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

TLDR

Stimuli‑responsive materials with complex practical functions are crucial for bioinspired artificial intelligence, yet creating hydrogels that simultaneously alter fluorescence color, brightness, and shape in response to a single stimulus remains difficult. This work designs a bilayer hydrogel that uses the aggregation‑induced emission luminogen TPE‑4Py to achieve such simultaneous changes. The bilayer actuator comprises a poly(acrylamide‑r‑sodium 4‑styrenesulfonate) matrix for both active and passive layers, with TPE‑4Py in the active layer; at acidic pH, protonation of TPE‑4Py alters fluorescence and electrostatic interactions with PAS chains trigger deformation. The resulting TPE‑4Py/PAS bilayer hydrogels demonstrate responsive actuation and hold promise for 3D/4D printing, soft robotics, and smart wearable devices.

Abstract

Abstract 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.