Multifunctional Gelatin‐Based Smart Films Integrating Thermochromic Encryption, Temperature‐Regulated Photothermal Management, Reprocessability, and Biodegradability for Sustainable Applications

ABSTRACT Multifunctional gelatin‐based smart films are engineered by incorporating hyperbranched polyglycerol (HBPG) as a plasticizer, dialdehyde β‐cyclodextrin (Da‐β‐CD) as a crosslinker, and thermochromic microcapsules (TCMs). Structural analyses, including FTIR, XPS, and NMR, confirm the formation of covalent Schiff base linkages between Da‐β‐CD and gelatin, alongside hydrogen bonding reorganization facilitated by HBPG. The optimized film (GHBT 2 ‐CD) exhibits enhanced tensile strength (28.7 MPa), hydrophobicity (water contact angle of 116°), UV‐blocking capability (>97%), and complete (100%) bacterial inhibition. Crucially, these films demonstrate programmable thermochromism for multilevel information encryption, enabling features such as laser‐writing, temperature‐gated message display (e.g., “SUST” decryption), and numeral switching (9→7→8) using TCMs with distinct transition temperatures (18°C, 28°C, and 38°C). Furthermore, they achieve dual‐modal encryption by combining the intrinsic fluorescence of gelatin (emission at 340 nm) with thermochromism, which enables four‐state displays (e.g., showing “Accept”). Additionally, the films provide self‐adaptive temperature regulation: their black state below 28°C significantly boosts solar heating (achieving a ΔT of +27°C in a 4°C ambient environment), while their pale‐yellow state above 28°C mitigates overheating (keeping the surface below 56°C in a 30°C ambient), an effect augmented by the phase‐change latent heat buffering of the TCMs. Finally, the films embody closed‐loop sustainability. The presence of dynamic Schiff base and hydrogen bond networks enables over 91% self‐healing efficiency using stimuli like water, heat, or vapor, facilitates physical reprocessing, and allows for tunable degradation rates dependent on pH or soil conditions (complete degradation within 24 h at pH = 2, and within 12 days in sludge). This work pioneers an all‐in‐one smart materials platform that bridges optical security, thermal management, and the principles of a circular economy.