Analysis about the Behavior and Modeling of pH-Sensitive Hydrogels with Different Ratios of Chitosan and Polyvinylpyrrolidone

Smart material can be defined as a material that can dock or convert energy between physical domains or as a material that can generate a response, in their characteristics, properties or geometries, when submitted to an external stimulus, for example, to heat, water presence, light, etc. In this paper, the second definition will be approached. Hydrogels are crosslinked materials that can absorb a big amount of water. They generally can be considered as smart materials once they exhibit sensibility to external stimuli like to pH variation, as will be approached in this paper. Thus, chitosan/polyvinylpyrrolidone hydrogels of three different ratios between these two polymers (1:1, 7:3 and 3:7) were synthesized and putted in aqueous solution with different pHs. The pH was adjusted adding drops of NaOH and HCl, slowly. After the collection of results and in order to understand the phenomena in a visual way, models of the molecules were also elaborated using the Avogadro software. Therefore, it was possible to realize that the greater the ratio of chitosan in the hydrogel, the greater its sensitivity to pH. Such characteristic is associated with the amino (-NH2) groups in it structure, which are capable of protonating and deprotonating (depending of the pH), generating charges under the chemical structure of the material, which will expand its volume in order to minimize the repulsion between charges. In addition, it was also noted that the hydrogel expansion is inversely proportional to the pH increase. By practical tests, it was possible to conclude that chitosan/PVP hydrogel with ratio 7:3 is the most interesting once it presented a greater quantity of chitosan in its composition, what implied in more rigidity than the others and greater ease of handling, resulting in more reliable results. This hydrogel also showed higher sensitivity to pH.

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.

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.

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.

Photoactivated growth factor release from bio-orthogonally crosslinkedhydrogels for the regeneration of corneal defects

In situ-forming hydrogels are an attractive option for corneal regeneration, and the delivery of growth factorsfrom such constructs have the potential to improve re-epithelialization and stromal remodeling. However,challenges persist in controlling the release of therapeutic molecules from hydrogels. Here, an in situ-forming bioorthogonallycrosslinked hydrogel containing growth factors tethered via photocleavable linkages (PC-HAColhydrogel) was developed to accelerate corneal regeneration. Epidermal growth factor (EGF) was conjugated tothe hydrogel backbone through photo-cleavable (PC) spacer arms and was released when exposed to mild intensityultraviolet (UV) light (2–5 mW/cm2, 365 nm). The PC-HACol hydrogel rapidly gelled within a few minuteswhen applied to corneal defects, with excellent transparency and biocompatibility. After subsequentexposure to UV irradiation, the hydrogel promoted the proliferation and migration of corneal epithelial cells invitro. The rate of re-epithelialization was positively correlated to the frequency of irradiation, verified through exvivo rabbit cornea organ culture studies. In an in vivo rat corneal wound healing study, the PC-HACol hydrogelexposed to UV light significantly promoted re-epithelialization, the remodeling of stromal layers, and exhibitedsignificant anti-scarring effects, with minimal α-SMA and robust ALDH3A1 expression. Normal differentiation ofthe regenerated epithelia after healing was evaluated by expression of the corneal epithelial biomarker, CK12.The remodeled cornea exhibited full recovery of corneal thickness and layer number without hyperplasia of theepithelium.

Chitosan/Sodium Alginate Multilayer pH-Sensitive Films Based on Layer-by-Layer Self-Assembly for Intelligent Packaging

The abuse of plastic food packaging has brought about severe white pollution issues around the world.Developing green and sustainable biomass packaging is an effective way to solve this problem.Hence,a chitosan/sodium alginate-based multilayer film is fabricated via a layer-by-layer(LBL)self-assembly method.With the help of superior interaction between the layers,the multilayer film possesses excellent mechanical properties(with a tensile strength of 50 MPa).Besides,the film displays outstanding water retention property(blocking moisture of 97.56%)and ultraviolet blocking property.Anthocyanin is introduced into the film to detect the food quality since it is one natural plant polyphenol that is sensitive to the pH changes ranging from 1 to 13 in food when spoilage occurs.It is noted that the film is also bacteriostatic which is desired for food packaging.This study describes a simple technique for the development of advanced multifunctional and fully biodegradable food packaging film and it is a sustainable alternative to plastic packaging.

White-light-induced synthesis of injectable alginate-based composite hydrogels for rapid hemostasis

Dear Editor,Timely and effective hemostasis is of great significance for reducing body damage and mortality of patients [1]. Alginate is generally considered to be an excellent hemostatic polymer-based biomaterial and has been approved by the Food and Drug Administration as Generally Recognized as Safe [2]. However, the violent crosslinking reaction and unstable structure at the wound site limit its clinical applications. Hence, we report a biocompatible and injectable composite hydrogel methacrylate alginate (Alg-AEMA)-based Eosin Y/N-phenylglycine (NPG)-initiated composite hydrogel (AEC) composed of photocrosslinkable alginate, viscosity modifiers and novel white light photoinitiator, namely Eosin Y/NPG system, for instant hemorrhage control.

Excellent lubricating hydrogels with rapid photothermal sterilization for medical catheters coating

Bacterial infection and tissue damage caused by friction are two major threats to patients’health in medical catheter implantation.Hydrogels with antibacterial and lubrication effects are competitive candidates for catheter coating materials.Photothermal therapy(PTT)is a highly efficient bactericidal method.Here,a composite hydrogel containing MXene nanosheets and hydrophilic 3-sulfopropyl methacrylate potassium salt(SPMK)is reported,which is synthesized through the one-pot method and heat-initiated polymerization.The hydrogel shows excellent antibacterial performance against Escherichia coli(E.coli)and Staphylococcus aureus(S.aureus)in 3 min in the air or 20 min in the water environment under near-infrared light(NIR;808 nm)irradiation.The friction coefficient of the hydrogel is about 0.11,which is 48%lower than that without SPMK.The rapid photothermal sterilization is attributed to the outstanding antibacterial ability and thermal effect of photoactivated MXene.The ultra-low friction is the result of the hydration lubrication mechanism.This study provides a potential strategy for the surface coatings of biomedical catheters,which enables rapid sterilization and extremely low interface resistance between catheters and biological tissues.

Wet tissue adhesive polymeric powder hydrogels for skeletal muscle regeneration

Volumetric muscle loss(VML)frequently results from traumatic incidents and can lead to severe functional disabilities.Hydrogels have been widely employed for VML tissue regeneration,which are unfortunately ineffective because of the lack of intimate contact with injured tissue for structural and mechanical support.Adhesive hydrogels allow for strong tissue connections for wound closure.Nevertheless,conventional adhesive hydrogels exhibit poor tissue adhesion in moist,bleeding wounds due to the hydration layer at the tissue–hydrogel interfaces,resulting in insufficient performance.In this study,we developed a novel,biocompatible,wet tissue adhesive powder hydrogel consisting of dextran-aldehyde(dex-ald)and gelatin for the regeneration of VML.This powder absorbs the interfacial tissue fluid and buffer solution on the tissue,spontaneously forms a hydrogel,and strongly adheres to the tissue via various molecular interactions,including the Schiff base reaction.In particular,the powder composition with a 1:4 ratio of dex-ald to gelatin exhibited optimal characteristics with an appropriate gelation time(258 s),strong tissue adhesion(14.5 kPa),and stability.Dex-ald/gelatin powder hydrogels presented strong adhesion to various organs and excellent hemostasis compared to other wet hydrogels and fibrin glue.A mouse VML injury model revealed that the dex-ald/gelatin powder hydrogel significantly improved muscle regeneration,reduced fibrosis,enhanced vascularization,and decreased inflammation.Consequently,our wet-adhesive powder hydrogel can serve as an effective platform for repairing various tissues,including the heart,muscle,and nerve tissues.

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.

Wrecking neutrophil extracellular traps and antagonizing cancer-associated neurotransmitters by interpenetrating network hydrogels prevent postsurgical cancer relapse and metastases

Tumor-promoting niche after incomplete surgery resection(SR)can lead to more aggressive local progression and distant metastasis with augmented angiogenesis-immunosuppressive tumor microenvironment(TME).Herein,elevated neutrophil extracellular traps(NETs)and cancer-associated neurotransmitters(CANTs,e.g.,catecholamines)are firstly identified as two of the dominant inducements.Further,an injectable fibrin-alginate hydrogel with high tissue adhesion has been constructed to specifically co-deliver NETs inhibitor(DNase I)-encapsulated PLGA nanoparticles and an unselectiveβ-adrenergic receptor blocker(propranolol).The two components(i.e.,fibrin and alginate)can respond to two triggers(thrombin and Ca2+,respectively)in postoperative bleeding to gelate,shaping into an interpenetrating network(IPN)featuring high strength.The continuous release of DNase I and PR can wreck NETs and antagonize catecholamines to decrease microvessel density,blockade myeloid-derived suppressor cells,secrete various proinflammatory cytokines,potentiate natural killer cell function and hamper cytotoxic T cell exhaustion.The reprogrammed TME significantly suppress locally residual and distant tumors,induce strong immune memory effects and thus inhibit lung metastasis.Thus,targetedly degrading NETs and blocking CANTs enabled by this in-situ IPN-based hydrogel drug depot provides a simple and efficient approach against SR-induced cancer recurrence and metastasis.

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].

Characterization of pH-sensitive Poly (acrylic acid-co-N-vinyl-2-pyrrolidone) Hydrogels Prepared by Gamma Radiation

The pH-sensitive copolymer hydrogels were prepared with the monomers of acrylic acid and N-vinyl-2-pyrrolidone based on gamma radiation technique. The morphology of the hydrogels was monitored by using scanning electron microscope. The influence of absorbed dose, monomer composition and concentration on the swelling ratio (SR) of the hydrogels were investigated in detail. The effect of pH and temperature of the swelling medium on the swelling behavior of the hydrogels were also examined. The results show that the SR of the copolymer hydrogels decreases with the monomer concentration and absorbed dose increasing. The copolymer hydrogels show a better pH-sensitive behavior. In alkaline solution, the SR of the hydrogels is much higher than in acid solution.