Connecting the branches of multistable non-Euclidean origami by crease stretching.

Non-Euclidean origami is a promising technique for designing multistable deployable structures folded from nonplanar developable surfaces. The impossibility of flat foldability inherent to non-Euclidean origami results in two disconnected solution branches each with the same angular deficiency but opposite handedness. We show that these regions can be connected via "crease stretching," wherein the creases exhibit extensibility in addition to torsional stiffness. We further reveal that crease stretching acts as an energy storage method capable of passive deployment and control. Specifically, we show that in a Miura-Ori system with a single stretchable crease, this is achieved via two unique, easy to realize, equilibrium folding pathways for a certain wide set of parameters. In particular, we demonstrate that this connection mostly preserves the stable states of the non-Euclidean system, while resulting in a third stable state enabled only by the interaction of crease torsion and stretching. Finally, we show that this simplified model can be used as an efficient and robust tool for inverse design of multistable origami based on closed-form predictions that yield the system parameters required to attain multiple, desired stable shapes. This facilitates the implementation of multistable origami for applications in architecture materials, robotics, and deployable structures.

Plant-inspired multi-stimuli and multi-temporal morphing composites.

Plants are inspiring models for adaptive, morphing systems. In addition to their shape complexity, they can respond to multiple stimuli and exhibit both fast and slow motion. We attempt to recreate these capabilities in synthetic structures, proposing a fabrication and design scheme for multi-stimuli and multi-temporal responsive plant-inspired composites. We leverage a hierarchical, spatially tailored microstructural and compositional scheme to enable both fast morphing through bistability and slow morphing through diffusion processes. The composites consisted of a hydrogel layer made of gelatine and an architected particle-reinforced epoxy bilayer. Using magnetic fields to achieve spatially distributed orientations of magnetically responsive platelets in each epoxy layer, complex bilayer architectural patterns in various geometries were realised. This feature enabled the study of plant-inspired complex designs,viafinite element analysis and experiments. We present the design and fabrication strategy utilizing the material properties of the composites. The deformations and temporal responses of the resulting composites are analysed using digital image correlation. Finally, we model and experimentally demonstrate plant-inspired composite shells whose stable shapes closely mimic those of the Venus flytrap, while maintaining the multi-stimuli and multi-temporal responses of the materials. The key to achieving this is to tune the local in-plane orientations of the reinforcing particles in the bilayer shapes, to induce distributed in-plane mechanical properties and shrinkage. How these particles should be distributed is determined using finite element modelling. The work presented in this study can be applied to autonomous applications such as robotic systems.

Magnetically driven in-plane modulation of the 3D orientation of vertical ferromagnetic flakes.

External magnetic fields are known to attract and orient magnetically responsive colloidal particles. In the case of 2D microplatelets, rotating magnetic fields are typically used to orient them parallel to each other in a brick-and-mortar fashion. Thanks to this microstructure, the resulting composites achieve enhanced mechanical and functional properties. However, parts with complex geometries require their microstructure to be specifically tuned and controlled locally in 3D. Although the tunability of the microstructure along the vertical direction has already been demonstrated using magnetic orientation combined with sequential or continuous casting, controlling the particle orientation in the horizontal plane in a fast and effective fashion remains challenging. Here, we propose to use rotating magnetic arrays to control the in-plane orientation of ferromagnetic nickel flakes distributed in curable polymeric matrices. We experimentally studied the orientation of the flakes in response to magnets rotating at various frequencies and precessing angles. Then, we used COMSOL to model the magnetic field from rotating magnetic arrays and predicted the resulting in-plane orientations. To validate the approach, we created composites with locally oriented flakes. This work could initiate reverse-engineering methods to design the microstructure in composite materials with intricate geometrical shapes for structural or functional applications.

Extreme Frequency Conversion from Soliton Resonant Interactions.

We present a metastructure architecture with a bistable microstructure that enables extreme broadband frequency conversion. We use numerical and experimental tools to unveil the relationship between input excitations at the unit cell level and output responses at the macrostructural level. We identify soliton-lattice mode resonances resulting in input-independent energy transfer into desired metabeam vibration modes as long as transition waves are triggered within the metastructure. We observe both low-to-high and high-to-low incommensurate frequency interactions in the metabeams, thus enabling energy exchange between bands 2 orders of magnitude apart. This behavior generalizes fluxon-cavity mode resonance in superconducting electronics, providing a general method to extreme frequency conversion in mechanics. Importantly, the introduced architecture allows for expanding the metamaterials design paradigm by fundamentally breaking the dependence of macroscopic dynamics on the unit cell properties. The resulting input-independent nature implies potential applications in broadband frequency regulation and energy transduction.

Dome-Patterned Metamaterial Sheets.

The properties of conventional materials result from the arrangement of and the interaction between atoms at the nanoscale. Metamaterials have shifted this paradigm by offering property control through structural design at the mesoscale, thus broadening the design space beyond the limits of traditional materials. A family of mechanical metamaterials consisting of soft sheets featuring a patterned array of reconfigurable bistable domes is reported here. The domes in this metamaterial architecture can be reversibly inverted at the local scale to generate programmable multistable shapes and tunable mechanical responses at the global scale. By 3D printing a robotic gripper with energy-storing skin and a structure that can memorize and compute spatially-distributed mechanical signals, it is shown that these metamaterials are an attractive platform for novel mechanologic concepts and open new design opportunities for structures used in robotics, architecture, and biomedical applications.

Filtered Mechanosensing Using Snapping Composites with Embedded Mechano-Electrical Transduction.

Mechanosensing is ubiquitous in natural systems. From the skin ridges of our finger tips to the microscopic ion channels in cells, mechanosensors allow organisms to probe their environment and gather information needed for processing, decision making, and actuation. Despite technological advances in synthetic mechanosensing, it remains challenging to achieve this functionality at the scale of large stiff structures where both the amount of data to sense locally and the diversity of input stresses that the sensors have to withstand require highly tunable systems. Filtered sensing using mechanical displacement is an effective strategy developed by organisms to cope with large sets of stimuli. Inspired by this biological strategy, we fabricate bistable elements that can passively filter mechanical inputs, translate them into electrical signals, and be reset to their original sensing state using an external magnetic field. These multiple functionalities are achieved using hierarchically structured composites that can be arranged in large-area arrays. The filtering capability and fast passive response of our mechanosensors are experimentally demonstrated using simple electrical circuits and magnets. Thanks to their scalability and applicability to a wide range of material systems, these low-power sensors are avenues for the fabrication of load-bearing structures that are able to sense, compute, communicate, and autonomously adapt in response to external magneto-mechanical stimuli.

Bioinspired spring origami.

Origami enables folding of objects into a variety of shapes in arts, engineering, and biological systems. In contrast to well-known paper-folded objects, the wing of the earwig has an exquisite natural folding system that cannot be sufficiently described by current origami models. Such an unusual biological system displays incompatible folding patterns, remains open by a bistable locking mechanism during flight, and self-folds rapidly without muscular actuation. We show that these notable functionalities arise from the protein-rich joints of the earwig wing, which work as extensional and rotational springs between facets. Inspired by this biological wing, we establish a spring origami model that broadens the folding design space of traditional origami and allows for the fabrication of precisely tunable, four-dimensional-printed objects with programmable bioinspired morphing functionalities.

Input-Independent Energy Harvesting in Bistable Lattices from Transition Waves.

We demonstrate the utilisation of transition waves for realising input-invariant, frequency-independent energy harvesting in 1D lattices of bistable elements. We propose a metamaterial-inspired design with an integrated electromechanical transduction mechanism to the unit cell, rendering the power conversion capability an intrinsic property of the lattice. Moreover, focusing of transmitted energy to desired locations is demonstrated numerically and experimentally by introducing engineered defects in the form of perturbation in mass or inter-element forcing. We achieve further localisation of energy and numerically observe a breather-like mode for the first time in this type of lattice, improving the harvesting performance by an order of magnitude. Our approach considers generic bistable unit cells and thus provides a universal mechanism to harvest energy and realise metamaterials effectively behaving as a capacitor and power delivery system.

Programmable snapping composites with bio-inspired architecture.

The development of programmable self-shaping materials enables the onset of new and innovative functionalities in many application fields. Commonly, shape adaptation is achieved by exploiting diffusion-driven swelling or nano-scale phase transition, limiting the change of shape to slow motion predominantly determined by the environmental conditions and/or the materials specificity. To address these shortcomings, we report shape adaptable programmable shells that undergo morphing via a snap-through mechanism inspired by the Dionaea muscipula leaf, known as the Venus fly trap. The presented shells are composite materials made of epoxy reinforced by stiff anisotropic alumina micro-platelets oriented in specific directions. By tailoring the microstructure via magnetically-driven alignment of the platelets, we locally tune the pre-strain and stiffness anisotropy of the composite. This novel approach enables the fabrication of complex shapes showing non-orthotropic curvatures and stiffness gradients, radically extending the design space when compared to conventional long-fibre reinforced multi-stable composites. The rare combination of large stresses, short actuation times and complex shapes, results in hinge-free artificial shape adaptable systems with large design freedom for a variety of morphing applications.

Unidirectional Transition Waves in Bistable Lattices.

We present a model system for strongly nonlinear transition waves generated in a periodic lattice of bistable members connected by magnetic links. The asymmetry of the on-site energy wells created by the bistable members produces a mechanical diode that supports only unidirectional transition wave propagation with constant wave velocity. We theoretically justify the cause of the unidirectionality of the transition wave and confirm these predictions by experiments and simulations. We further identify how the wave velocity and profile are uniquely linked to the double-well energy landscape, which serves as a blueprint for transition wave control.

High plasma levels of soluble ST2 but not its ligand IL-33 is associated with severe forms of pediatric dengue.

Identification of early determinants of dengue disease progression, which could potentially enable individualized patient care are needed at present times. Soluble ST2 (sST2) has been recently reported to be elevated in the serum of children older than 2 years old and adults with dengue infection and it was correlated with secondary infections as well as with severe presentations of the disease. The mechanism by which secreted ST2 is linked to severe dengue and plasma leakage remains unclear. One possibility is that IL-33 ligand may be elevated, contributing to membrane bound ST2 as part of the immune activation in dengue infection. We determined plasma levels of sST2 and the ligand IL-33 in 66 children with acute secondary dengue infections clinically classified using the guidelines of the World Health Organization, 2009. Dengue infection showed significant increases in cytokines IL-12p70, IL-10, IL-8, IL-6, IL-1ß and TNFα measured by flow cytometry based assay compared to uninfected individuals. In contrast, IL-33 levels remained unchanged between infected and uninfected individuals. The levels of sST2 positively correlated with values of IL-6 and IL-8 and inversely correlated with number of median value of platelet levels. In addition to circulating cytokine positive correlations we found that sST2 and isoenzyme creatine kinase-MB (CK-MB), a marker of myocardial muscle damage present in severe dengue cases were associated. Our pediatric study concluded that in dengue infections sST2 elevation does not involve concomitant changes of IL-33 ligand. We propose a study to assess its value as a predictor factor of disease severity.