Abstract
<title>Abstract</title> <p>Harnessing chemical reaction networks to regulate hydrogel actuators offers a promising route toward bioinspired smart materials with autonomous and programmable behaviours. Herein, we report a multi-stimuli-responsive bilayer hydrogel actuator that responds to both pH and metal ions. The bilayer actuator comprises two polyacrylamide-based layers, one functionalised with 1-vinylimidazole (VIm) and the other with methacrylic acid (MAA). The orthogonal ionizable groups impart distinct swelling responses across different pH regimes, enabling programmable bidirectional motion, while VIm's metal-ion coordination provides an additional stimulus-responsive mode. To emulate adaptive processes found in nature, the actuator was coupled with a newly developed autonomous NaOH–Sultone pH-clock. Addition of NaOH rapidly raises the pH to ~12, while the slower hydrolysis of Sultone generates sulfonic acid and gradually returns the system to the acidic region (~2.5), thereby creating a broad temporal pH window. Under these dynamically evolving chemical conditions, the bilayer displayed self-regulated bidirectional motion without any external intervention, converting transient chemical signals into programmed mechanical deformation. The pH-clock enables autonomous bidirectional actuation, driving the actuator from 0° to 140°, back through 0°, and subsequently to -135°. To further enhance its biomimetic character, a pH-responsive aggregation-induced emission luminogen (AIEgen) was incorporated into the VIm-containing layer. The resulting material exhibited autonomous, time-dependent fluorescence modulation synchronised with the evolving pH environment, thereby coupling macroscopic motion with transient luminescence. By integrating a new pH-clock with a multi-responsive hydrogel architecture, the system achieved simultaneous regulation of mechanical actuation and optical output, producing adaptive, life-like behaviour and providing a versatile platform for next-generation autonomous soft materials.</p>