Reversible color-changing polymer hydrogels mediated by urea-urease clock reaction for temporary information display

Abstract

Inspired by the natural world's fascinating capacity for color change, researchers have developed various responsive hydrogels that shift colors. Among these, hydrogels that react to pH changes are particularly notable for their unique properties. The urea-urease autocatalytic reaction, a key pH clock reaction, is especially effective in temporarily adjusting these hydrogels' properties and enabling color changes in response to stimuli. In this study, we synergize the urea-urease clock reaction with the pH-sensitive color transformation of neutral red (NR), thereby establishing an NR-urea-urease clock reaction system. This system exhibits a dynamic color cycle from yellow to red and back to yellow. By incorporating this color transition mechanism into polymer hydrogels, we successfully initiate a pH change within the system. This innovation paves the way for a smart material capable of displaying temporary information through enzymatic reactions. The temporal variation in information display is finely tuned by adjusting the urea and urease concentrations. Such reversible color-changing hydrogels hold promising prospects for applications in secure information transmission and dynamic camouflage, marking a significant step forward in systems chemistry and materials science.