Shape Reconfiguration Research Articles

Multistable Twist Metastructures with Enhanced Collapsibility and Multidimensional Programmability

Multistable metastructures with compression-twist coupling offer promising applications in reusable protective devices, deployable structures and reconfigurable robotics. However, existing designs based on either Kresling origami or truss-based mechanisms, suffer from limited deformability, due to the accumulation of bending deformation in creases or trusses. Herein, we propose a novel multistable twist metastructure by integrating hinged beams with Kresling-inspired trusses. A two-step procedure, combining 3D printing and interlocking assembling, is utilized to fabricate the multistable twist samples. This multistable twist mechanism leverages the elastic instability and shape reconfiguration of hinged beams, enabling transitions between stable configurations with minimal bending in the trusses. This approach achieves exceptional collapsibility with a reusable maximum allowable compression up to 80% of the structural height. Additionally, the compression-twist coupling of trusses protects hinged beams from severe tensile damage. Furthermore, our strategy offers multidimensional programmability. Geometric design tailors configuration stability (i.e., multi/bistability, monostability, monotonicity), while arraying method controls deformation modes. This culminates in the realization of customized functions of impact resistance and vibration mitigation. Specially, by incorporating trusses, negative stiffness with loop hysteresis can be programmed to enhance energy dissipation, which facilitates to damping the impact and vibration. Experimental tests confirm the compatibility of excellent collapsibility, programmability and multifunctionality. This finding underscores the potential of such multistable metastructure with compression-twist coupling for designing next-generation reusable multifunctional devices.

Spatio-Selective Reconfiguration of Mechanical Metamaterials Through the Use of Dynamic Covalent Chemistries.

Mechanical metamaterials achieve unprecedented mechanical properties through their periodically interconnected unit cell structure. However, their geometrical design and resulting mechanical properties are typically fixed during fabrication. Despite efforts to implement covalent adaptable networks (CANs) into metamaterials for permanent shape reconfigurability, emphasis is given to global rather than local shape reconfiguration. Furthermore, the change of effective material properties like Poisson's ratio remains to be explored. In this work, a non-isocyanate polyurethane elastomeric CAN, which can be thermally reconfigured,is introduced into a metamaterial architecture. Structural reconfiguration allows for the local and global reprogramming of the Poisson's ratio with change of unit cell angle from 60° to 90° for the auxeticand 120° to 90° for the honeycomb metamaterial. The respective Poisson's ratio changes from -1.4 up to -0.4 for the auxetic and from +0.7 to +0.2 for the honeycomb metamaterial. Carbon nanotubes are deposited on the metamaterials to enable global and spatial electrothermal heating for on-demand reshaping with a heterogeneous Poisson's ratio ranging from -2 to ≈0 for a single auxetic or +0.6 to ≈0 for a single honeycomb metamaterial. Finite element simulations reveal how permanent geometrical reconfiguration results from locally and globally relaxed heated patterns.

Shape-Morphing in Oxide Ceramic Kirigami Nanomembranes.

Interfacial strain engineering in ferroic nanomembranes can broaden the scope of ferroic nanomembrane assembly as well as facilitate the engineering of multiferroic-based devices with enhanced functionalities. Geometrical engineering in these material systems enables the realization of 3-D architectures with unconventional physical properties. Here, 3-D multiferroic architectures are introduced by incorporating barium titanate (BaTiO3, BTO) and cobalt ferrite (CoFe2O4, CFO) bilayer nanomembranes. Using photolithography and substrate etching techniques, complex 3-D microarchitectures including helices, arcs, and kirigami-inspired frames are developed. These 3-D architectures exhibit remarkable mechanical deformation capabilities, which can be attributed to the superelastic behavior of the membranes and geometric configurations. It is also demonstrated that dynamic shape reconfiguration of these nanomembrane architectures under electron beam exposure showcases their potential as electrically actuated microgrippers and for other micromechanical applications. This research highlights the versatility and promise of multi-dimensional ferroic nanomembrane architectures in the fields of micro actuation, soft robotics, and adaptive structures, paving the way for incorporating these architectures into stimulus-responsive materials and devices.

Intelligent Reversible Reconfigurable Metamaterials Based on a Two-Way Shape Memory Polymer.

The development of intelligent reversible reconfigurable metamaterials has great significance in constructing three-dimensional metamaterials and introducing reversible tunability into metamaterials. Here, we introduce an intelligent metamaterial consisting of a two-way shape memory polymer (2W-SMP) ethylene vinyl acetate copolymer (EVA) actuator substrate and a patterned flexible-rigid film. Mechanical buckling of the 2W-SMP substrate was controlled by thermal stimulation. This makes it possible to afford an ability to initiate 3D structure formation or shape reconfiguration remotely in an on-demand fashion. In addition, the shape of the 2W-SMP substrate is temperature-dependent, allowing repeatable reversible deformation through temperature control after a single programming. Therefore, the electromagnetic properties of metamaterials can also be repeatedly and reversibly tuned between 9.15 and 10.82 GHz. Experimental demonstrations include the deformation and tunable electromagnetic properties of intelligent reversible reconfigurable metamaterial cells. The results create many opportunities for advanced programmable three-dimensional metamaterials.

Thermadapt shape memory AB-copolymer networks exhibiting tunable properties and kinetics of topological rearrangement

Polycaprolactone (PCL) based thermadapt shape memory polymers (SMPs) have exhibited superiority over traditional analogues by allowing shape-editing to reconfigure permanent shapes into more complex geometrical shapes, driven by the pursuit of advanced functionalities for high-value applications. Nevertheless, although transesterification-based PCL networks exhibit impressive shape reconfigurability as prototypical thermadapt SMPs, there are still constraints in terms of the need for significant flexibility in architectural adjustment and property modulation without compromising reconfigurability, which would be relevant for practical applications. Here, we present a simple yet efficient strategy to create PCL-based thermadapt SMPs that possess a highly tunable structure and properties, as well as exceptional reconfigurability. The family of SMPs, called thermadapt shape memory AB copolymer networks (AB-CPNs), was synthesized by UV-initiated free radical polymerization between PCL diacrylate as crosslinker and 4-hydroxybutyl acrylate (HBA) as comonomer. The thermadapt AB-CPNs allow for significant structural alterations with 0 wt% to 70 wt% HBA while maintaining excellent shape memory and shape reconfigurability effects. The insertion of the polymer segment containing free hydroxyls not only promises tunable material properties but also makes network rearrangement easier since dynamic hydroxy-ester bonds are more active than dynamic ester-ester bonds. It is envisioned that the thermadapt shape memory AB-CPNs with widely tunable macroscopic properties will drive progress in the real-world applications of SMP devices with complicated geometric structures.

Water-Induced Shape-Locking Magnetic Robots.

Untethered magnetic soft robots capable of performing adaptive locomotion and shape reconfiguration open up possibilities for various applications owing to their flexibility. However, magnetic soft robots are typically composed of soft materials with fixed modulus, making them unable to exert or withstand substantial forces, which limits the exploration of their new functionalities. Here, water-induced, shape-locking magnetic robots with magnetically controlled shape change and water-induced shape-locking are introduced. The water-induced phase separation enables these robots to undergo a modulus transition from 1.78MPa in the dry state to 410MPa after hydration. Moreover, the body material's inherent self-healing property enables the direct assembly of morphing structures and magnetic soft robots with complicated structures and magnetization profiles. These robots can be delivered through magnetic actuation and perform programmed tasks including supporting, blocking, and grasping by on-demand deformation and subsequent water-induced stiffening. Moreover, a water-stiffening magnetic stent is developed, and its precise delivery and water-induced shape-locking are demonstrated in a vascular phantom. The combination of untethered delivery, on-demand shape change, and water-induced stiffening properties makes the proposed magnetic robots promising for biomedical applications.

AI-based Prediction of Protein Corona Composition on DNA Nanostructures.

DNA nanotechnology has emerged as a powerful approach to engineering biophysical tools, therapeutics, and diagnostics because it enables the construction of designer nanoscale structures with high programmability. Based on DNA base pairing rules, nanostructure size, shape, surface functionality, and structural reconfiguration can be programmed with a degree of spatial, temporal, and energetic precision that is difficult to achieve with other methods. However, the properties and structure of DNA constructs are greatly altered in vivo due to spontaneous protein adsorption from biofluids. These adsorbed proteins, referred to as the protein corona, remain challenging to control or predict, and subsequently, their functionality and fate in vivo are difficult to engineer. To address these challenges, we prepared a library of diverse DNA nanostructures and investigated the relationship between their design features and the composition of their protein corona. We identified protein characteristics important for their adsorption to DNA nanostructures and developed a machine-learning model that predicts which proteins will be enriched on a DNA nanostructure based on the DNA structures' design features and protein properties. Our work will help to understand and program the function of DNA nanostructures in vivo for biophysical and biomedical applications.

High‐performance shape memory characteristics by integrating urea linkages into the polyurethane elastomer

AbstractShape memory polymers have been widely researched to develop multifunctional materials that respond smartly to external stimulations and programmed signals. Among them, shape memory polyurethane (SMPU) is drawing great attention owing to its highly tunable properties and ease of integrating new functions. However, the effect of urea bonds on SMPU elastomers has rarely been investigated because of the extreme reactivity of amine crosslinkers. In this study, we used diethanolamine (DEOA), which contains a secondary amine, as the crosslinker for SMPU synthesis. Unlike other crosslinkers containing primary amines, they can form urea bonds in a more gentle manner. The urea bonds reinforce the intermolecular interactions between the hard segments with strong hydrogen bonding, thus increasing the phase separation and degree of crystallization. Consequently, the urea‐containing SMPU exhibits improved mechanical strength and shape memory abilities for both fixing and recovery. Moreover, the transcarbamoylation reaction, which enables the reconfiguration of the original shape, is observed. The introduction of the urea bonds into the SMPU elastomer can be beneficial in achieving flawless shape memory performances in various sensitive applications.

Intrinsic Permanent Shape Reconfigurable Semicrystalline Biopolyester Thermoset.

Catalyst-free, volatile organic solvent (VOC)-free synthesis of biobased cross-linked polymers is an important sustainable feature in polyesterification. To date, these polyesters have been extensively studied for their fundamental sustainability across various uses. The ultimate potential sustainability for these materials, however, is constrained to static structural parts due to their intractable rigid three-dimensional (3D) network. Here, we reveal intrinsic dynamic exchangeable bonds within this type of cross-linked semicrystalline network, poly(1,8-octanediol-co-1,12-docanedioate-co-citrate) (PODDC), enabling permanent shape reconfigurability. Annealing at slightly above melting-transition temperature (Tm) allows for shape reconfigurability up to nine times, comparable in performance to the existing bond-exchange systems. No reagents are involved from synthesis to shape reconfiguration, suggesting an exciting feature exhibited by this sustainable cross-linked material without the need for further chemical modification. We further extend this benefit of reconfigurability to enable flexible shape design in a smart shape-memory polymer (SMP), showing it as one of its potential applications. After its applications, it can undergo hydrolytic degradation. We envision that such multifaceted sustainability for the material will attract interest in environmentally friendly applications such as fabricating external part of soft robots and shape-morphing devices with reduced environmental impact.

Photothermally Reconfigurable Biomimetic Photonic Structures Prepared via Crystallization of Polydopamine‐Incorporated Core–Shell Nanoparticles

AbstractSome creatures have periodic nanostructures and chromophores in their flexible organs that allow them to control the color and shape of their skin. Artificial photonic structures that can mimic the aforementioned ability of these natural structures are researched extensively. In this study, polydopamine‐incorporated core–interlayer–shell (CIS‐PDA) nanoparticles capable of shape reconfiguration and expressing vivid structural colors are designed. These nanoparticles can be readily assembled to produce colloidal photonic crystals (CPhCs) and can exhibit vivid structural colors by virtue of their light‐absorbing capability. Soft CPhC films prepared with these nanoparticles undergo stable elastic deformation at 15% strain and exhibit mechanochromic properties. Specifically, the PDA in the CIS nanoparticles can absorb broadband light and exhibit a photothermal effect resembling that of melanosomes in living organisms, which enables self‐healing between multiple CPhC films. Due to their favorable properties, the CPhC films prepared in this study represent promising photothermally reconfigurable photonic materials. Moreover, arbitrarily shaped 2D or 3D surfaces are conformally coated with the films via microimprinting or vacuum wrapping, courtesy of the reconfigurability of these films. These findings suggest that CPhC films prepared with CIS‐PDA nanoparticles can be used as form‐free mechanochromic strain sensors and nonfading optical films for industrial products.

Shape reconfiguration for underwater propeller efficiency improvement

Shape reconfiguration for underwater propeller efficiency improvement

Multistability of segmented rings by programming natural curvature

Multistable structures have widespread applications in the design of deployable aerospace systems, mechanical metamaterials, flexible electronics, and multimodal soft robotics due to their capability of shape reconfiguration between multiple stable states. Recently, the snap-folding of rings, often in the form of circles or polygons, has shown the capability of inducing diverse stable configurations. The natural curvature of the rod segment (curvature in its stress-free state) plays an important role in the elastic stability of these rings, determining the number and form of their stable configurations during folding. Here, we develop a general theoretical framework for the elastic stability analysis of segmented rings (e.g., polygons) based on an energy variational approach. Combining this framework with finite element simulations, we map out all planar stable configurations of various segmented rings and determine the natural curvature ranges of their multistable states. The theoretical and numerical results are validated through experiments, which demonstrate that a segmented ring with a rectangular cross-section can show up to six distinct planar stable states. The results also reveal that, by rationally designing the segment number and natural curvature of the segmented ring, its one- or multiloop configuration can store more strain energy than a circular ring of the same total length. We envision that the proposed strategy for achieving multistability in the current work will aid in the design of multifunctional, reconfigurable, and deployable structures.

3D printable carbon nanotubes-based composites with reconfigurable shapes and properties

In this work, we developed an efficient approach to fabricating composites of carbon nanotubes (CNT) with shape reconfiguration ability and Joule heating behavior by incorporating the direct ink writing (DIW) technique. Our 3D printable ink consisted of a high concentration of CNT stabilized by polyvinylpyrrolidone (PVP) in an aqueous polyvinyl alcohol (PVA) solution. The rheology of the ink was tuned by the amounts of CNT and PVP. The printed objects underwent the freeze-thaw process to form weak hydrogels induced by the crystallization of PVA. Subsequently, the hydrogels were immersed in a deep eutectic solvent (DES) bath consisting of choline chloride and glycerol. This process replaced the water in the hydrogels with DES and led to mechanically tough DES/CNT gels. We utilized the high stretchability of DES/CNT gel to achieve complex geometries that would be challenging to accomplish solely with DIW. After reshaping the DES/CNT gels, the target shape was fixed by further solvent exchange with ethanol and drying. The final CNT composites showed a high electric conductivity of up to 33.94 S/m and exhibited remarkable Joule heating performance using a low applied voltage (5 V). Additionally, we successfully achieved a spatial variation of mechanical stiffness, electrical conductivity, and Joule heating across the printed objects by a selective solvent removal process. In short, this work expands the scope of possible shapes and properties of CNT-based composites.

Magic Furniture: Design Paradigm of Multi-Function Assembly.

Assembly-based furniture with movable parts enables shape and structure reconfiguration, thus supporting multiple functions. Although a few attempts have been made for facilitating the creation of multi-function objects, designing such a multi-function assembly with the existing solutions often requires high imagination of designers. We develop the Magic Furniture system for users to easily create such designs simply given multiple cross-category objects. Our system automatically leverages the given objects as references to generate a 3D model with movable boards driven by back-and-forth movement mechanisms. By controlling the states of these mechanisms, a designed multi-function furniture object can be reconfigured to approximate the shapes and functions of the given objects. To ensure the designed furniture easy to transform between different functions, we perform an optimization algorithm to choose a proper number of movable boards and determine their shapes and sizes, following a set of design guidelines. We demonstrate the effectiveness of our system through various multi-function furniture designed with different sets of reference inputs and various movement constraints. We also evaluate the design results through several experiments including comparative and user studies.

Deployable support truss for parabolic cylindrical antennas with shape reconfiguration

The increasing scarcity of orbit resources has directed the focus onto the versatility of space antennas. Through shape reconfiguration, large antennas can achieve enhanced task compliance. In this paper, a two-degree-of-freedom (DOF) deployable support truss with shape reconfiguration is designed for parabolic cylindrical antennas. A design strategy is presented for the support truss, in which the synchronous deployment is realized first through the expansion of basic deployable units. The branch chains are then supplemented to realize the controllable reconfiguration of the entire support truss. Moreover, the mobility and kinematic analyses of the basic modules on the support truss are conducted to parametrically analyze the DOF space and realize the expected reconfiguration. The unit number and structure parameters of the support truss can influence the mimicking preciseness. To fulfill the mimicking error requirement with a more concise mechanism, a parameter optimization method based on the genetic algorithm is proposed to achieve the minimum number of the required deployable units. Simulation of the deployment and reconfiguration of the support truss as well as the verification test conducted on the principle prototype demonstrate the feasibility of the mechanism design. This paper may provide candidates for support trusses of large reconfigurable antennas with enhanced task flexibility and efficiency, and serve as references for the design of deployable mechanisms with the reconfiguration function.

Reconfigurable 4D printing via mechanically robust covalent adaptable network shape memory polymer.

4D printing enables 3D printed structures to change shape over "time" in response to environmental stimulus. Because of relatively high modulus, shape memory polymers (SMPs) have been widely used for 4D printing. However, most SMPs for 4D printing are thermosets, which only have one permanent shape. Despite the efforts that implement covalent adaptable networks (CANs) into SMPs to achieve shape reconfigurability, weak thermomechanical properties of the current CAN-SMPs exclude them from practical applications. Here, we report reconfigurable 4D printing via mechanically robust CAN-SMPs (MRC-SMPs), which have high deformability at both programming and reconfiguration temperatures (>1400%), high Tg (75°C), and high room temperature modulus (1.06 GPa). The high printability for DLP high-resolution 3D printing allows MRC-SMPs to create highly complex SMP 3D structures that can be reconfigured multiple times under large deformation. The demonstrations show that the reconfigurable 4D printing allows one printed SMP structure to fulfill multiple tasks.

Durable semi-interpenetrating polymer network containing dynamic boroxine bonds for multi-shape manipulated deformation

Shape-shifting materials with multiple shape manipulation, integrated with durability, shape reconfiguration, shape memory, and reversible deformation, are in high demand for applications in soft robotics, electrical devices, and other fields, but remain a significant technical challenge. In this study, we present a straightforward approach to develop a semi-interpenetrating polymer network (named PVP-VPBA-PEGDMA) crosslinked with dynamic boroxine bonds to address these challenges. The typical PVP-VPBA2-PEGDMA0.2 exhibits high mechanical strength of 38.5 MPa, exceptional self-healing capability (with up to 89.4 % efficiency), and recyclability, ensuring remarkable durability during shape-changing process. Notably, the PVP-VPBA-PEGDMA can be programmatically transformed from 2D sheets into a variety of 3D shapes using humidity-induced solid-state plasticity, which is facilitated by humidity-sensitive dynamic boroxine bonds. The PVP-VPBA-PEGDMA can be folded like paper through origami techniques, and maintain permanent shape configurations, highly suitable for complex shape morphing applications. Moreover, the PVP-VPBA-PEGDMA, in their temporary geometries, can power a model car using shape memory, demonstrating substantial actuation ability and mechanical performance. Leveraging the asymmetric humidity-triggered behavior of the PVP-VPBA-PEGDMA, various functional humidity-responsive devices have been developed, including a crawling robot, a hat, and a conveyor belt with wet sorting capability. Given the programmable shape reconfiguration, shape memory and reversible shape-changing ability of PVP-VPBA-PEGDMA, it opens up numerous potential applications in soft robotics, flexible electronic devices, and intelligent sensors.

Soft Micromotors with Switchable Motion Enabled by 3D-to-3D Shape Reconfiguration

Soft Micromotors with Switchable Motion Enabled by 3D-to-3D Shape Reconfiguration

Large deformation of trees in a strong wind

Understanding the dynamic response of trees to a strong wind is crucial to alleviating the damages and losses of tree forests caused by windstorms. Previous studies have elucidated small deformations of a broad range of tree species, yet mathematical models that can accurately pinpoint the location and severity of wind-induced damages are still lacking. To bridge this gap, the present work puts forward the first geometrically accurate, physics-based model to capture large deformation of trees induced by a strong wind. The proposed model incorporates a branched tree architecture to represent the topology of a realistic tree. The large, dynamic deformation of the trunk and branches of the tree is described by a system of nonlinear partial differential equations derived from structural theories rooted in classical mechanics. The aerodynamic loading is quantified based on the instantaneous relative velocity between the wind and the tree. The proposed model could successfully reproduce the effects of aerodynamic damping by capturing the nonlinear interplays between the wind and the tree, in contrast to prior analytical models that relied on empirical assumptions of the damping coefficients. The model further reveals a reduction in the drag force due to wind-induced shape reconfiguration, which is enhanced exponentially as a function of the wind speed. The proposed modeling framework could aid in the development of novel forest management strategies to mitigate wind-induced economic and environmental losses.

Intrinsically Multistable Soft Actuator Driven by Mixed-Mode Snap-Through Instabilities.

Actuators utilizing snap-through instabilities are widely investigated for high-performance fast actuators and shape reconfigurable structures owing to their rapid response and limited reliance on continuous energy input. However, prevailing approaches typically involve a combination of multiple bistable actuator units and achieving multistability within a single actuator unit still remains an open challenge. Here, a soft actuator is presented that uses shape memory alloy (SMA) and mixed-mode elastic instabilities to achieve intrinsically multistable shape reconfiguration. The multistable actuator unit consists of six stable states, including two pure bendingstates and four bend-twist states. The actuator is composed of a pre-stretched elastic membrane placed between two elastomeric frames embedded with SMA coils. By controlling the sequence and duration of SMA activation, the actuator is capable of rapid transition between all six stable states within hundreds of milliseconds. Principles of energy minimization are used to identify actuation sequences for various types of stable state transitions. Bendingand twisting angles corresponding to various prestretch ratios are recorded based on parameterizations of the actuator's geometry. To demonstrate its application in practical conditions, the multistable actuator is used to perform visual inspection in a confined space, light source tracking during photovoltaic energy harvesting, and agilecrawling.