Multicolor fluorescent cellulose hydrogels actuators: Lanthanide-ligand metal coordination, synergetic color-changing and shape-morphing, and antibacterial activity

The development of stimulus-responsive materials with multifunctionality is important for achieving bionic artificial intelligence. However, stimulus-responsive cellulose hydrogels that simultaneously change their shape and fluorescent color under a single stimulus are difficult to fabricate. Here smart, multicolor fluorescent cellulose hydrogels were prepared from cellulose, levofloxacin, epichlorohydrin, and lanthanide ions (Eu3+ or Tb3+). The hydrogels were incorporated with pan paper into synergetic color-changing and shape-morphing actuators (Eu-CLF and Tb-CLF actuators). Besides fluorescing with the metal ligands, levofloxacin possesses antibacterial activity. The fluorescence color of Eu-CLF hydrogel in Tb3+ solution changed from red to yellow, whereas that of Tb-CLF hydrogel in Eu3+ solution changed from green to red. Both the Eu-CLF and Tb-CLF hydrogels fluoresced blue and green in alkali and acid solution, respectively. The actuator thus achieves synergetic color-changing and shape-morphing under a single external stimulus (acidic/alkaline switching). Such an activator shaped like a bionic flower and an intelligent octopus-type soft robot with camouflaging ability were then prepared. This study provides an elegant strategy for developing advanced multi-responsive multicolor tunable behaviors for bionic soft robots, biosensors, and camouflaged robots.