds known for their diverse beneficial properties,such as anti-inflammatory,antitumor,immunomodulatory,antiviral,and anticoagulant effects.These polysaccharides form hydrogels hold immense promise in biomedicine,particularly in tissue engineering,drug delivery systems and wound healing.This review comprehensively explores the sources and structural characteristics of the three important sulfated polysaccharides extracted from different algae species.It elucidates the gelation mechanisms of these polysaccharides into hydrogels.Furthermore,the biomedical applications of these three sulfated polysaccharide hydrogels in wound healing,drug delivery,and tissue engineering are discussed,highlighting their potential in the biomedicine.

Development of biomedical hydrogels for rheumatoid arthritis treatment

Rheumatoid Arthritis(RA)is an autoimmune disorder that hinders the normal functioning of bones and joints and reduces the quality of human life.Every year,millions of people are diagnosed with RA worldwide,particularly among elderly individuals and women.Therefore,there is a global need to develop new biomaterials,medicines and therapeutic methods for treating RA.This will improve the Healthcare Access and Quality Index and also relieve administrative and financial burdens on healthcare service providers at a global scale.Hydrogels are soft and cross-linked polymeric materials that can store a chunk of fluids,drugs and biomolecules for hydration and therapeutic applications.Hydrogels are biocompatible and exhibit excellent mechanical properties,such as providing elastic cushions to articulating joints by mimicking the natural synovial fluid.Hence,hydrogels create a natural biological environment within the synovial cavity to reduce autoimmune reactions and friction.Hydrogels also lubricate the articulating joint surfaces to prevent degradation of synovial surfaces of bones and cartilage,thus exhibiting high potential for treating RA.This work reviews the progress in injectable and implantable hydrogels,synthesis methods,types of drugs,advantages and challenges.Additionally,it discusses the role of hydrogels in targeted drug delivery,mechanistic behaviour and tribological performance for RA treatment.

Tuning mechanical behaviors of highly entangled hydrogels with the random distribution of mobile entanglements

Highly entangled hydrogels exhibit excellent mechanical properties,including high toughness,high stretchability,and low hysteresis.By considering the evolution of randomly distributed entanglements within the polymer network upon mechanical stretches,we develop a constitutive theory to describe the large stretch behaviors of these hydrogels.In the theory,we utilize a representative volume element(RVE)in the shape of a cube,within which there exists an averaged chain segment along each edge and a mobile entanglement at each corner.By employing an explicit method,we decouple the elasticity of the hydrogels from the sliding motion of their entanglements,and derive the stress-stretch relations for these hydrogels.The present theoretical analysis is in agreement with experiment,and highlights the significant influence of the entanglement distribution within the hydrogels on their elasticity.We also implement the present developed constitutive theory into a commercial finite element software,and the subsequent simulations demonstrate that the exact distribution of entanglements strongly affects the mechanical behaviors of the structures of these hydrogels.Overall,the present theory provides valuable insights into the deformation mechanism of highly entangled hydrogels,and can aid in the design of these hydrogels with enhanced performance.

Light-based 3D printing of stimulus-responsive hydrogels forminiature devices:recent progress and perspective

Miniature devices comprising stimulus-responsive hydrogels with high environmental adaptability are now considered competitive candidates in the fields of biomedicine,precise sensors,and tunable optics.Reliable and advanced fabricationmethods are critical formaximizing the application capabilities ofminiature devices.Light-based three-dimensional(3D)printing technology offers the advantages of a wide range of applicable materials,high processing accuracy,and strong 3D fabrication capability,which is suitable for the development of miniature devices with various functions.This paper summarizes and highlights the recent advances in light-based 3D-printed miniaturized devices,with a focus on the latest breakthroughs in lightbased fabrication technologies,smart stimulus-responsive hydrogels,and tunable miniature devices for the fields of miniature cargo manipulation,targeted drug and cell delivery,active scaffolds,environmental sensing,and optical imaging.Finally,the challenges in the transition of tunable miniaturized devices from the laboratory to practical engineering applications are presented.Future opportunities that will promote the development of tunable microdevices are elaborated,contributing to their improved understanding of these miniature devices and further realizing their practical applications in various fields.

Advanced Nanocomposite Arabic Gum Polyacrylic Acid Hydrogels for Flexible Supercapacitors

In this work,the fabrication and characterization of the nanocomposite hydrogel,as a solid electrode in electro-chemical cell and gel electrolyte material using Indium titanium oxide/polyethylene terephthalate(ITO/PET)flex-ible substrate for double-layer supercapacitors have been reported.The nanocomposite hydrogel composed of Arabic gum(AG),Acrylic acid(AA),reduced graphene oxide(RGO),and silver nanoparticles(AgNPs)was fab-ricated via a physical cross-linked polymerization reaction,in which the ascorbic acid was used as a reducing agent to generate AgNPs and to convert Graphene oxide(GO)to RGO during the polymerization reaction.The morphology and structural characteristics of nanocomposite hydrogel were investigated using atomic force microscopy(AFM),scanning electron microscope(SEM),Fourier transfer infrared(FTIR),and X-rayfluores-cence(XRF).Additionally,the effect of RGO and AgNPs on hydrogel stability was assessed through Thermogra-vimetric analysis(TGA)and differential scanning calorimetry(DSC),while its mechanical properties were studied using the nanoindentation test.Electrochemical impedance spectroscopy(EIS),and cyclic voltammetry(CV)were also conducted to study the electrochemical properties of the prepared hydrogel.The effects of AgNPs,RGO,and water content were all considered in the study of supercapacitor performance.The microstructural tests showed that the nanocomposite hydrogel has a relatively high swelling rate,which has a crucial effect on the capa-citance.Furthermore,the effects of increasing AgNP concentration and water content in the hydrogel matrix showed a significant improvement in its electrochemical performance,compared with that for Arabic gum poly acrylic acid(AGPAA)hydrogel itself,were the specific capacitance exhibited a significant enhancement,convert-ing from a low value to a substantially higher capacitance value.Moreover,when the nanocomposite hydrogel was used as the working electrode in an electrochemical cell with a hydrochloric acid(HCl)electrolyte solution,it exhibited good electrode performance.Additionally,using(ITO/PET)as aflexible substrate for nanocomposite hydrogel shows an improvement in their suitability for supercapacitor applications.Therefore,it is suggested that the fabricated hydrogel supercapacitor has potential applications in thefield of renewable and clean energy harvesting.

Thermosensitive and Wound-Healing Gelatin-Alginate Biopolymer Hydrogels Modified with Humic Acids

The main goal of the article is the creation and study of thermosensitive and wound-healing gelatin-alginate bio-polymer hydrogels modified with humic acids.Their rheological properties,swelling and contraction behavior were experimentally investigated,elucidated using Fourier transform infrared spectroscopy and used to achieve the physiological melting point,which is necessary for successful drug delivery.It has been shown that in the gelatin-alginate-humic acid biopolymer hydrogels systems,it is possible to obtain a gel-sol transition temperature close to the physiological temperature of 37°C,which is important for drug delivery in the treatment of wounds.By changing the type and concentration of humic acids in the gelatin-alginate hydrogel,it turned out to be achiev-able to regulate the softening time of the gel on the human body in the range from 6 to 20 min,which provides the possibility of controlled prolonged delivery of drugs.Based on the study of the influence of calcium ions on the properties of humic acids and ion exchange,as well as the interaction of humic acids,sodium alginate and gelatin with the formation of tighter gel networks,approaches to regulate the rate of softening of hydrogels at physiological temperature and their swelling,which simulates the absorption of exudate,were proposed and implemented.In addition,low shrinkage of the hydrogel surface due to cross-linking of gelatin-alginate networks when modified with humic acids was experimentally confirmed,which is important for avoiding problems of wound contracture and contour deformations when using dressings for wound healing.Thus,the developed opti-mized innovative biopolymer hydrogels synergistically combine the outstanding properties of natural molecular polymers and humic acids and are promising for the creation of effective medicines for wound healing.

Biomimetic fibril-like injectable hydrogels for wound management

Soft tissue repair and regeneration present a significant clinical challenge.Soft hydrogels have emerged as a promising solution for promoting stem cell differentiation and facilitating soft tissue formation[1].Various materials,including synthetic polymers like polydimethyl siloxane and natural polymers like proteins,have been be used as hydrogel matrix for hydrogel preparation[2,3].However,the limited biodegradability,inhomogeneous network structure,and inadequate mechanical properties of these hydrogels hinder their long-term application in complex environments in vivo.Inspired by the nanostructure of collagen fibrils,Li et al.developed a strategy for creating injectable nanofibrillar hydrogels by combining self-assembly and chemical crosslinking of nanoparticles[4].Moreover,injectable hydrogels offer advantages as implantable materials,including better defect filling and reduced risk of infection compared to prefabricated hydrogels[5].

Controlled release behaviors of chitosan/α,β- glycerophosphate thermo-sensitive hydrogels

Chitosan/α,β-glycerophosphate （CS/α,β-GP） thermo-sensitive hydrogels presented flowable solution state at low temperature and semisolid hydrogel when the ambient temperature increased. In this research, different concentrations of metronida- zole encapsulated, CS and α,β-GP, as well as different acid solvents, were chosen to evaluate their influences on the drug release behaviors from CS/α,β-GP hydrogels. It was found that there was a sustaining release during the first 3 h followed by a plateau. SEM images showed that drugs were located both on the surface and in the interior of hydrogels. The optimal preparation conditions of this hydrogel for drug release were as follows： 1.8% （w/v） CS in HAc solvent, 5.6% （w/v） a, 13-GP and 5g/L metronidazole encapsulation. Cytotoxicity evaluation found no toxic effect. In order to control the release rate, 2.5 g/L chitosan microspheres with spherical shape and smooth surface were incorporated, and it was found that the initial release process was alleviated, while drug concentration had no obvious effect on the release rate. It could be concluded that the metronidzole release behaviors could be optimized according to practical applica- tions.

Kinetics analysis of volume phase transition of intelligent neutral thermo-sensitive hydrogels

In this work,utilizing the first law of thermodynamics and the Flory mean-field theory,the kinetic deformation studies concerning the volume phase transition of the neutral thermo-sensitive hydrogels were performed analytically.The hydrogel was assumed as a biphasic mixture medium in the framework of the continuum mixture theory.From the energy conservation of the thermodynamics system of the hydrogel,the governing equations for the kinetics of the nonlinear large deforma-tion were derived.The explicit analytical expressions of the effective stress tensor and the chemical potential of the fluid of the thermo-sensitive hydrogel PNIPA were also obtained from the Helmholtz free energy,which can model the steady-static volume phase transition quantitatively.

Self-Healing Liquid Metal Magnetic Hydrogels for Smart Feedback Sensors and High-Performance Electromagnetic Shielding

Hydrogels exhibit potential applications in smart wearable devices because of their exceptional sensitivity to various external stimuli.However,their applications are limited by challenges in terms of issues in biocompatibility,custom shape,and self-healing.Herein,a conductive,stretchable,adaptable,self-healing,and biocompatible liquid metal GaInSn/Ni-based composite hydrogel is developed by incorporating a magnetic liquid metal into the hydrogel framework through crosslinking polyvinyl alcohol(PVA)with sodium tetraborate.The excellent stretchability and fast self-healing capability of the PVA/liquid metal hydrogel are derived from its abundant hydrogen binding sites and liquid metal fusion.Significantly,owing to the magnetic constituent,the PVA/liquid metal hydrogel can be guided remotely using an external magnetic field to a specific position to repair the broken wires with no need for manual operation.The composite hydrogel also exhibits sensitive deformation responses and can be used as a strain sensor to monitor various body motions.Additionally,the multifunctional hydrogel displays absorption-dominated electromagnetic interference(EMI)shielding properties.The total shielding performance of the composite hydrogel increases to~62.5 dB from~31.8 dB of the pure PVA hydrogel at the thickness of 3.0 mm.The proposed bioinspired multifunctional magnetic hydrogel demonstrates substantial application potential in the field of intelligent wearable devices.

Thixotropic composite hydrogels based on agarose and inorganic hybrid gellants

Water can be used as oxidant in conjunction with metal particles to form metal-water propellant to increase the energy of propellant.For this application,water needs to be stored in form of solid and capable of becoming liquid when use.Stable and thixotropic hydrogel has good potential as water-retaining material and oxidant of metal-based propellant.In this study,we prepared organic/inorganic composite hydrogels by combining inorganic gellants hectorite and fumed silica with organic gellant agarose,respectively.The total content of the gellants can be reduced to less than 2%by adding agarose.The influence of agarose on water content,phase transition temperature,centrifugal stability and other basic physical properties of composite hydrogels were discussed.The results show that the composite hydrogels have better thixotropy and stability than pure inorganic hydrogels,and the gel-sol transformation can be realized by applying shear force or heating to the phase transition temperature.The composite hydrogels have good shear thinning ability and improved mechanical stability.Fumed silica/agarose hydrogels have better physical stability,while the thixotropy and shear thinning ability of hectorite/agarose hydrogels are better.

Adhesive hydrogels in osteoarthritis:from design to application

Osteoarthritis(OA)is the most common type of degenerative joint disease which affects 7%of the global population and more than 500 million people worldwide.One research frontier is the development of hydrogels for OA treatment,which operate either as functional scaffolds of tissue engineering or as delivery vehicles of functional additives.Both approaches address the big challenge:establishing stable integration of such delivery systems or implants.Adhesive hydrogels provide possible solutions to this challenge.However,few studies have described the current advances in using adhesive hydrogel for OA treatment.This review summarizes the commonly used hydrogels with their adhesion mechanisms and components.Additionally,recognizing that OA is a complex disease involving different biological mechanisms,the bioactive therapeutic strategies are also presented.By presenting the adhesive hydrogels in an interdisciplinary way,including both the fields of chemistry and biology,this review will attempt to provide a comprehensive insight for designing novel bioadhesive systems for OA therapy.

Lignin-based Hydrogels for Biological Application

Lignin is the most abundant aromatic compound found in nature.The rich functional groups of lignin are responsible for its antibacterial,antioxidant,anti-ultraviolet,and biocompatible properties.As modified lignin has a higher molecular weight,water solubility,and better surface activity,it is a good candidate for the construction of new biological materials.Ligninbased hydrogels are a type of functional materials with broad application prospects in the biomedical field.This review aimed to introduce the biological properties of lignin and the application of lignin-based hydrogels in the biological field.

Engineering Smart Composite Hydrogels for Wearable Health Monitoring

Growing health awareness triggers the public's concern about health problems. People want a timely and comprehensive picture of their condition without frequent trips to the hospital for costly and cumbersome general check-ups. The wearable technique provides a continuous measurement method for health monitoring by tracking a person's physiological data and analyzing it locally or remotely.During the health monitoring process,different kinds of sensors convert physiological signals into electrical or optical signals that can be recorded and transmitted, consequently playing a crucial role in wearable techniques. Wearable application scenarios usually require sensors to possess excellent flexibility and stretchability. Thus, designing flexible and stretchable sensors with reliable performance is the key to wearable technology. Smart composite hydrogels, which have tunable electrical properties, mechanical properties, biocompatibility, and multi-stimulus sensitivity, are one of the best sensitive materials for wearable health monitoring. This review summarizes the common synthetic and performance optimization strategies of smart composite hydrogels and focuses on the current application of smart composite hydrogels in the field of wearable health monitoring.

Fabricating Cationic Lignin Hydrogels for Dye Adsorption

Due to the low content of adsorption-active groups in lignin,its application in the field of adsorption is limited.Herein,we first prepared cationic kraft lignin acrylate,from which a cationic lignin(CKLA)hydrogel was further prepared by cationic kraft lignin acrylate,acrylamide,and N,N’-methylenebisacrylamide.The morphology,compression properties and swelling properties of CKLA hydrogels were investigated.The prepared CKLA hydrogel was applied as an adsorbent for Congo red.The effect of CKLA hydrogel dosages,initial concentration of Congo red,and pH on adsorption efficiency was investigated.The maximum Congo red removal efficiency was obtained at the initial concentration of Congo red of 50 mg/L,pH 7,and 5 mg dosage of CKLA hydrogel with 20%cationic lignin content.After five cycles of adsorption,the adsorption efficiency of the hydrogel for Congo red still reached more than 80%.The CKLA hydrogel showed pseudo-second-order adsorption kinetics for Congo red adsorption.These results demonstrate the potential of the CKLA hydrogel as an adsorbent for water treatment.