This review presents the recent progress of mussel-inspired hydrogels from fundamental interaction mechanisms and design principles to promising applications.

Mussel-inspired conductive hydrogels are attractive for the development of next-generation self-adhesive, flexible skinlike sensors. However, despite extensive progress, there are still some daunting challenges that hinder their applications, such as inferior optical transparency, low catechol content (e.g., poor adhesion), as well as limited sensation performances. Here, we report a dopamine-triggered gelation (DTG) strategy for fabricating mussel-inspired, transparent, and conductive hydrogels. The DTG design leverages on the dual functions of dopamine, which serves as both polymerization initiator and dynamic mediator to elaborate and orchestrate the cross-linking networks of hydrogels, allowing for pronounced adhesion, robust elasticity, self-healing ability, excellent injectability and three-dimensional printability, reversible and tunable transparent-opaque transition, and thermoresponsive feature. These preferable performances enable DTG hydrogels as self-adhesive, flexible skinlike sensors for achieving multiple sensations toward pressure, strain, and temperature, even an extraordinary visual perception effect, making it a step closer in the exploration of future biomimetic skin.

Daytime passive radiative cooling is a promising electricity-free pathway for cooling terrestrial buildings. Current research interest in this cooling strategy mainly lies in tailoring the optical spectra of materials for strong thermal emission and high solar reflection. However, environmental heat gain poses a crucial challenge to building cooling at subambient temperatures. Herein, we devise a scalable thermal insulating cooler (TIC) consisting of hierarchically hollow microfibers as the building envelope that simultaneously achieves passive daytime radiative cooling and thermal insulation to reduce environmental heat gain. The TIC demonstrates efficient solar reflection (94%) and long-wave infrared emission (94%), yielding a temperature drop of about 9 °C under sunlight of 900 W/m 2 . Notably, the thermal conductivity of the TIC is lower than that of air, thus preventing heat flow from external environments to indoor space in the summer, an additional benefit that does not sacrifice the radiative cooling performance. A building energy simulation shows that 48.5% of cooling energy could be saved if the TIC is widely deployed in China.

Owing to its 100% theoretical salt rejection capability, membrane distillation (MD) has emerged as a promising seawater desalination approach to address freshwater scarcity. Ideal MD requires high vapor permeate flux established by cross-membrane temperature gradient (∆T) and excellent membrane durability. However, it’s difficult to maintain constant ∆T owing to inherent heat loss at feedwater side resulting from continuous water-to-vapor transition and prevent wetting transition-induced membrane fouling and scaling. Here, we develop a Ti3C2Tx MXene-engineered membrane that imparts efficient localized photothermal effect and strong water-repellency, achieving significant boost in freshwater production rate and stability. In addition to photothermal effect that circumvents heat loss, high electrically conductive Ti3C2Tx MXene also allows for self-assembly of uniform hierarchical polymeric nanospheres on its surface via electrostatic spraying, transforming intrinsic hydrophilicity into superhydrophobicity. This interfacial engineering renders energy-efficient and hypersaline-stable photothermal membrane distillation with a high water production rate under one sun irradiation.

Hydrogels have emerged as a landmark soft material for a wide range of applications such as in biomedical devices, soft robotics, artificial electronic skins, and Internet of Things (IoT). To...

Shaping soft and conductive materials into preferential architectures via 3D printing is highly attractive for numerous applications ranging from tactile devices to bioelectronics. A landmark type of soft and conductive materials is hydrogels/ionogels. However, 3D‐printed hydrogels/ionogels still suffer from a fundamental bottleneck: limited stability in their electrical–mechanical properties caused by the evaporation and leakage of liquid within hydrogels/ionogels. Although photocurable liquid‐free ion‐conducting elastomers can circumvent these limitations, the associated photocurable process is cumbersome and hence the printing quality is relatively poor. Herein, a fast photocurable, solid‐state conductive ionoelastomer (SCIE) is developed that enables high‐resolution 3D printing of arbitrary architectures. The printed building blocks possess many promising features over the conventional ion‐conducting materials, including high resolution architectures (even ≈50 µm overhanging lattices), good Young's modulus (up to ≈6.2 MPa), and stretchability (fracture strain of ≈292%), excellent conductivity tolerance in a wide range of temperatures (from −30 to 80 °C), as well as fine elasticity and antifatigue ability even after 10 000 loading–unloading cycles. It is further demonstrated that the printed building blocks can be programmed into 3D flexible tactile sensors such as gyroid‐based piezoresistive sensor and gap‐based capacitive sensor, both of which exhibit several times higher in sensitivity than their bulky counterparts.

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