Origami, the traditional paper art, is a folding technique in which elegant and complex three-dimensional (3D) objects are produced from planar sheets.[1] 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 [2] to plants. [3] To date, novel folding pathways have been harnessed to fabricate nanoscale DNA-based objects [4,5] as well as nano-and mesoscale structures, such as 3D metallic objects [6][7][8][9] and silicon solar cells [10] that are lithographically patterned and spontaneously folded via surface tension effects. [11,12] 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 [13][14][15] with a wet-folding origami technique [16] 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, [17] ceramic, [18] or polymeric inks, [19,20] 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.We first created periodic structures of varying lattice geometry and number of layers by direct-write assembly (Fig. 1b). As one example, we fabricated a 3-layer square lattice (15.4 mm  12.1 mm) composed of stacked linear arrays of ink filaments (diameter, D ¼ 235 mm) aligned with the x-or y-axis, such that their orientation is orthogonal to the previous layer. The square lattices have a center-to-center spacing that varies between 0.5-3 mm, with a typical value of 0.55 mm (top image in Fig. 1b). We also produced two wavy patterns. The first lattice (1-layer, 11 mm  17 mm) consists of a planar array of sinusoidal patterned filaments (D ¼ 258 mm) with a wavelength (l) of

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Titanium and its alloys find widespread use in skeletal implants and biomedical devices (e.g., stents and orthodontic applications) owing to their excellent corrosion resistance, bio-compatibility, static and fatigue strength, and lack of magnetism (an important property for magnetic imaging). [1] Microporous titanium provides two additional advantages for implant applications: first, it reduces the stiffness of the material, thus reducing stress shielding, [2,3] and, second, it improves implant anchorage by allowing bone ingrowth. [4][5][6] To date, powder metallurgy approaches have been widely used to create porous Ti structures, through partial sintering, [7][8][9] inclusion of pore formers, [10][11][12][13] expansion of pores pressurized with argon or hydrogen gas, [14,15] or replication of cellular polymers. [16,17] Embrittlement often arises during processing due to the strong chemical affinity of titanium at elevated temperature with atmospheric oxygen, carbon, and nitrogen. Alternate efforts have focused on producing microarchitectured titanium, composed of lattice or truss structures with struts arranged periodically in space. These structures exhibit an outstanding combination of low density, high strength and stiffness, and good damage tolerance. [18] To date, production methods for microarchitectured titanium have focused on replication precision casting, [19,20] sintering of stacked wire arrays, [21] as well as selective electron beam, [22][23][24] or laser [25] sintering of Ti powders.Recently, we introduced a new method for creating 3D microarchitectured Ti structures that combines: [26] (i) direct ink writing (DIW) of planar lattices composed of two layers of orthogonally oriented, patterned TiH 2 filament arrays, followed by (ii) rolling of these pliable lattices into scrolls, or folding into complex three-dimensional shapes, and finally (iii) heat-treating to reduce the hydride to metallic titanium. This new method is characterized by its simplicity, high shape versatility, and ability to control local geometry, as well as scalability to larger structures. [26] Here, we use this novel COMMUNICATION[*] Prof.