Injectable Granular Hydrogels as Colloidal Assembly Microreactors for Customized Structural Colored Objects.

While structural coloration has captured considerable interests across different areas in the past decades, the development of macroscopic objects with tailorable structural colors remains a challenge due to the difficulty of large-scale fabrication of finely ordered nanostructures and poor processability of their constituent materials. In this work, a type of photonic granular hydrogel is developed as a novel printable ink for constructing customized structural colored objects. The magnetochromatic ink exhibits dynamic properties such as shear thinning and self-healing, enabling direct writing of macroscopic structural colored patterns by extrusion 3D printing. Further, the modularity of the photonic ink allows additive color mixing, which obviates the need for arduous nano-synthesis and expands on the color abundance of structural colored materials in a simple yet efficient manner. These characteristics grant novel photonic inks with great applicability to a variety of fields including switchable color displays, sensors, etc.