Cholesteric cellulose liquid crystal ink for three-dimensional structural coloration

Color reproduction is an important aspect of three-dimensional (3D) printing in terms of creating a colored visual appearance with high fidelity and stability. To this end, structural color is an ideal coloring mechanism, which processes unique nonfading ability and tunable optical features. In this study, we propose a printable structural color ink composed of cholesteric cellulose liquid crystals together with gelatin and a thermal-responsive hydrogel. The ink maintains a cholesteric liquid crystalline state that gives rise to the structural color, and the rheology properties of the ink are optimized by gelatin, which allows the ink to flow during printing and form self-supporting structures after printing. The incorporation of the hydrogel further enables shape maintenance of the ink after printing via in situ ultraviolet-crosslinking. Based on this, we print a series of graphics and 3D objects with angle-independent color appearances and demonstrate the versatility of the printing system in different substrates. Moreover, the printed objects possess dual thermal responsiveness, which results in visible color changes around body temperature. These performances, together with the biocompatibility of the constituents, indicate that the present ink represents a leap forward to the next-generation 3D printing and would unlock a wide range of real-life applications.