Graphene Hybrid Tough Hydrogels with Nanostructures for Tissue Regeneration.

Over the past few decades, hydrogels have attracted considerable attention as promising biomedical materials. However, conventional hydrogels require improved mechanical properties, such as brittleness, which significantly limits their widespread use. Recently, hydrogels with remarkably improved toughness have been developed; however, their low biocompatibility must be addressed. In this study, we developed a tough graphene hybrid hydrogel with nanostructures. The resultant hydrogel exhibited remarkable mechanical properties while representing an aligned nanostructure that resembled the extracellular matrix of soft tissue. Owing to the synergistic effect of the topographical properties, and the enhanced biochemical properties, the graphene hybrid hydrogel had excellent stretchability, resilience, toughness, and biocompatibility. Furthermore, the hydrogel displayed outstanding tissue regeneration capabilities (e.g., skin and tendons). Overall, the proposed graphene hybrid tough hydrogel may provide significant insights into the application of tough hydrogels in tissue regeneration.

Engineering Tough Supramolecular Hydrogels with Structured Micropillars for Tunable Wetting and Adhesion Properties.

Soft-lithography is widely used to fabricate microstructured surfaces on plastics and elastomers for designable physical properties such as wetting and adhesions. However, it remains a big challenge to construct high-aspect-ratio microstructures on the surface of hydrogels due to the difficulty in demolding from the gel with low strength and stiffness. Demonstrated here is the engineering of tough hydrogels by soft-lithography to form well-defined micropillars. The mechanical properties of poly(acrylamide-co-methacrylic acid) hydrogels with dense hydrogen-bond associations severely depend on temperature, with Young's modulus increasing from 8.1 MPa at 15 °C to 821.8 MPa at -30 °C, enabling easy demolding at low temperatures. Arrays of micropillars are maintained on the surface of the gel, and can be used at room temperature when the gel restores soft and stretchable. The hydrogel also exhibits good shape-memory property, favoring tailoring the morphology with a switchable tilt angle of micropillars. Consequently, the hydrogel shows tunable wetting and adhesion properties, as manifested by varying contact angles and adhesion strengths. These surface properties can also be tuned by geometry and arrangement of micropillars. This facile strategy by harnessing tunable viscoelasticity of supramolecular hydrogels should be applicable to other soft materials, and broaden their applications in biomedical and engineering fields.

Biomimetic Transparent Layered Tough Aerogels for Thermal Superinsulation and Triboelectric Nanogenerator.

Transparent aerogels are ideal candidates for thermally insulating windows, solar thermal receivers, electronics, etc. However, they are usually prepared via energy-consuming supercritical drying and show brittleness and low tensile strength, significantly restricting their practical applications. It remains a great challenge to prepare transparent aerogels with high tensile strength and toughness. Herein, biomimetic transparent tough cellulose nanofiber-based nanocomposite aerogels with a layered nanofibrous structure are achieved by vacuum-assisted self-assembly combined with ambient pressure drying. The nacre-like layered homogeneous nanoporous structures can reduce light scattering and effectively transfer stress and prevent stress concentration under external forces. The aerogels exhibit an attractive combination of excellent transparency and hydrophobicity, high compressive and tensile strengths, high toughness, excellent machinability, thermal superinsulation, and wide working temperature range (-196 to 230 °C). It is demonstrated that they can be used for superinsulating windows of buildings and high-efficient thermal management for electronics and human bodies. In addition, a prototype of transparent flexible aerogel-based triboelectric nanogenerator is developed. This work provides a promising pathway toward transparent tough porous materials for energy saving/harvesting, thermal management, electronics, sensors, etc.

Autonomous Underwater Self-Healable Adhesive Elastomers Enabled by Dynamical Hydrophobic Phase-Separated Microdomains.

High-efficient underwater self-healing materials with reliable mechanical attributes hold great promise for applications in ocean explorations and diverse underwater operations. Nevertheless, achieving these functions in aquatic environments is challenging because the recombination of dynamic interactions will suffer from resistance to interfacial water molecules. Herein, an ultra-robust and all-environment stable self-healable polyurethane-amide supramolecular elastomer is developed through rational engineering of hydrophobic domains and multistrength hydrogen bonding interactions to provide mechanical and healing compatibility as well as efficient suppression of water ingress. The coupling of hydrophobic chains and hierarchical hydrogen bonds within a multiphase matrix self-assemble to generate dynamical hydrophobic hard-phase microdomains, which synergistically realize high stretchability (1601%), extreme toughness (87.1 MJ m-3), and outstanding capability to autonomous self-healing in various harsh aqueous conditions with an efficiency of 58% and healed strength of 12.7 MPa underwater. Furthermore, the self-aggregation of hydrophobic clusters with sufficient dynamic interactions endows the resultant elastomer with effective instantaneous adhesion (6.2 MPa, 941.9 N m-1) in extremely harsh aqueous conditions. It is revealed that the dynamical hydrophobic hard-phase microdomain composed of hydrophobic barriers and cooperative reversible interactions allows for regulating its mechanical enhancement and underwater self-healing efficiency, enabling the elastomers as intelligent sealing devices in marine applications.

A Near-Infrared Photothermal-Responsive Underwater Adhesive with Tough Adhesion and Antibacterial Properties.

Developing tunable underwater adhesives that possess tough adhesion in service and easy detachment when required remains challenging. Herein, a strategy is proposed to design a near infrared (NIR) photothermal-responsive underwater adhesive by incorporating MXene (Ti3C2Tx)-based nanoparticles within isocyanate-modified polydimethylsiloxane (PDMS) polymer chains. The developed adhesive exhibits long-term and tough adhesion with an underwater adhesion strength reaching 5.478 MPa. Such strong adhesion is mainly attributed to the covalent bonds and hydrogen bonds at the adhesive-substrate interface. By making use of the photothermal-response of MXene-based nanoparticles and the thermal response of PDMS-based chains, the adhesive possesses photothermal-responsive performance, exhibiting sharply diminished adhesion under NIR irradiation. Such NIR-triggered tunable adhesion allows for easy and active detachment of the adhesive when needed. Moreover, the underwater adhesive exhibits photothermal antibacterial property, making it highly desirable for underwater applications. This work enhances the understanding of photothermal-responsive underwater adhesion, enabling the design of tunable underwater adhesives for biomedical and engineering applications.

A Shape Memory Hydrogel with Excellent Mechanical Properties, Water Retention Capacity, and Tunable Fluorescence for Dual Encryption.

Information encryption platforms with reliable encryption performance, excellent mechanical performance, and high water retention capacity are highly desired. In this study, a tough double-network hydrogel is designed using the first network of a polyion complex containing lanthanide complexes via one-pot polymerization and the second network of a poly (N-hydroxyethyl acrylamide) (PHEAA) obtained by deep eutectic solvent (DES)-assisted introduction and subsequent photopolymerization. In this system, the pH-induced shape memory function and pH-/wavelength-dependent fluorescence allow the use of the prepared hydrogel as a dual-encryption platform. Owing to its high response reversibility, the hydrogel-based platform exhibits both a high security level and the advantages of rewritability, reprogrammability, and reusability. Additionally, the excellent mechanical properties and water retention capacity owing to the solvent exchange process involving the low-volatility solvent DES and the resulting introduction of the second network of PHEAA offer high practical application value for the hydrogel-based dual encryption platform, demonstrating its potential for information security protection.

Super-Strong, Super-Stiff, and Super-Tough Fluorescent Alginate Fibers with Outstanding Tolerance to Extreme Conditions.

The combination of multiple physical properties is of great importance for widening the application scenarios of biomaterials. It remains a great challenge to fabricate biomolecules-based fibers gaining both mechanical strength and toughness which are comparable to natural spider dragline silks. Here, by mimicking the structure of dragline silks, a high-performance fluorescent fiber Alg-TPEA-PEG is designed by non-covalently cross-linking the polysaccharide chains of alginate with AIEgen-based surfactant molecules as the flexible contact points. The non-covalent cross-linking network provides sufficient energy-dissipating slippage between polysaccharide chains, leading to Alg-TPEA-PEG with highly improved mechanical performances from the plastic strain stage. By successfully transferring the extraordinary mechanical performances of polysaccharide chains to macroscopic fibers, Alg-TPEA-PEG exhibits an outstanding breaking strength of 1.27 GPa, Young's modulus of 34.13 GPa, and toughness of 150.48 MJ m-3, which are comparable to those of dragline silk and outperforming other artificial materials. More importantly, both fluorescent and mechanical properties of Alg-TPEA-PEG can be well preserved under various harsh conditions, and the fluorescence and biocompatibility facilitate its biological and biomedical applications. This study affords a new biomimetic designing strategy for gaining super-strong, super-stiff, and super-tough fluorescent biomaterials.

Rapid Preparation Triggered by Visible Light for Tough Hydrogel Sensors with Low Hysteresis and High Elasticity: Mechanism, Use and Recycle-by-Design.

Hydrogels have emerged as promising candidates for flexible devices and water resource management. However, further applications of conventional hydrogels are restricted due to their limited performance and lack of a recycling strategy. Herein, a tough, flexible, and recyclable hydrogel sensor via a visible-light-triggered polymerization is rapidly created. The Zn2+ crosslinked terpolymer is in situ polymerized using g-C3N4 as the sole initiator to form in situ chain entanglements, endowing the hydrogels with low hysteresis and high elasticity. In the use phase, the hydrogel sensor exhibited high ion conductivity, excellent mechanical properties, fast responsiveness, high sensitivity, and remarkable anti-fatigue ability, making it exceptionally effective in accurately monitoring complex human movements. At the end-of-life (EOL), leveraging the synergy between the photodegradation capacity of g-C3N4 and the adsorption function of the hydrogel matrix, the post-consumer hydrogel is converted into water remediation materials, which not only promoted the rapid degradation of organic pollutants, but also facilitated collection and reuse. This innovative strategy combined in situ entangling reinforcement and tailored recycle-by-design that employed g-C3N4 as key blocks in the hydrogel to achieve high performance in the use phase and close the loop through the reutilization at EOL, highlighting the cost-effective synthesis, specialized structure, and life cycle management.

Elastomer Particle Monolayers Formed by the Compression of Poly(methyl acrylate) Microparticles at an Air/Water Interface.

In the previous study (Green Chem., 2023, 25, 3418), highly stretchable and mechanically tough poly(methyl acrylate) (pMA) microparticle-based elastomers can be formed by drying a microparticle-containing aqueous dispersion. This discovery has the potential to overcome the mechanical weakness of industrially produced aqueous latex films. However, in 3D-arranged particle films, structural complexity, such as the existence of defects, makes it difficult to clearly understand the relationship between the particle film structure and its mechanical properties. In this study, 2D-ordered pMA particle monolayers at the air/water interface of a Langmuir trough are prepared. Under high compression at the air/water interface, the microparticles contact their neighboring particles, and the resulting monolayers can be successfully transferred onto a solid substrate. The compression of the monolayer films is linked to an increase in the elastic modulus of the monolayer film on the solid substrate as evident from the local Young's modulus mapping using atomic force microscopy. Thus, pMA particle films with different mechanical properties can be created using a Langmuir trough.

Mechanically Robust and Electrically Conductive Hybrid Hydrogel Electrolyte Enabled by Simultaneous Dual In Situ Sol-Gel Technique and Free Radical Copolymerization.

Mechanically robust and ionically conductive hydrogels poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonate-lithium)/TiO2/SiO2 (P(AM-co-AMPSLi)/TiO2/SiO2) with inorganic hybrid crosslinking are fabricated through dual in situ sol-gel reaction of vinyltriethoxysilane (VTES) and tetrabutyl titanate (TBOT), and in situ radical copolymerization of acrylamide (AM), 2-acrylamide-2-methylpropanesulfonate-lithium (AMPSLi), and vinyl-SiO2. Due to the introduction of the sulfonic acid groups and Li+ by the reaction of AMPS with Li2CO3, the conductivity of the ionic hydrogel can reach 0.19 S m-1. Vinyl-SiO2 and nano-TiO2 are used in this hybrid hydrogel as both multifunctional hybrid crosslinkers and fillers. The hybrid hydrogels demonstrate high tensile strength (0.11-0.33 MPa) and elongation at break (98-1867%), ultrahigh compression strength (0.28-1.36 MPa), certain fatigue resistance, self-healing, and self-adhesive properties, which are due to covalent bonds between TiO2 and SiO2, as well as P(AM-co-AMPSLi) chains and SiO2, and noncovalent bonds between TiO2 and P(AM-co-AMPSLi) chains, as well as the organic frameworks. Furthermore, the specific capacitance, energy density, and power density of the supercapacitors based on ionic hybrid hydrogel electrolytes are 2.88 F g-1, 0.09 Wh kg-1, and 3.07 kW kg-1 at a current density of 0.05 A g-1, respectively. Consequently, the ionic hybrid hydrogels show great promise as flexible energy storage devices.

Molecular mechanism of abnormally large nonsoftening deformation in a tough hydrogel.

Tough soft materials usually show strain softening and inelastic deformation. Here, we study the molecular mechanism of abnormally large nonsoftening, quasi-linear but inelastic deformation in tough hydrogels made of hyperconnective physical network and linear polymers as molecular glues to the network. The interplay of hyperconnectivity of network and effective load transfer by molecular glues prevents stress concentration, which is revealed by an affine deformation of the network to the bulk deformation up to sample failure. The suppression of local stress concentration and strain amplification plays a key role in avoiding necking or strain softening and endows the gels with a unique large nonsoftening, quasi-linear but inelastic deformation.

Biomimetic Ultratough, Strong, and Ductile Artificial Polymer Fiber Based on Immovable and Slidable Cross-links.

It remains a challenge to artificially fabricate fibers with the macroscopic mechanical properties and characteristics of spider silk. Herein, a covalently cross-linked double-network strategy was proposed to disrupt the inverse relation of strength and toughness in the fabrication of ultratough and superstrong artificial polymer fibers. Our design utilized a strong fishnet-like structure based on immovable cellulose nanocrystal cross-links to mimic the function of the ß-sheet nanocrystallites and a slidable mechanically interlocked network based on polyrotaxane to imitate the dissipative stick-slip motion of the ß-strands in spider silk. The resultant fiber exhibited superior mechanical properties, including gigapascal tensile strength, a ductility of over 60%, and a toughness exceeding 420 MJ/m3. The fibers also showed robust biological functions similar to those of spider silks, demonstrating mechanical enhancement, energy absorption ability, and shape memory. A composite with our artificial fibers as reinforcing fibers exhibited remarkable tear and fatigue resistance.

Scale-Spanning Strong Adhesion Using Cellulose-Based Microgels.

Adhesive gels derived from biobased sustainable materials have extremely broad application prospects, such as in flexible smart materials and biomedicine fields. Combining high toughness and strong, persisting repeatable adhesion has always been a daunting challenge for adhesive gels. However, bulk gels based on polysaccharides as the most abundant bio-based compounds usually possess a high toughness but weak interfacial adhesion due to the strong hydration potential. Herein, a novel kind of highly tough microgel membranes with rough surfaces is fabricated using loosely chemically cross-linked dihydroxypropyl cellulose (cDHPC) microgels (average size = 1.25 ± 0.03 µm). Such microgel membranes exhibit strong, instant, and persisting adhesion to various substrates with different surface roughness. Slight chemical cross-linking and multiple physical interactions within microgels and resulting microgel membranes lead to high tensile strength and toughness of 0.23 ± 0.03 MPa and 73.8 ± 9.3 KJ m-3 , respectively. The maximum adhesive strength and debonding work exceed 320 ± 0.50 KPa and 160.97 ± 0.20 J m-2 , respectively. After five cycles (re-lap after detaching), the adhesive strength still remains above 200 KPa. Their adhesive properties outperform most bio-based adhesive gels and even petroleum-based gels, which are based on synergistic molecular and microscaled topological interactions.

Strong, Tough, and Anti-Swelling Supramolecular Conductive Hydrogels for Amphibious Motion Sensors.

Conductive polymer hydrogels (CPHs) are widely employed in emerging flexible electronic devices because they possess both the electrical conductivity of conductors and the mechanical properties of hydrogels. However, the poor compatibility between conductive polymers and the hydrogel matrix, as well as the swelling behavior in humid environments, greatly compromises the mechanical and electrical properties of CPHs, limiting their applications in wearable electronic devices. Herein, a supramolecular strategy to develop a strong and tough CPH with excellent anti-swelling properties by incorporating hydrogen, coordination bonds, and cation-π interactions between a rigid conducting polymer and a soft hydrogel matrix is reported. Benefiting from the effective interactions between the polymer networks, the obtained supramolecular hydrogel has homogeneous structural integrity, exhibiting remarkable tensile strength (1.63 MPa), superior elongation at break (453%), and remarkable toughness (5.5 MJ m-3 ). As a strain sensor, the hydrogel possesses high electrical conductivity (2.16 S m-1 ), a wide strain linear detection range (0-400%), and excellent sensitivity (gauge factor = 4.1), sufficient to monitor human activities with different strain windows. Furthermore, this hydrogel with high swelling resistance has been successfully applied to underwater sensors for monitoring frog swimming and underwater communication. These results reveal new possibilities for amphibious applications of wearable sensors.

Ultra-Tough Waterborne Polyurethane-Based Graft-Copolymerized Piezoresistive Composite Designed for Rehabilitation Training Monitoring Pressure Sensors.

Effective training is crucial for patients who need rehabilitation for achieving optimal recovery and reducing complications. Herein, a wireless rehabilitation training monitoring band with a highly sensitive pressure sensor is proposed and designed. It utilizes polyaniline@waterborne polyurethane (PANI@WPU) as a piezoresistive composite material, which is prepared via the in situ grafting polymerization of PANI on the WPU surface. WPU is designed and synthesized with tunable glass transition temperatures ranging from -60 to 0 °C. Dipentaerythritol (Di-PE) and ureidopyrimidinone (UPy) groups are introduced, endowing the material with good tensile strength (14.2 MPa), toughness (62 MJ-1 m-3 ), and great elasticity (low permanent deformation: 2%). Di-PE and UPy enhance the mechanical properties of WPU by increasing the cross-linking density and crystallinity. Combining the toughness of WPU and the high-density microstructure derived by hot embossing technology, the pressure sensor exhibits high sensitivity (168.1 kPa-1 ), fast response time (32 ms), and excellent stability (10 000 cycles with 3.5% decay). In addition, the rehabilitation training monitoring band is equipped with a wireless Bluetooth module, which can be easily applied to monitor the rehabilitation training effect of patients using an applet. Therefore, this work has the potential to significantly broaden the application of WPU-based pressure sensors for rehabilitation monitoring.

Toughening Hydrogels by Forming Robust Hydrazide-Transition Metal Coordination Complexes.

Energy dissipation based on dynamic fracture of metal ligands is an effective way to toughen hydrogels for specific applications in biomedical and engineering fields. Exploration of new kinds of metal-ligand coordinates with robust bonding strength is crucial for the facile synthesis of tough gels. Here a hydrogel toughening strategy based on the formation of robust coordination complexes between the hydrazide ligands and zinc ions is reported. The resultant hydrogels exhibit high strength and toughness at room temperature. Their mechanical properties show temperature dependence due to the dynamic nature of coordination bonds. In addition, the amine group of hydrazides in the gel matrix provides a reactive site for Schiff's base reaction, enabling surface modification without influence on overall mechanical performances of the gel. The hydrazide ligands are easy to synthesize and can coordinate very well with several transition metals. Such a metal-ligand coordination should be suitable to develop tough soft materials with versatile applications.

Nanoparticle-Reinforced Tough Hydrogel as a Versatile Platform for Pharmaceutical Drug Delivery: Preparation and in Vitro Characterization.

Natural polymer-based hydrogels are excellent for encapsulating hydrophilic drugs, but they are mechanically weak and degrade easily. In this communication, we exploit the electrostatic interaction between nanosilicates (nSi) and gelatin methacrylate (GelMA) to form a mechanically tough nanocomposite hydrogel for pharmaceutical drug delivery. These hydrogels, prepared at subzero temperatures to form cryogels, displayed macroporous structures, which favors cell infiltration. The designed tough cryogel also showed a slower rate of degradation. Furthermore, we encapsulated the small molecule metformin and sustained the drug release under physiological conditions. Cryogel-loaded metformin reduced the effect of endothelial cell injury caused by nutrient deprivation in vitro. Finally, we hypothesize that this versatile nanocomposite material will find use in diverse biomedical applications.

The effects of Yakson touch and gentle human touch on preterm infants: A systematic review and meta-analysis.

We aim to collect the evidence of efficacy of Gentle Guman Touch (GHT) and Yakson Touch in preterm neonates as pain relief, heart rate, oxygen saturation, and urine cortisol level. We made our search through PubMed, Web of Science, Scopus, and Cochrane by the mid of March 2023. Randomized control trials (RCTs) were included, and the Cochrane risk of bias tool was utilized to assess their quality. Using Review Manager software, a meta-analysis was conducted. We computed the mean difference (MD) with a 95% confidence interval (CI) for the continuous data. During the examination, the Neonatal Infant Pain Scale (NIPS) was significantly reduced in the touch group compared to the control group (MD = -3.40, 95% CI [-4.15 to -2.64], P-value= 0.00001). After the examination, the NIPS score was also reduced by both Yakson touch and GHT compared to the control (MD = -2.14, 95% CI [-3.42 to -0.85], P-value <0.00001). Yakson touch and GHT are non-pharmacological, easy, and safe methods that can be used for painful interventions to reduce the pain experience of preterm infants from variable interventions. Both methods improved infant sleep and behavior. Preterm infants' heart rates and oxygen saturation were unaffected by Yakson touch or GHT.

What do you bring to the table? Exploring psychological attributes that predict successful military training.

The psychological characteristics that new recruits bring when starting military basic training (MBT) may help or hinder successful completion rates. The first part of this study explores how psychological characteristics assessed at the start of MBT influence retention and performance outcomes upon completion. At the start and upon completing MBT, a sample of 204 UK male Infantry recruits undergoing a 26-week Combat Infantryman's Course were assessed on personality traits (psychoticism, neuroticism, and extroversion); a set of relevant cognitions (i.e. effortful control); motivation (i.e. internalization of military core values); and an assessment of mentally tough behavior. Recruits who successfully completed MBT were significantly higher in age, psychoticism, and mentally tough behavior. The second part of the study explored how MBT influenced these variables across time. A subsample of 132 male Infantry recruits that passed basic military training first time were analyzed. Across the 26-week course, there was a significant increase in extraversion, and a significant decrease in neuroticism, and external regulation. Results differed slightly when we removed the lowest passing group from the analysis and whether MANOVA or Logistic Regression analysis was used. Results indicate that what you bring to the table will influence pass and retention rates.

Gangs, violence, and fear: punitive Darwinism in El Salvador.

This article evaluates the factors impacting support for tough on crime policies in El Salvador. Examining theoretical and empirical scholarly work, we look at how fear, together with social and political contexts drive public appetite for punitive policies towards criminals. We show that President Nayib Bukele is responding to public opinion and has implemented tough on crime policies at the expense of human rights violations and democratic institutions. Society favors candidates who are the "toughest" against criminal actors. Political candidates from all sides of the ideological spectrum tap into the fear of the populace to win votes, leading to punitive Darwinism. We provide an empirical assessment of which theoretically relevant factors are statistically associated with punitivism in the Salvadoran context, using multiple regression analysis of high-quality public opinion survey data from LAPOP.