In situ self-layering bilayer alginate-gelatin hydrogels enabling synergistic adhesion and sensing for pressure distribution recognition.

Hydrogel-based wearable devices often struggle to integrate strong adhesion, long-term stability, and reliable sensing within a single system. Here, we present a one-step water-oil phase separation strategy that enables the in situ self-layering of bilayer hydrogels with robust interfacial coupling. The top poly(acrylamide-acrylic acid)-gelatin-alginate (poly(AM-AA)-gelatin-alginate) network provides mechanical resilience and environmental durability, while the bottom poly(butyl acrylate-2-hydroxyethyl acrylate)-glycerol-polycaprolactone methacrylic anhydride (poly(BA-HEA)-GPCL-MA) adhesive layer ensures strong yet reversible adhesion to diverse surfaces. This integrated architecture achieves a rare balance between adhesion, water retention stability, and sensing reliability, overcoming the long-standing trade-off in hydrogel-based electronics. Deformation-induced modulation of ionic conduction pathways endows the hydrogel with sensitive electromechanical sensing, enabling precise human-motion detection and Morse-code communication via controlled finger movements. As proof-of-concept, a 4 × 4 pressure-mapping array was integrated into robotic grippers, enabling tactile feedback to distinguish soft and rigid objects such as balloons and bottles. This work highlights a versatile design strategy for multifunctional hydrogels, paving new opportunities for smart interfaces, advanced human-machine interaction, and adaptive soft robotic systems.