Single-Layer 4D Printing System Using Focused Light: A Tool for Untethered Microrobot Applications

Four-dimensional (4D) printing is a promising technique that can produce shape-morphing materials to designated stimuli. However, as bilayered structures with varying mechanical properties are required in conventional methods, structural limitations—such as thickness or curvature of the structure—have hindered the application of 4D printing technology. Herein, we demonstrate a novel single-layer 4D printing system using focused light (SPROUT) for rapid 4D printing with exceptionally high curvature in a microscale structure. According to the SPROUT technique, a single-layer material is encoded along the longitudinal direction with an anisotropic density gradient using focused light that possesses a prescribed photon intensity gradient. The folding and unfolding of the printed single-layer material are reversible and repeatable with protic or aprotic stimuli. Finally, with high SPROUT curvature, this system enabled the fabrication of an untethered microrobotic gripper to demonstrate soft robotics and smart actuators.