Shape Reconfiguration Research Articles

A novel origami mechanical metamaterial based on Miura-variant designs: exceptional multistability and shape reconfigurability

Conventional rigid-foldable stacked Miura-ori (SMO) mechanical metamaterials could exhibit multistability and reconfigurability corresponding to compressive/extensive deformations only. In this research, the investigation aims to advance the state-of-the-art by extending the multistable reconfigurability to other types of deformations. To tackle this, a novel stacking strategy is proposed, which evolves the traditional SMO cell to a new variant, referred to as a stacked Miura-ori variant (SMOV) cell. The SMOV cell could present eight distinct stable configurations; by switching among them, one can program the underlying kinematical and mechanical properties. Based on the SMOV cell, a three-cell metamaterial beam and a 3 × 3 × 3 metamaterial cube are constructed, and their exceptional multistability and reconfigurability are studied. The beam could exhibit inclined and curved stable configurations that cannot be achieved with the conventional SMO design, and the associated longitudinal sections are tunable. For the cube, the achievable stable configurations are further enriched by the three admissible stacking methods and the unique capability of reconfiguring the inner units without altering the overall shape of the cube. Overall, based on the proposed design innovations, the current level of multistable reconfigurability is significantly expanded, which would provide brand new solutions for developing smart origami metamaterials with environmental and functional adaptability.

NIR Light‐Triggered Shape Memory Polymers Based on Mussel‐Inspired Iron–Catechol Complexes

AbstractShape memory polymers (SMPs) with the permanent shape reconfiguration capability have received much research interest because they are capable of diversified tasks and the ability to work in conditions that required complex geometry. However, most of such SMPs are thermally triggered, which limits their applications. Inspired by reversible mussel adhesive protein chemistry, NIR light‐triggered SMPs with the permanent shape reconfiguration capability are prepared. The polymer networks are constructed using biocompatible polyethylene glycol, which is crosslinked based on catechol–Fe3+ coordination. The polymer networks have a uniform network structure and exhibit a considerable one‐way shape memory effect (1W‐SME) as well as a good two‐way shape memory effect (2W‐SME) under stress conditions. Taking advantage of the dynamic nature of the catechol–Fe3+ coordination, the permanent shape of the polymers could be reconfigured. Moreover, the catechol–Fe3+ complexes have a broad absorption in the NIR window, which bestows the polymers with excellent NIR light‐triggered SME. Further, the great potential of the obtained polymers in biomedical and electronic applications is presented. Owing to the NIR‐triggered 1W‐SME and the permanent shape reconfiguration capability, the polymer could be used as a personalizing vascular stent. Additionally, the polymer could be applied in light‐driven switches based on the NIR light‐triggered 2W‐SME.

Design of Shape Reconfigurable, Highly Stretchable Honeycomb Lattice With Tunable Poisson’s Ratio

The mechanical behaviors of lattice structures can be tuned by arranging or adjusting their geometric parameters. Once fabricated, the lattice’s mechanical behavior is generally fixed and cannot adapt to environmental change. In this paper, we developed a shape reconfigurable, highly stretchable lattice structure with tunable Poisson’s ratio. The lattice is built based on a hexagonal honeycomb structure. By replacing the straight beam with curled microstructure, the stretchability of the lattice is significantly improved. The Poisson’s ratio is adjusted using a geometric angle. The lattice is 3D printed using a shape memory polymer. Using its shape memory effect, the lattice demonstrates tunable shape reconfigurability as the ambient temperature changes. To capture its high stretchability, tunable Poisson’s ratio and shape reconfigurability, a phase evolution model for lattice structure is used. In the theoretical model, the effects of temperature on the material’s nonlinearity and geometric nonlinearity due to the lattice structure are assumed to be decoupled. The theoretical shape change agrees well with the Finite element results, while the theoretical model significantly reduces the computational cost. Numerical results show that the geometrical parameters and the ambient temperature can be manipulated to transform the lattice into target shapes with varying Poisson’s ratios. This work provides a design method for the 3D printed lattice structures and has potential applications in flexible electronics, soft robotics, and biomedicine.

Photo‐Triggered Shape Reconfiguration in Stretchable Reduced Graphene Oxide‐Patterned Azobenzene‐Functionalized Liquid Crystalline Polymer Networks

AbstractIn recent years, the “Kirigami” have been exploited to engineer stretchable electronics that exhibit enhanced deformability without sacrificing their mechanical and electrical properties. However, kirigami‐inspired engineering is often limited to passive mechanical stretching for 3D shape morphing. To counter this problem, in this study, azobenzene‐functionalized liquid crystalline polymer networks (azo‐LCNs) are monolithically integrated with patterned reduced graphene oxide (rGO), called azo‐LCN/rGO, to achieve on‐demand shape reconfiguration in response to external stimuli (UV, NIR, solar rays, and portable light); in addition, the azo‐LCN/rGO exhibit highly enhanced mechanical and electrical properties. The cross‐sectional area and thickness of rGO patterns are controlled using a masking technique and evaporative self‐assembly. By the spatial patterning of rGO, insulating azo‐LCNs are converted into electrically conducting structures (381.9 S cm−1). The elastic modulus of <2 µm thick azo‐LCN can be tailored in the range of 1.3–6.4 GPa by integration with rGO layers of thickness less than 2 µm. Upon UV irradiation, azo‐LCN/rGO exhibit both for/backward in‐plane bending as well as out‐of‐plane chiral twisting, thus overcoming the typical trade‐off relationship between elastic modulus and deformability. Finally, an on‐demand contactless shape reconfiguration in azo‐LCN/rGO by UV irradiation in conjunction with passive mechanical strain is demonstrated.

Voxelated three-dimensional miniature magnetic soft machines via multimaterial heterogeneous assembly.

Small-scale soft-bodied machines that respond to externally applied magnetic field have attracted wide research interest because of their unique capabilities and promising potential in a variety of fields, especially for biomedical applications. When the size of such machines approach the sub-millimeter scale, their designs and functionalities are severely constrained by the available fabrication methods, which only work with limited materials, geometries, and magnetization profiles. To free such constraints, here, we propose a bottom-up assembly-based 3D microfabrication approach to create complex 3D miniature wireless magnetic soft machines at the milli- and sub-millimeter scale with arbitrary multimaterial compositions, arbitrary 3D geometries, and arbitrary programmable 3D magnetization profiles at high spatial resolution. This approach helps us concurrently realize diverse characteristics on the machines, including programmable shape morphing, negative Poisson's ratio, complex stiffness distribution, directional joint bending, and remagnetization for shape reconfiguration. It enlarges the design space and enables biomedical device-related functionalities that are previously difficult to achieve, including peristaltic pumping of biological fluids and transport of solid objects, active targeted cargo transport and delivery, liquid biopsy, and reversible surface anchoring in tortuous tubular environments withstanding fluid flows, all at the sub-millimeter scale. This work improves the achievable complexity of 3D magnetic soft machines and boosts their future capabilities for applications in robotics and biomedical engineering.

Reconfigurable and Renewable Nano‐Micro‐Structured Plastics for Radiative Cooling

AbstractPassive radiative technology enables sustainable cooling by synchronously emitting heat and reflecting solar light without any energy consumption. However, the consumption of non‐recyclable and non‐renewable radiative materials in large quantities may eventually cause resource waste and environmental issues. Herein, reconfigurable and renewable nano‐micro‐structured plastics for future eco‐friendly and large‐scale radiative cooling applications are developed. The plastics are facilely prepared from a locally confined polymerization method, which not only enables the customization of nano/micro‐structures for thermal emission and sunlight reflection but also provides physically cross‐linked networks for damage repairing, shape reconfiguration, and recyclable usage. Compared with traditional plastics applied on electronic devices, the nano‐micro‐structured plastic achieves much higher cooling efficiency with a temperature drop of 8.6 °C on electronic circuits and 7.5 °C cooling improvements under sunlight. With the excellent cooling performance and the recycling potential, the nano‐micro‐structured plastics open an environmentally sustainable pathway to address the thermal issues encountered by electronic devices and challenges of global warming.

Vitrimer Transition Temperature Identification: Coupling Various Thermomechanical Methodologies

Vitrimers hold great promise as adaptive materials capable of shape reconfigurability, welding, and self-healing due to dynamic covalent reactions occurring above the vitrimer transition temperatur...

A paper fortune teller-inspired reconfigurable soft pneumatic gripper

Soft pneumatic grippers (SPGs) have shown great grasping performances for various objects due to their simplicity, adaptability and rapid response. However, there are few SPGs that can grasp both flat and non-planar targets robustly. A reconfigurable mechanism that can transform the gripper into different states for grasping varied objects is desired by such versatile SPGs. Paper fortune teller (PFT) is a distinctive origami with 2D/3D shape switchability and 3D shape reconfigurability. In this paper, we propose a novel reconfigurable SPG which is inspired from PFT and augmented with an indirect vacuum adhesion (IVA) mechanism. The resultant gripper can not only lift flat-surface objects such as a piece of square glass (278 g) with the IVA force in its pad shape, but also pick up non-planar objects such as an orange (151 g) in a traditional grasping way in its four-converging-fingered shape. The experimental results reveal that our gripper can produce a maximum IVA force of about 4.24 N on acrylic plates and a maximum pulling force of about 2.10 N on 3D-printed non-planar objects respectively. The gripper’s traditional grasping robustness is also demonstrated when non-planar objects are placed irregularly (allowing up to 55 mm multi-orientation offsets or 20° multi-orientation drift angles). This new SPG design realizes the multi-function nature of origami transformation and is expected to promote the application of origami and soft gripper technologies.

Reinforcement Learning-Based Complete Area Coverage Path Planning for a Modified hTrihex Robot.

One of the essential attributes of a cleaning robot is to achieve complete area coverage. Current commercial indoor cleaning robots have fixed morphology and are restricted to clean only specific areas in a house. The results of maximum area coverage are sub-optimal in this case. Tiling robots are innovative solutions for such a coverage problem. These new kinds of robots can be deployed in the cases of cleaning, painting, maintenance, and inspection, which require complete area coverage. Tiling robots’ objective is to cover the entire area by reconfiguring to different shapes as per the area requirements. In this context, it is vital to have a framework that enables the robot to maximize the area coverage while minimizing energy consumption. That means it is necessary for the robot to cover the maximum area with the least number of shape reconfigurations possible. The current paper proposes a complete area coverage planning module for the modified hTrihex, a honeycomb-shaped tiling robot, based on the deep reinforcement learning technique. This framework simultaneously generates the tiling shapes and the trajectory with minimum overall cost. In this regard, a convolutional neural network (CNN) with long short term memory (LSTM) layer was trained using the actor-critic experience replay (ACER) reinforcement learning algorithm. The simulation results obtained from the current implementation were compared against the results that were generated through traditional tiling theory models that included zigzag, spiral, and greedy search schemes. The model presented in the current paper was also compared against other methods where this problem was considered as a traveling salesman problem (TSP) solved through genetic algorithm (GA) and ant colony optimization (ACO) approaches. Our proposed scheme generates a path with a minimized cost at a lesser time.

Elevation of mechanically robust and reprocessable thermoset polyurea composites towards permanent shape reconfiguration controlled by heat and electricity

Accompanying with tremendous efforts devoted to prompting recycling and mitigating disposal problems pertinent to obsolete polymer materials, it is imperative to ameliorate thermoset polymer composites that are both mechanically robust and reprocessable. Herein, we devised and prepared a series of dynamic thermoset polyurea composites (HTPU-x) by embedding CB into pristine thermoset polyurea matrix and merely using commodity raw materials. Through incorporating the dynamically sterling nature of urea bonds, the devised HTPU-x can simultaneously maintain superhigh breaking strength and elongations at break even after multiple cycles under hot press, manifesting both extraordinary mechanical properties, extraordinary reprocessability and exceptional multiple recyclability. Especially, amalgamation of the conductivity of carbon black and the dynamic nature of urea bonds can not only furnish these HTPU-x with conventional elastic shape memory performance, but also equip them with plastic shape memory and permanent shape reconfiguration under heat and electricity. Furthermore, HTPU-x can be reshaped and reconfigured to various permanent shapes in several seconds at a safe voltage. With enabling traditionally thermoset polymer composites with more upgraded functions, this designed scheme of mechanically robust HTPU-x provides a facilitating approach to reprocess and recycle the wasted thermoset polymer composites.

Post-synthesis modification of slide-ring gels for thermal and mechanical reconfiguration.

Ring-sliding behavior in polyrotaxanes imbues gels, elastomers, and glasses with remarkable stress-dissipation and actuation properties. Since these properties can be modulated and tuned by structural parameters, many efforts have been devoted to developing synthetic protocols that define the structures and properties of slide-ring materials. We introduce post-synthetic modifications of slide-ring gels derived from unmodified α-cyclodextrin and poly(ethylene glycol) polyrotaxanes that enable (i) actuation and control of the thermo-responsive lower critical solution temperature (LCST) behavior of ring-modified slide-ring hydrogels, and (ii) chemically bonding separate gels into hybrid or shape-reconfigured macro-structures with a slide-ring adhesive solution. The mechanical properties of the post-modified gels have been characterized by shear rheology and uniaxial tensile tests, while the corresponding xerogels were characterized by wide-angle X-ray scattering. These demonstrations show that post-synthetic modification offers a practical solution for re-configuring the properties and shapes of slide-ring gels.

Shape memory microparticles with permanent shape reconfiguration ability and near infrared light responsiveness

Smart changing microparticles with controllable shapes have attracted considerable attentions due to their potential applications in microactuators, micromotors and biomedical devices. In this work, a shape memory microsphere based on cellulose acetate (CA) was developed by a simple emulsion solvent evaporation method to perform on-demand shape switch under heat stimulus. The morphology of CA microparticles before and after thermal programing were carefully investigated by both optical microscope and scanning electron microscope, demonstrating their excellent microscopic shape memory properties and shape reconfiguring ability as needed. The temporary and permanent shapes of CA microparticles both can be changed arbitrarily by regulating the stretching condition via a film stretching process to meet various requests. Considering the more convenience of near infrared (NIR) light than direct heat for application, the additional NIR light-induced microscopic shape memory performance was realized by the introduction of multi-walled carbon nanotube into CA microspheres, which can further improve their versatile application potential in various fields.

Transient Dynamics of a Miura-Origami Tube during Free Deployment

With excellent folding-induced deformability and shape reconfigurability, origami-based designs have shown great potentials in developing deployable structures. Noting that origami deployment is essentially a dynamic process, while its dynamical behaviors remain largely unexplored owing to the challenges in modeling. This research aims at advancing the state of the art of origami deployable structures by exploring the transient dynamics under free deployment, with the Miura-origami tube being selected as the object of study because it possesses relatively simple geometry, exceptional kinematic properties, and wide applications. In detail, a preliminary free deployment test is performed, which indicates that the transient oscillation in the transverse direction is nonnegligible and the tube deployment is no longer a single-degree-of-freedom (SDOF) mechanism. Based on experimental observations, four assumptions are made for modeling purposes, and a 2N-DOF dynamic model is established for an N-cell Miura-origami tube to predict the transient oscillations in both the deploying and the transverse directions. Employing the settling times and the overshoot values as the transient dynamic indexes, a comprehensive parameter study is then carried out. It reveals that both the physical and geometrical parameters will significantly affect the transient deploying dynamics, with some of the parameter dependence relationships being counter-intuitive. The results show that the relationships between the transient dynamic behaviors and the examined parameters are sometimes contradictory in the deploying and the transverse directions, suggesting the necessity of a compromise in design.

Magnetic Multimaterial Printing for Multimodal Shape Transformation with Tunable Properties and Shiftable Mechanical Behaviors

Magnetic soft materials (MSMs) have shown potential in soft robotics, actuators, metamaterials, and biomedical devices because they are capable of untethered, fast, and reversible shape reconfigurations as well as controllable dynamic motions under applied magnetic fields. Recently, magnetic shape memory polymers (M-SMPs) that incorporate hard magnetic particles in shape memory polymers demonstrated superior shape manipulation performance by realizing reprogrammable, untethered, fast, and reversible shape transformation and shape locking in one material system. In this work, we develop a multimaterial printing technology for the complex structural integration of MSMs and M-SMPs to explore their enhanced multimodal shape transformation and tunable properties. By cooperative thermal and magnetic actuation, we demonstrate multiple deformation modes with distinct shape configurations, which further enable active metamaterials with tunable physical properties such as sign-change Poisson's ratio. Because of the multiphysics response of the M-MSP/MSM metamaterials, one distinct feature is their capability of shifting between various global mechanical behaviors such as expansion, contraction, shear, and bending. We anticipate that the multimaterial printing technique opens new avenues for the fabrication of multifunctional magnetic materials.

Advanced reconfigurable scaffolds fabricated by 4D printing for treating critical-size bone defects of irregular shapes

While scaffold-based tissue engineering has been widely used to treat bone critical-size defects, challenges such as implantation of scaffolds in defects with irregular shapes and implantation of scaffolds through minimally invasive surgery remain in the tissue engineering field. Customized bioactive bone tissue engineering scaffolds with reconfigurable capability for both easy scaffold implantation and perfect shape fitting in irregularly shaped bone defects are therefore needed. Herein, applying 4D printing, photothermal-responsive shape memory bone tissue engineering scaffolds are constructed by incorporating black phosphorus nanosheets and osteogenic peptide into β-tricalcium phosphate/poly(lactic acid-co-trimethylene carbonate) (TCP/P(DLLA-TMC)) nanocomposite scaffolds. When near-infrared irradiation is applied to customized scaffolds on-demand, scaffold temperature rapidly increases to 45 °C, enabling scaffold shape reconfiguration for easy scaffold implantation and precise fitting in irregular bone defects. Once the implantation is finished, scaffold temperature rapidly decreases to 37 °C and scaffolds display mechanical properties comparable to those of human cancellous bone. The improved osteogenesis in bone defect sites is then initiated through pulsed peptide release from scaffolds. Compact integration of reconfigurable scaffolds in rat cranial bone defects and improved new bone formation are demonstrated through micro-computed tomography and histochemical analyses. This study shows a facile method to clinically treat bone defects of irregular shapes.

Eugenol-derived reconfigurable high-performance epoxy resin for self-deployable smart 3D structures

Fabricating biobased reconfigurable high performance epoxy resins for self-deployable 3D smart structures is an interesting issue with great challenge. Herein, a biobased trifunctional epoxy monomer (tris(2-methoxy-4-(oxiran-2-ylmethyl)phenyl) phosphate, TMOPP) was derived from eugenol and cured by 4,4′-dithiodianiline (DTDA) to form the dynamic cross-linked TMOPP/DTDA resin. The integrated properties including thermal, mechanical and flame retardancy of TMOPP/DTDA resin are studied systemically. Compared with commercial epoxy resin (diglycidyl ether of bisphenol A (DGEBA)/DTDA), TMOPP/DTDA resin has higher glass transition temperature (217 °C) and tensile strength (95.2 MPa), while these properties are superior to those of biobased dynamic cross-linked epoxy resins reported in literatures. TMOPP/DTDA resin also shows excellent flame retardancy with UL-94 V-0 rating. The trifunctional aromatic structure of TMOPP and the compact cross-linked structure of TMOPP/DTDA resin play a principle role in the outstanding performances. At the same time, permanent shape reconfigurability and self-deployable ability of TMOPP/DTDA resin was exhibited by the transformation from planar film into a 3D “rocking chair” structure. These results provide a new method to produce biobased reconfigurable high performance epoxy resin in a simple and sustainable way, while expand the application of dynamic cross-linked epoxy resins in self-deployable 3D smart structures.

Effect of temperature on the programmable helical deformation of a reconfigurable anisotropic soft actuator

Shape reconfiguration is ubiquitous in nature and widely used in many applications such as soft robotics, metamaterials, energy absorption and tissue engineering. Shape reconfigurable soft actuators, due to their ability to adapt and adjust in complex and unpredictable working environment, have been designed by the use of various delicate structures and active materials. However, soft actuators that exhibit reconfigurable helical deformation have not been proposed; they have the advantage of integrating both bending and twisting actuations in one deformation mode. In this work, we present a thermal-induced shape reconfigurable soft actuator that shows reversible actuations with vastly shape differences under thermal stimulus. It exhibits helical deformation at lower temperature and mainly in-plane bending at relatively higher temperature. The reversible shape transition is controlled by a thermal stimulus that changes the anisotropy of the structure, which consists of shape memory polymer fibers embedded in a homogeneous elastic matrix. A theoretical model is proposed based on the minimum potential energy that incorporates the thermomechanical behavior of the shape memory polymer fibers. Experiments are conducted and the results agree well with the theoretical modeling. Using the theoretical model, we establish design principles for reconfigurable soft actuators whose functional response is programmable given the architecture and external stimulus. A six-handed helical soft actuator, constructed to demonstrate its programmable deformation, is utilized to catch a living fish in water.

Modeling and Simulation of Thin Layered Composites Under Non-mechanical Stimuli

This study presents a nonlinear deformation analysis of a thin composite plate undergoing shape reconfigurations triggered by electric field inputs. The composite plate consists of electro-active and inactive (substrate) layers. Prescribing electric field inputs to the electro-active layer induces large curvatures in the composites, while the in-plane stretch is relatively small. This has a consequence that only shapes with zero (or nearly zero) Gaussian curvature can be attained by prescribing the electric field, which leads to snap-through shape reconfigurations in order to achieve developable surfaces. When the substrate is made of an elastic layer, the shape returns to its original planar configuration upon removal of the electric field. In order to fully or partially retain the reconfigured shape upon removing the electric field input, a substrate layer made of a shape memory polymer is considered. Shape reconfigurations and retentions of the composites having elastic substrate and shape memory substrate are simulated.

Actuation and locomotion driven by moisture in paper made with natural pollen

Here we describe the development of a humidity-responsive sheet of paper that is derived solely from natural pollen. Adaptive soft material components of the paper exhibit diverse and well-integrated responses to humidity that promote shape reconfiguration, actuation, and locomotion. This mechanically versatile and nonallergenic paper can generate a cyclically high contractile stress upon water absorption and desorption, and the rapid exchange of water drives locomotion due to hydrodynamic effects. Such dynamic behavior can be finely tuned by adjusting the structure and properties of the paper, including thickness, surface roughness, and processing conditions, analogous to those of classical soapmaking. We demonstrate that humidity-responsive paper-like actuators can mimic the blooming of the Michelia flower and perform self-propelled motion. Harnessing the material properties of bioinspired systems such as pollen paper opens the door to a wide range of sustainable, eco-friendly, and biocompatible material innovation platforms for applications in sensing, actuation, and locomotion.

Sequence-Rearranged Cocrystalline Polymer Network with Shape Reconfigurability and Tunable Switching Temperature.

Switching temperature (Tsw) is a key parameter governing the service condition of shape memory polymers (SMPs). However, tuning Tsw of SMPs often requires sophisticated synthesis or intricate processing. Herein, we report a simple yet effective strategy to prepare the SMPs with tunable Tsw and good reconfigurability by using the cocrystalline polyesters as the reversible phase. The cocrystallizable copolyesters with rearranged sequences were prepared by the transesterification of mixed polyester diols and then photo-cross-linked to achieve the SMP networks. Cocrystallization of copolymer blocks endows the SMP networks tunable melting point and relatively high crystallinity, affording the network good shape fixing and recovery ability at body temperature. Besides, the dynamic nature of transesterification, that enables the network to have good shape reconfigurability, allows for the easy processing of SMPs with complicated shapes. The reconfigurable SMPs capable of actuating at the body temperature show great potential for use as biomedical devices.