Poly(<i>N</i>-Isopropylacrylamide) Microgel Containing Hydrogel Enables Cooling/Water Induced Shape Recovery and Transient Image Display

In this study, we developed a poly(N-isopropylacrylamide)(PNIPAm) microgel-based hydrogel with thermo- and salt-responsive dual shape memory performance and anticounterfeit capabilities. A series of PAAm-MG hydrogels were fabricated by introducing PNIPAm microgel into the PAAm network. The hydrophobic aggregation of PNIPAm chains could be induced by both temperature and salt, serving as temporary crosslinks to stabilize the temporary shapes, and resulting in shape recovery triggered by cooling and water. The shape memory properties could be regulated by both the PNIPAm microgel content and the NaCl solution concentration. Moreover, secret information could be encoded on the surface of the hydrogel via salt printing at room temperature, due to the local phase transition of PNIPAm chains. The encoded information could be encrypted in a warm environment, decrypted in cold water at 25 °C, and erased over time due to salt diffusion, achieving temporary information display.