Printed origami structures.

Final page numbers not assigned T IO N Origami, the traditional paper art, is a folding technique in which elegant and complex three-dimensional (3D) objects are produced from planar sheets. Significant scientific and technological interest in origami assembly methods have emerged due to the recognition that nature utilizes controlled folding and unfolding schemes to produce intricate architectures ranging from proteins to plants. To date, novel folding pathways have been harnessed to fabricate nanoscale DNA-based objects as well as nanoand mesoscale structures, such as 3D metallic objects and silicon solar cells that are lithographically patterned and spontaneously folded via surface tension effects. However, the ability to assemble printed structures of arbitrary 3D form, composition, and functionality with the ease, low cost, and versatility of paper origami has not yet been demonstrated. Here, we combine direct-write assembly with a wet-folding origami technique to create 3D shapes that range from simple polyhedrons to intricate origami forms, which are then transformed to metallic and ceramic structures by thermal annealing. Direct ink writing provides an attractive, non-lithographic approach for meeting the demanding design rules and form factors required for origami-based assembly. In this filamentbased printing method, a concentrated ink is extruded through a tapered cylindrical nozzle that is translated using a three-axis (x-y-z), motion-controlled stage (Fig. 1a). Although this method is capable of printing simple planar and 3D structures from myriad materials, including metallic, ceramic, or polymeric inks, it is difficult to pattern high aspect ratio structures without deformation (or slumping) and nearly impossible to directly pattern complex structures with large unsupported regions, such as overhanging features. By combining printing and origami methods, we demonstrate a powerful new approach to overcome such limitations.