A resilin-like retractable and stretchable hydrogel

Hydrogels mimicking the mechanical responses of biomaterials can lead to new applications of these materials. An example of such biomaterials is resilin protein, which is primarily responsible for power-amplified activities in many species like locomotion, feeding, and defense. To mimic the power-amplified activities in biological species, a synthetic material needs to be highly stretchable, resilient, and retractable. Here, we present a hydrogel system synthesized through a simple chemical reaction scheme using hydrophilic acrylic acid and methacrylamide, and hydrophobic poly(propylene glycol) diacrylate [PPGDA]. These gels show tunable elastic modulus of 15-100 kPa, stretchability up to 8.6 times, and resilience of 98%. These gels achieve a retraction velocity of 16 m/s and an acceleration of 4×10³ m/s² when released from a stretched state. These values are comparable to those observed in biological species during power amplification. Because of their high stretchability and resilience, these gels have been utilized to launch projectiles over a long distance. The stability of these gels in a saline environment opens up their application in developing undersea soft-robotics, prosthetics, and engineered devices.