Lanthanide-Ion-Coordinated Supramolecular Hydrogel Inks for 3D Printed Full-Color Luminescence and Opacity-Tuning Soft Actuators

Stimuli-triggered simultaneous shape-morphing and color-changing can be found in many natural species. Developing synthetic materials and systems with these bioinspired properties could potentially transform a range of applications from autonomous soft robots to tissue engineering. Here, the design and additive manufacturing of a new lanthanide-ion-coordinated supramolecular hydrogel are reported, whose luminescence and opacity can be dynamically tuned in response to different humidity or hydration/dehydration conditions. The fluorescence color tuning is provided by the competing effect between nonconjugated chromophores and the dynamically coordinated Eu3+ ions, while the opacity change resulted from the phase separation/dissolution of the neutralized zwitterionic polymers in a dehydrated/hydrated state. To demonstrate camouflageable soft actuators, multimaterial direct ink writing is harnessed to manufacture hydrogel-based actuators with controlled shape, luminescence, and opacity change on demand.