Transforming architectures inspired by origami.

Paper folding is found across cultures for both aesthetic and functional purposes, with its most widely recognized exponent being the ancient art form of origami. More recently, there has been an upsurge of interest for translating origami designs into mathematics, natural sciences, engineering, and architecture. Across these different fields, origami is becoming a fountain of inspiration for new reconfigurable and multifunctional materials and structures. However, the use of origami designs as engineering elements is typically compromised by limitations in structural performance. A new study by Filipov et al. (1) presents an innovative approach for the design of strikingly rigid deployable structures. Their strategy is based on tubular building blocks, which are themselves built on Miura-ori; a regular folding pattern that maps a flat sheet into a one degree-offreedom deployable structure (2). Two neighboring Miura tubes can be set in a zig-zag (“zipper”) arrangement; together, the pair is remarkably stiff and effectively possesses a single degree of freedom by resisting other bending and twisting modes. These zipper tubes can then be combined to generate other structures, including more complex tubular systems and cellular assemblies. In Fig. 1 A and B, we present two particular examples from their study: a model bridge with loadbearing capacity and an architectural canopy that can be deployed to cover a wide span. Filipov et al. (1) borrow well-established tools from structural mechanics that are commonly used in civil and mechanical engineering and port them to this new emerging field of origami-inspired design. Much of the recent research inspired by origami spans across fields, from mathematics, physics, and computer science to materials engineering, biotechnology, aerospace, and architecture. In mathematics and computational origami, the kinematics is usually simplified by considering rigid panels (also known as rigid foldable origami), with a focus on geometry and topological considerations (3–5). There is a substantial body of literature in this domain (6) and powerful simulations tools have been developed to produce remarkably complex crease patterns for origami (7). A drawback of these approaches is that they tend to exclude considerations on mechanical properties, which are required if we are to predict the mechanical response of origami structures. With the goal of rationalizing the coupling of the mechanics and geometry of origami, the physics and mechanics communities has stormed the field with great interest. The epicenter of the activity is on configurations based on the Miuraori pattern and revolves primarily around issues related to the strong geometrically nonlinear behavior with multistability (8), tunable metamaterials (9), and self-assembled structures at different scales (10). On the robotics and fabrication front, there have also been significant advances in programmable foldable sheets (11), printable self-foldable robots (12), and self-folding microstructures and nanostructures (13), to mention just a few examples. Starting from a structural mechanics viewpoint, Filipov et al. (1) base their study on techniques originally developed for frame structures (14) that have been adapted to study the mechanics of foldable structures by relaxing the condition of rigidity of the planar faces (15). Here, origami was modeled as a pin-jointed truss structure and each fold represented by a bar element,