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Currently, most hydrogel sensors require an isolation layer to prevent current from damaging the skin. However, the mismatch of mechanical property between the isolation layer and the hydrogel sens...

Breaking through the conventional way of conferring anti-icing ability on hydrogels with addition of organic solvents or inorganic salts, here a novel anti-icing hydrogel with toughness, adhesiveness and high transparency was successfully fabricated by introducing antifreeze protein (AFPS, inspired by fish) into a chemical crosslinking network copolymerized with acrylamide and 2-acrylamide-2-methylpropanesulfonic acid. The hydrogel exhibited surprising stretchability (up to 2400% tensile strain), high transparency (over 90% transmittance) and outstanding reversible adhesive performance bonding to different materials and even human skin. Meanwhile, the inhibition of ice crystal growth based on AFPS molecules also conferred anti-icing ability on the hydrogels, so that the toughness and adhesiveness of the hydrogels remained stable at −10 °C. Additionally, the existence of sulfonic groups also endowed the hydrogels with deformation sensitivity to act as strain or pressure sensors to accurately monitor human motions and even subtle physiological signals. Therefore, the novel anti-icing strategy would provide new insight for a new generation of hydrogel sensors.

The thermochromic materials have received widespread attention due to their ability to adjust color under the environmental stimuli. However, it is still a challenge in the sensitivity of transmittance on temperature. Here, a novel type of thermochromic hydrogel is proposed and demonstrated to improve the sensitivity of transmittance to temperature. At different temperatures, the size of the micelle could be changed, giving the thermochromic ability for the hydrogel. As the temperature gradually increases to the thermochromic transition temperature (TTT), the hydrogels undergo a transition from opaque to transparent (90%) at 550 nm visible radiation the same as the near-infrared region. The reverse process occurs when the temperature drops below TTT. Meanwhile, TTT could be adjusted over a range of temperature from 25 to 35 °C by changing the content of potassium tartrate hemihydrate. This hydrogel provides a new approach to obtain thermochromic materials and has wide potential application in temperature ...

Currently, flexible wearable hydrogel-based sensors have attracted considerable attention due to their promising applications in a variety of fields. However, concurrently integrating toughness, adhesiveness, self-healing ability, and conductivity into the hydrogel is still a great challenge. Here, casein sodium salt from bovine milk (sodium casein, SC) and polydopamine (PDA, inspired by mussels) were successfully introduced into the polyacrylamide (PAAm) hydrogel system to fabricate a tough and adhesive SC-PDA hydrogel. The hydrogel exhibits splendidly reversible adhesive behavioral bonding toward various materials and even human skin. Moreover, based on the dynamic cross-linking of SC and PDA in the system, the hydrogel has superstretching ability, excellent fatigue resistance, and rapid self-healing ability. In addition, the existence of sodium ions also endowed the SC-PDA hydrogel with sensitive deformation-dependent conductivity to act as a flexible strain and pressure sensor for directly monitoring large-scale human motions (e.g., joint bending) and tiny physiological signals (e.g., speaking and breathing). Therefore, the strategy would broaden the path of a new generation of hydrogel-based sensors for wide applications.

In general, chitosan should be dissolved in strong acidic media (such as acetic acid) before it could be applied as hydrogels. However, it was found that chitosan could also be dissolved in the ferric solution to form ferric-chitosan complex via coordination interaction. Subsequently, the ferric-chitosan complex was successfully introduced into the hydrogel system to obtain tough, adhesive and conductive chitosan-polyacrylamide double network (CS-PAAm DN) hydrogels. Surprisingly, CS-PAAm DN hydrogel could repeatedly adhere to various solid materials and biological tissues through physical interactions. The maximum peeling force was 256 N/m on the aluminum surface. Moreover, the hydrogel exhibited adequate mechanical performance (135 kPa, 2332%). And the introduction of ferric chloride could also endow the hydrogel with conductive performance. As a result, the strategy based on tough, adhesive and conductive polysaccharide hydrogels mediated by ferric solution would broaden the path to fabricate a new generation of soft materials for wide applications.

Hydrophobic association hydrogels have attracted great attention of many researchers and been widely utilized in tissue engineering stents, drug delivery carriers, wound dressings, and biosensors as intelligent materials due to their excellent mechanical and self-healing properties. Here, we mainly introduced different mechanisms on hydrophobic association hydrogels with high mechanical and excellent self-healing properties. The mechanisms included not only hydrophobic association, but also synergistic effect with latex particles, nanoparticles, electrostatic effect, metal complex, hybrid crosslinking and double network. Based on these achievements, moreover, we forecast the hydrophobic association interaction would exhibit more meaningful influence on assisting the performance of hydrogels for wide applications of biomedical, industrial, agricultural fields.

In recent years, the use of smart windows to adjust sunlight to achieve energy conversion has received increasing attention. In this paper, a novel smart window was easily prepared by using thermochromic hydrogels as an interlayer and indium tin oxide films as an electric heating layer. The shielding transmission rates of visible and near-infrared light reached 88.3 and 85.4% at the temperature of 25 °C, respectively. However, the transmittance at a light wavelength of 550 nm was greater than 70% after applying voltage. The smart windows with different components could possess thermochromic temperature ranging from 28 to 35 °C, which was suitable for daily life. The smart window could maintain a stable reversible thermochromic transition. Importantly, the time of light transition and the demand of energy efficiency could be adjusted by controlling the magnitude of the output voltage, which benefited the development of energy-efficient materials.

As a flexible material, hydrogels have attracted considerable attention in the exploration of various wearable sensor devices. However, the performance of the existing hydrogels is often too single, which limits its further application. Here, a conductive hydrogel with adhesiveness, toughness, self-healing and anti-swelling properties was successfully prepared by adding 2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC) to the polyacrylic acid/ferric ionic (PAA/Fe3+) cross-linking system. Based on the existence of three types of non-covalent interactions in the hydrogel system, including electrostatic interaction, coordination interaction and hydrogen bonds, the hydrogel possessed excellent mechanical properties (tensile stress and strain were 827 kPa and 1652 %, respectively), self-healing properties (self-healing efficiency reached 83.3 % at room temperature) and anti-swelling properties. In addition, the introduction of HACC also successfully gave the hydrogel outstanding adhesiveness. Moreover, the existence of iron ions provided sensitive conductivity to the hydrogel, which could be used as a flexible sensor for directly monitoring various motions. Therefore, this simple strategy for preparation of multifunctional hydrogels would expand the application of a new generation of hydrogel-based sensors.

Conductive hydrogels had demonstrated significant prospect in the field of wearable devices. However, hydrogels suffer from a huge limitation of freezing when the temperature falls below zero. Here, a novel conductive organohydrogel was developed by introducing polyelectrolytes and glycerol into hydrogels. The gel exhibited excellent elongation, self-healing, and self-adhesive performance for various materials. Moreover, the gel could withstand a low temperature of -20 °C for 24 h without freezing and still maintain good conductivity and self-healing properties. As a result, the sample could be applied for motion detection and signal transmission. For example, it can respond to finger movements and transmit network signals like network cables. Therefore, it was envisioned that the effective design strategy for conductive organohydrogels with antifreezing, toughness, self-healing, and self-adhesive properties would provide wide applications of flexible wearable devices.

Based on the tough double-network hydrogel, a further crosslinked DN network hydrogel was developed and named joint double network (JDN) hydrogel. The JDN hydrogel consisting of ionically cross-linked sodium alginate (SA) as the first network, the chemically cross-linked poly (acrylamide-acrylic acid) (PAMAAc) as the second network and both of them combined together by ferric ions. As a result, SA/PAMAAc-Fe3+ hydrogels exhibited high mechanical strength with tensile stress of 1.26 MPa and tensile strain of 653%. Ultraviolet–visible spectroscopy, rheological and swelling tests also illustrated that the JDN structure greatly improved the mechanical properties of hydrogels because of close integration of internal networks. Moreover, the SA/PAMAAc-Fe3+ JDN hydrogel also owned high water content of 85%, free-plasticity, and excellent electrical property, which allowed it to be easily molded various shapes for tough electronic devices, flexible electrodes, and wearable equipment.

Adhesive hydrogels tend to exhibit poor mechanical property, therefore it’s still challenging to integrate excellent adhesiveness and toughness in one hydrogel. In this work, we utilized a hybrid crosslinking strategy to design an adenine-mediated hydrogel by introducing adenine and N,N′-methylene bisacrylamide (MBA) into polyacrylamide hydrogel. The hybrid crosslinking hydrogel exhibited a tunable adhesive performance and mechanical strength, based on the balance of cohesion and adhesion through changing the contents of acrylated adenine (Aa) and MBA. The hydrogel can adhere to various solid substrate surfaces strongly as well as biological tissue. The hybrid crosslinking hydrogel also exhibited repeatable and durable adhesiveness, which still possessed robust adhesion on aluminum substrate after 20 peeling cycles. In addition, the synergistic effect of the physical and chemical crosslinking in the hydrogel network endowed hydrogel with superior mechanical properties. The hybrid crosslinking hydrogel could be stretched to over 2700% with fracture stress of 127 kPa and toughness of 931 kJ/m3. Meanwhile, the hydrogel displayed excellent self-recover ability and fatigue resistance. The adenine-mediated hybrid crosslinking hydrogel shows potential as materials for tissue engineering.

Traditional hydrophobic association (HA) hydrogels can obtain excellent mechanical properties in the presence of anionic surfactants. However, such surfactants are sensitive to salt solutions, resulting in large fluctuation of mechanical properties for hydrogels. Here, a combined surfactant consisting of anionic surfactants (sodium dodecyl sulfate, SDS) and amphoteric surfactants (dodecyl dimethyl betaine, BS-12) was successfully introduced into HA hydrogels as stable physical crosslinking points. The resulting SDS/BS-12-HA hydrogels exhibited high tensile stress up to about 700 kPa. Moreover, the hydrogels demonstrated salt-inactive, self-healing and fatigue resistance properties owing to their unique dynamic and reversible physical crosslinking structure. Therefore, it's envisioned that this work may open a new method to develop a soft salt-inactive material with stable and excellent mechanical properties for extending the application range of hydrogels.

Hybrid crosslinking hydrogels have exhibited excellent mechanical properties, however, the relationship between chemical and physical crosslinking in the various deformation stages is still indistinct. Here, a hybrid hydrogel was explored by inducing low density of chemical crosslinking into latex particle hydrogels (LP-Gel), in which latex particles act as physical crosslinking centers for inducing efficient aggregation of hydrophobic chains. The resulting hybrid hydrogel exhibited extraordinary mechanical performance. It is found that the role of chemical and physical crosslinking was different during different deformation levels. The synergistic effects of chemical and physical crosslinking allow hydrogels to dissipate a large number of energy, significantly enhancing the mechanical strength of hydrogels. Moreover, the hybrid hydrogel exhibited puncture resistant, excellent ductility and rapid recovery.

Dual physically cross-linked hydrogels, which are triggered by cationic latexes as hydrophobic association and ionic crosslinking centers, were easily fabricated via a one-pot in situ polymerization method. First, the hydrophobic alkyl chains of hydrophobic monomers are adsorbed on the surface of latex microspheres and stabilized in the presence of surfactants, forming hydrophobic association centers as the first physical crosslinking points. Meanwhile, the anionic sulfate radicals dissociated by persulphate are attracted towards the cationic molecular chains of latex microspheres through ionic interactions, forming the secondary physical crosslinking centers, and initiate the copolymerization between acrylamide and hydrophobic vinyl monomers. The fabricated hydrogel exhibited high tensile strength of 1.32MPa, a remarkable toughness of 4.53MJm-3, excellent self-recovery properties and fatigue resistance. Therefore, the current work provides a promising strategy for designing novel hydrogels via multiple physical interactions and devoid of any chemical crosslinking. The novel design of hydrogels can enhance their mechanical properties and expand their biomedical applications.

In our previous work, poly(butyl acrylate) (PBA) latex microspheres (LMs) were embedded within hydrogels to enhance their mechanical strength. Herein, acrylonitrile (AN) components were added to the latex system to prepare novel poly(butyl acrylate-acrylonitrile) (P(BA-AN)) LMs. LMs were able to adsorb hydrophobic hexadecyl methacrylate (HMA) due to hydrophobic interactions, stabilized by using sodium dodecyl sulfate as a surfactants. The HMA could occur radical copolymerization with acrylamide (AAm) under the redox initiators to form P(HMA-AAm)-P(BA-AN) hydrogels. The intra and interchain non-permanent binding could be promoted in P(BA-AN) LMs due to the dipole-dipole interactions of -CN groups from acrylonitrile. As a result, P(BA-AN) LMs were utilized to fabricate tough hydrogels as crosslinking centers for hydrophobic association. The mechanical properties of the hydrogels exhibited a fracture stress of 775 KPa, an ultrastretchable strain of 3600% and a fracture energy of approximately 7600 KJ/m3. This innovative design strategy for LMs capable of strong physicochemical interactions, including electrostatic and hydrogen-bond interactions and coordination effects, may open a novel direction for the production of tough hydrogels.

Herein, different long alkyl chains (C1, C6, C12, and C16) were introduced as hydrophobic segments to enhance the performance of hydrogels reinforced by latex particles (LP-Gel). Poly(butyl acrylate) (PBA) latex particles (LPs) were employed as hydrophobic association cross-linking centers. First, the PBA latex particles were prepared via emulsion polymerization, and then, LP-Gel with high mechanical strength was prepared via one-pot free radical polymerization using acrylamide as a monomer, LP as a cross-linking center, and methacrylate as a hydrophobic molecule. It was found that the length of the hydrophobic alkyl chains from methacrylate has a significant effect on the mechanical performance and swelling degree of the hydrogels. The short alkyl chains exhibited weak hydrophobic interactions, and the resulting LP-Gel had a low mechanical strength. However, the long alkyl chains can effectively entangle with LPs through strong hydrophobic interactions, which significantly enhance the mechanical strength of the hydrogels. As a result, the LP-Gel exhibits a maximum fracture stress of 1.2 MPa and elongation of 2336%. This study will have a profound impact on the understanding of hydrogels toughened by hydrophobic alkyl chains of different lengths.

In this investigation, a tough hydrogel was reinforced by macromolecular microspheres (MMs) as hydrophobic association centers via free radical polymerization with different initiation systems. The thermal initiator is potassium persulfate and the redox initiators include potassium persulfate and N,N,N′,N′-tetramethylethylenediamine (TMEDA). The mechanical measurements showed that the hydrogel with a redox initiation system possesses a tensile strength of 1.55 MPa, which is much higher than the hydrogel with a thermal initiator. Moreover, the hydrogel with redox initiators exhibited rapid self-recovery to its 90% original dimension in several seconds and low swelling property. The large difference in the morphology of hydrogels before and after swelling was due to the tight entanglement of molecular chains in the internal structure of hydrogels with redox initiators. As a result, the hydrophobic association hydrogels toughened by MMs with excellent mechanical properties would be useful for biomedical applications of tough tissue engineering, such as tendon, muscle, and blood vessel.

In this manuscript, hydrogels with pH-tunable mechanical properties were prepared via transforming the non C–C covalent synergistic interactions of hydrogen bonding, metal ion coordination and hydrophobic effects. The fracture stress of hydrogels exhibited a tendency to firstly decrease and then increase with an increase of pH from 3.0 to 9.0. That is, the fracture stress was enhanced due to the synergistic interactions of hydrophobic effects and hydrogen bonding among carboxylic acid groups at pH 3.0. Then, the strength gradually decreased due to the disappearance of hydrogen bonding at pH from 3.0 to 5.0. Moreover, the fracture stress was also significantly enhanced at pH over 5.0 due to the synergistic interactions of hydrophobic effects and metal ion coordination. Consequently, it is envisioned that the strategy to design novel hydrogels with pH-tunable mechanical properties would provide more interesting directions for hydrogels based on non C–C covalent synergistic interactions in potential biomedical applications.

In recent years, nature-inspired conductive hydrogels have become ideal materials for the design of bioactuators, healthcare monitoring sensors, and flexible wearable devices. However, conductive hydrogels are often hindered by problems such as the poor mechanical property, nonreusability, and narrow operating temperature range. Here, a novel skin-inspired gel is prepared via one step of blending polyvinyl alcohol, gelatin, and glycerin. Due to their dermis-mimicking structure, the obtained gels possess high mechanical properties (fracture stress of 1044 kPa, fracture strain of 715%, Young's modulus of 157 kPa, and toughness of 3605 kJ m-3). Especially, the gels exhibit outstanding strain-sensitive electric behavior as biosensors to monitor routine movement signals of the human body. Moreover, the gels with low temperature tolerance can maintain good conductivity and flexibility at -20 °C. Interestingly, the gels are capable of being recovered and reused by heating injection, cooling molding, and freezing-thawing cycles. Thus, as bionic materials, the gels have fascinating potential applications in various fields, such as human-machine interfaces, biosensors, and wearable devices.

Herein, cationic latex particles (CL) of different particle sizes were introduced as a cross-linking center to enhance the mechanical properties of the hydrophobically-associated hydrogels (P(AAm-co-HMA)-CL). Firstly, cationic polymethylmethacrylate (PMMA) latex particles were synthesized via soap-free emulsion polymerization. Subsequently, P(AAm-co-HMA)-CL hydrogels with outstanding mechanical properties were prepared using acrylamide as the monomer, hexadecyl methacrylate as the hydrophobic molecule, and CL as the cross-linking center. The size of CL had a significant effect on the mechanical properties and self-recovery properties of the P(AAm-co-HMA)-CL hydrogels. The hydrogel with larger CL size exhibited low mechanical properties due to weak hydrophobic interactions. In contrast, the hydrogel with small CL size displayed excellent mechanical properties due to an effective entanglement of the hydrophobic chains with the smaller size CL, which significantly affects the mechanical properties of the hydrogel. As a result, the maximum fracture stress and fracture strain of the hydrogel were up to 1.47 MPa and 2847%, respectively. This study can have a profound impact on the development of the technology of toughening hydrogels with latex particles.

Conventional hydrogel electrolytes tend to deteriorate significantly or even deactivate at high or low operating temperatures, which has become the main obstacle to the development of current temperature-tolerance supercapacitors. Herein, a groundbreaking temperature-tolerant strategy was firstly proposed that a novel hydrogel electrolyte with wide operating temperature was successfully prepared. Phosphoric acid (PA) and water as mixed solvents were utilized to dissolve chitosan (CS) in the chemical crosslinking polyacrylamide (PAAm) network to obtain tough and adhesive CS-PAAm hydrogels. Meanwhile, based on the existence of phosphoric acid molecules, the CS-PAAm hydrogels showed extremely high conductivity and wide range of temperature-tolerance from −60 °C to 100 °C. Surprisingly, the adhesiveness and toughness remained almost unchanged. Then, CS-PAAm hydrogels as electrolytes were successfully coupled with activated carbon electrodes to construct supercapacitors, which presented excellent flexibility and electrochemical stability over a wide temperature range from −60 °C to 100 °C. Therefore, it is foreseeable that this simple and effective strategy would provide novel insight and opportunity for a new generation of flexible energy storage devices with wide temperature-tolerance.

Hydrogels flexible wearable sensors have gained widespread attention. However, there was a great challenge to prepare the flexible hydrogel sensor with rapid response, wide strain monitoring ranges, great sensitivity and self-adhesion. Therefore, the greatly sensitive and rapidly responsive strain sensor with wide monitoring range and self-adhesion was prepared by introducing sodium caseinate (SC) and reduced graphene oxide (rGO) into the polyacrylamide hydrogel due to ions and electrons provide two different ways of conducting electricity. Casein not only imparted excellent adhesion to the hydrogel, but also provided a good ionic conductive pathway. In addition, the introduction of rGO could offer an electronic pathway. Therefore, the obtained hydrogel exhibited excellent rapid response (190 ms), high sensitivity (Gauge factor, GF = 13.14) and wide strain monitoring range (0.1–1100%). As a result, SC/rGO/PAAm hydrogels could detect sensitive locomotor signals (for example speaking) and large-scale mankind movements for example knee bending). It was believed that the ion and electron conduction would provide a new mechanism to preparing greatly sensitive hydrogel strain sensor.

Novel renewable thermoplastic elastomers were synthesized by sequential polymerization of lysine- and itaconic acid-derived monomers. Ring-opening polymerization of lysine-based O-carboxyanhydride monomer using diethylene glycol as an initiator gave well-defined α,ω-dihydroxy functionalized lysine-derived polyesters. The Mn of these polyesters increased with the monomer conversion while retaining relatively narrow molecular weight distributions. Based on the successful controlled polymerization and esterification of α,ω-dihydroxy with 2-bromoisobutyryl bromide, the resultant Br-PL-Br macroinitiator was used for the atom transfer radical polymerization of N-phenylitaconimide (PhII). Three poly(N-phenylitaconimide)-b-polyester-b-poly(N-phenylitaconimide) triblock copolymers were prepared containing 12 − 25 mol% PPhII, as determined by 1H NMR spectroscopy. The properties of the obtained triblock copolymer are evaluated as high-performance and renewable thermoplastic elastomer materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016

Hydrogels have been applied in flexible strain sensors due to good conductivity, stretchability and sensitivity to strain. However, gaining rapid and effective self-healing hydrogels for the durability of flexible strain sensors is still a challenging. Herein, we report a tough, conductive hydrogel that can rapidly self-healing at room temperature. The hydrogel is fabricated by incorporating polystyrene-co-poly (N,N-dimethylacrylamide) (P (St-co-DMAA)) microspheres prepared by emulsion polymerization into hydrophobic association hydrogels networks composed of polyacrylamide-co-poly (hexadecyl methacrylate) (PAAm-co-PHMA), sodium dodecyl sulfate (SDS) and sodium chloride (NaCl). The hydrogel possesses a dual dynamic crosslinking comprising of multiple hydrogen bonds and hydrophobic association. The multiple hydrogen bonds formed between the outer regions of microspheres and PAAm chains provide rapid self-healing of hydrogels and contribute to re-association of hydrophobic chains and further improve self-healing efficiency. (99% Self-healing efficiency at room temperature for 2 h). At the same time, the dual crosslinking also gives the hydrogel good mechanical properties and fatigue resistance. In addition, the existence of sodium ions and chloride ions also endowed the hydrogel high sensitive deformation-dependent conductivity, make the hydrogel able to sensitive sensing of large and small strain signals (e.g. finger bending and breathing). And the sensing ability of hydrogel can be also recovered quickly after self-healing. Therefore, this strategy will expand the application range of a new generation of hydrogels such as self-healing conductors, robotic electronic skin and strain sensors, etc.

The stretchable hydrogels provide potential alternatives to bionic skins. However, skin simulation remains seriously challenging due to its complex nature, including mechanical property, protective effect, and sensory capability. Herein, conductive gels toughened by sodium alginate fibers in oil-water system were developed for preparation of skin-like ionic sensors. The dynamic network was constructed by polyvinyl alcohol and sodium alginate fibers, providing a wide scope of mechanical properties, such as high toughness, anti-fatigue fracture and remodelability. Moreover, salts imparted good conductivity to gels. As a result, gels exhibited sensory capability toward stress and strain, so they were considered sensors to monitor various movements of human body. In particular, gels demonstrated temperture tolerance ranging from −20 °C to 40 °C and non-drying for 6 days at 25 °C. In this study, gels showed complex intelligence similar to natural skin, and might find applications in artificial intelligence, human-mechanial interactions, and smart wearable devices.

The introduction of SiO2 particles as crosslinking points into hydrogels has been recognized as a suitable way for toughening hydrogels, due to their versatile functionalization and large specific surface area. However, chemically linked SiO2 nanocomposite hydrogels often exhibited negligible fatigue resistance and poor self-recoverable properties due to the irreversible cleavage of covalent bonds. Here, we proposed a novel strategy to improve stretchability, fatigue resistance and self-recoverable properties of hydrogels by using SiO2-g-poly(butyl acrylate) core–shell inorganic–organic hybrid latex particles as hydrophobic crosslinking centers for hydrophobic association. The obtained hydrogel could distribute the surrounding applied stress by disentanglement of the hybrid latex particles from hydrophobic segments. Based on this strategy, the formulated hydrogels showed an excellent tensile strength of 1.48 MPa, superior stretchability of 2511% and remarkable toughness of 12.62 MJ m−3. Moreover, the hydrogels owned extraordinary anti-fatigue, rapid self-recovery and puncture resistance properties. Therefore, this strategy provided a novel pathway for developing advanced soft materials with potential applications in biomedical engineering, such as tendons, muscles, cartilages, etc.

Toughness, strechability and compressibility for hydrogels were ordinarily balanced for their use as mechanically responsive materials. For example, macromolecular microsphere composite hydrogels with chemical crosslinking exhibited excellent compression strength and strechability, but poor tensile stress. Here, a novel strategy for the preparation of a super-tough, ultra-stretchable and strongly compressive hydrogel was proposed by introducing core–shell latex particles (LPs) as crosslinking centers for inducing efficient aggregation of hydrophobic chains. The core–shell LPs always maintained a spherical shape due to the presence of a hard core even by an external force and the soft shell could interact with hydrophobic chains due to hydrophobic interactions. As a result, the hydrogels reinforced by core–shell LPs exhibited not only a high tensile strength of 1.8 MPa and dramatic elongation of over 20 times, but also an excellent compressive performance of 13.5 MPa at a strain of 90%. The Mullins effect was verified for the validity of core–shell LP-reinforced hydrogels by inducing aggregation of hydrophobic chains. The novel strategy strives to provide a better avenue for designing and developing a new generation of hydrophobic association tough hydrogels with excellent mechanical properties.

In this study, a novel strategy was designed to prepare rapidly recoverable, anti-fatigue, super-tough double-network hydrogels by introducing macromolecular microspheres (MMs) as cross-linking centers for hydrophobic associations. MMs were prepared via emulsion polymerization using butyl acrylate (BA) as a main component and dicyclopentyl acrylate (DCPA) as a cross-linker. Then, a double-network (DN) hydrogel was prepared using gelatin as the first network and a copolymer of acrylamide and hexadecyl methacrylate stabilized by MMs as the second network. As a result, the DN hydrogels that were toughened by MMs exhibited an excellent fracture strength of 1.48 MPa and a fracture strain of 2100%. Moreover, the hydrogels exhibited rapid recoverability and fatigue resistance. Therefore, the strategy would open up a novel avenue for the toughening of DN hydrogels for biomedical applications.

Herein, a novel double network polyvinyl alcohol/gelatin/glycerol (PVA/GEL/GL) organohydrogel is reported and fabricated. The existence of GEL improves the high mechanical strength based on the strong hydrogen bonds from PVA and GL, endowing the organohydrogels with excellent flexibility and biocompatibility. Especially, PVA/GEL/GL organohydrogels can maintain excellent mechanical flexibility at −25 °C, and possess remarkable non-drying even at 85 °C. It also exhibits good mildewproof property after 15 days. Meanwhile, remoldability endows organohydrogels to be recycled and reused, even as substitute materials for soil to cultivate plants. Thus, PVA/GEL/GL organohydrogels as a biological material have great potential great potential in fields of biomedicine, and even industry and agriculture.

The gel-based sensor was extensively investigated due to the flexible and extensible properties. Here, a flexible, excellent mechanical (fracture energy of 5238 kJ/m3) and anti-freezing ionic conductive carboxymethyl cellulose-based organohydrogel sensor was prepared via Fe3+ cross-linked sodium carboxymethyl cellulose (CMC) as the first network and covalently cross-linked polyacrylamide as the second network in the co-solvents of water and ethylene glycol. Owing to the clipping transportation of Fe3+ in the water channels, the gel sensor had good sensitivity (GF = 1.4, 0˜30% strain) and fast strain-responsiveness (0.98 s) to monitor the subtle motions of human body. The CMC-based organohydrogel with high strain-sensitivity exhibited more potential applications of next-generation bioelectronic materials and devices.

In this work, a hybrid cross-linked polyacrylamide (PAM)/cationic micelle hydrogel is fabricated by introducing the cationic micelles into the chemically cross-linked PAM network. The cationic micelles act as the physical cross-linking points through the strong electrostatic interaction with anionic initiator potassium persulfate. Thereafter, in situ free radical polymerization is initiated thermally from the cationic micelle surface to form the hybrid cross-linked network. The synergistic effect between chemical and physical cross-link endows the hydrogel with excellent mechanical and recoverable properties. The resulting hydrogel exhibits tensile stress of 481 kPa and fracture toughness of 1.65 MJ m−3. It is found that the chemical cross-linking can inhibit the hysteresis of the hybrid hydrogel, exhibiting good elasticity in the tensile loading–unloading test. Moreover, dynamic rheological measurements show that the hybrid hydrogels possess fewer defects of network and exhibit excellent self-recovery behavior. Thus, this investigation provides a different view for the design of new high elastic and tough hydrogels containing hybrid physical and chemical cross-linking networks.