Dual Physically Cross-Linked Hydrogels Incorporating Hydrophobic Interactions with Promising Repairability and Ultrahigh Elongation

Novel dual physically cross-linked (DPC) hydrogels with great tensile strength, ultrahigh elongation, and promising repairability are designed by introducing cellulose nanocrystal (CNC) or hydrophobized CNC (CNC-C8) into polymers physically cross-linked by hydrophobic forces. C18 alkyl chain is grafted to N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) for hydrophobic monomer (DMAPMA-C18), and C8 to CNC surface for hydrophobic CNC (CNC-C8). CNC-C8 (or CNC) DPC hydrogels are synthesized, with monomers N,N-dimethylacrylamide (DMAc) and DMAPMA-C18 polymerized to form the first network physically cross-linked by hydrophobic interactions, on which the secondary cross-linking points are formed by hydrophobic interactions between CNC-C8 and DMAPMA-C18, electrostatic interactions between CNC-C8 (or CNC) and DMAPMA, as well as hydrogen bonding between CNC-C8 (or CNC) and DMAc. Compared with optimum CNC DPC hydrogels of the highest tensile strength (238 ± 8 kPa), the optimum CNC-C8 DPC hydrogel with 0.0675 w/v% DMAPMA-C18 and 0.4 w/v% CNC-C8 possesses stronger tensile strength of 331 ± 32 kPa and excellent elongation of 4268% ± 1446% as well, demonstrating the enhanced mechanical property of the hydrogel by introduced hydrophobic interactions. In addition, such DPC hydrogel can be facilely repaired with tetrahydrofuran (THF) on the cut surfaces while retaining good tensile stress and elongation behaviors.     

Hybrid Shear-Thinning Hydrogel Integrating Hyaluronic Acid with ROS-Responsive Nanoparticles

Nanoparticle (NP) supra-assembly offers unique opportunities to tune macroscopic hydrogels’ mechanical strength, material degradation, and drug delivery properties. Here, synthetic, reactive oxygen species (ROS)-responsive NPs are physically cross-linked with hyaluronic acid (HA) through guest-host chemistry to create shear-thinning NP/HA hydrogels. A library of triblock copolymers composed of poly(propylene sulfide)-b-poly(N,N-dimethylacrylamide)-b-poly(N,N-dimethylacrylamide-co-N-(1-adamantyl)acrylamide) are synthesized with varied triblock architectures and adamantane grafting densities and then self-assembled into NPs displaying adamantane on their surface. Self-assembled NPs are mixed with β-cyclodextrin grafted HA to yield eighteen NP/HA hydrogel formulations. The NP/HA hydrogel platform demonstrates superior mechanical strength to HA-only hydrogels, susceptibility to oxidative/enzymatic degradation, and inherent cell-protective, antioxidant function. The performance of NP/HA hydrogels is shown to be affected by triblock architecture, guest/host grafting densities, and HA composition. In particular, the length of the hydrophilic second block and adamantane grafting density of self-assembled NPs significantly impacts hydrogel mechanical properties and shear-thinning behavior, while ROS-reactivity of poly(propylene sulfide) protects cells from cytotoxic ROS and reduces oxidative degradation of HA compared to HA-only hydrogels. This study provides insight into polymer structure-function considerations for designing hybrid NP/HA hydrogels and identifies antioxidant, shear-thinning hydrogels as promising injectable delivery platforms for small molecule drugs and therapeutic cells.     

Hydration-Induced Void-Containing Hydrogels for Encapsulation and Sustained Release of Small Hydrophilic Molecules

Efficient encapsulation and sustained release of small hydrophilic molecules from traditional hydrogel systems are challenging due to the large mesh size of 3D networks and high water content. Furthermore, the encapsulated molecules are prone to early release from the hydrogel prior to use, resulting in a short shelf life of the formulation. Here, a hydration-induced void-containing hydrogel (HVH) based on hyperbranched polyglycerol-poly(propylene oxide)-hyperbranched polyglycerol (HPG-PPG-HPG) as a robust and efficient delivery system is presented for small hydrophilic molecules. Specifically, after the HPG-PPG-HPG is incubated overnight at 4 °C in the drug solution, it is hydrated into a hydrogel containing micron-sized voids, which can encapsulate hydrophilic drugs and achieve 100% drug encapsulation efficiency. In addition, the voids are surrounded by a densely packed polymer matrix, which restricts drug transport to achieve sustained drug release. The hydrogel/drug formulation can be stored for several months without changing the drug encapsulation and release properties. HVH hydrogels are injectable due to shear thinning properties. In rats, a single injection of the HPG-PPG-HPG hydrogel containing 8 µg of tetrodotoxin (TTX) produces sciatic nerve block lasting up to 10 h without any TTX-related systemic toxicity nor local toxicity to nerves and muscles.     

Skin-Inspired Double-Hydrophobic-Coating Encapsulated Hydrogels with Enhanced Water Retention Capacity

Traditional hydrogels always lose their flexibility and functions in dry environments because the internal water inevitably undergoes evaporation. In this study, a skin-inspired, facile, and versatile strategy for developing encapsulated hydrogels with excellent water retention capacity through a double-hydrophobic coating is proposed. The robust double-layer coating, which integrates a hydrophobic polymer coating with a hydrophobic oil layer simultaneously, can provide a barrier to prevent the evaporation of water. To overcome the weak interfacial strength between the hydrophilic hydrogel surface and the double-hydrophobic coating, (3-aminopropyl) triethoxysilane (APTES) is utilized as a chemical binding agent. Furthermore, the overall mechanical properties of the bulk hydrogel are not significantly affected, because the coating is only anchored to the surface and its thickness is much lower than that of the native hydrogel. Moreover, it is demonstrated that this proposed strategy particularly holds the capability of encapsulating various types and different shapes of hydrogels, leading to enhanced stability and a prolonged lifetime in air. Therefore, the proposed technology provides new insights for multifarious surface functionalization of hydrogel and broadens the range of hydrogel applications.     

Conductive “Smart” Hybrid Hydrogels with PNIPAM and Nanostructured Conductive Polymers

Stimuli‐responsive hydrogels with decent electrical properties are a promising class of polymeric materials for a range of technological applications, such as electrical, electrochemical, and biomedical devices. In this paper, thermally responsive and conductive hybrid hydrogels are synthesized by in situ formation of continuous network of conductive polymer hydrogels crosslinked by phytic acid in poly(N‐isopropylacrylamide) matrix. The interpenetrating binary network structure provides the hybrid hydrogels with continuous transporting path for electrons, highly porous microstructure, strong interactions between two hydrogel networks, thus endowing the hybrid hydrogels with a unique combination of high electrical conductivity (up to 0.8 S m^?1), high thermoresponsive sensitivity (significant volume change within several seconds), and greatly enhanced mechanical properties. This work demonstrates that the architecture of the filling phase in the hydrogel matrix and design of hybrid hydrogel structure play an important role in determining the performance of the resulting hybrid material. The attractive performance of these hybrid hydrogels is further demonstrated by the developed switcher device which suggests potential applications in stimuli‐responsive electronic devices.     

Bioinspired Highly Anisotropic,Ultrastrong and Stiff,and Osteoconductive Mineralized Wood Hydrogel Composites for Bone Repair

Anisotropic hydrogels mimicking the biological tissues with directional functions play essential roles in damage-tolerance, cell guidance and mass transport. However, conventional synthetic hydrogels often have an isotropic network structure, insufficient mechanical properties and lack of osteoconductivity, which greatly limit their applications for bone repair. Herein, inspired by natural bone and wood, a biomimetic strategy is presented to fabricate highly anisotropic, ultrastrong and stiff, and osteoconductive hydrogel composites via impregnation of biocompatible hydrogels into the delignified wood followed by in situ mineralization of hydroxyapatite (HAp) nanocrystals. The well-aligned cellulose nanofibrils endow the composites with highly anisotropic structural and mechanical properties. The strong intermolecular bonds of the aligned cellulose fibrils and hydrogel/wood interaction, and the reinforcing nanofillers of HAp enable the composites remarkable tensile strength of 67.8 MPa and elastic modulus of 670 MPa, three orders of magnitude higher than those of conventional alginate hydrogels. More importantly, the biocompatible hydrogel together with aligned HAp nanocrystals could effectively promote osteogenic differentiation in vitro and induce bone formation in vivo. The bone ingrowth into the hydrogel composite scaffold also yields good osteointegration. This study provides a low-cost, eco-friendly, feasible, and scalable approach for fabricating anisotropic, strong, stiff, hydrophilic, and osteoconductive hydrogel composites for bone repair.     

Ultra-Stretchable,Variable Modulus,Shape Memory Multi-Purpose Low Hysteresis Hydrogel Derived from Solvent-Induced Dynamic Micelle Sea-Island Structure

The rapid development of sensors and soft robotics has substantially increased the demand for unique hydrogels with diverse high performance. However, it remains a challenge to prepare a multi-purpose hydrogel via a facile approach. By virtue of copolymerization of acrylamide (AM) and acryloyl Pluronic 127 (PF127-DA), a novel type of ultra-stretchable (435–2716%, 10–40 wt%), variable modulus (0.36–112.79 MPa, 30 wt%), tough (1.13–7.17 MJ m⁻³, 10–40 wt%), low hysteresis (about 10%, 30 wt%), transparent (27.98–83.78%, 10–40 wt%), and shape memory (fixation ratio up to 97%, recovery ratio up to 100%, 10 wt%) hydrogels derived from dynamic micelle sea-island structure are prepared. The new strategy of using solvent-induced crystallization of the polyethylene oxide segments of PF127-DA molecular chain and matrix volume phase transition to achieve variable modulus and shape memory is a purely physical process that can be performed cyclically. Notably, this design reflects the important role of PF127-DA micelles in optimizing mechanical properties and intelligence. Additionally, PAM/PF127 hydrogels display a high sensitivity toward deformability, elasticity, solvent-induced shape memory, and variable modulus properties by which it can be used for stress sensors, damping pads, and mechanical bearing. These novel types of hydrogels could be applicable into multifunctional and adaptive platforms.     

Injectable,Micellar Chitosan Self-Healing Hydrogel for Asynchronous Dual-Drug Delivery to Treat Stroke Rats

Stroke is a common disease with high mortality worldwide. The endogenous neural regeneration during the intracerebral hemorrhage (ICH) stroke is restricted by the brain cavity, inflammation, cell apoptosis, and neural scar formation. Biomaterials serving as temporary supporting matrices are highly demanded as injectable implants for brain tissue regeneration. Herein, a chitosan micellar self-healing hydrogel (CM hydrogel) with comparable modulus (≈150 Pa) to brain, shape adaptability, and proper swelling (≈105%) is developed from phenolic chitosan (PC) and a micellar crosslinker (DPF). Two model drugs are individually packaged in the hydrophilic network and hydrophobic micelle cavities of CM hydrogel, and they feature asynchronous releasing kinetics, including a first-order rapid release for hydrophilic drug and a zero-order sustained release for hydrophobic drug. The dual-drug loaded CM (CMD) hydrogel delivers two clinical drugs corresponding to the anti-inflammatory and neurogenesis phases of the stroke to ICH rats through brain injection. The rats receiving CMD hydrogel show behavioral improvement (≈84% recovery) and balanced brain midline shift (≈0.98 left/right hemibrain ratio). Immunohistochemistry reveals neurogenesis (doublecortin- and nestin- positive cells) and evidence of angiogenesis (≈18 µm diameter vessels lined with CD31-positive cells). The injectable CMD hydrogel offers a novel asynchronous drug delivery platform for treating ICH stroke.     

Supplementary Networking of Interpenetrating Polymer System (SNIPSy) Strategy to Develop Strong & High Water Content Ionic Hydrogels for Solid Electrolyte Applications

To synthesize hydrogels that possess tensile strength and modulus together in MPas along with extensibility at high equilibrium water content (≥90 wt%) is challenging but important from the application perspective. Especially, such hydrogel compositions are useful for fabricating flexible electronics devices for subsea applications, where underwater risk-free implementation and optimum device performance at low temperature (≈0 °C) and high hydrostatic pressure (≤20 bar) conditions is desirable. The high water content of hydrogel is necessary to facilitate ion transportation, and mechanical strength is desirable to maintain a stable electrode–electrolyte interface under load. In this study, supplementary networking of an interpenetrating polymer system strategy is utilized to develop ionic hydrogels with tensile strength and Young's modulus values up to 2 and 1.67 MPa, respectively, at high equilibrium water content value up to 96%. Cost-effective, durable, rechargeable, and flexible batteries are fabricated using the Zn & Li ion soaked hydrogel as solid electrolyte without barrier. These batteries display minimal loss in capacity when immersed in water, deformed, exposed to flame, put under high load, and operated under low-temperature conditions suggesting the viability for subsea application.     

Antifreezing Zwitterionic Hydrogel Electrolyte with High Conductivity of 12.6 mS cm−1 at −40 °C through Hydrated Lithium Ion Hopping Migration

Hydrogel electrolytes have high room-temperature conductivity and can be widely used in energy storage device. However, hydrogels suffer from the inevitable freezing of water at subzero temperatures, resulting in the diminishment of their conductivity and mechanical properties. How to achieve high conductivity without sacrificing hydrogels’ flexibility at subzero temperature is an important challenge. To address this challenge, a new type of zwitterionic polymer hydrogel (polySH) electrolytes is fabricated. The anionic and cationic counterions on the polymer chains facilitate the dissociation of LiCl. The antifreezing electrolyte can be stretched to a strain of 325% and compressed to 75% at −40 °C and possesses an outstanding conductivity of 12.6 mS cm⁻¹ at −40 °C. A direct hopping migration mechanism of hydrated lithium-ion through the channel of zwitterion groups is proposed. The polySH electrolyte-based-supercapacitor (SC) exhibits a high specific capacitance of 178 mF cm⁻² at 60 °C and 134 mF cm⁻² at −30 °C with a retention of 81% and 71% of the initial capacitance after 10 000 cycles, respectively. The overall merits of the electrolyte will open up a new avenue for advanced ionic conductors and energy storage device in practical applications.     

Reversible Phase Change-Induced Hardening and Softening for Conditions-Adaptive and Mechanics-Reconfigurable Applications

The mechanical soft–hard transition of hydrogels is desired in conditions-adaptive deformation and mechanics reconfiguration applications. However, highly efficient, stimuli-responsive, and reversible transition strategies are hard to achieve. Inspired by the supercooling of salt-aqueous solutions, solid and supersaturated hydrogels are prepared based on a hydrophilic polymer network and salt-aqueous solution. The inner crystallization- or melting-induced reversible phase-change realizes the switch between the soft hydrogel (modulus: 0.1 MPa) and rigid composite (modulus: 24.0 MPa). The soft and supersaturated hydrogels easily deform to achieve diverse new 3D models and the unfamiliar soft–hard transition makes temporary shapes be efficiently fixed (hardening). Interestingly, the initial hydrogel's shapes can be regenerated relying on the resilience of the polyacrylamide network when the crystal is melted (softening). Shape memory, complex surface morphology replication, rapid mold application, and self-supporting laminated glass are accomplished by this unique crystallization-melting introduced soft–hard transition. This phase change soft-hard switching strategy will broaden the functionalities of hydrogels.     

Hydrophobized Hydrogels: Construction Strategies,Properties, and Biomedical Applications

Hydrogels, as 3D networks containing huge amount of water, display similarity to soft tissues, and thus they are of wide interest in tissue engineering. Hydrogels, due to biocompatibility and porous structure, are valuable therapeutic platforms for hydrophilic drugs. Over the last decade, there has been a strong emphasis on the development of hydrogel platforms with the ability to increase the solubility of hydrophobic drugs. However, the pronounced discrepancy between the hydrophilic character of hydrogels and the hydrophobic nature of numerous pharmacologically active compounds is problematic. In recent years, different strategies are applied using special polymer constructs or composite materials exploiting the advanced scientific knowledge in the area of polymer and lipid-based nano- and microcarriers hydrophobization of the hydrogel turns out to be not only valuable in terms of achieving the ability to dissolve poorly soluble drugs in water, but also proves to be crucial in obtaining bioadhesion in wet conditions, but also, unexpected abnormal water swelling behavior, as well as in mechanical properties such as the dissipation mechanism and self-healable hydrogel properties. This review is mainly focused on recent advances in the usage of hydrophobized hydrogels in biomedical applications.     

Barnacle Cement Proteins-Inspired Tough Hydrogels with Robust,Long-Lasting,and Repeatable Underwater Adhesion

The development of adhesives that can achieve robust and repeatable adhesion to various surfaces underwater is promising; however, this remains a major challenge primarily because the surface hydration layer weakens the interfacial molecular interactions. Herein, a strategy is proposed to develop tough hydrogels that are robust, reusable, and long-lasting for underwater adhesion. Hydrogels from cationic and aromatic monomers with an aromatic-rich composition inspired by the amino acid residuals in barnacle cement proteins are synthesized. The hydrogels are mechanically strong and tough (elastic modulus 0.35 MPa, fracture stress 1.0 MPa, and fracture strain 720%), owing to the interchain π–π and cation–π interactions. In water, the hydrogels firmly adhere to diverse surfaces through interfacial electrostatic and hydrophobic interactions (adhesion strength of 180 kPa), which allows for instant adhesion and reversibility (50 times). Moreover, the hydrogel shows long-lasting adhesion in water for months (100 days). Novel adhesive hydrogels may be useful in many applications, including underwater transfer, water-based devices, underwater repair, and underwater soft robots.     

Thermoresponsive Shape‐Memory Hydrogel Actuators Made by Phototriggered Click Chemistry

This article describes the design and synthesis of a new series of hydrogel membranes composed of trialkyne derivatives of glycerol ethoxylate and bisphenol A diazide (BA‐diazide) or diazide‐terminated PEG600 monomer via a Cu(I)‐catalyzed photoclick reaction. The water‐swollen hydrogel membranes display thermoresponsive actuation and their lower critical solution temperature (LCST) values are determined by differential scanning calorimetry. Glycerol ethoxylate moiety serves as the thermoresponsive component and hydrophilic part, while the azide‐based component acts as the hydrophobic comonomer and most likely provides a critical hydrophobic/hydrophilic balance contributing also to the significant mechanical strength of the membranes. These hydrogels exhibit a reversible shape‐memory effect in response to temperature through a defined phase transition. The swelling and deswelling behavior of the membranes are systematically examined. Due to the click nature of the reaction, easy availability of azide and alkyne functional‐monomers, and the polymer architecture, the glass transition temperature (T_g) is easily controlled through monomer design and crosslink density by varying the feed ratio of different monomers. The mechanical properties of the membranes are studied by universal tensile testing measurements. Moreover, the hydrogels show the ability to absorb a dye and release it in a controlled manner by applying heat below and above the LCST.     

Starfish-Inspired Cut-Resistant Hydrogel with Self-Growing Armor: Where Softness Meets Toughness

Many soft animals like starfish have developed armors to protect their soft bodies in order to survive in harsh environment. Inspired by this fact, special hydrogels with self-growing protective armors are developed by allowing sodium acetate to crystallize on hydrogel surface. Poly(acrylic acid) chains limit the crystalline region to the surface of the hydrogel by decreasing the pH value and limiting the movement of ions, and then creating a set of tough armor. This armor-protected hydrogel is able to withstand a high pressure (> 78 MPa) under cutting and prevent the penetration of sharp objects. Interestingly, the unique stimulated-precipitation mechanism allows the armor to repair itself after damage. Besides, the surface of hydrogel changes from “sticky” to “slippery”, which also helps to improve its protective ability. Moreover, the armor helps to retrain water in hydrogel network, and significantly improve the mechanical properties of hydrogels (maximum compressive stress >18 MPa, compressive strain > 90%). In addition, the hydrogel can keep soft and work durably at extreme temperatures (−50 °C and 80 °C) due to the high salt concentration. This study provides an innovative approach for designing armor-protected hydrogels with great potential in engineering applications such as actuators and sensors for harsh environments.     

Injectable Hydrogels from Triblock Copolymers of Vitamin E‐Functionalized Polycarbonate and Poly(ethylene glycol) for Subcutaneous Delivery of Antibodies for Cancer Therapy

In this study, ‘ABA’‐type triblock copolymers of vitamin E‐functionalized polycarbonate and poly(ethylene glycol) , i.e., VitE_m‐PEG‐VitE_m, with extremely short hydrophobic block VitE_m, are synthesized and employed to form physically cross‐linked injectable hydrogels for local and sustained delivery of Herceptin. The hydrogels are formed at low concentrations (4–8 wt%). By varying polymer composition and concentration, the rheological behavior, porosity, and drug release properties of hydrogels are readily tunable. The in vitro antitumor specificity and efficacy of Herceptin in hydrogel and solution are investigated by MTT assay against normal and human breast cancer cell lines with different HER2 expression levels. The results demonstrate that the Herceptin‐loaded hydrogel is specific towards HER2‐overexpressing cancer cells and cytotoxic action is comparable to that of the Herceptin solution. The biocompatibility and biodegradability of hydrogel are evaluated in mice with subcutaneous injection by histological examination. It is observed that the hydrogel does not evoke a chronic inflammatory response and degrades within 6 weeks post administration. Biodistribution and anti‐tumor efficacy studies performed in BT474 tumor‐bearing mice show that single subcutaneous injection of Herceptin‐loaded hydrogel at a site close to the tumor enhances the retention of the antibody within the tumor. This leads to superior anti‐tumor efficacy as compared to intravenous (i.v.) and subcutaneous (s.c.) delivery of Herceptin in solution. The tumor size shrank by 77% at Day 28. When the hydrogel is injected at a distal location away from the tumor site, anti‐tumor efficacy is similar to that of weekly i.v. injections of Herceptin solution over 4 weeks, with the number of injections reduced from 4 to 1. These findings suggest that this hydrogel has great potential for use in subcutaneous and sustained delivery of antibodies to increase therapeutic efficacy and/or improve patient compliance.     

Cationic Hybrid Hydrogels from Amino‐Acid‐Based Poly(ester amide): Fabrication,Characterization, and Biological Properties

A family of biodegradable, biocompatible, water soluble cationic polymer precursor, arginine‐based unsaturated poly (ester amide) (Arg‐UPEA), is reported. Its incorporation into conventional Pluronic diacrylate (Pluronic‐DA) to form hybrid hydrogels for a significant improvement of the biological performance of current synthetic hydrogels is shown. The gel fraction (G_f), equilibrium swelling ratio (Q_eq), compressive modulus, and interior morphology of the hybrid hydrogels as well as their interactions with human fibroblasts and bovine endothelial cells are fully investigated. It is found that the incorporation of Arg‐UPEA into Pluronic‐DA hydrogels significantly changes their Q_eq, mechanical strength, and interior morphology. The structure–property relationship of the newly fabricated hybrid hydrogels is studied in terms of the chemical structure of the Arg‐UPEA precursor, i.e., the number of methylene groups in the Arg‐UPEA repeating unit. The results indicate that increasing methylene groups in the Arg‐UPEA repeating unit increases Q_eq and decreases the compressive modulus of hydrogels. When compared with a pure Pluronic hydrogel, the cationic Arg‐UPEAs/Pluronic hybrid hydrogels greatly improve the attachment and proliferation of human fibroblasts on hydrogel surfaces. A bovine aortic endothelial cells (BAEC) viability test in the interior of the hydrogels shows that the positively charged hybrid hydrogels can significantly improve the viability of the encapsulated endothelial cell over a 2 week study period when compared with a pure Pluronic hydrogel.     

Biotissue-Inspired Anisotropic Carbon Fiber Composite Hydrogels for Logic Gates,Integrated Soft Actuators,and Sensors with Ultra-High Sensitivity

Natural biotissues like muscles, ligaments, and nerves have highly aligned structures, which play critical roles in directional signal transport, sensing, and actuation. Inspired by anisotropic biotissues, composite hydrogels with outstanding mechanical properties and conductivity are developed by compositing thermo-responsive poly (N-isopropylacrylamide) (PNIPAM) hydrogels with highly aligned carbon fibers (CFs). The anisotropic hydrogels show superior tensile strength (3.0 ± 0.3), modulus (74 ± 7.0 MPa), excellent electrical conductivity (≈670 S m⁻¹), and ultra-high sensitivity (gauge factor up to 647) along CFs, with an anisotropic ratio (AR) up to 740 over those in perpendicular direction. The extremely high AR in conductivity (more than 400) produces high-level output in parallel direction and low-level output in perpendicular direction with a direct current (DC) power supply, which is used to fabricate AND and OR gates. Moreover, the composite hydrogels are converted into thermo-responsive actuators with CFs twisted before compositing with PNIPAM/clay network. The pre-twisted CF helices impart internal stress that drives reversible actuation of hydrogel helices upon thermo-stimulating. The actuation is self-sensed due to the extremely high sensitivity of the composite hydrogels. Such biomimetic anisotropic self-sensing hydrogel actuators resemble natural biotissues with both actuation and sensing capabilities, and have promise applications for artificial robotics.     

Inorganic Ionic Oligomers Induced Organic-Inorganic Synergistic Toughening Enabling Mechanical Robust and Recyclable Nanocomposite Hydrogels

Mechanical robust hydrogels are ideal for applications in energy, environment, biomedicine, and structural engineering materials fields. However, high strength and high toughness are usually in conflict with each other, and simultaneously achieving both of them within a hydrogel has been challenging. Herein an organic-inorganic synergistic toughening strategy is reported via in-situ inorganic ionic polymerization of calcium phosphate oligomers within polymer composite networks composed of polyvinyl alcohol chains and aramid nanofibers. The composite hydrogels are provided with a prestress-induced hierarchically fibrous structure through the assembly, which resulted in the mechanical strength and toughness up to 24.15 ± 1.12 MPa and 15.68 ± 1.78 MJ m⁻³, respectively, surpassing most toughened hydrogels. Through lamination and crosslinking, bulk hydrogels with controllable mechanical anisotropy and significant energy absorption/dissipation ability are produced. Moreover, the recycling and regeneration of the hydrogels are easily realized owing to the physically crosslinked network and acid-induced dissolution of the inorganic units of the hydrogels, which lays a foundation for the sustainable large-scale production and application of the hydrogels. This study provides an alternative approach for the development of mechanical robust and recyclable nanocomposite hydrogels for various applications including soft body armor, flexible electronics, soft robotics, etc.     

Light‐Induced Swelling‐Responsive Conductive,Adhesive, and Stretchable Wireless Film Hydrogel as Electronic Artificial Skin

Light‐induced wireless soft electronic skin hydrogels with excellent mechanical and electronic properties are important for several applications, such as soft robotics and intelligent wearable devices. Precise control of reversible stretchability and capacitive properties depending on intermolecular interaction and surface characteristics remains a challenge. Here, a thin‐film hydrogel is designed based on titanium oxide (TiO₂) polydopamine–perfluorosilica carbon dot‐conjugated chitosan–polyvinyl alcohol‐loaded tannic acid with controllable hydrophobic–hydrophilic transition in the presence of UV–vis light irradiation. The shifting of surface wettability from hydrophobic to hydrophilic by irradiation affects thin‐film water permeability and swelling ratio. This allows the penetration of water into the matrix to change its mechanical strength, electronic properties, and adhesive behavior. Specifically, the hydrogel displays mechanical strain as high as 278% in response to light stimuli and demonstrates the ability to regain its initial state determining the elasticity of the fabricated material. Moreover, the thin‐film hydrogel shows an increase in conductivity to 1.096 × 10^?3 and 1.026 × 10^?3 S cm^?1 when irradiated with UV and visible light, respectively. The hydrogel exhibits capacitive reversibility that follows finger motion which can be identified directly or remotely using wireless connection, indicative of its possible applications as an artificial electronic skin.