Shape Transformation Research Articles

Programmable and reconfigurable hygro-thermo morphing materials with multifunctional shape transformation

Humidity responsive materials are increasingly attracting significant interest for soft robotics and deployable structures. Their shape-changing behavior is based on differential hygroscopic characteristics of the single components of their microscopic architecture. Although existing moisture-induced materials achieve morphing in various humidity conditions, practical operational environments involve the presence of uncontrolled humidity regimes, which restrict those materials to reach broad ranges of shapes. Here we describe programmable and reconfigurable composite materials based on natural fibres and shape memory polymers that extend the current one-to-one relation between external humidity and final actuated shape. The heating of flexible polymer networks permits to program the architecture of the natural fibres flax reinforcements and their spatial distribution within the composite, when a moisture gradient is present. Once cooled, the programmed materials create new sets of different shapes, even when exposed to the same humidity conditions. These multifunctional biobased materials also show large stiffness (>13 GPa) that make them suitable for structural load-bearing applications. New multifunctional shape transformations capabilities of these bio-based hygro-thermo composites are demonstrated in a bio-robotic grasping hand and a bio-frame for electro-adhesive gripping. These examples show the full functionality, structural integrity, programmability and remarkable mechanical properties of our multifunctional hygromorph biocomposites.

Mem3DG: modeling membrane mechanochemical dynamics in 3D using discrete differential geometry

Biomembranes adopt varying morphologies that are vital to cellular functions. Many studies use computational modeling to understand how various mechanochemical factors contribute to membrane shape transformations. Compared to approximation-based methods (e.g., finite element method), the class of discrete mesh models offers greater flexibility to simulate complex physics and shapes in three dimensions; its formulation produces an efficient algorithm while maintaining coordinate-free geometric descriptions. However, ambiguities in geometric definitions in the discrete context have led to a lack of consensus on which discrete mesh model is theoretically and numerically optimal; a bijective relationship between the terms contributing to both the energy and forces from the discrete and smooth geometric theories remains to be established. We address this and present an extensible framework, $\texttt{Mem3DG}$, for modeling 3D mechanochemical dynamics of membranes based on Discrete Differential Geometry (DDG) on triangulated meshes. The formalism of DDG resolves the inconsistency and provides a unifying perspective on how to relate the smooth and discrete energy and forces. To demonstrate, $\texttt{Mem3DG}$ is used to model a sequence of examples with increasing mechanochemical complexity: recovering classical shape transformations such as 1) biconcave disk, dumbbell, and unduloid and 2) spherical bud on spherical, flat-patch membrane; investigating how the coupling of membrane mechanics with protein mobility jointly affects phase and shape transformation. As high-resolution 3D imaging of membrane ultrastructure becomes more readily available, we envision Mem3DG to be applied as an end-to-end tool to simulate realistic cell geometry under user-specified mechanochemical conditions.

Colony-like protocell superstructures

We report the formation, growth, and dynamics of model protocell superstructures on solid surfaces, resembling single cell colonies. These structures, consisting of several layers of lipidic compartments enveloped in a dome-shaped outer lipid bilayer, emerged as a result of spontaneous shape transformation of lipid agglomerates deposited on thin film aluminum surfaces. Collective protocell structures were observed to be mechanically more stable compared to isolated spherical compartments. We show that the model colonies encapsulate DNA and accommodate non-enzymatic, strand displacement DNA reactions.

Oscillating membranes: autonomous shape-transforming sheets via chemo-mechanical “metabolism”

Living organisms have mastered the dynamic control of residual stresses within sheets to induce shape transformation and locomotion. For instance, the spatiotemporal pattern of action-potential in a heart induces a dynamical stress field that leads to shape changes and biological function. Such out-of-equilibrium structures inspired the emerging field of soft robotics. However, state-of-the-art attempts to replicate this ability in synthetic materials are still lacking.

Automated shape-transformable self-solar-tracking tessellated crystalline Si solar cells using in-situ shape-memory-alloy actuation

Photovoltaic energy systems in urban situations need to achieve both high electricity production and high capacity in restricted installation areas. To maximize power output, solar-tracking systems tilt solar arrays to track the sun’s position, and typically flat modules are used to maximize the cross-sectional area. Such tracking systems are complex and expensive, and flat modules cannot utilize omnidirectional incident light. For solar systems in urban environments, we have developed two-dimensional (2D) or three-dimensional (3D) tessellated solar-cell modules that use shape transformation, and combine solar tracking and an arch structure for use in restricted areas. The modules can use scattered and omnidirectional incident light. Simply by attaching shape-memory alloy strips to the surface of the solar panels, the shape of the array can be transformed in response to heat from sunlight. Compared to a perfect solar-tracking system, our simulation results indicate that the modules present a large cross-sectional area perpendicular to the direction of sunlight and provide superior tracking performance, resulting in a 60% increase in electricity production over the course of 1 day. In addition, by using different designs for the tessellation units, dome shaped or other 3D structures are possible, for specific applications and to meet aesthetic requirements.

A fast shape transformation using a phase-field model

We propose a numerical method for a fast shape transformation using a phase-field model. The governing equation is based on the modified Allen–Cahn (AC) equation. We numerically solve the equation by using the operator splitting technique. The alternating direction explicit (ADE) finite difference method is used to reduce the strict temporal step constraint when solving the diffusion term. Therefore, we can use a large temporal step size to simulate a fast shape transformation. The reaction term is solved by the separation of variables, and the fidelity term is solved using the semi-implicit scheme with a frozen coefficient. To demonstrate that the proposed method can simulate the fast shape transformation with simple or complex sources and targets, we perform several numerical experiments in the three-dimensional space. The computational experiments demonstrate that the shape transformation is fast and smooth.

Light-controlled multifunctional reconfigurable structures

Research development of stimuli-actuated materials has become a crucial driving force in advancing the frontiers of smart devices. Among various responsive mechanisms, localized and remote control can be offered by light stimuli. However, flexible design with complex geometries and multi-level functions for light-triggered reconfigurable structures remain significant challenges. Here, selectively kirigami-patterned reconfigurable structures based on light-responsive material are reported and their applications in biomimetic actuators and flexible electronics field are explored. More than a dozen sophisticated kirigami patterns are fabricated, programmable shape transformations from planar sheets are achieved reversibly under light illumination with finite element analysis guidance. Three biomimetic actuators composed of reconfigurable structures are generated with programmable and remote actuations. Furthermore, to extend functions of this strategy to flexible electronics field, a reconfigurable monopolar antenna is demonstrated. Three states of the antenna can be regulated and switched by light with different power densities. These results pave a facile scheme to realize the flexible and intricate design of light-controlled actuators with multiple functions.

Difference-frequency chirped-pulse dual-comb generation in the THz region: Temporal magnification of the quantum dynamics of water vapor lines by >60 000.

A new difference-frequency method based on electro-optic phase modulators (EOMs) and two free-running lasers is reported to perform chirped-pulse dual-comb spectroscopy in the THz region. A variation of a near-IR interleaving scheme we recently reported has been developed to interleave the EOMs' orders and sidebands and to map THz comb teeth into the radio-frequency region below 1MHz. The down-converted comb teeth are shown to have transform limited widths of 1Hz over a 1s time scale. The dual chirp-pulsed scheme is used to measure the complex line shapes of two water vapor lines below 600GHz and to temporally magnify the effects of rapid passage by more than 60 000. For the 11,0 ← 10,1 transition in H2O, a pressure dependent phase perturbation is observed in the rapid passage response over the magnified time scale in contrast to a uniform line shape transformation observed for the 21,1 ← 20,2 transition of D2O. The possible origins for this anomalous behavior are modeled and discussed. The method is applicable to any region where difference or sum frequency waves can be generated.

Porous Liquid‐Crystalline Networks with Hydrogel‐Like Actuation and Reconfigurable Function

AbstractA porous liquid‐crystalline network (LCN), prepared by using a template method, was found to exhibit peculiar actuation functions. The creation of porosity makes the initially hydrophobic LCN behave like a hydrogel, capable of absorbing a large volume of water (up to ten times the sample size of LCN). When the amount of absorbed water is relatively small (about 100 % swelling ratio), the porous LCN displays anisotropic swelling in water and, in the same time, the retained uniaxial alignment of mesogens ensures a thermally induced shape change associated with a LC‐isotropic phase transition. Combining the characteristic actuation mechanisms of LCN (order–disorder transition of mesogens) and hydrogel (water absorption), such porous LCNs can be explored for versatile stimuli‐triggered shape transformations. Moreover, the porosity enables loading/removal/reloading of functional fillers such as ionic liquids, photothermal dyes and fluorophores, which imparts the porous LCN actuator with reconfigurable functions such as ionic conductivity, light‐driven locomotion, and emissive color.

Porous Liquid-Crystalline Networks with Hydrogel-Like Actuation and Reconfigurable Function.

A porous liquid-crystalline network (LCN), prepared by using a template method, was found to exhibit peculiar actuation functions. The creation of porosity makes the initially hydrophobic LCN behave like a hydrogel, capable of absorbing a large volume of water (up to ten times the sample size of LCN). When the amount of absorbed water is relatively small (about 100 % swelling ratio), the porous LCN displays anisotropic swelling in water and, in the same time, the retained uniaxial alignment of mesogens ensures a thermally induced shape change associated with a LC-isotropic phase transition. Combining the characteristic actuation mechanisms of LCN (order-disorder transition of mesogens) and hydrogel (water absorption), such porous LCNs can be explored for versatile stimuli-triggered shape transformations. Moreover, the porosity enables loading/removal/reloading of functional fillers such as ionic liquids, photothermal dyes and fluorophores, which imparts the porous LCN actuator with reconfigurable functions such as ionic conductivity, light-driven locomotion, and emissive color.

Stress Communication between the Chain Movement and the Shape Transformation from 2D to 3D.

Shape memory polymers can change their initial shape under the stimulation of the external environment, but most of the stimulations require not only an external force but also a high temperature, which limits their application to a certain extent. Inspired by the unmatched elongation of cells on both sides of the mimosa petiole in nature, which leads to leaf closure, we designed a new type of shape transformation polymer, which can transform between 2D and 3D by simple stretching and releasing steps at room temperature. Surface patterning on one side of the sample film was realized via a coordination network of Fe3+-COOH to achieve different coordination gradients along its thickness. By this way, different movements of polymer chains along the thickness would lead to 2D-3D transformation upon releasing the stretched sample. Using this method, we obtained a series of transformations from customized 2D materials to complex 3D shapes and explored their potential application in information encryption transmission.

Multimaterial Lattice Structures With Thermally Programmable Mechanical Behaviors

Traditional lattice structures usually maintain their mechanical properties throughout their lifetime. Designing and manufacturing intelligent materials with environmental adaptability, programmatically sense and respond to external changes (such as light, pressure, solution, temperature, electromagnetic field, electrochemical reaction), and shape transformation, mode conversion and performance regulation with spatial and temporal modulation are still important scientific challenges in the field of artificial materials. In this paper, multimaterial lattice structures with thermally programmable mechanical response were proposed by using polymer materials with disparate glass transition temperatures and temperature dependencies and reasonably designing the spatial distribution of the materials. Combined with theoretical analysis and finite element simulation, the effects of the relative stiffness of constitute materials on Poisson's ratio, deformation mode and structural stability of the multimaterial lattice structures were studied. The elastic constants, crushing response and structural stability of multimaterial lattice structures are regulated by temperature control, which makes the multimaterial lattice structures show giant thermal deformation, hyperelasticity and shape memory effects. This paper opens up new avenues for the design and manufacture of adaptive protection equipment, biomedical devices, aerospace morphing structures, flexible electronic devices, self-assembly structures and reconfigurable soft robots.

Dark matter mass loss in galaxy flybys: dependence on impact parameter

Galaxy flybys, interactions where two independent halos inter-penetrate but detach at a later time and do not merge, occur frequently at lower redshifts. These interactions can significantly impact the evolution of individual galaxies - from the mass loss and shape transformation to the emergence of tidal features and formation of morphological disc structures. The main focus of this paper is on the dark matter mass loss of the secondary, intruder galaxy, with the goal of determining a functional relationship between the impact parameter and dark matter mass loss. Series of N-body simulations of typical galaxy flybys (10:1 mass ratio) with differing impact parameters show that the dark matter halo leftover mass of the intruder galaxy follows a logarithmic growth law with impact parameter, regardless of the way the total halo mass is estimated. The lost mass then, clearly, follows the exponential decay law. The stellar component stretches faster as the impact parameter decreases, following the exponential decay law with impact parameter. Functional dependence on impact parameter in all cases seems universal, but the fitting parameters are likely sensitive to the interaction parameters and initial conditions (e.g. the mass ratio of interacting galaxies, initial relative velocity of the intruder galaxy, interaction duration). While typical flybys, investigated here, could not be the sole culprit behind the formation of ultra-diffuse or dark matter deficient galaxies, they can still contribute significantly. Rare, atypical and stronger flybys are worth further exploring.

Thermo- and near infrared light-induced reversible multi-shape memory materials for actuators and sensors

Smart materials with reversible shape transformation have drawn enormous interest for their potential applications in various fields.

Light-driven sequential shape transformation of block copolymer particles through three-dimensional confined self-assembly.

Shape-controlled block copolymer (BCP) particles that respond to light stimulus have drawn great attention due to their promising applications in smart materials, yet polymeric particles with light-triggered controllable sequential shape transformation (SST) are still rarely reported. By confined co-assembly of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) and azo-containing light-responsive additives within emulsions, herein, we fabricated BCP particles with light-controlled SST behavior. Attributed to the quaternization of P2VP chains with bromoalkyl additives and the trans-cis isomerization of an azo group under UV light, the interfacial interactions between the BCPs and the surrounding aqueous phase are significantly varied; therefore, the particles exhibit three distinct phases in sequence: (1) elongation of ellipsoidal particles with increasing domain spacing; (2) shape transformation of elongated ellipsoidal particles into accordion-like particles; and (3) disassembly of polymer particles into small spheres. In addition, these particles with SST behavior can be used in light-controlled drug release at a high spatial-temporal resolution, demonstrating their potential in clinical settings and biomedicine.

A polymer-tethered particle confined in a slit

Shape transformations of hairy nanoparticles under confinement are studied using molecular dynamic simulations. We discuss the behavior of these particles in slits with inert or attractive walls. We assume that only chain-wall interactions are attractive. The impact of the strength of interactions with the walls and the width of the slits on the particle configuration is shown. In the case of attractive surfaces, we found new structures in which the chains are connected with both walls and form bridges between them: pillars, symmetrical and asymmetrical spools, and hourglasses. In wide pores with strongly attractive walls, hairy particles adsorb on one of the surfaces and form "mounds" or starfish-like strucures.

Magnetic Arthropod Millirobots Fabricated by 3D‐Printed Hydrogels

Magnetic Arthropod Millirobots Inspired by arthropod species in nature, magnetic arthropod millirobots have been fabricated of 3D-printed hydrogels. The joint structure can induce folding deformation and decrease the energy consumption. Multimodal locomotion and programmed shape transformation have been realized by a six-armed millirobot. The millirobot can manipulate foreign objects in porcine organs ex vivo with the assistance of endoscope imaging. More information can be found in article number 2100139 by Qian Deng, Jingda Tang, and co-workers.

AniGAN: Style-Guided Generative Adversarial Networks for Unsupervised Anime Face Generation

In this paper, we propose a novel framework to translate a portrait photo-face into an anime appearance. Different from existing translation methods which do not designate specific styles, we aim to synthesize anime-faces which are style-consistent with a given reference anime-face. However, unlike typical translation tasks, such anime-face translation is particularly challenging due to the large and complex variations of appearances among anime-faces. Existing methods often fail to transfer the styles of reference anime-faces to the generated anime-faces, or introduce noticeable artifacts/distortions in the local shapes of their generated anime-faces. We propose a novel GAN-based anime-face translator, called AniGAN, to synthesize high-quality anime-faces. Specifically, a new generator architecture is proposed to simultaneously transfer color/texture styles and transform local facial shapes into anime-like counterparts based on the style of a reference anime-face, while preserving the global structure of the source photo-face. New normalization functions are designed for the generator to further improve local shape transformation and color/texture style transfer. Besides, we propose a double-branch discriminator to learn domain-specific distributions through individual branches and learn cross-domain shared distributions via shared layers, helping generate visually pleasing anime-faces and effectively mitigate artifacts/distortions. Extensive experiments on benchmark datasets qualitatively and quantitatively demonstrate the superiority of our method over state-of-the-art methods.

Optimal airfoil design and wing analysis for solar-powered high altitude platform station

The ability of flying continuously over prolonged periods of time has become target of numerous research studies performed in recent years in both the fields of civil aviation and unmanned drones. High altitude platform stations are aircrafts that can operate for an extended period of time at altitudes 17 km above sea level and higher. The aim of this paper is to design and optimize a wing for such platforms and computationally investigate its aerodynamic performance. For that purpose, two-objective genetic algorithm, class shape transformation and panel method were combined and used to define different airfoils with the highest lift-to-drag ratio and maximal lift coefficient. Once the most suitable airfoil was chosen, polyhedral half-wing was modeled and its aerodynamic performances were estimated using the CFD approach. Flow simulations of transitional flow at various angles-of-attack were realized in ANSYS FLUENT and various quantitative and qualitative results are presented, such as aerodynamic coefficient curves and flow visualizations. In the end, daily mission of the aircraft is simulated and its energy requirement is estimated. In order to be able to cruise above Serbia in July, an aircraft weighing 150 kg must accumulate 17 kWh of solar energy per day.

A programmable bilayer hydrogel actuator based on the asymmetric distribution of crystalline regions.

A novel strategy to fabricate bilayer hydrogel actuators based on the asymmetric distribution of crystalline regions across the bilayer structures was proposed. By employing PVA polymer chains into an alkali solvent-derived chitosan hydrogel matrix, chitosan/PVA hybrid bilayer hydrogels with both excellent responsive bending and mechanical properties were obtained as pH-controlled manipulators. In the design, the chitosan/PVA hydrogels upon treatment with freeze-thawing cycles were taken as the first monolayer, where excessive crystalline regions appeared. The original chitosan/PVA hydrogel as the second monolayer was then integrated into one bilayer device through the chemical-crosslinking of epichlorohydrin at the interface. The results showed that the resultant chitosan/PVA bilayer hydrogel actuator with a weight ratio of 3 : 1 displayed better sensitivity upon exposure to stimuli. The actuation behaviors are strongly dependent on experimental parameters such as the pH, PVA content and the chemical-crosslinking density. It is proposed that the driving force originates from the asymmetric distribution of crystalline regions, thus resulting in differential swelling ratios between the monolayers. In addition, programmable 3D shape transformations were achieved by using the bilayer hydrogel with designed 2D geometric patterns, and the tailored gripper-like hydrogel actuator can successfully capture and transport the cargo. Moreover, this actuation behavior can be erased and re-written on demand under certain conditions. Taking advantage of this universal strategy, more attractive actuators derived from synthetic or natural polymers in combination with PVA are highly expected, which can be used as smart soft robots in various fields such as manipulators, grippers, and cantilever sensors.