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We report a mechano-diffusion mechanism that harnesses mechanical deformation to control particle diffusion in stretchable hydrogels with a significantly enlarged tuning ratio and highly expanded tuning freedom. 

Abstract While in-situ underwater adhesives are highly desirable for marine exploration and underwater robotics, existing underwater adhesives suffer from significantly reduced performance compared to air-cured adhesives, mainly due to difficulties in removing interfacial water molecules. Here, we develop a pressure-sensitive in-situ underwater adhesive featuring superabsorbent particles infused with functional silane and hydrogel precursors. When injected into an underwater crack, the particles quickly absorb water, swell, and fill the crack. Mechanical pressure is applied to improve particle-particle and particle-substrate interactions, while heat is utilized to trigger thermal polymerization of the hydrogel precursors. This process creates porous adhesives via bulk polymerization and forms covalent bonding with the substrate via surface silanization. Our experiments demonstrate that mechanical pressure significantly enhances the adhesive’s stretchability (from 3 to 5), stiffness (from 37 kPa to 78 kPa), fracture toughness (from 1 kJ/m²to 7 kJ/m²), and interfacial toughness with glass substrates (from 45 J/m²to 270 J/m²). 

In this study, we investigate three different polymeric networks in terms of their tensile strength as a function of stretching rate, or temperature, or medium viscosity. 

Abstract Mechanoresponsive color‐changing materials that can reversibly and resiliently change color in response to mechanical deformation are highly desirable for diverse modern technologies in optics, sensors, and robots; however, such materials are rarely achieved. Here, a fatigue‐resistant mechanoresponsive color‐changing hydrogel (FMCH) is reported that exhibits reversible, resilient, and predictable color changes under mechanical stress. At its undeformed state, the FMCH remains dark under a circular polariscope; upon uniaxial stretching of up to six times its initial length, it gradually shifts its color from black, to gray, yellow, and purple. Unlike traditional mechanoresponsive color‐changing materials, FMCH maintains its performance across various strain rates for up to 10 000 cycles. Moreover, FMCH demonstrates superior mechanical properties with fracture toughness of 3000 J m⁻², stretchability of 6, and fatigue threshold up to 400 J m⁻². These exceptional mechanical and optical features are attributed to FMCH's substantial molecular entanglements and desirable hygroscopic salts, which synergistically enhance its mechanical toughness while preserving its color‐changing performance. One application of this FMCH as a tactile sensoris then demonstrated for vision‐based tactile robots, enabling them to discern material stiffness, object shape, spatial location, and applied pressure by translating stress distribution on the contact surface into discernible images.