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.
