3D Mesostructures Research Articles

Curvature programming of freestanding 3D mesostructures and flexible electronics based on bilayer ribbon networks

Three-dimensional (3D) buckling assembly of flexible electronics from strategically designed two-dimensional (2D) precursor structures has enabled important applications in a variety of areas, owing to its versatile applicability to a broad range of length scales and high-performance materials, as well as to a rich diversity of 3D topologies. Rational design methods that allow direct mapping of 3D mesostructures onto unknown 2D precursor structures and loading parameters are foundational to these assembly technologies, but face scientific challenges, such as the high nonlinearity of spatial deformations and tricky bifurcation behaviors. While a few inverse design methods based on the beam theory, topology optimization and machine learning algorithms have been reported, the shape programming of freestanding 3D mesostructures/electronics with highly complex curvature distributions remains elusive. In this work, we propose a curvature programming method based on bilayer ribbon networks, along with a mold-assisted assembly strategy, as a new route to customizable freestanding 3D mesostructures and electronics. Combined mechanics modeling, finite element analyses and experimental measurements allow a clear understanding of nonlinear bending-stretching coupled deformations of bilayer ribbon networks during the 2D-to-3D transformation. A parameter domain with one-to-one mapping of the dimensionless curvature and the bending stiffness ratio is identified, offering a theoretical basis of the curvature programming. By introducing a discretization strategy, a variety of regular (e.g., circles, ellipses, spirals and toroids) and biomimetic 3D curved ribbons and mesosurfaces (e.g., mimicking wavy vines, diatoms and arbitrarily curled leaves) were inversely designed and experimentally realized. A device demonstration capable of strain/temperature sensing and micro-LEDs indication suggests application opportunities in bioelectronics and microelectromechanical systems.

3D identification and characterization of force chains in asphalt concrete based on continuum mesomechanics

Force chains occurring within particle assemblies have been extensively investigated based on granular mechanics; however, research on their identification and characterization in asphalt concrete, where coarse aggregates are dispersed in a viscoelastic asphalt mortar matrix, has been still very limited due to the lack of identifying criteria. A three-dimensional (3D) finite element (FE) simulation-based method was proposed to identify and characterize force chains of asphalt concrete from a continuum mesomechanics perspective. Stress concentration regions within the asphalt mortar matrix were treated as the main load-transfer regions (MLRs) between coarse aggregates. The MLRs were identified by a local detection method that inspects whether an asphalt mortar element is highly stressed in its local region. The load-transfer aggregates were then determined if their effective contact areas, i.e., the asphalt mortar elements sharing the nodes with aggregate elements, were found simultaneously containing an MLR, thereby enabling force chain identification. The compressive force chains in several 3D asphalt concrete mesostructures were determined and quantitatively characterized. The results indicate that the proposed method can effectively identify the force chains in asphalt concrete and their characteristics can be used to quantitatively evaluate the aggregate skeleton.

Kirigami pattern design for buckling-induced assembly 3D structures via topology optimization

Complex three-dimensional (3D) mesostructures are attracting an increasing interest due to their wide applications in microelectronics, biomedicine and other fields. A buckling-induced 3D structure can be assembled by buckling of a 2D plane precursor rapidly and precisely at low cost. However, the inverse design problem of finding 2D precursor configurations corresponding to the predetermined 3D mesostructures has not been well solved yet. In the present work, an inverse method is developed for buckling-induced assembly 3D structure design. Unlike the existing methods, the Moving Morphable Void (MMV) -based topology optimization approach is adopted for driving the inverse design. The voids in MMV are defined as kirigami cuts on the 2D precursor with explicit geometry parameters to generate complex buckling deformation. To cope with the costly non-linear optimization, the Equivalent Static Loads (ESL) method is incorporated, with which the non-linear optimization process can be transformed into a linear static optimization process. Therefore, the layout of the pattern of cuts is sought on the 2D precursor with linear sensitivity calculation. Some self-assembly numerical examples demonstrate the effectiveness and efficiency of the proposed approach.

Wavelength-Dependent Shaping of Azopolymer Micropillars for Three-Dimensional Structure Control.

Surfaces endowed with three-dimensional (3D) mesostructures, showing features in the nanometer to micrometer range, are critical for applications in several fields of science and technology. Finding a fabrication method that is simultaneously inexpensive, simple, fast, versatile, highly scalable, and capable of producing complex 3D shapes is still a challenge. Herein, we characterize the photoreconfiguration of a micropillar array of an azobenzene-containing polymer at different light wavelengths and demonstrate the tailoring of the surface geometry and its related functionality only using light. By changing the irradiated light wavelength and its polarization, we demonstrate the fabrication of various complex isotropic and anisotropic 3D mesostructures from a single original pristine geometry. Quantitative morphological analyses revealed an interplay between the decay rate of absorbed light intensity, micropillar volume preservation, and the cohesive forces between the azopolymer chains as the origin of distinctive wavelength-dependent 3D structural remorphing. Finally, we show the potentialities of this method in surface engineering by photoreshaping a single original micropillar surface into two sets of different mesostructured surfaces exhibiting tunable hydrophobicity in a wide water contact angle range. Our study opens up a new paradigm for fabricating functional 3D mesostructures in a simple, low-cost, fast, and scalable manner.

(Invited) 3D Morphable Electronic Systems Via Deterministic Microfolding

DNA and proteins fold in three dimensions (3D) to enable functions that sustain life. Emulation of such reversible folding schemes for functional materials can create promising opportunities for advancing a wide range of technologies. In particular, morphing 3D mesostructures via multiple dimensions for high-performance materials including monocrystalline silicon can enable unconventional designs in sensory robotics, biomedical devices, microelectronics, and microelectromechanical systems. Existing approaches to morphing functional materials mostly rely on planar processes, which often complicates needed mechanisms for structural reconfiguration and limits the choice of materials composition and dimension. This presentation will introduce a bioinspired microfolding strategy to realize 3D reconfigurable microelectronic systems in freestanding forms with various advanced materials and complex architectures. The microfolding mechanism allows access to any transitional states of the folded 3D structures in a reversible fashion, to modulate functionalities on demand. Demonstrations on microantennas for telecommunication, wearable accelerometers for tremor monitoring, and epicardial bioelectronic probes for cardiac mapping, all of which are achieved via the microfolding strategy, further highlight the high potential for a broad range of applications in healthcare and communications industry.

High-stretchability and low-hysteresis strain sensors using origami-inspired 3D mesostructures.

Stretchable strain sensors are essential for various applications such as wearable electronics, prosthetics, and soft robotics. Strain sensors with high strain range, minimal hysteresis, and fast response speed are highly desirable for accurate measurements of large and dynamic deformations of soft bodies. Current stretchable strain sensors mostly rely on deformable conducting materials, which often have difficulties in achieving these properties simultaneously. In this study, we introduce capacitive strain sensor concepts based on origami-inspired three-dimensional mesoscale electrodes formed by a mechanically guided assembly process. These sensors exhibit up to 200% stretchability with 1.2% degree of hysteresis, <22 ms response time, small sensing area (~5 mm2), and directional strain responses. To showcase potential applications, we demonstrate the use of distributed strain sensors for measuring multimodal deformations of a soft continuum arm.

Deep learning aided inverse design of the buckling-guided assembly for 3D frame structures

Buckling-guided assembly of three-dimensional (3D) mesostructures from pre-defined 2D precursor patterns has arisen increasing attention, owing to the compelling advantages in developing 3D electronic devices and systems with novel functionalities and/or capabilities. Establishments of rational inverse design methods that allow accurate mapping of the target 3D configuration onto the initial 2D precursor pattern are crucial to the widespread application of buckling-guided assembly methods. While a few methods (e.g., those based on theoretical models and generic algorithms) have been reported for the inverse design of 3D frame structures with interconnected ribbons, limitations still exist in their applicable 3D geometries or computational efficiency. In this work, we report an effective inverse design method based on the point-cloud deep learning neural network (DLNN) model for the buckling-guided assembly of 3D frame structures. A structure-based database in the point-cloud form is established based on massive finite element analyses (FEA) of postbuckling deformations for diverse 2D precursor patterns with different numbers of intersections. The well-trained deep learning models assisted by transfer learning strategy utilizing datasets in the constructed database are verified to establish the end-to-end implicit mapping between the 3D frame structure and corresponding 2D precursor pattern. Computational and experimental demonstrations over a bunch of complexly shaped structures, including those resembling 3D shapes of real-world objects, illustrate the high efficiency and accuracy of the proposed deep learning aided inverse design method. In comparison to previously reported methods based on genetic algorithms, the proposed inverse design method can save much more computational efforts, and does not require the initial guess of the 2D precursor pattern. Furthermore, the proposed inverse design method offers an excellent extensibility, as the size and diversity of the structure-based database can be continuously expanded in a sustainable manner, with the future development of buckling-guided assembly methods.

Electroadhesion-Mediated Interface Delamination for Assembly of Reconfigurable 3D Mesostructures

AbstractRecently developed buckling-guided assembly methods provide a unique route to the design and manufacture of 3D mesostructures and microelectronic devices with superior performances and unusual functions. Combined with loading-path controlled strategies and/or active material designs, reconfigurable 3D mesostructures with multiple stable 3D geometries can be formed, holding promising potentials for applications in tunable antennas and multimodal actuators. The existing strategies are, however, limited by the applicable range of material types or requirements for switching between various complicated loading paths. Here, we present an electroadhesion-mediated strategy to achieve controlled adhesion of the 3D mesostructure to the substrate during the buckling-guided assembly. This strategy allows an active control of the delamination behavior in the film/substrate system, such that a variety of reconfigurable 3D mesostructures can be accessed by designing the 2D precursor pattern and electrode layout. An electromechanical model is developed to capture the delamination behavior of the film/substrate system under combined compression and voltage loadings, which agrees well with experimental measurements. Based on this model, an equivalent interface energy is proposed to quantify the contributions of the electroadhesion and van der Waals’ interactions, which also facilitates simulations of the interface delamination with cohesive models in finite element analyses (FEAs). Furthermore, a variety of reconfigurable 3D mesostructures are demonstrated experimentally, and their geometric configurations are in close accordance with the results of FEA using the concept of equivalent interface energy.

A wrinkling-assisted strategy for controlled interface delamination in mechanically-guided 3D assembly

Mechanically-guided three-dimensional (3D) assembly is a recently established method for the fabrication of 3D structures and devices at micro/nanoscale. Such assembly methods typically involve a process of compressive buckling in a patterned high-modulus thin film integrated with a low-modulus elastomer substrate at selective regions. A successful assembly requires, simultaneously, a sufficiently strong interface in selective regions to stay undelaminated, and a sufficiently weak interface in remaining regions to be fully separated. However, such requirements are very challenging to meet for highly flexible 3D mesostructures or those with large-area suspended features. Here, we propose a wrinkling-assisted strategy to substantially facilitate the delamination at desired regions of the film/substrate system. An additional assisting layer is introduced such that a weaker film/assisting-layer interface replaces the original film/substrate interface, and the wrinkles formed in the assisting layer induce additional driving forces to separate the film/assisting-layer interface. An analytical model is developed to capture the delamination of the thin film from the wrinkled assisting layer, which is validated by both experiments and finite element analyses (FEA). The model shows that a combined material/geometry parameter governs the process of delamination in the bilayer film/substrate system, offering a useful design reference for the mechanically-guided 3D assembly. Furthermore, our experiments and FEA demonstrate that the wrinkling-assisted strategy can enable the assembly of highly flexible 3D mesostructures and those with large areas attached to the substrate in the initial configuration, which are particularly challenging to achieve by using previous strategies.

3D mesostructure generation of fully-graded concrete based on hierarchical point cloud and aggregate coarsening

• A novel method for generating fully-graded concrete mesostructures is presented. • Aggregate coarsening is performed to improve the achievable volume fraction. • 3D mesostructures of practical fully-graded dam concrete are generated. • The damage and cracking behavior of fully-graded concrete in tension is studied. The fully-graded concrete (FGC) is widely used in hydraulic mass concrete structures. An exquisite mesoscale model for FGC is essential for accurately simulating its complex damage and cracking behavior. However, due to the presence of massive aggregates and the requirement of high aggregate volume fraction, it is still challenging to generate the three-dimensional (3D) mesostructure of FGC close to reality. A novel and efficient method, termed the hierarchical point cloud method, is proposed for generating the 3D FGC mesostructures. Innovatively, a hierarchical four-level point cloud with a specific spatial structure is defined within the designated domain and serves as the basis for efficiently placing the four-graded aggregates in FGC. The aggregate coarsening is adopted as a supplementary way to achieve the target aggregate packing density in high volume fraction case. In addition, the four virtual aggregate storage piles containing sufficient aggregates within different grading segments are pre-established for providing the required four-graded aggregates. The method efficiency is evaluated by comparison with two traditional methods. The standard samples of mesostructure with an aggregate volume fraction of up to 63.63% are generated for the practical FGC used in Jinping-I arch dam. The numerical tension tests are further carried out for gaining insights into the damage and cracking behavior of FGC. The results show that the arrangement of relative large aggregates, especially the extra-large aggregates, dominates the localization of damage and the final crack distribution.

Magnetically encoded 3D mesostructure with high-order shape morphing and high-frequency actuation

Inspired by origami/kirigami, three-dimensional (3D) mesostructures assembled via a mechanics-guided approach, with reversible and maneuverable shape-morphing capabilities, have attracted great interest with regard to a broad range of applications. Despite intensive studies, the development of morphable 3D mesostructures with high-order (multi-degree-of-freedom) deformation and untethered high-frequency actuation remains challenging. This work introduces a scheme for a magnetically encoded transferable 3D mesostructure, with polyethylene terephthalate (PET) film as the skeleton and discrete magnetic domains as actuation units, to address this challenge. The high-order deformation, including hierarchical, multidirectional and blending shape morphing, is realized by encoding 3D discrete magnetization profiles on the architecture through ultraviolet curing. Reconfigurable 3D mesostructures with a modest structural modulus (∼3GPa) enable both high-frequency (∼55Hz) and large-deformation (∼66.8%) actuation under an alternating magnetic field. Additionally, combined with the shape-retention and adhesion property of PET, these 3D mesostructures can be readily transferred and attached to many solid substrates. On this basis, diverse functional devices, including a switchable colour letter display, liquid mixer, sequential flashlight and biomimetic sliding robot, are demonstrated to offer new perspectives for robotics and microelectronics.

Constructing Unique Mesoporous Carbon Superstructures via Monomicelle Interface Confined Assembly.

Constructing hierarchical three-dimensional (3D) mesostructures with unique pore structure, controllable morphology, highly accessible surface area, and appealing functionality remains a great challenge in materials science. Here, we report a monomicelle interface confined assembly approach to fabricate an unprecedented type of 3D mesoporous N-doped carbon superstructure for the first time. In this hierarchical structure, a large hollow locates in the center (∼300 nm in diameter), and an ultrathin monolayer of spherical mesopores (∼22 nm) uniformly distributes on the hollow shells. Meanwhile, a small hole (4.0-4.5 nm) is also created on the interior surface of each small spherical mesopore, enabling the superstructure to be totally interconnected. Vitally, such interconnected porous supraparticles exhibit ultrahigh accessible surface area (685 m2 g-1) and good underwater aerophilicity due to the abundant spherical mesopores. Additionally, the number (70-150) of spherical mesopores, particle size (22 and 42 nm), and shell thickness (4.0-26 nm) of the supraparticles can all be accurately manipulated. Besides this spherical morphology, other configurations involving 3D hollow nanovesicles and 2D nanosheets were also obtained. Finally, we manifest the mesoporous carbon superstructure as an advanced electrocatalytic material with a half-wave potential of 0.82 V (vs RHE), equivalent to the value of the commercial Pt/C electrode, and notable durability for oxygen reduction reaction (ORR).

Transforming 3D-printed mesostructures into multimodal sensors with nanoscale conductive metal oxides

Additively manufactured (AM) three-dimensional (3D) mesostructures exhibit geometrically optimal mechanical, thermal, and optical properties that could drive future microrobotics, energy harvesting, and biosensing technologies at the micrometer to millimeter scale. We present a strategy for transforming AM mesostructures into 3D electronics by growing nanoscale conducting films on 3D-printed polymers. This highly generalizable method utilizes precision atomic layer deposition (ALD) of conducting metal oxides on ultrasmooth photopolymer lattices printed by high-resolution microstereolithography. We demonstrate control of 3D electronic transport by tuning conformal growth of ultrathin amorphous and crystalline conducting metal oxides. To understand the scaling of 3D electrical properties, we apply graph theory to compute network resistance and precisely design the 3D mesostructures' conductivity. Finally, we demonstrate 3D-enhanced multimodal sensing of chemical, thermal, and mechanical stimuli, geometrically boosting sensitivity by 100× over 2D films and enabling a new class of low-power, 3D-printable sensors. • Microstereolithography is integrated with low-temperature atomic layer deposition • Conducting oxides (ZnO, AZO, SnO 2 ) functionalize 3D mesostructured lattices • Nanometer thickness control determines oxide coating electrostatics • The 3D geometries enhance sensor response to chemical, thermal, and mechanical stimuli Huddy et al. present a strategy for transforming additively manufactured mesostructures into 3D electronics by growing nanoscale conducting oxides on 3D-printed polymers. The authors apply graph theory to design mesostructures for sensing chemical and thermophysical stimuli, geometrically boosting sensitivity 100× over conventional films to enable a new class of 3D-printable sensors.

Mechanically Guided Hierarchical Assembly of 3D Mesostructures.

3D, hierarchical micro/nanostructures formed with advanced functional materials are of growing interest due to their broad potential utility in electronics, robotics, battery technology, and biomedical engineering. Among various strategies in 3D micro/nanofabrication, a set of methods based on compressive buckling offers wide-ranging material compatibility, fabrication scalability, and precise process control. Previously reports on this type of approach rely on a single, planar prestretched elastomeric platform to transform thin-film precursors with 2D layouts into 3D architectures. The simple planar configuration of bonding sites between these precursors and their assembly substrates prevents the realization of certain types of complex 3D geometries. In this paper, a set of hierarchical assembly concepts is reported that leverage multiple layers of prestretched elastomeric substrates to induce not only compressive buckling of 2D precursors bonded to them but also of themselves, thereby creating 3D mesostructures mounted at multiple levels of 3D frameworks with complex, elaborate configurations. Control over strains used in these processes provides reversible access to multiple different 3D layouts in a given structure. Examples to demonstrate these ideas through both experimental and computational results span vertically aligned helices to closed 3D cages, selected for their relevance to 3D conformal bio-interfaces and multifunctional microsystems.

Electron Microscopy of Nanoporous Crystals

ConspectusNanoporous crystals, such as silica mesoporous crystals (SMCs), zeolites, metal–organic frameworks (MOFs) and covalent organic frameworks (COFs), usually have unique geometrical features of periodically arranged pores from micro-, meso- to macro-scale. They have great potential to be structurally designed toward novel materials for various applications, such as storage, separation, and catalysis. In addition to the synthesis and applications of these materials, the structural analysis of nanoporous crystals is also critical for obtaining novel materials and unravelling their structure–property relationships. The crystal structure determines the pore size and connectivity of cages/channels, which are closely related to the performance of these materials in adsorption and catalysis. However, there are significant challenges in structural analysis due to small crystal size, electron-beam sensitivity, and local defects. Due to the strong interaction between electrons and matter, electron microscopy (EM) can provide rich structural information, which at the same time can also cause structural damage to samples. As early as 1960s, EM had been used to directly observe the lattice fringes of zeolites. Subsequently, the structures of many nanoporous crystals were solved and structural details such as defects, intergrowths, and surface structures were revealed by exploiting EM during the past decades. With the development of three-dimensional electron diffraction (3D ED) and low-dose high-resolution electron microscopy imaging, these approaches become more routine for solving the structure of nanocrystals and for revealing the local structural details. In this Account, we present our previous work on EM studies of several typical nanoporous materials, including SMCs, zeolites, MOFs, the TiO2@MIL-101 composite, and COFs. Various methods and strategies were developed and applied to different materials based on the characteristics of their structures. For example, 3D electrostatic potential maps of SMCs can be reconstructed by Fourier synthesis of crystal structure factors obtained from high-resolution TEM images, leading to the discovery of many 3D mesostructures. New zeolites/MOFs/COFs structures, which were not previously solved due to their structural complexity and small crystal size, have been determined using 3D ED data from nanosized crystals or using a combination of electron diffraction and high-resolution imaging. In addition, EM methods for determining the handedness of nanocrystals have also been developed and successfully applied to SMCs and STW zeolite based on high-resolution EM imaging or dynamical electron diffraction. Recently, a new strategy involving a combination of 3D ED and cryogenic protocol was proposed to study the structure, dynamics, and the host–guest interactions in a COF material. The direct-space strategy for structure solution, implemented using a genetic algorithm, was also demonstrated to be a successful approach for solving structures from low-resolution 3D ED data. By now, EM has become one of the most widely used methods in the study of nanoporous materials. We hope this Account will promote further developments of EM and stimulate the design and synthesis of new functional nanoporous materials.

Inverse design strategies for buckling-guided assembly of 3D surfaces based on topology optimization

Complex three-dimensional (3D) mesostructures in advanced functional materials are attracting increasing interest, due to their widespread applications. Mechanically-guided 3D assembly through compressive buckling provides deterministic routes to a rich diversity of 3D mesostructures and microelectronic devices, with feature sizes ranging from sub-microscale to millimeter-scale. Existing studies established inverse design methods that map the target 3D geometry onto an unknown 2D precursor, but mainly focusing on filamentary ribbon-type geometries. Although strategies relying on spatial thickness variation of 2D precursors have been reported to achieve inverse design of 3D surfaces, this could lead to a lack of compatibility with well-developed planar fabrication technologies. In the framework of buckling-guided 3D assembly, this paper presents a computational method based on topology optimization to solve the inverse design problem of 3D surfaces from 2D precursors with uniform thickness distributions. Specifically, curvy ribbon components were exploited to discretize nondevelopable target surfaces, and then optimized to ensure that the assembled 3D surface has the best match with the target geometry. Combined computational and experimental studies over a dozen of elaborate examples, encompassing both the caged and even general target surfaces, demonstrate the effectiveness and applicability of the proposed method.

Reconfiguration of multistable 3D ferromagnetic mesostructures guided by energy landscape surveys

Three-dimensional (3D) mesostructures that can reversibly change their geometries and thereby their functionalities are promising for a wide range of applications. Despite intensive studies, the lack of fundamental understanding of the highly nonlinear multistable states existing in these structures has significantly hindered the development of reconfigurable systems that can realize rapid, well-controlled shape changes. Herein we exploit systematic energy landscape analysis of deformable 3D mesostructures to tailor their multistable states and least energy reconfiguration paths. We employ a discrete shell model and minimum energy pathway methods to establish design phase diagrams for a controlled number of stable states and their energy-efficient reconfiguration paths by varying essential geometry and material parameters. Concurrently, our experiments show that 3D mesostructures assembled from ferromagnetic composite thin films of diverse geometries can be rapidly reconfigured among their multistable states in a remote, on-demand fashion by using a portable magnet, with the configuration of each stable state well maintained after the removal of the external magnetic field. The number of stable states and reconfigurable paths observed in experiments are in excellent agreement with computational predictions. In addition, we demonstrate a wide breadth of applications including reconfigurable 3D light emitting systems, remotely-controlled release of particles from a multistable structure, and 3D structure arrays that can form desired patterns following the written path of a magnetic “pen”. Our results represent a critical step towards the rational design and development of reconfigurable structures for applications including soft robotics, multifunctional deployable devices, and many others.

Transparent, Compliant 3D Mesostructures for Precise Evaluation of Mechanical Characteristics of Organoids.

Recently developed methods for transforming 2D patterns of thin-film materials into 3D mesostructures create many interesting opportunities in microsystems design. A growing area of interest is in multifunctional thermal, electrical, chemical, and optical interfaces to biological tissues, particularly 3D multicellular, millimeter-scale constructs, such as spheroids, assembloids, and organoids. Herein, examples of 3D mechanical interfaces are presented, in which thin ribbons of parylene-C form the basis of transparent, highly compliant frameworks that can be reversibly opened and closed to capture, envelop, and mechanically restrain fragile 3D tissues in a gentle, nondestructive manner, for precise measurements of viscoelastic properties using techniques in nanoindentation. Finite element analysis serves as a design tool to guide selection of geometries and material parameters for shape-matching 3D architectures tailored to organoids of interest. These computational approaches also quantitate all aspects of deformations during the processes of opening and closing the structures and of forces imparted by them onto the surfaces of enclosed soft tissues. Studies of cerebral organoids by nanoindentation show effective Young's moduli in the range from 1.5 to 2.5 kPa depending on the age of the organoid. This collection of results suggests broad utility of compliant 3D mesostructures in noninvasive mechanical measurements of millimeter-scale, soft biological tissues.

Reconfigurable Three‐Dimensional Mesotructures of Spatially Programmed Liquid Crystal Elastomers and Their Ferromagnetic Composites

AbstractReversible programming of 3D soft mesostructures is desired for many applications including soft robotics and biomedical devices. The large, reversible shape changes of liquid crystal elastomers (LCEs), which result from the coupling between the alignment of liquid crystal (LC) molecules and the macroscopic deformation of polymer networks, have attracted much attention for such applications. Here, a facile and versatile strategy is introduced to create reconfigurable, freestanding 3D mesostructures of LCEs and magnetic LCE composites that are inaccessible with existing techniques via spatially programming LC molecules through mechanical buckling. Demonstrations include experimental and theoretical results of more than 20 reconfigurable 3D LCE mesostructures of diverse configurations, from coils and spirals to structures that resemble fences and frameworks, with characteristic feature sizes and thicknesses ranging from micro to macro. The large, reversible shape‐switching behaviors of these structures over multiple cycles are also demonstrated. An LCE gripper is shown to grab/release objects of both regular and irregular geometries. Furthermore, a robot of ferromagnetic LCE composites that simultaneously responds to magnetic and thermal stimuli for diverse biomimetic behaviors, especially crawling underneath a narrow crack, illustrates the integration of other functional materials to LCEs for multifunctional systems.

Intervention of Polydopamine Assembly and Adhesion on Nanoscale Interfaces: State-of-the-Art Designs and Biomedical Applications.

The translation of mussel-inspired wet adhesion to biomedical engineering fields have catalyzed the emergence of polydopamine (PDA)-based nanomaterials with privileged features and properties of conducting multiple interfacial interactions. Recent concerns and progress on the understanding of PDA's hierarchical structure and progressive assembly are inspiring approaches toward novel nanostructures with property and function advantages over simple nanoparticle architectures. Major breakthroughs in this field demonstrated the essential role of π-π stacking and π-cation interactions in the rational intervention of PDA self-assembly. In this review, the recently emerging concepts in the preparation and application of PDA nanomaterials, including 3D mesostructures, low-dimensional nanostructures, micelle/nanoemulsion based nanoclusters, as well as other multicomponent nanohybrids by the segregation and organization of PDA building blocks on nanoscale interfaces are outlined. The contribution of π-electron interactions on the interfacial loading/release of π electron-rich molecules (nucleic acids, drugs, photosensitizers) and the exogenous coupling of optical energy, as well as the impact of wet-adhesion interactions on the nano-bio interface interplay, are highlighted by discussing the structure-property relationships in their featured applications including fluorescent biosensing, gene therapy, drug delivery, phototherapy, combined therapy, etc. The limitations of current explorations, and future research directions are also discussed.