Biomimetic wet-applicable adhesive as a stiffness-tunable binding interface for on-skin sensors and self-locking actuators

Both stimuli responsive strain sensors and actuators have drawn significant attention because they are promising in a wide span of applications, including wearable devices, stretchable electronics, and soft robotics. However, there are few researches focusing on achieving a wet-applicable, ultra-conformable, and stiffness-tunable interface, which is highly critical in these fields. Herein, we develop a novel wet stretchable adhesive that shows high binding strength to various substrates. Furthermore, by introducing hygroscopic calcium chloride (CaCl₂) into the system, the Young’s modulus of the adhesive film can be easily adjusted from higher than 1.5 GPa to lower than 0.01 MPa under ambient environment (ca. 25 °C, 70% relative humidity) because of the water uptake and the corresponding plasticizing effect. We further use this adhesive to fabricate a soft (skin-like modulus, 0.1-10.0 MPa), thin (~50 μm), highly sensitive (a gauge factor of ~2000 under 20% strain), and ultra-compliant on-skin strain sensor and a multi-responsive (heat, near infrared (NIR) light, voltage, and humidity) self-locking actuator. A new avenue has been created to address both sensing and actuating bottlenecks by introducing a wet-applicable adhesive as a versatile and robust binding interface.