A bioinspired reversible snapping hydrogel assembly

Controlling the response for stimuli-responsive shape changing polymers is critically important for their device applications. The snapping transformation of the Venus Flytrap has inspired the design of shape changing devices with a unique controlling mechanism in mechanical instability, yet their practical potential has been quite limited due to the irreversible nature. Herein, we report an approach to achieve an unprecedented reversible snapping. The material system is a hydrogel assembly that can be mechanically programmed to exhibit instability based bi-stable states. Taking advantages of the multi-responsiveness of the hydrogels allows reversible switching between the two stable states in an abrupt non-continuous (snap) fashion, with unique benefits in precise time-delayed deployment, accelerated deployment speed, and enhanced output force. The mechanism behind our design can be readily extended beyond hydrogels to enhance the performances of diverse multifunctional smart devices.