A simple and effective approach is demonstrated to fabricate tough metallosupramolecular hydrogel films of poly(acrylic acid) by one‐pot photopolymerization of the precursor solution in the presence of Zr4+ ions that form coordination complexes with the carboxyl groups and serve as the physical crosslinks of the matrix. Both as‐prepared and equilibrated hydrogel films are transparent, tough, and stable over a wide range of temperature, ionic strength, and pH. The thickness of the films can be easily tailored with minimum value of ≈7 μm. Owing to the fast polymerization and gelation process, kirigami structures can be facilely encoded to the gel films by photolithographic polymerization, affording versatile functions such as additional stretchability and better compliance of the planar films to encapsulate objects with sophisticated geometries that are important for the design of soft electronics. By stencil printing of liquid metal on the hydrogel film with a kirigami structure, the integrated soft electronics shows good compliance to cover curved surfaces and high sensitivity to monitor human motions. Furthermore, this strategy is applied to diverse natural and synthetic macromolecules containing carboxyl groups to develop tough hydrogel films, which will open opportunities for the applications of hydrogel films in biomedical and engineering fields.

Hydrogel-based soft electronics (HSE) is promising as implantable devices due to the similarity of hydrogel substrates to biologic tissues. Most existing HSE devices are based on conducting hydrogels that usually have weak mechanical properties, low conductivity, and poor patternability. Reported here is an HSE with good mechanical performance, high sensitivity, and versatile functions by stencil printing of liquid metal on a tough hydrogel, facilitating integration of multiple sensing units. Self-shaping ability is imparted to the HSE by creating gradient structure in the hydrogel substrate. The resultant HSE actively deforms into 3D configurations with zero or nonzero Gaussian curvature to fix on objects or organs with sophisticated geometries and maintains the sensing functions. The versatilities and potential applications of this HSE are demonstrated by monitoring motions of a rice field eel and beatings of a rabbit heart. Such HSE based on morphing substrate should pave the way for implantable electronics with better fixation and interfacial contact with the organs. The concept of morphing hydrogel devices can be extended to other soft electronics with responsive polymer films or elastomers as the substrates.

Recent years have witnessed the rapid development of sustainable materials. Along this line, developing biodegradable or recyclable soft electronics is challenging yet important due to their versatile applications in biomedical devices, soft robots, and wearables. Although some degradable bulk hydrogels are directly used as the soft electronics, the sensing performances are usually limited due to the absence of distributed conducting circuits. Here, sustainable hydrogel‐based soft electronics (HSE) are reported that integrate sensing elements and patterned liquid metal (LM) in the gelatin–alginate hybrid hydrogel. The biopolymer hydrogel is transparent, robust, resilient, and recyclable. The HSE is multifunctional; it can sense strain, temperature, heart rate (electrocardiogram), and pH. The strain sensing is sufficiently sensitive to detect a human pulse. In addition, the device serves as a model system for iontophoretic drug delivery by using patterned LM as the soft conductor and electrode. Noncontact detection of nearby objects is also achieved based on electrostatic‐field‐induced voltage. The LM and biopolymer hydrogel are healable, recyclable, and degradable, favoring sustainable applications and reconstruction of the device with new functions. Such HSE with multiple functions and favorable attributes should open opportunities in next‐generation electronic skins and hydrogel machines.

Viscoelasticity is a generic characteristic of soft biotissues and polymeric materials, affording them with unique time- and rate-dependent properties. Here, by spatiotemporally tailoring the viscoelasticity in tough supramolecular hydrogels, we...

The design of soft robots capable of navigation underwater has received tremendous research interest due to the robots' versatile applications in marine explorations. Inspired by marine animals such as jellyfish, scientists have developed various soft robotic fishes by using elastomers as the major material. However, elastomers have a hydrophobic network without embedded water, which is different from the gel-state body of the prototypes and results in high contrast to the surrounding environment and thus poor acoustic stealth. Here, we demonstrate a manta ray-inspired soft robot fish with tailored swimming motions by using tough and stiff hydrogels as the structural elements, as well as a dielectric elastomer as the actuating unit. The switching between actuated and relaxed states of this unit under wired power leads to the flapping of the pectoral fins and swimming of the gel fish. This robot fish has good stability and swims with a fast speed (∼10 cm/s) in freshwater and seawater over a wide temperature range (4−50 °C). The high water content (i.e., ∼70 wt %) of the robot fish affords good optical and acoustic stealth properties under water. The excellent mechanical properties of the gels also enable easy integration of other functional units/systems with the robot fish. As proof-of-concept examples, a temperature sensing system and a soft gripper are assembled, allowing the robot fish to monitor the local temperature, raise warning signals by lighting, and grab and transport an object on demand. Such a robot fish should find applications in environmental detection and execution tasks under water. This work should also be informative for the design of other soft actuators and robots with tough hydrogels as the building blocks.