In practical applications, long-term load cycles tend to cause fatigue damage to the ionogels and induce cracks, reduce their stability and accuracy, greatly decrease their service life, and increase operating costs. At present, no effective strategy has been developed to fundamentally solve the problem of crack propagation sensitivity of ionogels. For example, double network (DN) gels (such as poly(1-acrylamido-2-methylpropane sulfonic acid) (PAMPS)/ polyacrylamide (PAAM) hydrogel [18] ) prevent crack propagation through the fracture of primary and sacrificial networks. However, covalent crosslinking network is usually irreversible, and fatigue resistance is limited under long-term cyclic loading. [9,[18][19][20][21][22] Moreover, introducing reversible dynamic bonds (such as ionic and hydrogen bonds) into polymer networks can effectively enhance the selfhealing ability during fatigue damage or crack propagation. [13,[23][24][25][26][27] However, due to the lack of an additional energy dissipation mechanism, irreversible fatigue damage can be caused by crack propagation during long-term cyclic loading. Furthermore, reversible bonds cannot dissipate the stress concentration at the pre-cut crack tip and are unable to prevent crack propagation. [21] Microgels have been used as DN structure to enhance the mechanical properties of hydrogels. [21,28,29] The matrix polymers are chemically crosslinked rather than linear polymer segments, which greatly limits the deformability of the hydrogels. In addition, the chemically crosslinked single network outside the microgels leads to the catastrophic expansion of the crack at the notch of the hydrogels. Therefore, the crack propagation insensitivity and fatigue resistance were sacrificed. Addition of nanocomposites improved the toughness and strength of the hydrogels through the interaction between surface functional groups and external polymer matrix (hydrophobic association by amphiphilic triblock copolymer, strong hydrogen bond, and coordination bond). [19,22,[30][31][32][33] The hydrogels need residence time to recover the damaged mechanical properties under cyclic load due to the unstable mechanical properties of reversible bonds.Recyclability and mechanical stability of polymer networks are contradictory properties. The covalently crosslinked rigid network ensures the stability of the polymer framework at the expense of the regeneration and recycling capacity. The noncovalent bond in the reversible dynamic bond system is a weak Most gels and elastomers introduce sacrificial bonds in the covalent network to dissipate energy. However, long-term cyclic loading caused irreversible fatigue damage and crack propagation cannot be prevented. Furthermore, because of the irreversible covalent crosslinked networks, it is a huge challenge to implement reversible mechanical interlocking and reorganize the polymer segments to realize the recycling and reuse of ionogels. Here, covalent crosslinking of host materials is replaced with entanglement. The entangled microdomains are used as...

Electronic skin can detect minute electrical potential changes in the human skin and represent the body's state, which is critical for medical diagnostics and human–computer interface development. On the other hand, sweat has a significant effect on the signal stability, comfort, and safety of electronic skin in a real‐world application. In this study, by modifying the cation and anion of a poly(ionic liquid) (PIL) and employing a spinning process, a PIL‐based multilayer nanofiber membrane (PIL membrane) electronic skin with a dual gradient is created. The PIL electronic skin is moisture‐wicking and breathable due to the hydrophilicity and pore size‐gradients. The intrinsically antimicrobial activities of PILs allow the safe collection of bioelectrical signals from the human body, such as electrocardiography (ECG) and electromyography (EMG). In addition, a robotic hand may be operated in real‐time, and a preliminary human–computer interface can be accomplished by simple processing of the collected EMG signal. This study establishes a novel practical approach for monitoring and using bioelectrical signals in real‐world circumstances via the multifunctional electronic skin.

In this study,w ed eveloped as uperstrong and reversible adhesive,whichcan possess ahigh bonding strength in the "adhesive" state and detach with the application of heating.A ni onic crystal (IC) gel, in whicha nI Cw as immobilized within as oft-polymer matrix, were synthesized via in situ photo-crosslinking of aprecursor solution composed of N, N-dimethyl acrylamide (DMAA) and am elted IC.T he obtained IC gel is homogenous and transparent at melt point. When cooled to the phase transition temperature of the IC,the gel turns into the adhesive with the adhesion strength of 5.82 MPa(on glasses), due to the excellent wetting of melted gel and at hin layer of crystalline IC with high cohesive strength formed on the substrates.T he synergistic effects between IC, polymer networks and substrates were investigated by solid state 1 HNMR and molecular dynamics simulation. Sucha n adhesive layer is reversable and can be detached by heating and subsequent re-adhesion via cooling. This study proposed the new design of removable adhesives,w hich can be used in dynamic and complex environments.

The mechanical properties of most hydrogels (ionogels) are considerably affected by covalently crosslinked networks. However, the interactions between solvent/solvent molecules and solvent/polymer chains are usually ignored. Herein, a series of ultra-tough ionogels were prepared via a supramolecular solvent, halometallate ionic liquid, in which cations and coordinating anions form a 3D supramolecular network. The linear polymer chains are physically cross-linked with supramolecular solvents synergistically enhancing the strength (14.3 MPa), toughness (78 MJ m À 3 ), and Young's modulus (55 MPa) of ionogels, effectively dispersing the stress concentration under load, and obtaining better fatigue resistance and higher fracture energy (198 kJ m À 2 ). Furthermore, the reversible crosslinking enables green recovery and recycling of ionogels, simply by water. This strategy shows broad applicability based on a variety of supramolecular solvents and coordinatable polymers.

Muscles and some tough hydrogels can maintain perfect mechanical properties after millions of loading cycles owing to the anisotropic microstructures inside them. However, applications of intrinsic anisotropic microstructures in biological tissues and tough hydrogels are limited by the poor mechanical performance in the perpendicular direction relative to the alignment direction. Here, a universal strategy is proposed for developing hydrogels with unprecedented isotropic crack propagation resistance only depending on the interpenetrating entanglements of polymer chains (polyacrylamide (PAAM) or poly‐(1‐acrylanmido‐2‐methylpropanesulfonic acid) (PAMPS)) in deformable polymeric microspheres (PAMPS or PAAM). The deformable interpenetrating network in microspheres can transform the hydrogel from isotropic to anisotropic instantaneously in any load direction, and effectively alleviate the stress concentration at the crack tip, dissipate energy, and eliminate notch sensitivity. The best isotropic hydrogel displays an ultimate strain of 5300%, toughness of 18.9 MJ m–3, fracture energy of 157 kJ m–2, and fatigue threshold of 4.2 kJ m–2. Furthermore, the mechanical strength of hydrogels can be simply tuned by solvent replacement. The strategy presented here can be expanded to prepare other isotropic hydrogels with super tear‐resistant and anti‐fatigue properties, based on a wide variety of deformable microspheres and matrix polymers.