Active origami by 4D printing

TLDR

3D printing with multi‑material layers enables heterogeneous microstructures, and incorporating shape‑memory polymers creates active components that change shape over time, a concept known as 4D printing. The study aims to extend 4D printing to design and fabricate active origami that fold flat sheets into complex 3D structures. They fabricate active composites with shape‑memory polymer fibers embedded in elastomeric matrices as hinges, and use a theoretical model to guide design parameters for origami folding. The model enabled fabrication of multiple active origami structures—including a box, pyramid, and airplanes—and a directly printed 3D box that can be flattened and then recover its shape on demand.

Abstract

Recent advances in three dimensional (3D) printing technology that allow multiple materials to be printed within each layer enable the creation of materials and components with precisely controlled heterogeneous microstructures. In addition, active materials, such as shape memory polymers, can be printed to create an active microstructure within a solid. These active materials can subsequently be activated in a controlled manner to change the shape or configuration of the solid in response to an environmental stimulus. This has been termed 4D printing, with the 4th dimension being the time-dependent shape change after the printing. In this paper, we advance the 4D printing concept to the design and fabrication of active origami, where a flat sheet automatically folds into a complicated 3D component. Here we print active composites with shape memory polymer fibers precisely printed in an elastomeric matrix and use them as intelligent active hinges to enable origami folding patterns. We develop a theoretical model to provide guidance in selecting design parameters such as fiber dimensions, hinge length, and programming strains and temperature. Using the model, we design and fabricate several active origami components that assemble from flat polymer sheets, including a box, a pyramid, and two origami airplanes. In addition, we directly print a 3D box with active composite hinges and program it to assume a temporary flat shape that subsequently recovers to the 3D box shape on demand.