Direct-Printing Hydrogel-Based Platform for Humidity-Driven Dynamic Full-Color Printing and Holography

Hydrogel materials endow the flat optics platform with active tuning capability, owing to their remarkable humidity-responsive swelling behavior. Despite recent advances in hydrogel-based devices for spectral tuning, their complex patterning processing and limited functionality obstruct them from practical applications. Herein, a single-step direct-printing technique is originally demonstrated with an active hydrogel material platform for realizing unprecedented multi-field full-color display dynamics. Through exploring the dose-induced shrinkage on polyvinyl alcohol, the stepwise hydrogel nanocavities sandwiched by ultrathin metallic films can be directly printed by grayscale e-beam lithography. Due to the tunable structural coloration from hydrogel nanocavity scaling, multi-functionalities are successfully created for optical concealment, dynamic coloring, and dynamic full-color holography. By encoding the cavity-dependent transmission phase into the direct-printed hydrogel platform, it originally enables the projected full-color holographic dynamics in real-time by simply exhalation, beyond the static holographic display or monochromatic holographic switching. The proposed active displays can rapidly respond to the surrounding humidity change at a millisecond-level (< 150 ms). Such a direct-printing strategy for hydrogel nanocavity represents a critical advance toward the unprecedented dynamic full-color display, and suggests promising applications in optical security, gas sensing, multispectral imaging, full-color holography, and next-generation display techniques.