Live-shaping of hydrogel thin films with light.

Light-responsive hydrogels are attractive materials for mimicking dynamic microstructures in nature, providing platform for tunable devices in photonics, sensing, and biomedicine. However, these systems often suffer from limited spatial resolution and slow response times, restricting their utility in high-speed or high-precision applications. Here, we present a light-responsive hydrogel thin film platform capable of rapid, reconfigurable surface modulation with sub-micron spatial resolution and actuation frequencies up to 2 Hz. The system leverages photoswitchable host-guest interactions to induce reversible contraction-expansion in response to patterned illumination. Dual-wavelength control enables the generation of dynamic, migrating surface features capable of transporting micro-objects in real time. The approach is further extended to free-standing films, demonstrating functionality in laser beam steering. Additionally, surface patterns can be stabilized by drying and erased by humidity, offering a route to rewritable sensor tags.