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

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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.
Funding Information
  • Natural Science Foundation of Jilin Province (20260101017JJ)
  • National Natural Science Foundation of China (22275023)
  • Changbai Talent Program of Jilin Province
  • Jilin Province Doctoral Candidate Support Program (BST202511)

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