Light-Encoding of a Supramolecular Hydrogel for Assembly-Free Soft Machines Capable of Sequential and Multistage Shape-Morphing

Shape-morphing hydrogels can mimic the dynamism of living creatures and are popular for designing soft machines, such as actuators and robots. However, most existing shape-morphing hydrogels present a single morphing pathway between two shapes, sequential and multistage shape-morphing in real scenarios has rarely been captured. Although a strategy that assembles functional hydrogel components has been reported, it is likely to simultaneously increase the complexity and weaken the versatility of hydrogel machines. Here, a light-encoding strategy based on the dynamic coordination between the ferric iron and carboxyl group (Fe 3+ ─COO − ) to integrate the frame and actuating units into a single hydrogel without assembly is proposed. The spatiotemporal control of light irradiation is expected to make the light-encoding process sequential and reprogrammable. Results demonstrate that the light-encoded patterns determine the morphing route and further activate shape-morphing owing to swelling mismatch. The actuating units can be successively created by localized irradiation or elaborately turned by re-coordinating and light-encoding. This endows the encoded hydrogel with sequential and multistage shape-morphing behavior, similar to the living creatures. This strategy allows the design of assembly-free soft machines with sequential and multistage shape-morphing performance, which will benefit the design of more types of hydrogel machines.