Programmable Hygrothermal Shape-Morphing via Swelling-Memory Force Competition in Integrated Polyurethane Actuators

Abstract Self-regulating soft actuators that combine large, reprogrammable shape-morphing with mechanical robustness are essential for next-generation bioinspired sensors and soft robotics, yet water-triggered systems often suffer from weak hydrogel mechanics, delamination in multilayers, and limited autonomous regulation. Here, we report a pinecone-scale-inspired, integrated bilayer polyurethane actuator in which a hydrophobic polycaprolactone (PCL)-rich layer and a hydrophilic polyethylene glycol (PEG)/PCL layer are molecularly fused via dynamic oxime bonds to eliminate interfacial failure while enabling healability. Leveraging the intrinsic contrast in semi-crystallinity and hydrophilicity of the soft segments, we create a single-material platform with dual-force competition between swelling pressure and thermally activated shape memory recovery. At 20 °C, the actuator bends continuously from 0° to 360°, reaching a maximum bending angle of 360° at 1140 s, after which the bending angle remains stable, with the bending trajectory and final geometry precisely tuned by the PCL/PEG feed ratio and laminate angle. Under wet-heat conditions, it also shows reversible transparent–opaque transitions, enabling coupled actuation and visual hygrothermal reporting. This strategy offers a robust route to programmable hygrothermal actuators for underwater sensing, soft grippers, and bioelectronic interfaces.