Shape Transformation Research Articles

Stiffness Variable Polymers Comprising Phase-Changing Side-Chains: Material Syntheses and Application Explorations.

Stiffness variable materials have been applied in a variety of engineering fields that require adaptation, automatic modulation, and morphing because of their unique property to switch between a rigid, load-bearing state and a soft, compliant state. Stiffness variable polymers comprising phase-changing side-chains (s-SVPs) have densely grafted, highly crystallizable long alkyl side-chains in a crosslinked network. Such a bottlebrush network-like structure gives rise to rigidity modulation as a result of the reversible crystallization and melting of the side chains. The corresponding modulus changes can be more than 1000-fold within a narrow temperature span, from ≈102 MPa to ≈102 kPa or lower. Other important properties of the s-SVP, such as stretchability, optical transmittance, and adhesion, can also be altered. This work reviews the underlying molecular mechanisms in the s-SVP's, discusses the material's structure-property relationship, and summarizes important applications explored so far, including reversible shape transformation, bistable electromechanical transduction, optical modulation, and reversible adhesion.

Physical Properties and the Reconstruction of Unstable Decahedral Silver Nanoparticles Synthesized Using Plasmon-Mediated Photochemical Process.

Plasmon-mediated shape transformation from quasi-spherical silver nanoparticles (AgNPs) to silver nanoprisms (AgNPrs) and decahedral silver nanoparticles (D-AgNPs) under irradiation of blue LEDs (λ = 456 ± 12 nm, 80 mW/cm2) was studied at temperatures ranging between 60, 40, 30, 20, 10, and 0 °C. It was found that reaction temperature affected transformation rates and influenced the morphology distribution of final products. The major products synthesized at temperatures between 60 °C and 0 °C were AgNPrs and D-AgNPs, respectively. The D-AgNPs synthesized at such low temperatures are unstable and become blunt when light irradiation is removed after the photochemical synthesis. These blunt nanoparticles with pentagonal multiple-twinned structures can be further used as the seeds to reconstruct complete D-AgNPs after irradiating blue LEDs at various bath temperatures. Our results showed that these rebuilt D-AgNPs are much more stable when at higher bath temperatures. Furthermore, the rebuilt D-AgNPs (edge lengths ~41 nm) can grow into larger D-AgNPs (edge lengths ~53 nm) after the irradiation of green LEDs. Surface-enhanced Raman spectra of CV in AgNP colloids showed that D-AgNP colloids have better SERS enhancements factors than AgNPrs.

Programmable droplets: Leveraging digitally-responsive flow fields to actively tune liquid morphologies.

Stimulus-responsive materials enable programmable and adaptive behaviors. Typical solid-phase systems can only achieve small deformations for applications where shape transformations are beneficial or required. Liquids, in contrast, can self-assemble and achieve very high strains in a multifluid environment. Here we report liquid droplet formation by tuning flow potential within a confined fluidic cell. We digitally inject small volumes of liquid-pigment into an otherwise-transparent liquid layer, generating macroscopic droplet assembly over large areas constrained between closely-spaced plates. Droplet morphology is actively controlled by modulating outlet conditions to tune flow fields. Pattern stability is maintained through control over injection rate, interfacial viscosity difference, and interfacial surface tension. We demonstrate time-dependent droplet formation and migration to achieve spatially-tunable optical properties. Applied as a multi-cell array, we imagine this liquid mechanism will enable scalable pattern dynamics for active shading and visual display technologies.

Self-winding liquid crystal elastomer fiber actuators with high degree of freedom and tunable actuation

Liquid-crystal-elastomer (LCE) fiber actuators capable of reversible, large-scale, programmable deformation in response to external stimuli have great potential in many applications, including artificial muscles, robotics, and wearable devices. Despite their exciting prospects, limitations -such as few modes of shape transformation in a single actuator due to limited degree of freedom (DOF), difficulty to concurrently gain large length change and powerful stress, lack of scalable manufacturing method - seriously restrict their engineering applicability. Here we present bioinspired self-winding LCE fiber actuators that possess diverse controllable shape transformations (bending, twisting, coiling, and shortening), a combination of high contraction ratio (1750%) and high stress (∼3.4 MPa), long term photomechanical robustness (over 1000 photodeformation cycles without obvious fatigue), and readily, scalable manufacture. Our fiber actuators can simultaneously conduct two or three kinds of deformation and thus enables complex morphing behaviors to manipulate objects (grabbing, dragging, lifting, and winding), and even drive gear set. We envision that these self-winding fiber actuators combined with high DOF, tunable actuation, photomechanical robustness, and mass production could be developed as high-performance artificial muscles for broad engineering applications.

Three-dimensional volume reconstruction from multi-slice data using a shape transformation

We present a computational method for the 3D volume reconstruction from cross-sectional data. The proposed method is based on the Allen–Cahn (AC) equation with a source term. The source term is related to shape transformation from a source object to a target object. Using the operator splitting method, the governing equation is solved by splitting it into three steps. The numerical solution is obtained explicitly using the Euler's methods and the separation of variables. To reconstruct the 3D object from two slice data, we set one slice as the target data and the other data as the initial data. We solve the governing equation and stack intermediate solutions based on the relative fraction of the symmetric difference of two regions occupied by the target and source data. To demonstrate that the proposed method can reconstruct a 3D model through extracted intermediate slice data during shape transformation, we perform several computational tests. Furthermore, the proposed method is applied to a 3D volume reconstruction from multi-slice data of human vertebra.

Polymerization-Induced Self-Assembly (PISA) for in situ drug encapsulation or drug conjugation in cancer application

HypothesisWe describe the possibility of using the same block copolymer carriers prepared by PISA for in situ drug encapsulation or drug conjugation. ExperimentsBlock copolymers containing poly((ethylene glycol) methacrylate)–co-poly(pentafluorophenyl methacrylate)-b-poly(hydroxypropyl methacrylate) (P((PEGMA-co-PFBMA)-b-PHPMA)) were synthesized at 10 wt% using PISA. The first approach involved in situ Doxorubicin (DOX) loading during PISA, while the second exhibited surface functionalization of PISA-made vesicles with dual drug therapies, N-acetyl cysteine (NAC) and DOX using para-fluoro-thiol reaction (PFTR) and carbodiimide chemistry, respectively. Cytotoxicity, cell uptake, and cell apoptosis were assessed on MDA-MB-231 cell lines. FindingsP((PEGMA-co-PFBMA)-b-PHPMA) nanocarriers were prepared, showing size and shape transformations from spheres, cylinders to raspberry-forming vesicles. DOX was readily loaded into NPs during PISA with relatively high encapsulation efficiency of 70 %, whereas the plain PISA-made vesicles could be functionalized with NAC and DOX at high yields. DOX-free NPs showed biocompatibility, whilst DOX-conjugated NPs imparted a concentration-dependent cytotoxicity, as well as an enhanced cell uptake compared to free DOX. The results demonstrated that the same PISA-derived self-assemblies enabled either in situ drug encapsulation, or post-polymerization surface engineering with useful functionalities upon tuning the macro-CTA block, thus holding promises for future drug delivery and biomedical applications.

Mechanisms driving self-organization phenomena in random plasmonic metasurfaces under multipulse femtosecond laser exposure: a multitime scale study

Abstract Laser-induced transformations of plasmonic metasurfaces pave the way for controlling their anisotropic optical response with a micrometric resolution over large surfaces. Understanding the transient state of matter is crucial to optimize laser processing and reach specific optical properties. This article proposes an experimental and numerical study to follow and explain the diverse irreversible transformations encountered by a random plasmonic metasurface submitted to multiple femtosecond laser pulses at a high repetition rate. A pump-probe spectroscopic imaging setup records pulse after pulse, and with a nanosecond time resolution, the polarized transmission spectra of the plasmonic metasurface, submitted to 50,000 ultrashort laser pulses at 75 kHz. The measurements reveal different regimes, occurring in different ranges of accumulated pulse numbers, where successive self-organized embedded periodic nanostructures with very different periods are observed by post-mortem electron microscopy characterizations. Analyses are carried out; thanks to laser-induced temperature rise simulations and calculations of the mode effective indices that can be guided in the structure. The overall study provides a detailed insight into successive mechanisms leading to shape transformation and self-organization in the system, their respective predominance as a function of the laser-induced temperature relative to the melting temperature of metallic nanoparticles and their kinetics. The article also demonstrates the dependence of the self-organized period on the guided-mode effective index, which approaches a resonance due to system transformation. Such anisotropic plasmonic metasurfaces have a great potential for security printing or data storage, and better understanding their formation opens the way to smart optimization of their properties.

Dual-responsive nanoparticles with transformable shape and reversible charge for amplified chemo-photodynamic therapy of breast cancer

Herein, we designed a dual-response shape transformation and charge reversal strategy with chemo-photodynamic therapy to improve the blood circulation time, tumor penetration and retention, which finally enhanced the anti-tumor effect. In the system, hydrophobic photosensitizer chlorin e6 (Ce6), hydrophilic chemotherapeutic drug berberrubine (BBR) and matrix metalloproteinase-2 (MMP-2) response peptide (PLGVRKLVFF) were coupled by linkers to form a linear triblock molecule BBR-PLGVRKLVFF-Ce6 (BPC), which can self-assemble into nanoparticles. Then, positively charged BPC and polyethylene glycol-histidine (PEG-His) were mixed to form PEG-His@BPC with negative surface charge and long blood circulation time. Due to the acidic tumor microenvironment, the PEG shell was detached from PEG-His@BPC attributing to protonation of the histidine, which achieved charge reversal, size reduction and enhanced tumor penetration. At the same time, enzyme cutting site was exposed, and the spherical nanoparticles could transform into nanofibers following the enzymolysis by MMP-2, while BBR was released to kill tumors by inducing apoptosis. Compared with original nanoparticles, the nanofibers with photosensitizer Ce6 retained within tumor site for a longer time. Collectively, we provided a good example to fully use the intrinsic properties of different drugs and linkers to construct tumor microenvironment-responsive charge reversal and shape transformable nanoparticles with synergistic antitumor effect.

Microphase Separation‐Driven Sequential Self‐Folding of Nanocomposite Hydrogel/Elastomer Actuators

AbstractUntethered stimuli‐responsive soft materials with programmed sequential self‐folding are of great interest due to their ability to achieve task‐specific shape transformation with complex final configuration. Here, reversible and sequential self‐folding soft actuators are demonstrated by utilizing a temperature‐responsive nanocomposite hydrogel with different folding speeds but the same chemical composition. By varying the UV light intensity during the photo‐crosslinking of the nanocomposite hydrogel, different types of microstructures can be realized via phase separation mechanisms, which allow to control the folding speeds. The self‐folding structures are fabricated by integrating two dissimilar materials (i.e., a nanocomposite hydrogel and an elastomer) into hinge‐based bilayer structures via extrusion‐based 3D printing. It has been demonstrated that the folding kinetics can be accelerated by more than one order of magnitude due to the phase‐separated microstructure formed by the relatively weaker UV intensity (≈10 mW cm‐2) compared to the one formed by stronger UV intensity (≈100 mW cm‐2). 3D structures with sequential self‐folding capabilities are realized by prescribing actuation speeds and folding angles to specific hinges of the nanocomposite hydrogel. Sequential folding box and self‐locking latch structures are fabricated to demonstrate the ability to capture and hold objects underwater.

Magnetically responsive nanofibrous ceramic scaffolds for on-demand motion and drug delivery.

Smart biomaterials, featuring not only bioactivity, but also dynamic responsiveness to external stimuli, are desired for biomedical applications, such as regenerative medicine, and hold great potential to expand the boundaries of the modern clinical practice. Herein, a magnetically responsive three-dimensional scaffold with sandwich structure is developed by using hydroxyapatite (HA) nanowires and ferrosoferric oxide (Fe3O4) nanoparticles as building blocks. The magnetic HA/Fe3O4 scaffold is fully inorganic in nature, but shows polymeric hydrogel-like characteristics including a 3D fibrous network that is highly porous (>99.7% free volume), deformable (50% deformation) and elastic, and tunable stiffness. The magnetic HA/Fe3O4 scaffold has been shown to execute multimodal motion upon exposure to an external magnetic field including shape transformation, rolling and somersault. In addition, we have demonstrated that the magnetic scaffold can serve as a smart carrier for remotely controlled, on-demand delivery of compounds including an organic dye and a protein. Finally, the magnetic scaffold has exhibited good biocompatibility, supporting the attachment and proliferation of human mesenchymal stromal cells, thereby showing great potential as smart biomaterials for a variety of biomedical applications.

Investigation of the manufacture development of early Chinese ink in the Western Han dynasty

AbstractChinese ink, generally produced in a stick form, was often like pellets before the Western Han dynasty (202 bce–8 ce) according to literary records and a few archaeological discoveries. However, their composition and manufacture have not been scientifically analysed to date. In this study, the ink pellets roughly dated to 2000 years ago from two royal tombs of the Han dynasty (the Nanyue King's tomb and the Marquis of Haihun's tomb) were analyzed by micro‐/non‐destructive methods, including synchrotron radiation‐based micro‐computed tomography (SR‐μCT), Fourier‐transform infrared spectroscopy (FTIR) and pyrolysis gas chromatography mass spectrometry (Py‐GC/MS). The results reveal that they were made from pine soot, and the production technology of the later Haihun ink was more complex than that of the earlier Nanyue King ink. The microstructure of the ink pellets indicated that some kind of glue should be used in the Haihun ink, which is the earliest case of glue addition. Moreover, plant extracts, including borneol and cedar oil, were detected in the Haihun ink, reflecting another aspect of progress in ink production history. These technical breakthroughs imply that the Western Han dynasty is a critical period for the development of traditional ink manufacture, and the shape transformation of Chinese ink is closely related to the evolution of ink production technology during this specific period.

Unravelling the Mechanism of Viscoelasticity in Polymers with Phase-Separated Dynamic Bonds.

Incorporation of dynamic (reversible) bonds within polymer structure enables properties such as self-healing, shape transformation, and recyclability. These dynamic bonds, sometimes refer as stickers, can form clusters by phase-segregation from the polymer matrix. These systems can exhibit interesting viscoelastic properties with an unusually high and extremely long rubbery plateau. Understanding how viscoelastic properties of these materials are controlled by the hierarchical structure is crucial for engineering of recyclable materials for various future applications. Here we studied such systems made from short telechelic polydimethylsiloxane chains by employing a broad range of experimental techniques. We demonstrate that formation of a percolated network of interfacial layers surrounding clusters enhances mechanical modulus in these phase-separated systems, whereas single chain hopping between the clusters results in macroscopic flow. On the basis of the results, we formulated a general scenario describing viscoelastic properties of phase-separated dynamic polymers, which will foster development of recyclable materials with tunable rheological properties.

A brief review on mechanical designs for 4D printing

4D printing is a fast-developing technique which enables the transformation of shape, property, and function after a structure is manufactured. Here the ’fourth dimension’ refers to a time-dependent deformation, and thus 4D printing technique is closely related to the mechanical design strategies of materials and structures. This review concentrates on the recent progress of fundamental mechanical theories, analytical methods, and designing tools, for three categories of designing principles in 4D printing. The first type of 4D printing relies on active materials that respond to external stimuli. The second type includes a wide range of 4D-printed innovative structures, where the automatic actuation mainly comes from a combination of different deformation mechanisms. The third type of 4D printing focuses on mechanical designs related to the manufacturing process. The classification bridges the gaps between materials, microarchitectures, and large-scale structures, while some 4D printing strategies might involve more than one aforementioned design principle. This review provides reference and guidance for future 4D printings with customized deformation modes and multiple functionalities.

Four-dimensional design and programming of shape-memory magnetic helical micromachines

Diversified complex tasks put forward higher requirements on shape transformation abilities of magnetic microrobots. Shape memory polymers (SMPs) with desirable properties are ideal options for the development of microrobots. However, programming shape transformations for such small SMP robotic structures is still difficult. Here, a parametric design and programming method is reported for shape-memory magnetic helical micromachines. Through twice mechanically winding and annealing of UV lithography-modified ribbon-like polylactic acid fibers, the customization of permanent and temporary shapes of shape-memory helical micromachines was realized. Expected recoveries of helical micromachines from temporary shapes to permanent shapes were exhibited in response to thermal stimuli, showing diversified shape changes in helix angle, taper angle, length, diameter, and even chirality. Helical micromachines demonstrated controlled locomotion ability under rotating magnetic fields. Through dynamic design and shape programming, acceleration and direction reversal of swimming helical micromachines can be activated by environmental stimuli. Moreover, programmable shape-memory micro-components can be used to fabricate complex multi-component micromachines. This study provided an approach to overcome the programming difficulty of SMP microrobots. The shape-memory magnetic helical micromachines with programmable shape transformations and locomotion ability have great potential in various applications.

Shape memory micro-anchors with magnetic guidance for precision micro-vascular deployment

Transcatheter medical micro-devices through circulatory system show great potential for therapy but lack strategies to stably anchor them at the desired site in vascularized tissues to take actions. Here a shape memory functionalized biodegradable magnetic micro-anchor (SM2A) is developed to achieve magnetic guided endovascular localization through precisely controlled shape transformation. The SM2A comprises anisotropic polylactide-based microparticle embedded with superparamagnetic Fe3O4 nanoparticles, exhibiting thermally activated tunable shape recovery modes at a body-friendly temperature range to accomplished an efficient endovascular anchoring effect in both decellularized liver organ and rabbit ear embolization models. The SM2A can be anchored at the target micro-vessel, exhibiting a controlled radial expansion of the vessel wall yielding with estimated stresses of 7–26 kPa in contact stress and 38–218 kPa in von Mises stress. The SM2A is a promising platform to incorporate diagnostic or therapeutic agents for precision deployment and in-situ action.

Shape stabilization and laser triggered shape transformation of magnetic particle functionalized liquid metal motors

Liquid metal motors made from biologically benign gallium are promising candidates for various applications ranging from drug delivery to targeting and killing cancer cells directly. One of the main problems with this novel technology is the need to utilize a membrane, making it possible to maintain a defined shape in order to perform the required functions. For magnetic remote guidance, liquid metal motors can be doped with magnetic iron microparticles, forming a transition magnetic liquid. In an alternative approach liquid metal structures are coated with magnetite nanoparticles. We hereby present an approach to laminate biologically benign gallium-based magnetic liquid metal motors with a biodegradable and biocompatible macromolecular thin film to retain the initial shape. Thanks to the polymer lamination and by the help of magnetic fields, the presented liquid metal motors can be remotely guided. The shape retaining macromolecular thin film can be liquefied by photothermal effects such as laser irradiation in order to change the shape of the liquid metal motor into a droplet due to surface energy minimization, allowing for penetration of structures smaller than the initial motor size. This work uses a relatively large technical demonstrator to show the technical realization and properties of this novel system, which opens up new paths and potential applications.

Vesicle Geometries Enabled by Semiflexible Polymer.

Understanding and controlling vesicle shapes is fundamental challenge in biophysics and materials design. In this paper, we employ the Monte Carlo method to investigate the shape of soft vesicle induced by semiflexible polymer outside in two dimensions. The effect of bending stiffness of polymer and the strength of attractive interaction between vesicle and polymer on the shape of vesicle is discussed in detail in the present paper. It is found that the shape of vesicle is influenced by and . Typical shape of vesicles is observed, such as circular, cigar-like, double vesicle, and racquet-like. To engineer vesicle shape transformations is helpful for exploiting the richness of vesicle geometries for desired applications.

Three-Dimensional Shape Transformation of Eu3+-Containing Polymer Films through Modulating Dynamic Eu3+-Iminodiacetate Coordination

Shape-transformative materials that can autonomously adopt three-dimensional (3D) shapes in response to environmental stimuli are of interest for the development of sensors and soft robotics. We herein report a new synthetic strategy to fabricate shape-transformable Eu3+-containing interpenetrating polymer films consisting of poly(vinyl alcohol) (PVA) and poly(3-iminodiacetate-2-hydroxypropylmethacrylate-co-acrylic acid) (P(IDHPMA-co-AA)). Given the dynamic nature of Eu3+-iminodiacetate (IDA) coordination, ink patterning and water/Fe3+ diffusion are used to generate the in-plane or z-directional heterogeneities of Eu-IDA dynamic coordination in the polymer film, respectively. The heterogeneities can be visualized by the distribution of fluorescence emission of Eu3+. When subjected to high humidity, the differences in the swelling ratio and modulus as a result of chemical inhomogeneity further drive various 3D shape morphings, including rolling, helixing, twisting, surface buckling, and folding. Shape transformation is reversible upon the removal of moisture from the polymer films. The ink concentration and environmental humidity are demonstrated to impact the shape transformation kinetics and the final 3D shape along with other geometric parameters. Our work illustrates a novel way to fabricate new-generation biomimetic actuators and sensors.

Multi-functional stimuli-responsive biomimetic flower assembled from CLCE and MOF-based pedals

Simulating the structures and behaviors of living organisms are of great significance to develop novel multi-functional intelligent devices. However, the development of biomimetic devices with complex deformable structures and synergistic properties is still on the way. Herein, we propose a simple and effective approach to create the multi-functional stimuli-responsive biomimetic devices with independently pre-programmable colorful visual patterns, complex geometries and morphable modes. The metal organic framework (MOF)-based composite film acts as a rigidity actuation substrate to support and mechanically guide the spatial configuration of the soft chiral nematic liquid crystal elastomer (CLCE) sheet. We can directly program the structural color of the CLCE sheet by adjusting the thickness distribution without tedious chemical modification. By using this coordination strategy, we fabricate an artificial flower, which exhibits a synergistic effect of both shape transformation and color change like paeonia ‘Coral Sunset’ at different flowering stages, and can even perform different flowering behaviors by bending, twisting and curling petals. The assembled bionic flower is innovatively demonstrated to respond to local stimuli of humidity, heat or ultraviolet irradiation. Therefore, the spatial assembly of CLCE combined with functional MOF materials has a wide range of potential application in multi-functional integrated artificial systems.

Spontaneous Formation of Prebiotic Compartment Colonies on Hadean Earth and Pre‐Noachian Mars**

AbstractProminent among the models for protocells is the spherical biosurfactant shell, freely suspended in aqueous media. This model explains initial, but not subsequent events in the development process towards structured protocells. Taking into consideration the involvement of naturally occurring surfaces, which were abundant on the early Earth, feasible and productive pathways for the development of primitive cells are reported. Surfaces intrinsically possess energy, easily utilized by the interfacing amphiphiles, such as lipids, to attain self‐organization and spontaneous transformations. This work shows that the physical interaction of phospholipid pools with 20 Hadean Earth analogue materials as well as a Martian meteorite composed of fused regolith representing the ancient crust of Mars consistently lead to the shape transformation and autonomous formation of surfactant compartment assemblies. Dense, colony‐like protocell populations grow from these lipid deposits, predominantly at the grain boundaries or cleavages of the investigated natural surfaces, and remain there for several days. The model protocells in this study are able to autonomously develop, transform and pseudo‐divide, and encapsulate RNA as well as DNA. Moreover, they can accommodate non‐enzymatic, DNA strand displacement reactions. These findings suggest a feasible route towards the transformation from non‐living to living entities, and provide fresh support for the ‘Lipid World’ hypothesis.