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

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.