smiley[source] We show how to assemble an astronomical number of distinct smart materials that each recognize and morph into a unique shape. To design these, we stack copies of one oriented building block, and crack the three-dimensional jigsaw puzzle that governs the placement of these blocks. We illustrate our strategy by 3D printing a metacube, which reveals a smiley pattern when compressed, and which can recognize other patterns. These novel materials bridge the gap between matter and machine, and may radically change the way in which materials can mechanically actuate and sense information, in e.g., prosthetics, wearable tech and robots.

The structural complexity of metamaterials is limitless, although, in practice, most designs comprise periodic architectures that lead to materials with spatially homogeneous features. More advanced tasks, arising in, for example, soft robotics, prosthetics and wearable technology, involve spatially textured mechanical functionality, which requires aperiodic architectures. However, a naive implementation of such structural complexity invariably leads to geometric frustration (whereby local constraints cannot be satisfied everywhere), which prevents coherent operation and impedes functionality. Here we introduce a combinatorial strategy for the design of aperiodic, yet frustration-free, mechanical metamaterials that exhibit spatially textured functionalities. We implement this strategy using cubic building blocks—voxels—that deform anisotropically, a local stacking rule that allows cooperative shape changes by guaranteeing that deformed building blocks fit together as in a three-dimensional jigsaw puzzle, and three-dimensional printing. We show that, first, these aperiodic metamaterials exhibit long-range holographic order, whereby the two-dimensional pixelated surface texture dictates the three-dimensional interior voxel arrangement. Second, they act as programmable shape-shifters, morphing into spatially complex, but predictable and designable, shapes when uniaxially compressed. Third, their mechanical response to compression by a textured surface reveals their ability to perform sensing and pattern analysis. Combinatorial design thus opens a new avenue towards mechanical metamaterials with unusual order and machine-like functionalities.

Combinatorial design of textured mechanical metamaterials
C. Coulais, E. Teomy, K. de Reus, Y. Shokef, and M. van Hecke
Nature 535, 529 (2016)