Bioinspired Simultaneous Changes in Fluorescence Color, Brightness, and Shape of Hydrogels Enabled by AIEgens

Development of stimuli-responsive materials with complex practical functions is significant for achieving bioinspired artificial intelligence. It is challenging to fabricate stimuli-responsive hydrogels showing simultaneous changes in fluorescence color, brightness, and shape in response to a single stimulus. Herein, a bilayer hydrogel strategy is designed by utilizing an aggregation-induced emission luminogen, tetra-(4-pyridylphenyl)ethylene (TPE-4Py), to fabricate hydrogels with the above capabilities. Bilayer hydrogel actuators with the ionomer of poly(acrylamide-r-sodium 4-styrenesulfonate) (PAS) as a matrix of both active and passive layers and TPE-4Py as the core function element in the active layer are prepared. At acidic pH, the protonation of TPE-4Py leads to fluorescence color and brightness changes of the actuators and the electrostatic interactions between the protonated TPE-4Py and benzenesulfonate groups of the PAS chains in the active layer cause the actuators to deform. The proposed TPE-4Py/PAS-based bilayer hydrogel actuators with such responsiveness to stimulus provide insights in the design of intelligent systems and are highly attractive material candidates in the fields of 3D/4D printing, soft robots, and smart wearable devices.