Fluidic soft actuators are enlarging the robotics toolbox by providing flexible elements that can display highly complex deformations. Although these actuators are adaptable and inherently safe, their actuation speed is typically slow because the influx of fluid is limited by viscous forces. To overcome this limitation and realize soft actuators capable of rapid movements, we focused on spherical caps that exhibit isochoric snapping when pressurized under volume-controlled conditions. First, we noted that this snap-through instability leads to both a sudden release of energy and a fast cap displacement. Inspired by these findings, we investigated the response of actuators that comprise such spherical caps as building blocks and observed the same isochoric snapping mechanism upon inflation. Last, we demonstrated that this instability can be exploited to make these actuators jump even when inflated at a slow rate. Our study provides the foundation for the design of an emerging class of fluidic soft devices that can convert a slow input signal into a fast output deformation.

From stadium covers to solar sails, we rely on deployability for the design of large-scale structures that can quickly compress to a fraction of their size (1-4). Historically, two main strategies have been pursued to design deployable systems. The first and most common approach involves mechanisms comprising interconnected bar elements, which can synchronously expand and retract (5-7), occasionally locking in place through bistable elements (8, 9). The second strategy instead, makes use of inflatable membranes that morph into target shapes by means of a single pressure input (10-12). Neither strategy however, can be readily used to provide an enclosed domain able to lock in place after deployment: the integration of protective covering in linkage-based constructions is challenging and pneumatic systems require a constant applied pressure to keep their expanded shape (13-15). Here, we draw inspiration from origami, the Japanese art of paper folding, to design rigid-walled deployable structures that are multistable and inflatable. Guided by geometric analyses and experiments, we create a library of bistable origami shapes that can be deployed through a single fluidic pressure input. We then combine these units to build functional structures at the meter-scale, such as arches and emergency shelters, providing a direct pathway for a new generation of large-scale inflatable systems that lock in place after deployment and offer a robust enclosure through their stiff faces. Origami | Multistability | Inflatable structures | Deployable structuresLarge, deployable structures should ideally (i) occupy the minimum possible volume when folded; (ii) be autonomous when deploying; (iii) lock in place after deployment; and (iv) provide a structurally robust shell (if they are designed to define a closed environment). To satisfy all these requirements, we here present a novel approach with roots in the Japanese art of paper folding: origami. Extensively used in robotics (16-20), metamaterials (21-25) and structures (26-30), origami principles have potential to lead to efficient large-scale deployable structures as they offer (i) a versatile crease-based approach to shape design (31-33); (ii) an easy actuation through inflation, if enclosed (34-36); (iii) self-locking capabilities when designed to support multiple energy wells (37-44); and (iv) the possibility to create a protective environment through their faces. While previous origami systems have explored inflatability and multistability separately (34-44), here we show that these two properties can coexist, unlocking an unprecedented design space of meter-scale inflatable structures that harness multistability to maintain their deployed shape without the need for continuous actuation (see schematics in Fig. 1a) Triangular facets as a platform for bistable and inflatable structures. To create inflatable and bistable origami structures, we start by considering a triangular building block ABC and denote with α and β the internal angles enclosed by the edges AB-AC and AB-BC, res...

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The accuracy of Additive Manufacturing processes in fabricating porous biomaterials is currently limited by their capacity to render pore morphology that precisely matches its design. In a porous biomaterial, a geometric mismatch can result in pore occlusion and strut thinning, drawbacks that can inherently compromise bone ingrowth and severely impact mechanical performance. This paper focuses on Selective Laser Melting of porous microarchitecture and proposes a compensation scheme that reduces the morphology mismatch between as-designed and as-manufactured geometry, in particular that of the pore. A spider web analog is introduced, built out of Ti-6Al-4V powder via SLM, and morphologically characterized. Results from error analysis of strut thickness are used to generate thickness compensation relations expressed as a function of the angle each strut formed with the build plane. The scheme is applied to fabricate a set of three-dimensional porous biomaterials, which are morphologically and mechanically characterized via micro Computed Tomography, mechanically tested and numerically analyzed. For strut thickness, the results show the largest mismatch (60% from the design) occurring for horizontal members, reduces to 3.1% upon application of the compensation. Similar improvement is observed also for the mechanical properties, a factor that further corroborates the merit of the design-oriented scheme here introduced.

Inflatable structures have become essential components in the design of soft robots and deployable systems as they enable dramatic shape change from a single pressure inlet. This simplicity, however, often brings a strict limitation: unimodal deformation upon inflation. Here, multistability is embraced to design modular, inflatable structures that can switch between distinct deformation modes as a response to a single input signal. This system comprises bistable origami modules in which pressure is used to trigger a snap-through transition between a state of deformation characterized by simple deployment to a state characterized by bending deformation. By assembling different modules and tuning their geometry to cause snapping at different pressure thresholds, structures capable of complex deformations that can be preprogrammed and activated using only one pressure source are created. This approach puts forward multistability as a paradigm to eliminate a one-to-one relation between input signal and deformation mode in inflatable systems.