RT Journal Article SR Electronic T1 Dual-gradient enabled ultrafast biomimetic snapping of hydrogel materials JF Science Advances JO Sci Adv FD American Association for the Advancement of Science SP eaav7174 DO 10.1126/sciadv.aav7174 VO 5 IS 4 A1 Fan, Wenxin A1 Shan, Caiyun A1 Guo, Hongyu A1 Sang, Jianwei A1 Wang, Rui A1 Zheng, Ranran A1 Sui, Kunyan A1 Nie, Zhihong YR 2019 UL http://advances.sciencemag.org/content/5/4/eaav7174.abstract AB The design of materials that can mimic the complex yet fast actuation phenomena in nature is important but challenging. Herein, we present a new paradigm for designing responsive hydrogel sheets that can exhibit ultrafast inverse snapping deformation. Dual-gradient structures of hydrogel sheets enable the accumulation of elastic energy in hydrogels by converting prestored energy and rapid reverse snapping (<1 s) to release the energy. By controlling the magnitude and location of energy prestored within the hydrogels, the snapping of hydrogel sheets can be programmed to achieve different structures and actuation behaviors. We have developed theoretical model to elucidate the crucial role of dual gradients and predict the snapping motion of various hydrogel materials. This new design principle provides guidance for fabricating actuation materials with applications in tissue engineering, soft robotics, and active medical implants.