Freeform Manufacturing of Plant‐Based Structural Colors for Scalable Photonic and Mechanochromic Devices

Abstract

ABSTRACT Plant‐based, iridescent, and dynamically tunable structural colored materials are highly attractive for sustainable photonic devices. However, fabricating complex architectures at the decimeter‐scale with optical fidelity using plant‐derived materials remains challenging, limiting their use in photonic devices and adaptive actuation. Here, we introduce an aqueous two‐phase freeform fabrication strategy for vibrantly colored hydroxypropyl cellulose (HPC), where a robust immiscible aqueous environment is developed to preserve HPC cholesteric structures with < 3% shift in peak reflection wavelength over three days, enabling stable processing of large‐scale structural colored materials. Our technique involves a food‐grade support medium with low interfacial tension, allowing for embedded 3D printing of photonic structures and post‐extrusion recovery of the HPC cholesteric domains. Intricate constructs, including interlocking chainmail, with feature sizes down to ∼50 µm and color consistency over lengths exceeding ten centimeters, can be achieved. Additionally, this approach can be utilized to create non‐planar, mechanochromic hydrogel actuators with programmable multicolor designs, as demonstrated in an octopus‐inspired hydrogel actuator and a color‐shifting display for information encryption, camouflage, and human–machine interaction. Our green, freeform manufacturing approach provides new design possibilities for sustainable photonic devices and can be applied to industrially relevant applications.