A versatile hydrogel network-repairing strategy achieved by the covalent-like hydrogen bond interaction

A bifunctional catalyst of CoO/NBC composite for high-performance rechargeable flexible zinc-air battery

Rechargeable flexible zinc-air batteries (ZABs) represent a promising energy-supply device for wearable electronics due to their low cost, safety and high energy density, but their electrochemical performance often suffers from the sluggish reaction kinetics of air electrode and poor moisture-retention ability of polymer electrolytes. Here, we report a type of high-performance rechargeable flexible ZABs endowed by an efficient bifunctional catalyst for air electrode and a high moisture-retention hydrogel electrolyte. The designed nitrogen-boron co-doped carbon nanotube arrays loaded with cobalt oxide nanoparticles (CoO/NBC) with abundant catalytic active sites and oriented structure provide its excellent electrochemical catalytic activities for both oxygen reduction reaction and oxygen evolution reaction. Based on the bifunctional catalyst of CoO/NBC, the developed rechargeable ZABs exhibit a high open-circuit voltage of 1.44 V and a high energy density of 920.0 Wh kg-1, which are superior than commercial Pt/C + RuO2 and most reported non-precious metal catalysts. Furthermore, a trehalose modified polyacrylamide hydrogel electrolytes (trehalose/PAAm) with high moisture-retention has been synthesized to construct flexible ZABs, which not only exhibit outstanding electrochemical performance (1.39 V and 824.8 Wh kg-1), but also show excellent stability even after 400 charge/discharge cycles or being bent to any angle.

Exosomal miRNA combined with anti-inflammatory hyaluronic acid-based 3D bioprinted hepatic patch promotes metabolic reprogramming in NAFLD-mediated fibrosis

Non-alcoholic fatty liver disease (NAFLD) is a complex metabolic disorder, where the underlying molecular mechanisms are mostly not well-understood and therefore, warrants the need for therapeutic interventions targeting several metabolic pathways as a unified response. Of late, promising outcomes have been observed with mesenchymal stem cell-derived exosomes. However, reduced bioavailability due to systemic delivery and the need for repeated fresh isolation hinders their feasibility for clinical applications. In this regard, an 'off-the-shelf' 3D bioprinted hyaluronic acid-based hepatic patch to deliver encapsulated exosomes alone/or with hepatocytes (as dual-therapy) is developed as a holistic approach for ameliorating the disease condition and promoting tissue regeneration. The bioprinted hepatic patch demonstrated sustained and localized release of exosomes (∼82 % in 21 days), and healthy liver tissue-like mechanical properties while being biocompatible and biodegradable. Assessment in NAFLD rat models displayed alleviation of the altered biochemical parameters such as fat deposition, deranged liver functions, disrupted lipid, glucose, and insulin metabolism along with a reduction in localized inflammation, and associated liver fibrosis. The study suggests that a synergistic effect between the miRNA population of released exosomes, cell therapy, and the bioprinted matrix materials is crucial in targeting multiple complex metabolic pathways associated with the severity of the disease.

Highly stretchable, adhesive and conductive hydrogel for flexible and stable bioelectrocatalytic sensing layer of enzyme-based amperometric glucose biosensor

Highly stretchable, adhesive and conductive triblock hydrogel was synthesized and utilized as a flexible and stable bioelectrocatalytic sensing layer of enzyme-based amperometric glucose biosensor. The hydrogel was prepared through one-pot polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid, methacrylamide, and hydroxyethyl methacrylate. The physical and chemical properties of the hydrogel were characterized with X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and electrochemical techniques. Glucose oxidase (GOx) and chitosan (CTS) embedded hydrogel was drop-coated on glassy carbon electrode (GCE) and screen printed graphite electrode (SPGE). The resulting GOx/CTS/hydrogel-GCE and GOx/CTS/hydrogel-SPGE exhibited excellent mediated bioelectrocatalytic oxidation current for glucose. The calibration curve of glucose by the GOx/CTS/hydrogel-GCE showed the linear range from 0.25 to 15 mM with the sensitivity of 27.0 µA mM-1 cm-2. This GOx/CTS/hydrogel-based sensing layer coated on the SPGE was stable against bending, and the response to glucose was almost same irrespective of the bending angles (0, 30, 60, and 90 degree). In addition, the response to glucose was not interfered by various organic and inorganic interfering species, allowed to detect glucose in goat serum. Furthermore, the GOx/CTS/hydrogel-GCE kept its original activity of 99.64 % during 30 days' storage under dry state in refrigerator.

Load-Bearing Organogels: Hierarchical Anisotropic Composite Structure for High Mechanical Toughness and Antifatigue-Fracture Capability under Extreme Conditions

Gels with excellent mechanical properties and antifatigue-fracture capability are attractive materials for load-bearing applications; however, at extreme temperatures, they still suffer from catastrophic failure caused by freezing- or dehydration-induced crack propagation. Here, we present a series of hierarchical anisotropic composite organogels that are strong yet tough and antifatigue-fracture over a wide temperature range (-30 to 60 °C) through the combination strategies of freezing-casting, annealing, and solvent exchange with polyols. Such a hybrid design endows the gels with anisotropic and hierarchical structures and excellent tolerance to extreme temperatures, thus guaranteeing efficient energy dissipation and crack propagation resistance under both ambient and harsh conditions. For instance, the organogel obtained via solvent exchange with glycerol exhibited high strength (22.6 MPa), toughness (198.0 MJ/m3), fatigue threshold (6.92 kJ/m2), and particularly, a superhigh fracture energy (665.7 kJ/m2), which is even higher than anhydrous elastomers, metals, and alloys. Importantly, these values were further boosted at extreme temperatures, such as fatigue thresholds of 8.01 and 9.77 kJ/m2 at -30 and 60 °C, respectively. This work offers an attractive strategy for fabricating gel materials that are reliable for load-bearing applications under extreme conditions.

Design and applications of antifreeze polysaccharide-based hydrogels for cryoprotection and biotechnological advancements: A review

Polysaccharide-based hydrogels possess desirable characteristics such as flexibility, biocompatibility, and biodegradability. Nevertheless, these hydrogels frequently lose their inherent traits and functionality under low-temperature circumstances, which significantly restricts their potential applications in cold environments. Antifreeze hydrogels provide a promising solution to this challenge by maintaining their properties at cold temperatures, showcasing remarkable advantages. This review commences with a bibliometric analysis via VOS Viewer to acquire a comprehensive comprehension of the development tendencies in antifreeze hydrogels. It subsequently summarizes diverse antifreeze mechanisms in polysaccharide-based hydrogels, encompassing solute ion modification, organic alcohol modification, ion gels, eutectic gels, and intrinsic antifreeze properties through molecular chain polymerization. Additionally, the review explores the applications of antifreeze hydrogels in food preservation, flexible wearable devices, and energy storage. Finally, the future directions for the development of antifreeze polysaccharide-based hydrogels are deliberated, with an emphasis on the utilization of natural polysaccharide resources to create hydrogels that integrate antifreeze performance, mechanical properties, and stability, thereby facilitating advancements in related industries.

Self-Healing Hydrogels: Mechanisms and Biomedical Applications

Hydrogels have emerged as dependable candidates for tissue repair because of their exceptional biocompatibility and tunable mechanical properties. However, conventional hydrogels are vulnerable to damage owing to mechanical stress and environmental factors that compromise their structural integrity and reduce their lifespan. In contrast, self-healing hydrogels with their inherent ability to restore structure and function autonomously offer prolonged efficacy and enhanced appeal. These hydrogels can be engineered into innovative forms including stimulus-responsive, self-degradable, injectable, and drug-loaded variants, thereby enhancing their applicability in wound healing, drug delivery, and tissue engineering. This review summarizes the categories and mechanisms of self-healing hydrogels, along with their biomedical applications, including tissue repair, drug delivery, and biosensing. Tissue repair includes wound healing, bone-related repair, nerve repair, and cardiac repair. Additionally, we explored the challenges that self-healing hydrogels continue to face in tissue repair and presented a forward-looking perspective on their development. Consequently, it is anticipated that self-healing hydrogels will be progressively designed and developed for applications that extend beyond tissue repair to a broader range of biomedical applications.

Hydrogel tissue adhesive: Adhesion strategy and application

Hydrogel tissue adhesives have emerged as a promising alternative to conventional wound closure methods such as sutures and staples due to their operational simplicity demonstrated biocompatibility and capacity for multifunctional integration. However, complex and variable tissue microenvironments and dynamic adhesion surfaces still challenge the actual adhesion performance of adhesives, especially natural polymer-based adhesives. In addition, to expand the application of adhesives in biomedical fields, there is an urgent need to further improve tissue adhesion performance through composition design, adhesion mechanism research and bioeffect development. This review focuses on the adhesive properties of adhesives and their applications in biomedical fields. Adhesion-cohesion equilibria, forms of adhesion failure, methods for improving cohesion and various interfacial adhesion mechanisms are presented. Moreover, practical biomedical applications of tissue adhesives are reviewed, focusing on skin, heart, stomach, liver, and cornea. Finally, this review looks ahead to a new generation of multi-functional, strong adhesion tissue adhesives, in the hope of providing inspiration to those working in the field.

Hydrogel Electrolyte Film with Low-Temperature Adaptability for Flexible Quasi-Solid-State Batteries

Considering the merits and shortcomings of conventional hydrogels in terms of low-temperature adaptability, a new type of hydrogel electrolyte, reinforced by hydrogen bonding and containing just 6.8% water, is fabricated. This hydrogel film exhibits a high ionic conductivity of 3.9 mS cm-1 at room temperature and maintains its flexibility even at -40 °C. The hydrogel-based quasi-solid-state cell shows good cyclic stability performance, retaining 80.3% of its initial capacity after 800 cycles. Furthermore, it performs well in sub-zero conditions, retaining 89.6% of its capacity at -30 °C (0.5C) and releasing 56.4 mAh g-1 at -40 °C (0.1C). Notably, the cyclic stability of the LTE-based flexible full cell maintains well even under 180° bending and 15% stretching. This can be attributed to the polymer network with hydrophilic groups, which disrupts the hydrogen-bond networks of original water molecules and forms abundant new hydrogen bonding interactions between the polymer chains and water molecules. These interactions are crucial for improving low-temperature adaptability. Overall, this work offers a promising approach to creating low-temperature adaptable hydrogels that can be used to develop wearable energy-storage devices.

Preparation of interpenetrating networks from chitosan and poly(hydroxypropyl methacrylate) or p(hydroxyethyl methacrylate) for controlled release of doxorubicin and curcumin: Investigation of potential use in wound dressing

The IPNs hydrogel films based on chitosan (CS), 2-hydroxyethyl methacrylate (HEMA), and 2-hydroxypropyl methacrylate (HPMA) were prepared, and their potential for drug delivery and wound dressing was evaluated. The characterizations of the IPNs were examined through swelling tests, FTIR, DSC, SEM, mechanical properties, and BET analyses. The percent swelling of the CS/p(HEMA)1 and CS/p(HPMA)1 were obtained as 240 % and 110 %, respectively. The release behavior of prepared hydrogel formulations was investigated in two different pH values for DOX and CUR at pH 5.5 and 7.4, respectively, at varying drug concentrations. In vitro, drug release profiles revealed a time-dependent release pattern, with a maximum release observed at 48 h for all formulations. Among the IPNs, CS/p(HEMA)1 formulation containing CS/HEMA in a 1:1 ratio showed the highest drug release rates of 76.0 % for doxorubicin and 75.5 % for curcumin. MTT assays revealed that the IPNs formulations exhibit enhanced interaction with drugs, leading to an improved drug release rate. A marked decrease in cell viability was observed as the concentration of both drugs increased for testing the ATCC-CRL 2451 leukemia cell line in the prepared formulations. These findings highlight the potential of these composite hydrogels as efficient drug delivery systems for wound dressing applications.

Puncture-resistant hydrogels with high mechanical performance achieved supersaturated salt

Sufficient mechanical performance is the basic requirement for load-bearing and damage-resistant materials. However, the simultaneous optimization of mechanical properties is usually difficult in a single hydrogel. Herein, a supersaturated salt was employed to enhance the mechanical performance and damage resistance of hydrogels. By immersing the pre-formed hydrogel based on hydrophobic associations into supersaturated Na2SO4 solution (3.3 M), high-density and strong hydrophobic associations were constructed simultaneously in the network due to the contraction of hydrophilic chains and improvement of hydrophobic associations. Compared to the pristine hydrogel, this salt-treated hydrogel was transparent and showed a simultaneous enhancement in stiffness (E of 253 ± 7 MPa), strength (σ of 12.65 ± 0.07 MPa), and toughness (Γ of 19.6 ± 3.2 MJ m-3). It also displayed remarkable puncture and tear resistance with a puncture force of 66 N, a puncture energy of 370 mJ, and a tearing energy of 34 kJ m-2. This work provides a simple method to simultaneously optimize the contradictory mechanical properties and puncture resistance in a single hydrogel.

Hydro-locking in hydrogel for extreme temperature tolerance

Hydrogels consist of cross-linked polymers that are highly swollen with water. Water evaporation or freezing during temperature changes may lead to stiff and brittle hydrogels. We introduce a strategy called "hydro-locking," which involves immobilizing the water molecules within the polymer network of the hydrogel. This is accomplished by establishing robust connections between water molecules and the polymer by using sulfuric acid. A sacrificial network is introduced to shield the prime polymer network from collapsing. Under the hydro-locking mode, an alginate-polyacrylamide double-network hydrogel remains soft and stretchable within a temperature range that spans from -115° to 143°C. The strategy works with a range of hydrogels and solutions and may enable the preservation and observation of materials or even living organisms at extreme temperatures.

A Universal Strategy to Mitigate Microphase Separation via Cellulose Nanocrystal Hydration in Fabricating Strong, Tough, and Fatigue-Resistant Hydrogels

As a common natural phenomenon, phase separation is exploited for the development of high-performance hydrogels. Using supersaturated salt to create microphase-separated hydrogels with strengthened mechanical properties has gained widespread attention. However, such strengthened hydrogel loses its intrinsic flexibility, making the phase separation strategy unsuitable for the fabrication of stretchable and tough hydrogels. Here, a phase-engineering design strategy is introduced to produce stretchable yet tough hydrogels using supersaturated NaAc salt, by leveraging the hydration effect of cellulose nanocrystal (CNC) to mitigate microphase separation. The CNC-mitigated microphase-separated hydrogel presents unprecedented mechanical properties, for example, tensile strength of 1.8 MPa with a fracture strain of 4730%, toughness of 43.1 MJ m-3, fracture energy of 75.4 kJ m-2, and fatigue threshold up to 3884.7 J m-2. Furthermore, this approach is universal in synthesizing various microphase separation-enhanced polymer gels, including polyacrylic acid, poly(acrylic acid-co-acrylamide), gelatin, and alginate. These advancements provide insights into the incorporation of CNC-mediated microphase separation structures in hydrogels, which will foster the future development of high-performance soft materials.

Intrinsic Anti-Freezing, Tough, and Transparent Hydrogels for Smart Optical and Multi-Modal Sensing Applications

Hydrogels have received great attention due to their molecular designability and wide application range. However, they are prone to freeze at low temperatures due to the existence of mass water molecules, which can damage their flexibility and transparency, greatly limiting their use in cold environments. Although adding cryoprotectants can reduce the freezing point of hydrogels, it may also deteriorate the mechanical properties and face the risk of cryoprotectant leakage. Herein, the microphase-separated structures of hydrogels are regulated to confine water molecules in sub-6 nm nanochannels and increase the proportion of bound water, endowing the hydrogels with intrinsic anti-freezing properties, high mechanical strength, good stretchability, remarkable fracture energy, and puncture resistance. Even after being kept in liquid nitrogen for 1000 h, the hydrogel still maintains good transparency. The hydrogel can exhibit excellent low-temperature shape memory and intelligent optical waveguide properties. Additionally, the hydrogel can be assembled into strain and pressure sensors for flexible sensing at both room and low temperatures. The intrinsically anti-freezing microphase-separated hydrogel offers broad prospects in low-temperature electronic and optical applications.

Electrothermally powered synergistic fluorescence-colour/3D-shape changeable polymer gel systems for rewritable and programmable information display

Intelligent luminescent materials for rewritable and programmable information display have long been expected to be used to address potential environmental concerns stemming from the extensive use of disposable displays. However, most reported luminescence-colour changeable examples are chemically responsive and not well programmed to sequentially deliver different information within a single system. Additionally, they may suffer from residual chemical accumulation caused by the repeated addition of chemical inks and usually have poor rewritability. Herein, we draw inspiration from the bioelectricity-triggered information display mechanism of chameleon skin to report a robust electrothermally powered polymer gel actuator consisting of one soft conductive graphene/PDMS film and one humidity-responsive fluorescence-colour changeable CD-functionalized polymer (PAHCDs) gel layer. Owing to the good electrocaloric effect of the bottom graphene film and excellent hygroscopicity of the top PAHCDs gel layer, the as-designed actuator could be facilely controlled to exhibit reversible and synergistic 3D-shape/fluorescence-colour changeable behaviours in response to alternating electricity and humidity stimuli. On this basis, robust rewritable information display systems are fabricated, which enable not only on-demand delivery of written information, but also facile rewriting of lots of different information by the synergization of electroheat/humidity-triggered local 3D-deformation and fluorescence-colour changes. This work opens new avenues of research into rewritable information display and potentially inspires the future development of intelligent luminescent materials.

Coordinatively stiffen and toughen polymeric gels via the synergy of crystal-domain cross-linking and chelation cross-linking

Polymer gels have been widely used in flexible electronics, soft machines and impact protection materials. Conventional gels usually suffer from the inherent conflict between stiffness and toughness, severely hampering their applications. This work proposes a facile yet versatile strategy to break through this trade-off via the synergistic effect of crystal-domain cross-linking and chelation cross-linking, without the need for specific structure design or adding other reinforcements. Both effects are proven to boost the mechanical performance of the originally weak gel, and result in a stiff and tough conductive gel, achieving significant enhancements in elastic modulus and toughness by up to 366-, and 104-folds, respectively. The resultant gel achieves coordinatively enhanced stiffness (110.26 MPa) and toughness (219.93 MJ m-3), reconciling the challenging trade-off between them. In addition, the presented strategy is found generalizable to a variety of metal ions and polymers, offering a promising way to expand the applicability of gels.

Compressible, anti-fatigue, extreme environment adaptable, and biocompatible supramolecular organohydrogel enabled by lignosulfonate triggered noncovalent network

Achieving a synergy of biocompatibility and extreme environmental adaptability with excellent mechanical property remains challenging in the development of synthetic materials. Herein, a "bottom-up" solution-interface-induced self-assembly strategy is adopted to develop a compressible, anti-fatigue, extreme environment adaptable, biocompatible, and recyclable organohydrogel composed of chitosan-lignosulfonate-gelatin by constructing noncovalent bonded conjoined network. The ethylene glycol/water solvent induced lignosulfonate nanoparticles function as bridge in chitosan/gelation network, forming multiple interfacial interactions that can effectively dissipate energy. The organohydrogel exhibits high compressive strength (54 MPa) and toughness (3.54 MJ/m3), 100 and 70 times higher than those of pure chitosan/gelatin hydrogel, meanwhile, excellent self-recovery and fatigue resistance properties. Even when subjected to severe compression up to a strain of 0.5 for 500,000 cycles, the organohydrogel still remains intact. This organohydrogel also demonstrates notable biocompatibility both in vivo and vitro, environment adaptability at low temperature, as well as recyclability. Such all natural organohydrogel provides a promising route towards the development of high-performance load-bearing materials.

Self-Healing and Antifreezing/Antidrying Conductive Eutectohydrogel-Based Biosignal Monitoring Multisensors with Integrated Supercapacitor

A novel self-healing and antifreezing/antidrying conductive eutectohydrogel, ideal for wearable multifunctional sensors and supercapacitors, is reported. Conductive eutectohydrogel with self-healing and facilely tunable mechanical performance is obtained by incorporation of trehalose and phytic acid as reversible cross-linkers into a polyacrylamide network, forming the dynamic hydrogen bonding and electrostatic interactions. Furthermore, combined use of deep eutectic solvent with water ensures the air stability as well as the antifreezing/antidrying characteristics. The synthesized eutectohydrogel exhibits a self-healing efficiency of 90.7% after 24 h at room temperature, Young's modulus of 140.9 kPa, and strain at break of 352.8%. With the eutectohydrogel as a versatile platform, self-healing strain and temperature sensors, electrocardiogram electrodes, and supercapacitor are fabricated, recovering the device performance after self-healing from complete bisection and exhibiting stable performance over a wide temperature range from -20 to 50 °C. With a vertically integrated patch device of supercapacitor and strain sensor attached onto skin, various body movements are successfully detected using the energy stored in the supercapacitor, without performance degradation even after self-healing from complete bisection of the full patch device. This work demonstrates high potential application of the synthesized eutectohydrogel to flexible wearable devices featuring durability and longevity.

Predicting Fatigue Damage in Hydrogels Through Force-Induced Luminescence Enhancement

Fatigue damage of polymers occurs under long-term load cycling, resulting in irreversible fracture failure, which is difficult to predict. The real-time monitoring of material fatigue damage is of great significance. Here, tough hydrogels are prepared with force-induced confined luminescence enhancement of carbonated polymer quantum dot (CPD) clusters to realize the visualization of fracture process and the monitoring of fatigue damage. The enhanced interactions induced by force between the clusters and the polymer in the confined space inhibit the non-radiative leaps and promote the radiative leaps to quantify the fatigue damage into optical signals. Rigid CPDs with abundant active sites on the surface can form dynamic reversible bonds with polymer and dissipate stress concentration, which significantly enhances the crack propagation strain (8000%) and fracture energy (26.4 kJ m-2) of hydrogels. CPD hydrogels have a wide range of applications in novel information encryption and luminescent robotics.

Coordination and Hydrogen Bond Chemistry in Tungsten Oxide@Polyaniline Composite toward High-Capacity Aqueous Ammonium Storage

Aqueous ammonium ion batteries (AAIBs) have garnered significant attention due to their unique energy storage mechanism. However, their progress is hindered by the relatively low capacities of NH4 + host materials. Herein, the study proposes an electrodeposited tungsten oxide@polyaniline (WOx@PANI) composite electrode as a NH4 + host, which achieves an ultrahigh capacity of 280.3 mAh g-1 at 1 A g-1, surpassing the vast majority of previously reported NH4 + host materials. The synergistic interaction of coordination chemistry and hydrogen bond chemistry between the WOx and PANI enhances the charge storage capacity. Experimental results indicate that the strong interfacial coordination bonding (N: →W6+) effectively modulates the chemical environment of W atoms, enhances the protonation level of PANI, and thus consequently the conductivity and stability of the composites. Spectroscopy analysis further reveals a unique NH4 +/H+ co-insertion mechanism, in which the interfacial hydrogen bond network (N-H···O) accelerates proton involvement in the energy storage process and activates the Grotthuss hopping conduction of H+ between the hydrated tungsten oxide layers. This work opens a new avenue to achieving high-capacity NH4 + storage through interfacial chemistry interactions, overcoming the capacity limitations of NH4 + host materials for aqueous energy storage.

A Versatile Microporous Design toward Toughened yet Softened Self-Healing Materials

Realizing the full potential of self-healing materials in stretchable electronics necessitates not only low modulus to enable high adaptivity, but also high toughness to resist crack propagation. However, existing toughening strategies for soft self-healing materials have only modestly improves mechanical dissipation near the crack tip (ГD), and invariably compromise the material's inherent softness and autonomous healing capabilities. Here, a synthetic microporous architecture is demonstrated that unprecedently toughens and softens self-healing materials without impacting their intrinsic self-healing kinetics. This microporous structure spreads energy dissipation across the entire material through a bran-new dissipative mode of adaptable crack movement (ГA), which substantially increases the fracture toughness by 31.6 times, from 3.19 to 100.86 kJ m-2, and the fractocohesive length by 20.7 times, from 0.59 mm to 12.24 mm. This combination of unprecedented fracture toughness (100.86 kJ m-2) and centimeter-scale fractocohesive length (1.23 cm) surpasses all previous records for synthetic soft self-healing materials and even exceeds those of light alloys. Coupled with significantly enhanced softness (0.43 MPa) and nearly perfect autonomous self-healing efficiency (≈100%), this robust material is ideal for constructing durable kirigami electronics for wearable devices.

A Stretchable Conductive Material with High Fatigue Resistance for Strain Sensors

Intrinsically stretchable conductive materials based on elastic substrates and conductive components play important roles in biomedical applications, such as exercise rehabilitation monitoring and disease prediction. A persistent challenge is to combine high fatigue resistance with excellent mechanical properties in stretchable conductive materials. Herein, we present a stretchable conductive material with both good fatigue resistance and high tensile properties (∼3170%) based on poly(acrylic acid)-phytic acid-trehalose-polypyrrole (denoted as PPTP). The as-prepared PPTP hydrogel electrode showed no obvious cracking or delamination after 400 loading and unloading cycles and maintained good electrical signal transmission function after 1000 cycles. We further collected stable signals for human motion and handwriting using the stretchable hydrogel electrode as a strain sensor, demonstrating the potential application of the PPTP stretchable hydrogel electrode in biomedicine.

Heteroaggregation, disaggregation, and migration of nanoplastics with nanosized activated carbon in aquatic environments: Effects of particle property, water chemistry, and hydrodynamic condition

Nanosized activated carbon (NAC) as emerging engineered nanomaterials may interact with nanoplastics prevalent in aquatic environments to affect their fate and transport. This study investigated the effects of particle property (charge and concentration), water chemistry [electrolytes, pH, humic acid (HA), and sodium alginate (SA)], and hydrodynamic condition [wave (i.e., sonication) and turbulence (i.e., stirring)] on the heteroaggregation, disaggregation, and migration of NAC with positively charged amino-modified polystyrene (APS) or negatively charged bare polystyrene (BPS) nanoplastics. The homoaggregation rate of APS was slower than its heteroaggregation rate with NAC, with critical coagulation concentrations (CCC) decreasing at higher NAC concentrations. However, the homoaggregation rate of BPS was intermediate between its heteroaggregation rates under low (10 mg/L) and high (40 mg/L) NAC concentrations. The heteroaggregation rate of APS+NAC enhanced as pH increasing from 3 to 10, whereas the opposite trend was observed for BPS+NAC. In NaCl solution or at CaCl2 concentration below 2.5 mM, HA stabilized APS+NAC and BPS+NAC via steric hindrance more effectively than SA. Above 2.5 mM CaCl2, SA destabilized APS+NAC and BPS+NAC by calcium bridging more strongly than HA. The migration process of heteroaggregates was simulated in nearshore environments. The simulation suggests that without hydrodynamic disturbance, APS+NAC (971 m) may travel farther than BPS+NAC (901 m). Mild wave (30-s sonication) and intense turbulence (1500-rpm stirring) could induce disaggregation of heteroaggregates, thus potentially extending the migration distances of APS+NAC and BPS+NAC to 1611 and 2160 m, respectively. Conversely, intense wave (20-min sonication) and mild turbulence (150-rpm stirring) may further promote aggregation of heteroaggregates, shortening the migration distances of APS+NAC and BPS+NAC to 262 and 552 m, respectively. Particle interactions mainly involved van der Waals attraction, electrostatic repulsion, steric hindrance, calcium bridging, π-π interactions, hydrogen bonding, and hydrophobic interactions. These findings highlight the important influence of NAC on the fate, transport, and risks of nanoplastics in aquatic environments.

High Ion-Conductive Hydrogel: Soft, Elastic, with Wide Humidity Tolerance and Long-Term Stability

Ion-conductive hydrogels have received great attention due to their significant potential in flexible electronics. However, achieving hydrogels that simultaneously possess high ionic conductivity and stability under varying humidity conditions remains a challenge, limiting their practical applications. Herein, we propose a thermally controlled chemical cross-linking strategy to prepare an elastic and conductive hydrogel (ECH) of poly(vinyl alcohol) (PVA) with high content of H2SO4. The covalent cross-links formed effectively tackle the instability issue in high humidity of physically cross-linked PVA/H2SO4 hydrogels with high ionic conductivity, which were previously developed via the polymer-in-salt strategy. We systematically investigated the reaction conditions and clarified the methods to optimize the hydroxyl dehydration of PVA, resulting in excellent mechanical properties and ion conductivity simultaneously. The ECH demonstrates impressive ionic conductivity (up to 392 ± 49 mS cm-1) and elasticity (over 80% resilience upon stretching and compression after being equilibrated at various humidity levels for 24 days). Thanks to the excellent water retention of the high H2SO4 content, the ECH maintains an ionic conductivity exceeding 210 mS cm-1 for over 420 days at 50% relative humidity (RH) and retains over 100 mS cm-1 even after 3 days under extremely dry conditions (7% RH). These remarkable properties make the ECH an ideal candidate for applications requiring reliable ionic conductivity in diverse environmental conditions. Additionally, we demonstrated that the ECH can function as a stretchable Joule heater with high conformability for heating up objects with curved surfaces. The heating rate could reach a fast rate of ∼12 °C s-1 even when a human-safe alternating current voltage is below 36 V, attributed to the high ionic conductivity. We believe that the high performance and ease of fabrication make our hydrogels a promising candidate for use as electrolytes in flexible energy storage devices, electrolyte gates in electrochemical transistors, and artificial skin, which often face long-term stability challenges under varying humidity conditions.

A Facile One-Step Self-Assembly Strategy for Novel Carbon Dots Supramolecular Crystals with Ultralong Phosphorescence Controlled by NH4. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024;20:e2402236. [PMID: 38970543 DOI: 10.1002/smll.202402236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

A new methodological design is proposed for carbon dots (CDs)-based crystallization-induced phosphorescence (CIP) materials via one-step self-assembled packaging controlled by NH4 +. O-phenylenediamine (o-PD) as a nitrogen/carbon source and the ammonium salts as oxidants are used to obtain CDs supramolecular crystals with a well-defined staircase-like morphology, pink fluorescence and ultralong green room-temperature phosphorescence (RTP) (733.56 ms) that is the first highest value for CDs-based CIP materials using pure nitrogen/carbon source by one-step packaging. Wherein, NH4 + and o-PD-derived oxidative polymers are prerequisites for self-assembled crystallization so as to receive the ultralong RTP. Density functional theory calculation indicates that NH4 + tends to anchor to the dimer on the surface state of CDs and guides CDs to cross-arrange in an X-type stacking mode, leading to the spatially separated frontier orbitals and the through-space charge transfer (TSCT) excited state in turn. Such a self-assembled mode contributes to both the small singlet-triplet energy gap (ΔEST) and the fast inter-system crossing (ISC) process that is directly related to ultralong RTP. This work not only proposes a new strategy to prepare CDs-based CIP materials in one step but also reveals the potential for the self-assembled behavior controlled by NH4 +.

High-tear resistant gels crosslinked by DA@CNC for 3D printing flexible wearable devices

Photocurable gels have broad application prospects in biomedicine, bionics, flexible wearable devices and other fields. However, there are still some problems in the current photocurable gels, such as notch sensitivity, that is, poor tear resistance. In this study, we provided a photocurable gel with excellent tear resistance. The gel prepolymer is mainly composed of hydroxymethylacrylamide (NAM) and cellulose nanocrystals (CNC) modified with dopamine hydrochloride (DA), referred to as DA@CNC. After photocuring, the prepared gels show excellent mechanical properties such as tear resistance, elasticity and toughness. The introduction of DA@CNC not only endows gels with a large amount of energy dissipation through hydrogen bond crosslinking, but also effectively resists crack expansion as a nano-sized reinforcing phase, which greatly improves the tear resistance of the gels. Even at a 40 % gap, the elongation at break of the gel can still reach 1445 %. In addition, the DA can endow the gel with good electrical conductivity and excellent sensitivity (GF = 23.8). Some flexible wearable devices like finger sleeve and wristband can be customized by photocurable 3D printing using the gel with high toughness. This high-performance gel has great application potential in flexible wearable devices.

A Bio-Inspired Multifunctional Hydrogel Network with Toughly Interfacial Chemistry for Dendrite-Free Flexible Zinc Ion Battery

Flexible and high-performance aqueous zinc-ion batteries (ZIBs), coupled with low cost and safe, are considered as one of the most promising energy storage candidates for wearable electronics. Hydrogel electrolytes present a compelling alternative to liquid electrolytes due to their remarkable flexibility and clear advantages in mitigating parasitic side reactions. However, hydrogel electrolytes suffer from poor mechanical properties and interfacial chemistry, which limits them to suppressed performance levels in flexible ZIBs, especially under harsh mechanical strains. Herein, a bio-inspired multifunctional hydrogel electrolyte network (polyacrylamide (PAM)/trehalose) with improved mechanical and adhesive properties was developed via a simple trehalose network-repairing strategy to stabilize the interfacial chemistry for dendrite-free and long-life flexible ZIBs. As a result, the trehalose-modified PAM hydrogel exhibits a superior strength and stretchability up to 100 kPa and 5338 %, respectively, as well as strong adhesive properties to various substrates. Also, the PAM/trehalose hydrogel electrolyte provides superior anti-corrosion capability for Zn anode and regulates Zn nucleation/growth, resulting in achieving a high Coulombic efficiency of 98.8 %, and long-term stability over 2400 h. Importantly, the flexible Zn//MnO2 pouch cell exhibits excellent cycling performance under different bending conditions, which offers a great potential in flexible energy-related applications and beyond.

Boosting uranium extraction from Seawater by micro-redox reactors anchored in a seaweed-like adsorbent

Efficient extraction of uranium from seawater is expected to provide virtually infinite fuel sources to power nuclear reactors and thus enable sustainable development of nuclear energy. The extraction efficiency for uranium greatly depends on the availability of active adsorption sites on the adsorbents. Maximization of the utilization rate of the binding sites in the adsorbent is vital for improving adsorption capacity. Herein, micro-redox reactors functioned by Cu(I)/Cu(II) conversion are constructed internally in an adsorbent bearing both amidoxime and carboxyl groups to induce active regeneration of the inactivated binding sites to enhance uranium capture. This adsorbent has high adsorption capacity (962.40 mg-U/g-Ads), superior anti-fouling ability as well as excellent uranium uptake (14.62 mg-U/g-Ads) in natural seawater after 56 days, placing it at the top of high-performance sorbent materials for uranium harvest from seawater.

Rapidly Gelled Lipoic Acid-Based Supramolecular Hydrogel for 3D Printing of Adhesive Bandage

Developing a strongly adhesive, easily removable, and robust bandage is valuable in trauma emergencies. Poly(lipoic acid) (PLA)-based adhesives with good mechanical properties have been well-developed through a thermal ring-opening polymerization (ROP) method that is easiness. However, the additive manufacturing of PLA-based adhesives remains a challenge. Herein, α-lipoic acid (LA) and trometamol (Tris) are found to rapidly form a supramolecular hydrogel at room temperature with injectability and 3D printing potential. Meanwhile, the synthesized LA-grafted hyaluronic acid and cellulose nanocrystals are involved not only to optimize the extrusion of 3D printing but also to effectively promote fidelity and prevent the inverse closed-loop depolymerization of PLA in water. The hydrogel bandage exhibits strong adhesion to skin while it can be removed with no residue by water flushing, showing protection to neo-tissue during dressing replacement. The in vivo application of the hydrogel bandage significantly promoted wound healing by closing the wound, forming a physical barrier, and providing an anti-inflammatory effect, showing great potential in future clinical applications.

Recent advances in hydrogel-based flexible strain sensors for harsh environment applications

Flexible strain sensors are broadly investigated in electronic skins and human-machine interaction due to their light weight, high sensitivity, and wide sensing range. Hydrogels with unique three-dimensional network structures are widely used in flexible strain sensors for their exceptional flexibility and adaptability to mechanical deformation. However, hydrogels often suffer from damage, hardening, and collapse under harsh conditions, such as extreme temperatures and humidity levels, which lead to sensor performance degradation or even failure. In addition, the failure mechanism in extreme environments remains unclear. In this review, the performance degradation and failure mechanism of hydrogel flexible strain sensors under various harsh conditions are examined. Subsequently, strategies towards the environmental tolerance of hydrogel flexible strain sensors are summarized. Finally, the current challenges of hydrogel flexible strain sensors in harsh environments are discussed, along with potential directions for future development and applications.

High-Strength, Antiswelling Directional Layered PVA/MXene Hydrogel for Wearable Devices and Underwater Sensing

Hydrogel sensors are widely utilized in soft robotics and tissue engineering due to their excellent mechanical properties and biocompatibility. However, in high-water environments, traditional hydrogels can experience significant swelling, leading to decreased mechanical and electrical performance, potentially losing shape, and sensing capabilities. This study addresses these challenges by leveraging the Hofmeister effect, coupled with directional freezing and salting-out techniques, to develop a layered, high-strength, tough, and antiswelling PVA/MXene hydrogel. In particular, the salting-out process enhances the self-entanglement of PVA, resulting in an S-PM hydrogel with a tensile strength of up to 2.87 MPa. Furthermore, the S-PM hydrogel retains its structure and strength after 7 d of swelling, with only a 6% change in resistance. Importantly, its sensing performance is improved postswelling, a capability rarely achievable in traditional hydrogels. Moreover, the S-PM hydrogel demonstrates faster response times and more stable resistance change rates in underwater tests, making it crucial for long-term continuous monitoring in challenging aquatic environments, ensuring sustained operation and monitoring.

Polyelectrolyte-Mediated Modulation of Spatial Internal Stresses of Hydrogels for Complex 3D Actuators

Hydrogel actuators with complex 3D initial shapes show numerous important applications, but it remains challenging to fabricate such actuators. This article describes a polyelectrolyte-based strategy for modulating small-scale internal stresses within hydrogels to construct complex actuators with tailored 3D initial shapes. Introducing polyelectrolytes into precursor solutions significantly enhances the volume shrinkage of hydrogel networks during polymerization, allowing us to modulate internal stresses. Photopolymerization of these polyelectrolyte-containing solutions through a mask produces mechanically strong hydrogel sheets with large patterned internal stresses. Consequently, these hydrogel sheets attain complex 3D initial shapes at equilibrium, in contrast to the planar initial configuration of 2D actuators. We demonstrate that these 3D actuators can reversibly transform into other 3D shapes (i.e., 3D-to-3D shape transformations) in response to external stimuli. Additionally, we develop a predictive model based on the Flory-Rehner theory to analyze the polyelectrolyte-mediated shrinking behaviors of hydrogel networks during polymerization, allowing precise modulation of shrinkage and internal stress. This polyelectrolyte-boosted shrinking mechanism paves a route to the fabrication of high-performance 3D hydrogel actuators.

Mechanical Regulation of Polymer Gels

The mechanical properties of polymer gels devote to emerging devices and machines in fields such as biomedical engineering, flexible bioelectronics, biomimetic actuators, and energy harvesters. Coupling network architectures and interactions has been explored to regulate supportive mechanical characteristics of polymer gels; however, systematic reviews correlating mechanics to interaction forces at the molecular and structural levels remain absent in the field. This review highlights the molecular engineering and structural engineering of polymer gel mechanics and a comprehensive mechanistic understanding of mechanical regulation. Molecular engineering alters molecular architecture and manipulates functional groups/moieties at the molecular level, introducing various interactions and permanent or reversible dynamic bonds as the dissipative energy. Molecular engineering usually uses monomers, cross-linkers, chains, and other additives. Structural engineering utilizes casting methods, solvent phase regulation, mechanochemistry, macromolecule chemical reactions, and biomanufacturing technology to construct and tailor the topological network structures, or heterogeneous modulus compositions. We envision that the perfect combination of molecular and structural engineering may provide a fresh view to extend exciting new perspectives of this burgeoning field. This review also summarizes recent representative applications of polymer gels with excellent mechanical properties. Conclusions and perspectives are also provided from five aspects of concise summary, mechanical mechanism, biofabrication methods, upgraded applications, and synergistic methodology.

Ascorbyl palmitate nanofiber-reinforced hydrogels for drug delivery in soft issues

Nanofiber-based hydrogel delivery systems have recently shown great potential in biomedical applications, specifically due to their high surface-to-volume ratio of ultra-fine nanofibers and their ability to carry low solubility drugs. Herein, we introduce a visible light-triggered in situ-gelling drug vehicle (GAP Gel) composed of ascorbyl palmitate (AP) nanofibers and gelatin methacryloyl polymer. AP nanofibers form self-assembled structures through intermolecular interactions with a hydrophobic drug-loading core. We demonstrate that the hydrophilic periphery of AP nanofibers allows them to interact with other hydrophilic molecules via hydrogen bonds. The presence of AP nanofibers significantly enhances the viscoelasticity of GAP Gel in a concentration-dependent manner. Further, GAP Gel shows in vitro biocompatibility and sustained drug delivery efficacy when loaded with a hydrophobic antibiotic. Likewise, GAP Gel shows excellent in vivo biocompatibility when implanted in immunocompetent mice in various forms. Lastly, GAP Gels maintain cell viability when cultured in a 3D-environment over 7 days, establishing it as a promising and versatile hydrogel platform for the delivery of biotherapeutics.

3D-Printed Hydrogels with Engineered Nanocrystalline Domains as Functional Vascular Constructs

Three-dimensionally printed (3DP) hydrogel-based vascular constructs have been investigated in response to the impaired function of blood vessels or organs by replicating exactly the 3D structural geometry to approach their function. However, they are still challenged by their intrinsic brittleness, which could not sustain the suture piercing and enable the long-term structural and functional stability during the direct contact with blood. Here, we reported the high-fidelity digital light processing (DLP) 3D printing of hydrogel-based vascular constructs from poly(vinyl alcohol)-based inks, followed by mechanical strengthening through engineering the nanocrystalline domains and subsequent surface modification. The as-prepared high-precision hydrogel vascular constructs were imparted with highly desirable mechanical robustness, suture tolerance, swelling resistance, antithrombosis, and long-term patency. Notably, the hydrogel-based bionic vein grafts, with precise valve structures, exhibited excellent control over the unidirectional flow and successfully fulfilled the biological functionalities and patency during a 4-week implantation within the deep veins of beagles, thus corroborating the promising potential for treating chronic venous insufficiency.

Rapid Photothermal-Responsive Soft Hydrogel Actuator Contained Ti3C2Tx MXene and Laponite Clay with Enhanced Mechanical Properties

Photothermal responsive hydrogels are widely used in bionic soft actuators due to their remote-controlled capabilities and flexibility. However, their weak mechanical properties and limited responsiveness hinder their potential applications. To overcome this, we developed an innovative laponite/MXene/PNIPAm (LxMyPN) nanocomposite hydrogel that is mechanically robust and exhibits excellent photothermally responsive properties based on abundant hydrogen bonds. Notably, laponite clay is used as a co-cross-linking agent to improve the mechanical properties of LxMyPN hydrogel, while MXene nanosheets are added to promote the photothermal responsiveness. The resulting L3M0.4PN nanocomposite hydrogel exhibits enhanced mechanical properties, with a compressive strength of 0.201 MPa, a tensile strength of 90 kPa, and a fracture toughness of 27.25 kJ m-2. In addition, the L3M0.4PN hydrogel displays a deswelling ratio of 73.6% within 60 s and experiences an excellent volume shrinkage of 82.4% under light irradiation. Furthermore, hydrogel actuators with fast response behaviors are constructed and employed as grippers capable of grasping and releasing target objects. Overall, this high-strength and fast-responsive hydrogel actuator is beneficial to paving the way for remote controlled soft robots.

Constructing Dynamic Cross-Linking Networks as Durable Bifunctional Coating for Highly Stable Zinc Anodes

The serious dendrite growth and H2O-induced side reactions on the Zn electrode lead to a significant fading in the cycling performance, hindering the development of commercial applications of aqueous Zn-ion batteries (AZIBs). Herein, a novel bifunctional network coating of dynamically cross-linking sodium alginate with trehalose has been rationally constructed on the Zn anode (Zn@AT). Firstly, the AT coating possesses abundant zinophilic oxygen-containing functional groups, which are able to induce uniform Zn2+ ion flux. Secondly, the AT coating as a solid barrier can effectively inhibit H2O-induced side reactions by lowering the activity of H2O molecules. More specially, based on the dynamic cross-linking, AT network coating is endowed with self-healing capacity during cycling for durable battery operation. Consequentially, Zn@AT anodes in symmetric cells can cycle stably for 2787 h at 2 mA cm-2/2 mAh cm-2, and even achieve a significantly long cycle performance of 1087 h at large charge/discharge depths of 10 mA cm-2/10 mAh cm-2. Moreover, the Zn@AT//MnO2 full cell shows excellent specific capacity of 175 mAh g-1 after 400 cycles. This study lights an effective strategy to enhance the durability of Zn electrodes in AZIBs.

A strategy for tough and fatigue-resistant hydrogels via loose cross-linking and dense dehydration-induced entanglements

Outstanding overall mechanical properties are essential for the successful utilization of hydrogels in advanced applications such as human-machine interfaces and soft robotics. However, conventional hydrogels suffer from fracture toughness-stiffness conflict and fatigue threshold-stiffness conflict, limiting their applicability. Simultaneously enhancing the fracture toughness, fatigue threshold, and stiffness of hydrogels, especially within a homogeneous single network structure, has proven to be a formidable challenge. In this work, we overcome this challenge through the design of a loosely cross-linked hydrogel with slight dehydration. Experimental results reveal that the slightly-dehydrated, loosely cross-linked polyacrylamide hydrogel, with an original/current water content of 87%/70%, exhibits improved mechanical properties, which is primarily attributed to the synergy between the long-chain structure and the dense dehydration-induced entanglements. Importantly, the creation of these microstructures does not require intricate design or processing. This simple approach holds significant potential for hydrogel applications where excellent anti-fracture and fatigue-resistant properties are necessary.

MXene, protein, and KCl-assisted ionic conductive hydrogels with excellent anti-freezing capabilities, self-adhesive, ultra-stretchability, and remarkable mechanical properties for a high-performance wearable flexible sensor

Developing a hydrogel with switchable features and freeze tolerance is remarkably significant for designing flexible electronics to adjust various application needs. Herein, MXenes, AFPs (antifreeze proteins), and potassium chloride (KCl) were introduced to a polyacrylamide (PAM) polymer network to design an anti-freezing hydrogel. The ionic hydrogels are characterized by excellent ionic conductivity, presenting adjustable properties of remarkable mechanical strength and self-adhesion to meet individualized application demands. The capability of KCl and AFPs to inhibit ice crystals gives hydrogels with anti-icing properties under a low-temperature atmosphere. The PAM/MXene15/AFP30/KCl15 hydrogel demonstrated negligible hysteresis behavior, quick electromechanical response (0.10 s), and excellent sensitivity (gauge factor (GF) = 13.1 within the strain range of 1200-2000%). The resulting hydrogel could be immobilized on the animal or human skin to detect different body movements and physiological motions, offering reproducibility and precise accuracy as primary advantages. The approach of developing materials with tunable features, along with inorganic salt and the fish-inspired freeze-tolerance method, offers a new prospect for wearable gadgets.

Facile preparation of fatigue-resistant Mxene-reinforced chitosan cryogel for accelerated hemostasis and wound healing

The development of highly effective chitosan-based hemostatic materials that can be utilized for deep wound hemostasis remains a considerable challenge. In this study, a hemostatic antibacterial chitosan/N-hydroxyethyl acrylamide (NHEMAA)/Ti3C2Tx (CSNT) composite cryogel was facilely prepared through the physical interactions between the three components and the spontaneous condensation of NHEMAA. Because of the formation of strong crosslinked network, the CSNT cryogel showed a developed pore structure (~ 99.07 %) and superfast water/blood-triggered shape recovery, enabling it to fill the wound after contacting the blood. Its capillary effect, amino groups, negative charges, and affinity with lipid collectively induced rapid hemostasis, which was confirmed by in vitro and in vivo analysis. In addition, CSNT cryogel showed excellent photothermal antibacterial activities, high biosafety, and in vivo wound healing ability. Furthermore, the presence of chitosan effectively prevented the oxidation of MXene, thus enabling the long-term storage of the MXene-reinforced cryogel. Thus, our hemostatic cryogel demonstrates promising potential for clinical application and commercialization, as it combines high resilience, rapid hemostasis, efficient sterilization, long-term storage, and easy mass production.

Rapidly damping hydrogels engineered through molecular friction

Hydrogels capable of swift mechanical energy dissipation hold promise for a range of applications including impact protection, shock absorption, and enhanced damage resistance. Traditional energy absorption in such materials typically relies on viscoelastic mechanisms, involving sacrificial bond breakage, yet often suffers from prolonged recovery times. Here, we introduce a hydrogel designed for friction-based damping. This hydrogel features an internal structure that facilitates the motion of a chain walker within its network, effectively dissipating mechanical stress. The hydrogel network architecture allows for rapid restoration of its damping capacity, often within seconds, ensuring swift material recovery post-deformation. We further demonstrate that this hydrogel can significantly shield encapsulated cells from mechanical trauma under repetitive compression, owing to its proficient energy damping and rapid rebound characteristics. Therefore, this hydrogel has potential for dynamic load applications like artificial muscles and synthetic cartilage, expanding the use of hydrogel dampers in biomechanics and related areas.

A Short-Range Ordered α-MoO3 with Modulated Interlayer Structure via Hydrogen Bond Chemistry for NH4 + Storage

The layered orthorhombic molybdenum trioxide (α-MoO3) is a promising host material for NH4 + storage. But its electrochemical performances are still unsatisfactory due to the absence of fundamental understanding on the relationship between structure and property. Herein, NH4 + storage properties of α-MoO3 are elaborately studied. Electrochemistry together with ex situ physical characterizations uncover that irreversible H+/NH4 + co-intercalation in the initial cycle confines the electrochemically reactive domain to the near surface of α-MoO3 thus resulting in a low reversible NH4 + storage capacity. This issue can be resolved by decreasing ion diffusion pathway to construct short-range ordered α-MoO3 (SMO), which improves the specific capacity to 185 mAh g-1. SMO suffers from dissolution issue. In view of this the interlayer structure of SMO is reconstructed via hydrogen bond chemistry to reinforce the structural stability and it is discovered that the hydrogen bond network only with moderate intensity endows SMO with both high capacity and ability against dissolution. This work presents a new avenue to improve the NH4 + storage properties of α-MoO3 and highlights the important role of hydrogen bond intensity in optimizing electrochemical properties.

Dehydration-Toughing Dual-Solvent Gels with Viscoelastic Transition for Infectious Wound Treatment

The modulus of traditional biomedical hydrogels increases exponentially meditated by dehydration-stiffing mechanism, which leads to the failure of interface matching between hydrogels and soft tissue wounds. It is found in the study that the dual-solvent gels exhibit dehydration-toughening mechanism with the slowly increasing modulus that are always match the soft tissue wounds. Therefore, dual-solvent glycerol hydrogels (GCFen-gly DGHs) are prepared with hydrophobically modified catechol chitosan (hmCSC) and gelatin based on the supramolecular interactions. GCFen-gly DGHs exhibit excellent water retention capacity with a total solvent content exceeding 80%, permanent skin-like modulus within a range of 0.45 to 4.13 kPa, and stable photothermal antibacterial abilities against S, aureus, E. coli, as well as MRSA. Infectious full-thickness rat skin defect model and tissue section analysis indicate that GCFen-gly DGHs are able to accelerate infectious wound healing by alleviating the inflammatory response, promoting granulation tissue growth, re-epithelialization, collagen deposition, and vascular regeneration. As a result, GCFen-gly DGHs is expected to become the next-generation biological gel materials for infectious wound treatment.

Herbal Products-Powered Thermosensitive Hydrogel with Phototherapy and Microenvironment Reconstruction for Accelerating Multidrug-Resistant Bacteria-Infected Wound Healing

Wound healing and infection remain significant challenges due to the ineffectiveness against multidrug-resistant (MDR) bacteria and the complex oxidative wound microenvironments. To address these issues, thymoquinone-reinforced injectable and thermosensitive TQ@PEG-PAF-Cur hydrogels with dual functions of microenvironment reshaping and photodynamic therapy are developed. The hydrogel comprises natural compound thymoquinone (TQ) and poly (ethylene glycol)-block-poly (alanine-co-phenyl alanine) copolymers (PEG-PAF) conjugated with natural photosensitizer curcumin (Cur). The incorporation of TQ and Cur reduces the sol-to-gel transition temperature of TQ@PEG-PAF-Cur to 30°C, compared to PEG-PAF hydrogel (37°C), due to the formation of strong hydrogen bonding, matching the wound microenvironment temperature. Under blue light excitation, TQ@PEG-PAF-Cur generates significant amounts of reactive oxygen species such as H2O2, 1O2, and ·OH, exhibiting rapid and efficient bactericidal capacities against methicillin-resistant Staphylococcus aureus and broad spectrum β-lactamases Escherichia coli via photodynamic therapy (PDT). Additionally, Cur effectively inhibits the expressions of proinflammatory cytokines in skin tissue-forming cells. As a result, the composite hydrogel can rapidly transform into a gel to cover the wound, reshape the wound microenvironment, and accelerate wound healing in vivo. This collaborative antibacterial strategy provides valuable insights to guide the development of multifunctional materials for efficient wound healing.

Bioinspired Mechanically Robust and Recyclable Hydrogel Microfibers Based on Hydrogen-Bond Nanoclusters

Mechanically robust hydrogel fibers have demonstrated great potential in energy dissipation and shock-absorbing applications. However, developing such materials that are recyclable, energy-efficient, and environmentally friendly remains an enormous challenge. Herein, inspired by spider silk, a continuous and scalable method is introduced for spinning a polyacrylamide hydrogel microfiber with a hierarchical sheath-core structure under ambient conditions. Applying pre-stretch and twist in the as-spun hydrogel microfibers results in a tensile strength of 525 MPa, a toughness of 385 MJ m-3, and a damping capacity of 99%, which is attributed to the reinforcement of hydrogen-bond nanoclusters within the microfiber matrix. Moreover, it maintains both structural and mechanical stability for several days, and can be directly dissolved in water, providing a sustainable spinning dope for re-spinning into new microfibers. This work provides a new strategy for the spinning of robust and recyclable hydrogel-based fibrous materials.

Strongly plasticized gelatin-based hydrogel for flexible encapsulation of complex-shaped electronic devices

The growth of environmentally sensitive complex-shaped electronic devices (ECEDs) has led to a surging demand for flexible electromagnetic wave (EMW) absorbers. Herein, the water loss property of hydrogel was ingeniously applied for the flexible encapsulation (FE) of ECEDs. To be specific, saturated state (SGT) hydrogels were prepared by chemical cross-linking, and the hydrogen bond dissipation network promoted FE. Additionally, SGT has an effective absorption bandwidth (EAB) of 6.04 GHz at 1.65 mm due to the presence of dipole polarization. With the loss of water, SGT transitions to its natural state (NGT), and the decreasing conductivity leads to better impedance matching. NGT exhibited a broader EAB (9.20 GHz at 2.65 mm) and also strength and lightness (density of 0.3 g cm-3). Furthermore, the semi-automatic reversible cyclic transformation between SGT and NGT gels further broadens application scenarios. GT gel combines self-encapsulation and self-optimized performance as a potential EMW absorber for FE.

Self-healing, environmentally stable and adhesive hydrogel sensor with conductive cellulose nanocrystals for motion monitoring and character recognition

Conductive hydrogel-based sensors offer diverse applications in artificial intelligence, wearable electronic devices and character recognition management. However, it remains a significant challenge to maintain their satisfactory performances under extreme climatic conditions. Herein, a stretchable, self-adhesive, self-healing and environmentally stable conductive hydrogel was developed through free radical polymerization of hydroxyethyl acrylate (HEA) and poly(ethylene glycol) methacrylate (PEG) as the skeleton, followed by the incorporation of polyaniline-coated cellulose nanocrystal (CNC@PANI) as the conductive and reinforced nanofiller. Encouragingly, the as-prepared hydrogel (CHP) exhibited decent mechanical strength, satisfactory self-adhesion, prominent self-healing property (95.04 % after 60 s), excellent anti-freezing performance (below -60 °C) and outstanding moisture retention. The assembled sensor derived from CHP hydrogel possessed a low detection limit (0.5 % strain), high strain sensitivity (GF = 1.68) and fast response time (96 ms). Remarkably, even in harsh environmental temperatures from -60 °C to 80 °C, it reliably detected subtle and large-scale human motion for a long-term process (>10,000 cycles), manifesting its exceptional environmental tolerance. More interestingly, this hydrogel-based sensor could be assembled into a "writing board" for accurate handwritten numeral recognition. Therefore, the as-obtained multifunctional hydrogel could be a promising material applied in human motion detection and character recognition platforms even in harsh surroundings.

Lysine-Triggered Polymeric Hydrogels with Self-Adhesion, Stretchability, and Supportive Properties

Hydrogels, recognized for their flexibility and diverse characteristics, are extensively used in medical fields such as wearable sensors and soft robotics. However, many hydrogel sensors derived from biomaterials lack mechanical strength and fatigue resistance, emphasizing the necessity for enhanced formulations. In this work, we utilized acrylamide and polyacrylamide as the primary polymer network, incorporated chemically modified poly(ethylene glycol) (DF-PEG) as a physical crosslinker, and introduced varying amounts of methacrylated lysine (LysMA) to prepare a series of hydrogels. This formulation was labeled as poly(acrylamide)-DF-PEG-LysMA, abbreviated as pADLx, with x denoting the weight/volume percentage of LysMA. We observed that when the hydrogel contained 2.5% w/v LysMA (pADL2.5), compared to hydrogels without LysMA (pADL0), its stress increased by 642 ± 76%, strain increased by 1790 ± 95%, and toughness increased by 2037 ± 320%. Our speculation regarding the enhanced mechanical performance of the pADL2.5 hydrogel revolves around the synergistic effects arising from the co-polymerization of LysMA with acrylamide and the formation of multiple intermolecular hydrogen bonds within the network structures. Moreover, the acid, amine, and amide groups present in the LysMA molecules have proven to be instrumental contributors to the self-adhesion capability of the hydrogel. The validation of the pADL2.5 hydrogel's exceptional mechanical properties through rigorous tensile tests further underscores its suitability for use in strain sensors. The outstanding stretchability, adhesive strength, and fatigue resistance demonstrated by this hydrogel affirm its potential as a key component in the development of robust and reliable strain sensors that fulfill practical requirements.

Carboxymethyl cellulose and metal-organic frameworks immobilized into polyacrylamide hydrogel for ultrahigh efficient and selective adsorption U(VI) from seawater

Metal-organic frameworks (MOF)-polymer hybrid hydrogel solves the processable forming of MOF powder and energy consumption of uranium extraction. However, the hybrid hydrogel by conventional synthesis methods inevitably lead to MOF agglomeration, poor filler-polymer interfacial compatibility and slowly adsorption. Herein, we designed that ZIF-67 was implanted into the carboxymethyl cellulose/polyacrylamide (CMC/PAM) by network-repairing strategy. The carboxyl and amino groups on the surface of CMC/PAM drive the uniform growth of ZIF-67 inside the CMC/PAM, which form an array of oriented and penetrating microchannels through coordination bonds. Our strategy eliminate the ZIF-67 agglomeration, increase the interfacial compatibility between MOF and polymer. The method also improve the free and fast diffusion of uranium in CMC/PAM/ZIF-67 hydrogel. According to the experimental, these enhancements synergistically enabled the CMC/PAM/ZIF-67 have a maximum adsorption capacity of 952 mg g-1. The adsorption process of CMC/PAM/ZIF-67 fits well with pseudo-second-order model and Langmuir isotherm. Meanwhile, the CMC/PAM/ZIF-67 maintain a high removal rate (87.3 %) and chemical stability even during ten adsorption-desorption cycles. It is worth noting that the adsorption amount of CMC/PAM/ZIF-67 in real seawater is 9.95 mg g-1 after 20 days, which is an ideal candidate adsorbent for uranium extraction from seawater.

Anti-Freezing and Ultrasensitive Zwitterionic Betaine Hydrogel-Based Strain Sensor for Motion Monitoring and Human-Machine Interaction

Ultrasensitive and reliable conductive hydrogels are significant in the construction of human-machine twinning systems. However, in extremely cold environments, freezing severely limits the application of hydrogel-based sensors. Herein, building on biomimetics, a zwitterionic hydrogel was elaborated for human-machine interaction employing multichemical bonding synergies and experimental signal analyses. The covalent bonds, hydrogen bonds, and electrostatic interactions construct a dense double network structure favorable for stress dispersion and hydrogen bond regeneration. In particular, zwitterions and ionic conductors maintained excellent strain response (99 ms) and electrical sensitivity (gauge factor = 14.52) in the dense hydrogel structure while immobilizing water molecules to enhance the weather resistance (-68 °C). Inspired by the high sensitivity, zwitterionic hydrogel-based strain sensors and remote-control gloves were designed by analyzing the experimental signals, demonstrating promising potential applications within specialized flexible materials and human-machine symbiotic systems.

Hydrogen Bonds-Pinned Entanglement Blunting the Interfacial Crack of Hydrogel-Elastomer Hybrids

Anchoring a layer of amorphous hydrogel on an antagonistic elastomer holds potential applications in surface aqueous lubrication. However, the interfacial crack propagation usually occurs under continuous loads for amorphous hydrogel, leading to the failure of hydrogel interface. This work presents a universal strategy to passivate the interfacial cracks by designing a hydrogen bonds-pinned entanglement (Hb-En) structure of amorphous hydrogel on engineering elastomers. The unique Hb-En structure is created by pinning well-tailored entanglements via covalent-like hydrogen bonds, which can amplify the delocalization of interfacial stress concentration and elevate the necessary fracture energy barrier within hydrogel interface. Therefore, the interfacial crack propagation can be suppressed under single and cyclic loads, resulting in a high interfacial toughness over 1650 J m-2 and an excellent interfacial fatigue threshold of 423 J m-2. Such a strategy universally works on blunting the interfacial crack between hydrogel coating and various elastomer materials with arbitrary shapes. The superb fatigue-crack insensitivity at the interface allows for durable aqueous lubrication of hydrogel coating with low friction.