Extended Data Fig. 1: Comparison of WRAP film with heat shrink film and spider dragline silk.

a, Photographs of heat shrink polymer (polyvinyl chloride) wrapping a tissue-mimicking agarose gel with irregular shape. It contracted to wrap tightly around the hydrogel under 120 °C within seconds. The post-contraction film is much harder (GPa) than its underlying gel (kPa). b, Photographs of WRAP film wrapping an agarose gel with irregular shape. It contracted when dropped water to conformally wrap around the underlying agarose gel and became a soft hydrogel thin film within seconds. c, Schematic of the structure responsible for supercontraction in spider dragline silk. Silk’s supercontraction results from its hierarchical structure consisting of water-penetrable amorphous domains crosslinked by stable β-sheet crystalline domains. The highly oriented polymer chains in the amorphous domains are fixed by hydrogen bonds. Water from wetting breaks these bonds and induces molecular chain recoiling, causing large contractions. d, WRAP film is constructed by stable PEG-α-CD inclusion complex crystalline domains and water-penetrable semi-crystalline PEO domains. WRAP film has oriented PEO crystallites and microporous structure. Break of PEO crystallites by penetrated water causes PEO chain’s recoil and WRAP film’s contraction. Scale bar: 1 cm (a,b); 1 µm (d). Experiments in d were repeated six times with similar results.