Firefly-Inspired 3D Printable Multi-Stimuli-Responsive Fluorescent Hydrogels with Adaptive Luminescence

Bioluminescent organisms, such as fireflies, jellyfish, and glow worms, possess a superb capacity for environment-interactive luminescence, enabling them to adapt to their surroundings. However, developing artificial luminescent materials that mimic the wet, soft, flexible, and multistimuli-responsive nature of bioluminescent organisms remains a challenge. Here, we present a rational design strategy for multistimuli-responsive fluorescent hydrogels in diverse and complex shapes, mimicking the bioluminescent behavior of fireflies. The fluorescence is activated and enhanced by natural and sustainable stimuli─water and temperature─and can be reversibly deactivated on-demand, similar to the role of oxygen and temperature in the firefly bioluminescence. Specifically, the designed molecular additives integrated within the hydrogel matrix increase fluorescence intensity and enhance the reversible and repetitive responsiveness to surrounding solvents without diminishing fluorescence intensity. Moreover, the hydrogel matrix responding to temperature changes enables control of fluorescence. Furthermore, the hydrogel precursor, designed for good printability, allows 3D printing of diverse-shaped fluorescent hydrogel structures, including artificial fluorescent organism models and fluorescence-patterned displays. This capability extends to implementing on-demand dynamic information encryption-decryption display with controllable fluorescent intensity and on-off rates. The proposed design strategy and free-form fabrication of fluorescent hydrogels could provide a viable path toward advanced fluorescent hydrogel development.