Formwork for concrete construction remains one of the most resource-intensive, polluting, and constraining components of the construction sector, relying on prefabricated molds that demand extensive material, labor, and on-site preparation. We introduce a self-deploying formwork system based on multistable tubes that transform from a compact configuration to a full-scale structural mold with integrated steel reinforcement. We demonstrate this concept by deploying a steel-reinforced 2.36 m high structure within 14 seconds. We further observed that the polymer shell of the multistable tubes increases the structural strength by a factor of three, significantly enhancing their load-bearing capacity. The demonstrated concept paves the way for the creation of concrete castings with minimal on-site intervention, enabling a scalable pathway toward rapid, low-carbon construction methods.

Origami-inspired tubular structures provide a versatile platform for shape morphing, with multistability achieved predominantly through crease-network geometry. Expanding the range of morphing behaviors can therefore require increasingly intricate crease patterns that become more difficult to model and fabricate, ultimately constraining the realizable morphing landscape. Here, we expand the design space of origami-inspired structures beyond geometry by introducing localized instabilities within the crease network, thereby creating compliant multistable structures whose local fold architectures govern global deformation and stability through both constitutive mechanics and geometric constraints. To relate local fold architectures to global multistability, we develop and experimentally validate a modeling framework in which compliant folds are represented as continuous fields that capture spatially varying bistable mechanics. Force- and displacement-controlled design maps demonstrate that global deformation and stability can be programmed through the fold architecture's local parameters. Redistributing bistability within a fixed crease-network topology shifts the global response between compliant, spatially distributed deformation in semi-bistable architectures and discrete transitions within a hierarchically organized space of stable configurations in fully bistable architectures. These results establish a local-to-global design principle for programming both the stable configurations of a structure and the transition pathways connecting them, expanding the design space for multistable metamaterials, adaptive morphing structures, and soft robotic systems.

Floating particles deform the liquid-gas interface, which may lead to capillary repulsion or attraction and aggregation of nearby particles (e.g. the Cheerios effect). Previous studies employed the superposition of capillary multipoles to model interfacial deformation for circular or ellipsoidal particles. However, the induced interfacial deformation depends on the shape of the particle and becomes more complex as the geometric complexity of the particle increases. This study presents a generalised solution for the liquid-gas interface near complex anisotropic particles using the domain perturbations approach. This method enables a closed-form solution for interfacial deformation near particles with an anisotropic shape, as well as the varying height of the pinned liquid-gas contact line. We verified the model via experiments performed with fixed particles held at the water level with shapes such as a circle, hexagon and square, which have either flat or sinusoidal pinned contact lines. Although in this study we concentrate on the equilibrium configuration of the liquid-gas interface in the vicinity of particles placed at fixed positions, our methodology paves the way to explore the interactions among multiple floating anisotropic particles and, thus, the role of particle geometry in self-assembly processes of floating particles.

Metamaterials are structures composed of repeating unit-cells which enable macro-scale properties not found in nature. Since metamaterials are typically solid structures with predetermined interconnections, it is challenging to leverage their unique properties for many critical applications that require fluid-like behavior, such as heat engines or cooling cycles. Recent research suggested overcoming this limitation by creating a mechanical metafluid', which is a lubricated suspension of multistable unit-cells. However, realization of this concept necessitates the ability to control both velocity and state of the metafluid. Here, we propose the use of time-varying magnetic fields as a mechanism to manipulate metafluids. We focus on a lattice of magnetic multistable capsules enclosing gas and suspended within a liquid-filled tube. We derive the governing equations and examine one-dimensional fluid mechanics of the metafluid, both theoretically and experimentally, at the viscous limit under magnetic actuation. By applying time-varying magnetic fields, we control both the local compression and expansion of the capsules, as well as the entire flow field. Our theoretical results are compared with experimental data, showing good agreement. This work paves the way for the utilization of mechanical metamaterials to applications that require fluid-like behavior, thus extending the scope of metamaterial applications.

Herein, The study of multistable structures, particularly those that can twist, has attracted significant attention in recent years. This ability to transition between multiple stable geometries of these structures paves the way for advances in diverse applications, such as morphing structures and robot actuation mechanisms. Conventional methods of designing and fabricating these structures often involve complex and resource‐intensive fabrication processes, which restrict their widespread adoption and limit their miniaturization. Here, we present a novel inflatable multistable twisting structure, based on helical folds of an elastic tube. Our fabrication approach utilizes directed mechanical instability as a method for a rapid fabrication, which is readily implemented at various length scales. We developed a theoretical model for the deformation of the bistable helical elements comprising the twisting structure, and compared the theoretical results to the experimental data. Furthermore, we demonstrate our fabrication methodology using a variety of polymers, including medical grade polymers, as well as various inner radii ranging from 5 mm to 44 μm and thicknesses of the tubes’ walls ranging from 250 μm to 19 μm.

Developing large-scale storage of intermittent renewable energy to meet growing energy demands is a pressing current need. Multiphase single flow batteries are a promising solution for such grid-scale energy storage, demonstrating an affordable redox flow battery design that reduces both cell and balance of plant costs. However, their major limitation is the considerable variance in electrolyte conductivity under different battery flow conditions and electrolyte properties, with no current predictive model to comprehensively understand and optimize it. Here, we develop an analytical model for such emulsion electrolytes with a continuous aqueous-based phase and dispersed reactant-rich phase, which enables electrolyte resistance prediction. We show that a key mechanism affecting electrolyte conductivity is the formation of a sedimented layer along the flow channel, revealing the critical effect of non-aqueous phase sedimentation. Experimental validation using a zinc-bromine single flow battery demonstrates excellent agreement with theoretical results during both transient and steady operations, allowing extraction of challenging-to-measure parameters, such as the in-situ size of dispersed phase droplets. This foundational model is essential in minimizing power losses, improving electrolyte and cell designs, and holds broad applicability across diverse chemistries for single-flow batteries.

Three billion years of evolution have produced a vast variety of protein molecules, whose functions are directly dependent on their ability to assume and maintain specific shapes. Proteins are defined by the sequence and chemical characteristics of their amino acids, which dictate their 3D shape and function, ranging from enzymatic activity to immune responses. Here, we explore a synthetic form of linear structure that can be bent in a programmable way into various specific 3D shapes inspired by the way functional proteins are defined using genetic codes. This synthetic structure is based on non-circular multistable corrugated tubes, which can be fabricated at various length scales and cross-sectional shapes, thus enabling the modification of their properties. Additionally, the cross-section shape can be rewritten multiple times, allowing for the repair of structural damage and the rewriting of the properties of the structure's multi-stability. A numerical model is used to describe the bending energy landscape of different cross-sections. The proposed reprogrammable 3D shapes of a rewritable 1D metamaterial are promising candidates for futuristic robotic systems, complex deployable structures, catheter devices, and energy absorption and harvesting. This article presents a new concept for creating 3D structures from 1D metamaterial using a systematically programmable process. Longitudinal extension and radial bending in discrete "digital" steps that are repeatable with 0.08% error are specified. This work for the first time enables the use of versatile multistable structures, with multistable properties written onto the structure as needed. image

Articulated swimming robots have a promising potential for various marine applications. A common theoretical model assumes ideal fluid, where the viscosity is negligible and the swimmer-fluid interaction is induced by reactive forces originating from added mass effect. Some previous works used this model to study planar multi-link swimmers under kinematic input prescribing all joint angles. Inspired by biological swimmers in nature that utilize body flexibility, in this work we consider an underactuated three-link swimmer where one joint is periodically actuated while the other joint is passive and viscoelastic. Analysis of the swimmer’s nonlinear dynamics reveals that its motion depends significantly on the amplitude and frequency of the actuated joint angle. Optimal frequency is found where the swimmer’s net displacement per cycle is maximized, under symmetric periodic oscillations of the passive joint. In addition, upon crossing critical values of amplitude or frequency, the system undergoes a bifurcation where the symmetric periodic solution loses stability and asymmetric solutions evolve, for which the swimmer moves along an arc. We analyze these phenomena using numerical simulations and analytical methods of perturbation expansion, harmonic balance, Floquet theory and Hill’s determinant. The results demonstrate the important role of parametric excitation in stability and bifurcations of motion for flexible underactuated locomotion.

Purcell's planar three-link microswimmer is a classic model of swimming in low-Reynolds-number fluid, inspired by motion of flagellated microorganisms. Many works analyzed this model, assuming that the two joint angles are directly prescribed in phase-shifted periodic inputs. In this work, we study a more realistic scenario by considering an extension of this model which accounts for joints' elasticity and mechanical actuation of periodic torques so that the joint angles are dynamically evolving. Numerical analysis of the swimmer's dynamics reveals multiplicity of periodic solutions, depending on parameters of the inputs-frequency and amplitude of excitation, joints' stiffness ratio, as well as joint's activation. We numerically study swimming direction reversal, as well as bifurcations, stability transitions, and symmetry breaking of the periodic solutions, which represent the effect of buckling instability observed in swimming microorganisms. The results demonstrate that this variant of Purcell's simple model displays rich nonlinear dynamic behavior with actuated-elastic joints. Similar results are also obtained when studying an extended model of a six-link microswimmer.

Hydraulic fracturing for oil and gas production from shale formations, as well as natural geological phenomena, involve the propagation of thin viscous films within elastic media. For viscous fluids, stress diverges as the thickness of the film tends to zero, arresting the propagation of the film, and thus implying the contact line paradox. For free-surface films, this paradox is resolved by considering a precursor film, leading to Tanner's law. This approach was extended recently for viscous films between a thin elastic plate and a rigid solid, allowing calculation of the film propagation rate. In this work, we examine the effect of a pre-wetting layer on the rate of propagation of a viscous flow within an infinitely deep and long domain. We analyse the linear and nonlinear dynamic problems, and perform a self-similarity analysis. We find that peeling front propagation scales as time to the power of 1/9 and 1/3 for thin and thick pre-wetting layer limits, respectively. Our results contribute to the understanding of the contact line paradox in elastic media and the crucial role of the pre-wetting layer in resolving it.

Growing soft materials which follow a three dimensional (3D) path in space are critical to applications such as search and rescue and minimally invasive surgery. Herein, a concept for a single-input growing multi-stable soft material, based on a constrained straw-like structure is presented. This class of materials are capable of maneuvering and transforming their configuration by elongation while executing multiple turns. This is achieved by sequenced actuation of bi-stable frusta with predefined constraints. Internal viscous flow and variations in the stability threshold of the individual cells enable sequencing and control of the robot's movement so as to follow a desired 3D path as the structure grows. A theoretical description of the shape and dynamics resulting from a particular set of constraints is derived. To validate the model and demonstrate the suggested concept, experiments of maneuvering in models of residential and biological environments are presented. In addition to performing complex 3D maneuvers, the tubular structure of these robots may also be used as a conduit to reach inaccessible regions, which is demonstrated experimentally.

The thermodynamic properties of fluids play a crucial role in many engineering applications, particularly in the context of energy. Fluids with multistable thermodynamic properties may offer new paths for harvesting and storing energy via transitions between equilibria states. Such artificial multistable fluids can be created using the approach employed in metamaterials, which controls macro-properties through micro-structure composition. In this work, the dynamics of such "metafluids" is examined for a configuration of calorically-perfect compressible gas contained within multistable elastic capsules flowing in a fluid-filled tube. The velocity-, pressure-, and temperature-fields of multistable compressible metafluids is studied by both analytically and experimentally, focusing on transitions between different equilibria. The dynamics of a single capsule is first examine, which may move or change equilibrium state, due to fluidic forces. The interaction and motion of multiple capsules within a fluid-filled tube is then studied. It shows that such a system can be used to harvest energy from external temperature variations in either time or space. Thus, fluidic multistability allows specific quanta of energy to be captured and stored indefinitely as well as transported as a fluid, via tubes, at standard atmospheric conditions without the need for thermal isolation.

The stability of holes in solid thin films is crucial, as an absence of holes is necessary in some applications and holes are needed in others. We develop an axisymmetric two grain model with a central hole, with surface diffusion governing the exterior surfaces and mean curvature motion governing the grain boundary. The model can exhibit grooving, wetting, dewetting, as well as void, hole, and hillock formation. Here, we extend an earlier work [Zigelman and Novick-Cohen, J. Appl. Phys. 130, 175301 (2021)], where it was shown for an axisymmetric single grain system with a hole at the center that there exists a critical effective radius, which is independent of the contact angle. The stability of the steady states, which consist of coupled nodoidal and catenoidal surfaces, is analyzed numerically by imposing the steady state configurations as initial conditions. This approach yields stability criteria in terms of (i) the effective energy, (ii) the ratio between the maximal thickness of the inner and outer grains, (iii) a generalized effective radius, and (iv) the ratio between the mean curvature of the exterior surfaces and the total volume of the system. Some of these criteria partially reflect the Rayleigh stability criterion. Hillock formation tends to be stabilizing. Modes of instability include growth of one grain at the expense of the other, breakup induced by grooving, and hole closure.

We explore a specific small geometry containing a single thin bounded grain on a substrate with a hole at its center. By employing a mathematical model based on surface diffusion, no flux boundary conditions, and prescribed contact angles, we study the evolution of the hole as well as the exterior surface of the grain, based on energetic considerations and dynamic simulations. Our results regarding the formation and evolution of holes in thin films in small geometries shed light on various nonlinear phenomena associated with wetting and dewetting.

Redox flow batteries (RFBs) are an emerging electrochemical technology envisioned towards storage of renewable energy. A promising sub-class of RFBs utilizes single-flow membraneless architectures in an effort to minimize system cost and complexity. To support multiple functions, including reactant separation and fast reactant transport to electrode surfaces, electrolyte flow must be carefully designed and optimized. In this work, we propose adding a secondary channel adjacent to a permeable battery electrode, solving for the flow field and analysing the effects on the reactant concentration boundary layer at the electrode. We find that an adjacent channel with gradually changing thickness leads to a desired nearly uniform flow through the electrode to the adjacent channel. Consequently, the thickness of the concentration boundary layer is significantly reduced, increasing reactant transport to the electrode surface to 140% of the rate of a battery with a constant width adjacent channel, and 350% of the rate with no adjacent channel. Overall, this theory provides insight into the important role of flow physics for this promising sub-class of flow batteries, and can pave the way to improved energy efficiency of such flow batteries.

We propose to incorporate fluids within multistable metamaterials to tailor a desired dynamic response, dictate the magnitude of rate-dependent dissipation, control the sequence and pattern of phase transition, and more. As a simple example we focus on straws, which are commonly used to transfer fluids and are constructed from a one-dimensional (1D) lattice of bistable elements. We first solve for the dynamics of a single element in the unstable spinodal state, reducing or increasing the pressure locally. Using a longwave approximation, we then model viscous flow and solid phase change within a 1D lattice of bistable frusta. The model is compared with experiments, showing excellent agreement.

Previous experiments and analyses have demonstrated that elastic boundaries reduce the speed of sound and alter the acoustic waves in fluid-filled tubes. Similar effects will occur in any configuration with deformable boundaries and fluid-fluid interfaces. In this work, we study the propagation of nonlinear acoustic waves in 1D liquid-filled tubes with superhydrophobic longitudinal grooved boundaries. Recently, grooved channels have attracted significant interest because of their reduced friction to flow, but such configurations also allow for a new kind of sound wave behavior due to the dependence of the pressure on the triple-phase contact line. We derive a model which contains an interplay between the pressure and the shape of the liquid-gas interface, subject to the hysteresis of the contact line, which is a dominant mechanism for energy dissipation. Our results present front propagation, showing an order of magnitude reduction in the speed of sound, as well as oscillation patterns in which the liquid is pinned in one part of the channel yet oscillating in the rest of the channel.

Investigating and tailoring the thermodynamic properties of different fluids is crucial to many fields. For example, the efficiency, operation range, and environmental safety of applications in energy and refrigeration cycles are highly affected by the properties of the respective available fluids. Here, we suggest combining gas, liquid and multistable elastic capsules to create an artificial fluid with a multitude of stable states. We study, theoretically and experimentally, the suspension's internal energy, equilibrium pressure-density relations, and their stability for both adiabatic and isothermal processes. We show that the elastic multistability of the capsules endows the fluid with multistable thermodynamic properties, including the ability of capturing and storing energy at standard atmospheric conditions, not found in naturally available fluids.

Questions regarding the stability of holes and arrays of holes in solid thin films have attracted much attention over the past few decades since an absence of holes is necessary for certain devices to operate properly and a presence of holes is needed in various industrial applications. Here, we study the energetic and dynamic stability of a single axisymmetric grain with a hole at its center, under the assumption that the exterior surface evolves by surface diffusion. Our energetic considerations enable us to formulate a criterion in terms of a critical effective hole radius, which distinguishes between energetically stable and unstable steady state hole configurations and which, somewhat surprisingly, is independent of the contact angle at the substrate and should be readily measurable in experiments. The set of steady states for the system is characterized in terms of admissible nodoidal surfaces, whose dynamic stability is studied via numerical simulation of the full non-linear dynamic problem for zero-volume perturbations. Our dynamic stability study confirms and extends our conclusions based on energetic considerations. Our results, moreover, confirm and extend the classical results of Srolovitz and Safran [J. Appl. Phys. 60, 247–254 (1986); J. Appl. Phys. 60, 255–260 (1986)] and Wong et al. [J. Appl. Phys. 81, 6091–6099 (1997); Acta Mater. 45, 2477–2484 (1997)]. Furthermore, our studies of the steady states and their stability contribute to our understanding of various phenomena observed in experiments: void formation, hillock formation, hole induction and propagation, ligament formation and evolution, blistering prior to film rupture, etc. Importantly, our study shows that in order to relate theory with experiments, careful monitoring of spatial variations in the mean curvature in experiments is required.

Abstract The efficiency, operation range, and environmental safety of energy and refrigeration cycles are determined by the thermodynamic properties of available fluids. We here suggest combining gas, liquid and multistable elastic capsules to create an artificial fluid with a multitude of stable states. We study, theoretically and experimentally, the suspension’s internal energy, equilibrium pressure-density relations and their stability for both adiabatic and isothermal processes. We show that the elastic multistability of the capsules endows the fluid with multistable thermodynamic properties, including the ability of capturing and storing energy at standard atmospheric conditions, not found in naturally available fluids.