image: Printed 2D and 3D microstructures in different structural colors. (A) Logo of 2D Max Planck Society in different colors. The patterns are printed at different driving electric fields, yielding different structural colors. (B) 2D Taiji logo in various colors and combinations. The patterns of different sizes are printed to test the resin's printing resolution limit. A pattern can be printed in different colors by selectively printing certain parts at one driving electric field strength and other parts at a different driving electric field strength. (C) 3D microscale frames. The frames are printed in liquid crystal cells with a 65 μm gap at different driving electric field strengths.
Credit: Feng et al.
A microscale 3D printing technique uses a resin that can be dynamically tuned to create different colors during printing. The authors demonstrate the technique by creating a colorful replica of a famous statue that is smaller than the diameter of a human hair.
3D printing an object with multiple colors at the macroscale is relatively easy. Different colored materials can be fed into the nozzle in sequence as the object is built. But microscale 3D printing typically does not use extrusion-based methods. The microscale technique known as two-photon polymerization (TPP) uses lasers carefully aimed at a vat of resin to cure individual pixels, known as voxels. To incorporate multiple colors requires time-consuming realignment. Metin Sitti and colleagues developed an electric field-coupled TPP system for on-demand modulation of 3D-printed structural color. The resin is made of oblique helicoidal cholesteric liquid crystals, a material that changes color when exposed to electric fields of varying strengths. The electrical current changes the angle of bent-shaped liquid crystals, which changes how the crystals look under white light, moving from violet to green to red as the field strength decreases. The authors demonstrate their technique by creating a microscale replica of the Chinese traditional statue, Galloping Horse Treading on a Flying Swallow, in multiple colors. According to the authors, the technique could be used in optics and anticounterfeiting.
Journal
PNAS Nexus
Article Title
Electric field-coupled two-photon polymerization system for on-demand modulation of 3D-printed structural color
Article Publication Date
13-May-2025