Frontal Polymerization Preparation of Multifunctional Janus Hydrogels for Soft Actuation and Wearable Sensing Applications

Abstract Janus hydrogels have garnered widespread interest due to their inherent anisotropic dual-faced architecture and functionality, which make them especially valuable for diverse applications, including smart wound dressing, soft actuators, and wearable sensors. Herein, multifunctional Janus hydrogels with structural and functional duality are facilely, rapidly, and one-step synthesized by frontal polymerization (FP) within 10 min. Through strong interfacial coupling, the two constituent layers form a stable Janus architecture capable of withstanding large deformations. Besides, the resultant hydrogels demonstrate tunable mechanical properties, exceptional extensibility (>500%), and great self-healing and self-adhesive performance. Crucially, the anisotropic Janus design engenders pronounced gradients in the microporous morphology and solvent uptake behavior. This asymmetry in the swelling capacity between the two layers drives solvent-induced bending deformation, allowing the bilayer hydrogels to operate as efficient underwater soft actuators for grasping objects. Furthermore, the hydrogel is engineered into a flexible, stretchable, and antifreeze multimodal wearable sensor for real-time human-motion tracking and information transmission. Overall, this study presents a time-efficient, energy-conserving, and versatile approach to constructing multifunctional Janus hydrogels, thereby advancing the development of soft actuation systems and intelligent wearable electronics.