Time-Encoded Geometric Encryption Enabled by Shape-Memory Hydrogel with Photoisomerization-Gated Autonomous Recovery

Leveraging spatiotemporal shape-changing of information-bearing morphologies, materials with predetermined autonomous-shape-morphing potentially offer a unique form of time-encoded geometric communication in contrast to existing optical encryption methods. However, fundamental mechanisms and control strategies underlying the spatiotemporal programmability remain insufficiently explored, thus the information capacity and security levels are still restricted. Here we report a non-thermal and spatiotemporally controllable strategy to gate the morphing kinetics of shape-memory hydrogel via photoisomerization. Upon functionalization of azobenzene moieties, multiple amide-amide hydrogen bonds are incorporated into the poly(acrylamide) hydrogel. These hydrogen bonds, with strong time-temperature dependence, act as stress-damping units that decelerate the network's inherent elastic recovery, providing a mechanism for time-encoded autonomous-shape-morphing. Photoisomerization of the pendant azobenzene moieties modulate the thermodynamic state of the hydrogen bonds, thus can control the morphing kinetics. Through orthogonal time and photo-spatial programming of the dynamic interactions, the hydrogel can autonomously execute sophisticated shape transformations along predetermined pathways, thereby serving as a carrier for storing geometric information. This work demonstrates the feasibility of time-encoded shape morphing and establishes an alternative strategy to conventional optics-based encryption, providing enhanced data capacity and security through time-dependent geometric encoding.