pH and Thermo Dual-Responsive Fluorescent Hydrogel Actuator.

As one of the most important smart materials, fluorescent hydrogel actuators can produce both color and shape changes under external stimuli. In the present work, an effective approach to develop a novel fluorescent hydrogel actuator with pH and thermo dual responsiveness is proposed. Through incorporating pH-responsive perylene tetracarboxylic acid (PTCA), which is a typical fluorescent moiety with aggregation-caused quenching (ACQ) effect, into an anisotropic poly(N-isopropylacrylamide)-polyacrylamide (PNIPAm-PAAm) structure, the obtained hydrogel exhibits stable thermoresponsive shape deformation and switchable fluorescence performance upon a pH trigger. Therefore, fluorescence-quenching-based and actuation-based information can be revealed when exposed to UV light and immersed into warm water, respectively. Moreover, the thermoresponsive actuating behavior can be applied to further hide the fluorescence-quenching-based images. The present work may provide new insights into the design and preparation of novel stimuli-responsive hydrogel actuators.

Shape Memory Hydrogels with Simultaneously Switchable Fluorescence Behavior.

Realization of shape memory process in polymeric hydrogels at ambient condition is a significant development to shape memory materials. The sound understanding of the dynamic shape memory process is fundamentally important but limited. Here, a novel shape memory hydrogel with simultaneously switchable fluorescence behavior is developed. The hydrogel is prepared by incorporating a pH-responsive fluorescent molecule, perylene tetracarboxylic acid, into chitosan-based hydrogel, and the assembly and disassembly of chitosan chains into microcrystals upon the trigger of pH are applied as reversible crosslinks to achieve shape memory effect. Therefore, the formation and disassociation of microcrystalline chitosan, and the switchable fluorescence performance happen concurrently, which bring convenience to monitoring the shape memory process by fluorescent imaging. Moreover, the erasable fluorescence behavior also gives the hydrogel potential applications in information storage.