Shape Reconfiguration Research Articles

Biocompatible shape-memory poly(propylene carbonate)/silk fibroin blend with body temperature responsiveness.

The high value-added medical applications surely represent the leading edge of the shape-memory materials (SMPs) field. Herein, the biomedical SMPs were easily prepared via incorporating silk fibroin (SF) into poly(propylene carbonate) (PPC) through directly melt blending. Based on the intrinsic glass transition of PPC at ∼37 °C, the blends showed a body temperature responsiveness without a complex procedure for adjusting the switching temperature. By varying the SF content, the blend exhibited tunable shape-memory effects (SME), with a first enhancing but then worsening shape recoverability and a stable and excellent shape fixity. And the blend with 3 wt% SF achieved the best SME, enabling an efficient shape reconfiguration under a 37 °C water bath. It was revealed that SF acted as physical cross-links to connect the PPC chains forming a shape-memory network, thus can well retard irreversible the chain slipping of PPC, leading to the improvement of recoverability. Moreover, the results obtained from cell compatibility testing showed the huge application potential of this material in the biomedical field. This work proposed a facile preparation strategy for developing biocompatible body heat actuated shape-memory materials.

Additive manufacturing of flexible polymer-derived ceramic matrix composites

ABSTRACT It remains challenging to broaden the application fields of ceramics, largely because the hardness and brittleness of ceramics mean that they cannot undergo shape reconfiguration. In this study, we developed an ultraviolet light-curable preceramic polymer slurry, and this slurry was used for digital light processing printing of flexible green parts in designed shapes. These parts were subsequently transformed into complex structures by an assisted secondary molding strategy that enabled the morphology of their green and pyrolyzed forms to be well controlled. The collapse of bulk pyrolyzed parts was avoided by impregnating their precursors with silicon nitride (Si3N4) particles. The effects of different proportions of Si3N4 on the weight loss, shrinkage, density, porosity, and mechanical properties of the pyrolyzed composites were investigated, and the bending strength and Vickers hardness of the composites with 10 wt.% Si3N4 were found to be 130.61 ± 16.01 MPa and 6.43 ± 0.12 GPa, respectively.

Discriminative Transition Sequences of Origami Metamaterials for Mechanologic

Transitions of multistability in materials are exploited for various functions and applications, such as spectral gap tuning, impact energy trapping, and wave steering. However, a fundamental and comprehensive understanding of the transitions, either quasistatic or dynamic transitions, has not yet been acquired, especially in terms of the sequence predictability and tailoring mechanisms. This research, utilizing the stacked Miura‐ori‐variant (SMOV) structure that has multistable shape reconfigurability as a platform, uncovers the deep knowledge of quasistatic and dynamic transitions and proposes the corresponding versatile formation and tuning of mechanical logic gates. Through theoretical, numerical, and experimental means, discriminative and deterministic quasistatic transition sequences, including reversible and irreversible ones, are uncovered, where they constitute a transition map that is editable upon adjusting the design parameters. Via applying dynamic excitations and tailoring the excitation conditions, reversible transitions between all stable configurations become attainable, generating a fully connected transition map. Benefiting from the nonlinearity of the quasistatic and dynamic transitions, basic and compound mechanical logic gates are achieved. The versatility of the scheme is demonstrated using a single SMOV to realize different complex logic operations without increasing structural complexity, showing its unique computing power and inspiring the avenue for efficient physical intelligence.

Harnessing β-Hydroxyl Groups in Poly(β-Amino Esters) toward Robust and Fast Reprocessing Covalent Adaptable Networks

Poly(β-amino esters) (PBAEs), which include tertiary amines at the β-position of ester linkages, are promising in biomaterials due to their biodegradability and pH responsiveness. Such characteristics in the molecular structure are also appealing for designing catalyst-free covalent adaptable networks (CANs), but this has rarely been explored in the literature. Herein, we synthesize a series of PBAE-based CANs by aza-Michael addition, using diacrylate monomers with and without β-hydroxyl groups, and a triamine crosslinker. By leveraging hydrogen bonding, the thermal and mechanical properties of these PBAE-based CANs are effectively tuned through the monomer composition. Owing to the numerous tertiary amines serving as internal catalysts, these CANs undergo catalyst-free network exchange through a dynamic aza-Michael reaction. Interestingly, increasing the amount of β-hydroxyl groups accelerates overall stress relaxation from the synergistic effects of transesterification (associative type) at lower temperatures and dynamic aza-Michael reaction (dissociative type) at higher temperatures. Based on these features, we successfully demonstrate the reprocessing and healing at elevated temperatures under mild pressure, as well as shape memory and shape reconfiguration. Thus, controlling the β-hydroxyl group concentration in PBAE-based CANs is a useful strategy for enhancing both the mechanical strength and reprocessing rate.

Thermomechanical analysis (TMA) of vitrimers

Vitrimers are an exciting class and new generation of polymer materials combining the strength of a traditional thermoset polymer with the reprocessability of a traditional thermoplastic polymer. However, a key debate in literature has surrounded the best method to identify the vitrimer topology freezing temperature (Tv), above which dynamic covalent bond exchange reactions occur, allowing for self-healing, recycling, and shape reconfigurability of vitrimers. While common methods in literature to identify the Tv include stress relaxation, creep, and fluorescence, we herein validate thermomechanical analysis (TMA) as a reliable method for Tv identification. TMA provides several clear advantages as it is less time and sample intensive than stress relaxation. Furthermore, it is performed in compression to match application conditions, provides more consistent results than creep, and identifies the coefficient of thermal expansion (α). We demonstrate that expansion TMA is a valuable tool in Tv identification by validating several clearly accepted trends in literature; TMA validates that the Tv increases with decreasing catalyst concentration and increasing heating rate while showing negligible variation with increasing applied force. Finally, we report an increasing α with increasing catalyst concentration for our vitrimer material. By taking advantage of such a fast and reliable method to identify Tv, we believe this fundamental study will support future vitrimer research.

Enormous-stiffness-changing polymer networks by glass transition mediated microphase separation

The rapid development of flexible electronics and soft robotics has an urgent demand for materials with wide-range switchable stiffness. Here, we report a polymer network that can isochorically and reversibly switch between soft ionogel and rigid plastic accompanied by a gigantic stiffness change from about 600 Pa to 85 MPa. This transition is realized by introducing polymer vitrification to regulate the liquid–liquid phase separation, namely the Berghmans’ point in the phase diagram of binary gel systems. Regulating the Lewis acid-base interactions between polymer and ionic liquids, the stiffness-changing ratio of polymer network can be tuned from 10 to more than 105. These wide-range stiffness-changing ionogels show excellent shape adaptability and reconfigurability, which can enhance the interfacial adhesion between ionogel and electrode by an order of magnitude and reduce interfacial impedance by 75%.

Magnetorotational supernovae: a nucleosynthetic analysis of sophisticated 3D models

ABSTRACT Magnetorotational supernovae are a rare type of core-collapse supernovae where the magnetic field and rotation play a central role in the dynamics of the explosion. We present the post-processed nucleosynthesis of state-of-the-art neutrino-MHD supernova models that follow the post explosion evolution for few seconds. We find three different dynamical mechanisms to produce heavy r-process elements: (i) a prompt ejection of matter right after core bounce, (ii) neutron-rich matter that is ejected at late times due to a reconfiguration of the protoneutronstar shape, (iii) small amount of mass ejected with high entropies in the centre of the jet. We investigate total ejecta yields, including the ones of unstable nuclei such as 26Al, 44Ti, 56Ni, and 60Fe. The obtained 56Ni masses vary between $0.01\!-\!1\, \mathrm{M_\odot }$. The latter maximum is compatible with hypernova observations. Furthermore, all of our models synthesize Zn masses in agreement with observations of old metal-poor stars. We calculate simplified light curves to investigate whether our models can be candidates for superluminous supernovae. The peak luminosities obtained from taking into account only nuclear heating reach up to a few $\sim 10^{43} \, \mathrm{erg\, s^{-1}}$. Under certain conditions, we find a significant impact of the 66Ni decay chain that can raise the peak luminosity up to $\sim 38{{\ \rm per \, cent}}$ compared to models including only the 56Ni decay chain. This work reinforces the theoretical evidence on the critical role of magnetorotational supernovae to understand the occurrence of hypernovae, superluminous supernovae, and the synthesis of heavy elements.

A Novel Cam-Based Variable Stiffness Actuator: Pitch Curve Synthetic Approach for Reconfiguration Design

Variable stiffness actuators (VSA) have attracted much attention because of their potential for human-like interaction behaviors. This paper devotes to improving the VSA’s versatility. VSA with different characteristics can be obtained by shape reconfiguration of its internal driving cams. The proposed VSA mainly includes a variable stiffness module and a cam-based driven module. A common node connects the two modules. It is placed in the common grooves of the dual cams. Kinematically, the radial position of the node can be changed for stiffness adjustment by cam differential motion. Mechanically, the driven force on this node can be resolved into two orthogonal directions by cam groove, one for stiffness adjustment and another for position balance., The paper establishes the analytical relationship between the pressure angle of the cam pitch curve, stiffness adjustment speed and accuracy, and load distribution. Furtherly, the pitch curve synthetic approach for VSA reconfiguration is provided. A special cam shape with a favorable load distribution is proposed to verify the method. The correctness of the design was effectively proved by experiments in the virtual model and physical prototype.

Shape reconfiguration through origami folding sets an upper limit on drag

Mechanisms of drag reduction through shape reconfiguration have been extensively studied on model geometries of plates and beams that deform primarily in bending. Adding an origami crease pattern to such plates produces a distinct class of deformation modes, with large shape changes along selected degrees of freedom. Here, we investigate the impact of those creases on reconfiguration processes and on drag, focusing on the waterbomb base as a generic case. When placed in a uniform airflow, this origami unit folds into a compact structure, whose frontal area collapses with increasing flow velocity. It enhances drag reduction to the point that fluid loading eventually ceases to increase with flow speed, reaching an upper limit. We further show that this limit is adjustable through the origami structural parameters: the stiffness and rest angle of the folds, and their pattern. Experimental results, corroborated by a fluid–elastic theoretical model, point to a scenario consistent with the previous literature: reconfiguration is governed by a dimensionless Cauchy number that measures the competition between fluid loading and elastic resistance to deformation, here embodied in creases. This foldable system yet stands out through the rare passive drag-capping lever it provides, a valuable asset for self-protection in strong wind.

Photoinduced Dual Shape Programmability of Covalent Adaptable Networks with Remarkable Mechanical Properties.

As classic shape memory polymers featuring shape reconfiguration of temporary state, covalent adaptable networks containing reversible bonds can enable permanent-state reconfigurability through topological rearrangement via dynamic bond exchange. Yet, such an attractive dual shape programmability is limited by the actuation mode of direct heat transfer and poor mechanical properties, restricting its control precision and functionality. Herein, we presented a method to create nanocomposites with photomodulated dual shape programmability and remarkable mechanical properties leading the fields of covalent adaptable networks. MXene, whose photothermal efficiency was revealed to be regulated by the etching method and delamination, was introduced into polyurethane networks. Upon adjusting the light intensity, the dual shape programmability of both permanent and temporary states could be accomplished, which exhibited potential in information recognition, photowriting paper, etc. Furthermore, owing to the dynamic transcarbamoylation at elevated temperatures, such a phototriggered dual shape programmability could be maintained after the self-healing and reprocessing.

Tunable dynamics in Yoshimura origami by harnessing pneumatic pressure

The unique merits of origami structures and origami metamaterials are the folding-induced shape reconfigurability and the associated evolution of mechanical properties. However, currently, there is a lack of mature solutions on how to achieve active tuning, and the tunability is stuck in static properties. Therefore, this study proposes a pneumatic scheme to overcome the above two bottleneck problems. Specifically, by integrating a pneumatic bladder with a monostable Yoshimura-ori structure, a pneumatic Yoshimura origami (PYO) cell is designed. Compared with the conventional approach making use of the origami multistability, the pressure scheme is simpler in design, more accurate in regulation, and richer in configurations. To exploit the PYO structure for tunable dynamics, the dynamic model is developed via a nonlinear system identification approach, in which the overall system, including the structure itself and the friction contact, is represented as a nonlinear spring-damper element, with the constitutive profile identified via the weighted least square method from the dynamic experimental data. Based on the developed model, the pressure tunability is then explored in a 6-cell PYO structure and a PYO metamaterial. Through comprehensive linear dispersion analyses and numerical simulations, we reveal that pressure could effectively tune the passbands of the 6-cell structure so that the transmission of vibration, at certain frequencies, can be qualitatively switched between amplification and attenuation; from another perspective, pressure could also be tailored for programming the stopbands of the PYO metamaterial to achieve the shift between propagation and prohibition. The results of this investigation could provide useful guidelines for the development of intelligent origami structures/metamaterials with excellent tunability, and meanwhile, open a new perspective of origami dynamics research.

3D Printed Fractal Metamaterials with Tunable Mechanical Properties and Shape Reconfiguration

AbstractLattice metamaterials constructed by curved microstructures exhibit large stretchability and are promising in soft electronics and soft robotics. Fractal structures are particularly efficient in improving stretchability as it shows multiple‐order uncurling. However, the development of fractal metamaterials is hindered by hierarchical structures and large deformations. In this study, a design framework combining experiments, hierarchical theoretical models, and finite element simulations is developed to program the mechanical behaviors of fractal metamaterials. For 3D printing, a digital design tool is developed to visualize the structure and automatically generate the manufacturing representations. Results show that large stretchability (≈360%), bionic stress–strain curve matching, and imperfection insensitivity can be programmed by tuning the geometric parameters. An integrated device of an electromyogram sensor embedded in an imperfection‐insensitive fractal metamaterial that matches the J‐shaped stress–strain curve of human skin is demonstrated. Light‐emitting diode devices based on fractal metamaterial with shape reconfiguration are also presented. This st paves a new way to realize multifunctional soft devices using fractal metamaterials.

Magneto-active soft matter with reprogrammable shape-morphing and self-sensing capabilities

Interest in creating soft active matter that can repeatedly undergo shape morphing and self-sensing in response to external stimuli is growing. Magneto-active soft matter (MASM) with untethered, fast, and reversible shape reconfiguration is highly desirable for diverse applications in biomedical devices, wearable devices, soft robotics. In this work, we develop a heat-assisted magnetic reprogramming strategy for fabricating MASMs capable of reprogrammable shape-morphing and self-sensing functions. The magnetic reprogramming strategy is based on heating thermoplastic matrix above its melting point and reorienting soft-magnetic particle chains by applying magnetic fields during cooling. By reprogramming magnetization profiles through particle chain reconstruction of printed architecture, we demonstrate multiple deformation modes with distinct shape-morphing. This magnetic reprogramming approach enabled multiscale and reprogrammable soft machines with the tunable actuation response, such as adaptive grasping of a soft gripper. In addition, in combining with the unique sensing mechanism of triboelectric skin (tribo-skin), the self-sensing performance of MASMs is realized by using electrical signals to identify the deformation and contact behaviors. We anticipate that the magnetic reprogramming strategy and multimaterial 3D printing-assisted technique can open new avenues for the fabrication of multifunctional MASMs.

Self-Reporting Joule Heating Modulated Stiffness of Polymeric Nanocomposites for Shape Reconfiguration.

Shape reconfigurable devices, e.g., foldable phones, have emerged with the development of flexible electronics. But their rigid frames limit the feasible shapes for the devices. To achieve freely changeable shapes yet keep the rigidity of devices for user-friendly operations, stiffness-tunable materials are desired, especially under electrical control. However, current such systems are multilayer with at least a heater layer and a structural layer, leading to complex fabrication, high cost, and loss of reprocessability. Herein, we fabricate covalent adaptable networks-carbon nanotubes (CAN-CNT) composites to realize Joule heating controlled stiffness. The nanocomposites function as stiffness-tunable matrices, electric heaters, and softening sensors all by themselves. The self-reporting of softening is used to regulate the power control, and the sensing mechanism is investigated by simulating the CNT-polymer chain interactions at the nanoscale during the softening process. The nanocomposites not only have adjustable mechanical and thermodynamic properties but also are easy to fabricate at low cost and exhibit reprocessability and recyclability benefiting from the dynamic exchange reactions of CANs. Shape and stiffness control of flexible display systems are demonstrated with the nanocomposites as framing material, where freely reconfigurable shapes are realized to achieve convenient operation, wearing, or storage, fully exploiting their flexible potential.

Monolithically Assembled 3D Soft Transformable Robot

Transformable Robot In article number 2200051, Hong Suk Kang, Dong-Gyun Kim, Jong-Chan Lee, and co-workers present photo-controllable liquid crystalline networks (pc-LCNs) comprising static and dynamic covalent dual-cross-links. The tailored network architecture of pc-LCNs enable UV-controllable reversible assembly/disassembly and shape reconfiguration capabilities, while maintaining visible light-responsive actuation behaviors, thus realizing a building-block-like, monolithically assembled 3D soft transformable robot capable of versatile locomotion.

Shape-reconfigurable transparent wood based on solid-state plasticity of polythiourethane for smart building materials with tunable light guiding, energy saving, and fire alarm actuating functions

Transparent wood (TW) is a promising light and thermal management material that has enormous potential for energy-efficient engineering applications. However, almost all the polymers currently used to fabricate TW fall under the thermosetting or thermoplastic category, exhibiting extremely monotonous performance and lack of intelligence. Herein, a smart shape-reconfigurable TW is developed through infiltration the polythiourethane covalent adaptable networks (PTU CANs) into the delignified wood (DW) scaffolds. Benefiting from the solid-state plasticity and thermadapt shape-memory behavior of PTU CANs and the highly aligned cellulose nanofibers of the DW scaffolds, the resulting TW exhibits reconfigurable shape memory behavior, excellent optical properties (transmittance of ∼90% and tunable light guiding effects), and low thermal conductivity (212.8 mW m−1K−1). In addition, the tensile strength, modulus, and toughness of TW are 60.14 MPa, 2.09 GPa, and 1.19 MJ m−3, respectively. Moreover, the reconfigurable shape-memory performance of the TW allows it to be used as a smart actuator for designing a fire alarm system. Compared with traditional TW, the TW reported in this work not only maintains high optical transmittance, but also exhibits excellent reconfigurable shape memory properties, which can promote the high-value utilization for TW. The incorporation of the shape reconfiguration, light guiding, energy saving, and fire alarm actuating properties to the TW opens a new avenue for the design and development of advanced functional and intelligent building materials.

Shape reconfiguration and functional self-healing of thermadapt shape memory epoxy vitrimers by exchange reaction of disulfide bonds

Epoxy-based shape memory materials still face many challenges from preparation to application. Designing dynamic covalent bonds into the cross-linked network of epoxy can bring many new properties to them, which is expected to solve some of the problems faced. In this paper, epoxy vitrimers with different contents of exchangeable disulfide bonds were synthesized by the polymerization of hydrogenated epoxy resins with diacids containing dynamic disulfide bonds. The effect of disulfide bond content on the properties of epoxy vitrimers was systematically studied. By activating the exchange reaction of disulfide bonds, the permanent shape of epoxy vitrimers can be reconfigured, even from two to three dimensions. The time required for reconfiguring is affected by the content of disulfide bonds, the more disulfide bonds, the shorter the time required. The epoxy vitrimers with more content of disulfide bonds were found to have lower recovery ratio loss after the same shape memory cycle by thermal bending experiments. More importantly, the epoxy vitrimers with more content of disulfide bonds also exhibited better functional self-healing properties. The decreased recovery ratio can be healed by periodic heat treatment, thus ensuring that the epoxy vitrimers perform more shape memory cycles and maintain a high shape recovery ratio. These experimental results will serve as a basis for expanding the range of applications and prolonging the service life of epoxy-based shape memory materials.

Vitrimer Composites: Understanding the Role of Filler in Vitrimer Applicability

Vitrimers, a subset of covalent adaptable networks (CANs), are a class of polymer material capable of self-healing and shape reprocessing at temperatures above their topology freezing temperature (Tv), where dynamic covalent bond exchange reactions dominate. In particular, epoxy vitrimers have the strength of a traditional epoxy at low temperatures (T < Tg) coupled with the processing capabilities of a thermoplastic at high temperatures (T > Tv). In addition, epoxy vitrimer composites are attractive as a potential industrial material due to their enhanced thermomechanical performance. While this class of epoxy materials is of significant interest, research on these composites is still premature, and the influence of filler is poorly understood. Herein, we demonstrate the impact of filler addition upon the thermomechanical properties, self-healing, and shape processing capabilities of the resulting vitrimer composites when incorporated with either graphene or clay. We report that filler concentration and dispersion both play a key role in creep suppression, increases in the Tv, and improved mechanical properties (e.g., modulus and strength) irrespective of filler composition. Meanwhile, filler addition does not considerably impact composite shape memory or shape reconfigurability but increases the self-healing capabilities. However, increases in composite modulus require additional heat and stress to allow for comparable shape change compared with their neat counterparts. Vitrimer composites facilitate a unique tunability previously impossible via chemical variations alone. By varying filler composition, concentration, and dispersion quality, composite design with tailorable Tv, strength, and processability is possible, making it suitable for various applications (e.g., actuators, strain sensors, coatings).

Recyclability of Vitrimer Materials: Impact of Catalyst and Processing Conditions.

With sustainability at the forefront of material research, recyclable polymers, such as vitrimers, have garnered increasing attention since their introduction in 2011. In addition to a traditional glass-transition temperature (Tg), vitrimers have a second topology freezing temperature (Tv) above which dynamic covalent bonds allow for rapid stress relaxation, self-healing, and shape reprogramming. Herein, we demonstrate the self-healing, shape memory, and shape reconfigurability properties as a function of experimental conditions, aiming toward recyclability and increased useful lifetime of the material. Of interest, we report the influence of processing conditions, which makes the material vulnerable to degradation. We report a decreased crosslink density with increased thermal cycling and compressive stress. Furthermore, we demonstrate that shape reconfigurability and self-healing are enhanced with increasing compressive stress and catalyst concentration, while their performance as a shape memory material remains unchanged. Though increasing the catalyst concentration, temperature, and compressive stress clearly enhances the recovery performance of vitrimers, we must emphasize its trade-off when considering the material degradation reported here. While vitrimers hold great promise as structural materials, it is vital to understand how experimental parameters impact their properties, stability, and reprocessability before vitrimers reach their true potential.

Dynamic response of flexible viscoelastic kerf structures of freeform shapes

Kerfing which is also known as relief cutting is a technique used to create flexible freeform surfaces out of rigid planar surfaces. Due to their pleasing aesthetics, flexibility, and ability to be molded into desired freeform shapes, they have several potential applications in engineering and architecture. The flexibility and reconfigurability of kerf structures depend on several kerf parameters such as cut density, size of the unit cell, cut thickness, cut pattern, etc. This study focuses on using kerf structures to create freeform surfaces and understanding their dynamic response in terms of mode shapes, resonance frequencies, and stress wave propagation of reconfigurable large-scale kerf structures. The effect of kerf cut density and unit cell size on the unit-cell modal behaviors is first investigated using both mathematical modeling and experiments. A beam element model is used to capture deformations of kerf structures. Next, the shape reconfigurable behaviors of two kerf panels with uniform cut density and transitioning cut density are presented. The dynamic response of these two kerf panels is then examined. The analysis of large-scale kerf panels demonstrated the capability of the beam element model to capture the modal response of kerf panels. The flexibility of the kerf panels enables local and global shape reconfigurations, which can alter the dynamic response (i.e., modal response and stress wave propagation) of the kerf panels. We perform a comparative study on the effect of shape reconfiguration (local and global) on the modal response and stress propagation behavior of the kerf panel. Overall, these findings would help design kerf structures for indoor and outdoor architectures with desired performance requirements.