Bilayer encapsulation strategy enabled ultra-stretchable electronic skin for human-machine interaction

Wearable bioelectronic sensors are transforming human-machine interaction by enabling real-time multimodal physiological monitoring and therapeutic functions. However, the existing stretchable strain sensors often struggle to maintain high stretchability and electrical reliability under large deformations, which limits their potential for seamless interaction. Herein, we propose a bilayer encapsulation (BE) strategy that leverages elastomeric films with a gradient modulus to effectively redistribute mechanical stress and significantly enhance stretchability. Moreover, by patterning the Cu/PI membrane into serpentine geometries and combining this design with the BE strategy, the strain sensor achieves a stretchability of up to 127%, which is three to five times higher than that of the conventional single-layer designs. The moduli of each layer can be independently tuned by controlling the curing agent content and the bilayer thickness, without altering the commonly used polydimethylsiloxane substrate. Owing to its excellent conformal contact with human skin, the device enables real-time HMI applications, including motion monitoring and robot arm control. This universal strategy simplifies fabrication and holds promise for advancing real-time health monitoring and embodied intelligence without the requirement for pre-training.