Two-dimensional lattice structures with specific geometric features have been reported to have a negative Poisson’s ratio, termed as auxetic metamaterials, that is, stretching-induced expansion in ...the transversal direction. In this paper, we designed a novel auxetic metamaterial; by utilizing the shape memory effect of the constituent materials, the in-plane moduli and Poisson’s ratios can be continuously tailored. During deformation, the curved meshes ensure the rotation of the mesh joints to achieve auxetics. The rotations of these mesh joints are governed by the mesh curvature, which continuously changes during deformation. Because of the shape memory effect, the mesh curvature after printing can be programmed, which can be used to tune the rotation of the mesh joints and the mechanical properties of auxetic metamaterial structures, including Poisson’s ratios, moduli, and fracture strains. Using the finite element method, the deformation of these auxetic meshes was analyzed. Finally, we designed and fabricated gradient/digital patterns and cylindrical shells and used the auxetics and shape memory effects to reshape the printed structures.
There are prevailing concerns with the critical dimensions when conventional theories break down. Here we find that the Griffith criterion remains valid for cracks down to 10 nm but overestimates the ...strength of shorter cracks. We observe the preferred crack extension along the zigzag edge in graphene, and explain this phenomenon by local strength-based failure rather than energy-based Griffith criterion. These results provide a mechanistic basis for reliable applications of graphene in miniaturized devices and nanocomposites.
Swelling-induced shape transformation has been widely investigated and applied to the design and fabrication of smart polymer devices, such as soft robotics, biomedical devices, and origami patterns. ...Previous shape-shifting designs using soft hydrogels have several limitations, including relatively small actuation force, slow responsive speed, and relatively complicated fabrication process. In this paper, we develop a novel hydrophilic/hydrophobic composite structure by using photopolymers. The rubbery nature of the materials used in this composite provides desirable actuation speed and actuation force. The photocurable polymer system could be easily patterned by using the digital light processing technique. Experiments and theoretical analysis were conducted to study the actuation process. We also fabricated several three-dimensional water-responsive shape-shifting structures, including structures with sequential actuation behavior. Finally, the directional bending behavior of the hydrophilic/hydrophobic bilayer plate was investigated.
The three-dimensional (3D) printing of flexible and stretchable materials with smart functions such as shape memory (SM) and self-healing (SH) is highly desirable for the development of future 4D ...printing technology for myriad applications, such as soft actuators, deployable smart medical devices, and flexible electronics. Here, we report a novel ink that can be used for the 3D printing of highly stretchable, SM, and SH elastomer via UV-light-assisted direct-ink-write printing. An ink containing urethane diacrylate and a linear semicrystalline polymer is developed for the 3D printing of a semi-interpenetrating polymer network elastomer that can be stretched by up to 600%. The 3D-printed complex structures show interesting functional properties, such as high strain SM and SM -assisted SH capability. We demonstrate that such a 3D-printed SM elastomer has the potential application for biomedical devices, such as vascular repair devices. This research paves a new way for the further development of novel 4D printing, soft robotics, and biomedical devices.
Magnetic soft materials (MSMs) have shown potential in soft robotics, actuators, metamaterials, and biomedical devices because they are capable of untethered, fast, and reversible shape ...reconfigurations as well as controllable dynamic motions under applied magnetic fields. Recently, magnetic shape memory polymers (M-SMPs) that incorporate hard magnetic particles in shape memory polymers demonstrated superior shape manipulation performance by realizing reprogrammable, untethered, fast, and reversible shape transformation and shape locking in one material system. In this work, we develop a multimaterial printing technology for the complex structural integration of MSMs and M-SMPs to explore their enhanced multimodal shape transformation and tunable properties. By cooperative thermal and magnetic actuation, we demonstrate multiple deformation modes with distinct shape configurations, which further enable active metamaterials with tunable physical properties such as sign-change Poisson’s ratio. Because of the multiphysics response of the M-MSP/MSM metamaterials, one distinct feature is their capability of shifting between various global mechanical behaviors such as expansion, contraction, shear, and bending. We anticipate that the multimaterial printing technique opens new avenues for the fabrication of multifunctional magnetic materials.
Shape‐programmable soft materials that exhibit integrated multifunctional shape manipulations, including reprogrammable, untethered, fast, and reversible shape transformation and locking, are highly ...desirable for a plethora of applications, including soft robotics, morphing structures, and biomedical devices. Despite recent progress, it remains challenging to achieve multiple shape manipulations in one material system. Here, a novel magnetic shape memory polymer composite is reported to achieve this. The composite consists of two types of magnetic particles in an amorphous shape memory polymer matrix. The matrix softens via magnetic inductive heating of low‐coercivity particles, and high‐remanence particles with reprogrammable magnetization profiles drive the rapid and reversible shape change under actuation magnetic fields. Once cooled, the actuated shape can be locked. Additionally, varying the particle loadings for heating enables sequential actuation. The integrated multifunctional shape manipulations are further exploited for applications including soft magnetic grippers with large grabbing force, reconfigurable antennas, and sequential logic for computing.
A novel magnetic shape‐memory polymer, which is a composite consisting of two types of magnetic particles in an amorphous shape‐memory polymer matrix, integrates multiple shape‐manipulation functions, including untethered rapid reversible shape change, sequential actuation, reprogrammability, and shape locking. Applications including soft magnetic grippers with large grabbing force, sequential logic for computing, and reconfigurable antennas are exploited.
Active Materials for Functional Origami Leanza, Sophie; Wu, Shuai; Sun, Xiaohao ...
Advanced materials (Weinheim),
March 1, 2024, 2024-Mar, 2024-03-00, 20240301, Letnik:
36, Številka:
9
Journal Article
Recenzirano
In recent decades, origami has been explored to aid in the design of engineering structures. These structures span multiple scales and have been demonstrated to be used toward various areas such as ...aerospace, metamaterial, biomedical, robotics, and architectural applications. Conventionally, origami or deployable structures have been actuated by hands, motors, or pneumatic actuators, which can result in heavy or bulky structures. On the other hand, active materials, which reconfigure in response to external stimulus, eliminate the need for external mechanical loads and bulky actuation systems. Thus, in recent years, active materials incorporated with deployable structures have shown promise for remote actuation of light weight, programmable origami. In this review, active materials such as shape memory polymers (SMPs) and alloys (SMAs), hydrogels, liquid crystal elastomers (LCEs), magnetic soft materials (MSMs), and covalent adaptable network (CAN) polymers, their actuation mechanisms, as well as how they have been utilized for active origami and where these structures are applicable is discussed. Additionally, the state‐of‐the‐art fabrication methods to construct active origami are highlighted. The existing structural modeling strategies for origami, the constitutive models used to describe active materials, and the largest challenges and future directions for active origami research are summarized.
Origami has emerged as a popular design strategy for engineering structures. Further, active materials can be integrated with origami for lightweight, programmable, self‐deployable structures relevant to numerous aerospace, metamaterial, and biomedical applications. This review details active material actuation mechanisms, active origami applications, state‐of‐the‐art fabrication methods, as well as origami modeling, and provides insights into the future of active origami research.
Pure cellulose nanocrystal (CNC) aerogels with controlled 3D structures and inner pore architecture are printed using the direct ink write (DIW) technique. While traditional cellulosic aerogel ...processing approaches lack the ability to easily fabricate complete aerogel structures, DIW 3D printing followed by freeze drying can overcome this shortcoming and can produce CNC aerogels with minimal structural shrinkage or damage. The resultant products have great potential in applications such as tissue scaffold templates, drug delivery, packaging, etc., due to their inherent sustainability, biocompatibility, and biodegradability. Various 3D structures are successfully printed without support material, and the print quality can be improved with increasing CNC concentration and printing resolution. Dual pore CNC aerogel scaffolds are also successfully printed, where the customizable 3D structure and inner pore architecture can potentially enable advance CNC scaffold designs suited for specific cell integration requirements.
Liquid crystal elastomers (LCEs) are renowned for their large, reversible, and anisotropic shape change in response to various external stimuli due to their lightly cross‐linked polymer networks with ...an oriented mesogen direction, thus showing great potential for applications in robotics, bio‐medics, electronics, optics, and energy. To fully take advantage of the anisotropic stimuli‐responsive behaviors of LCEs, it is preferable to achieve a locally controlled mesogen alignment into monodomain orientations. In recent years, the application of 4D printing to LCEs opens new doors for simultaneously programming the mesogen alignment and the 3D geometry, offering more opportunities and higher feasibility for the fabrication of 4D‐printed LCE objects with desirable stimuli‐responsive properties. Here, the state‐of‐the‐art advances in 4D printing of LCEs are reviewed, with emphasis on both the mechanisms and potential applications. First, the fundamental properties of LCEs and the working principles of the representative 4D printing techniques are briefly introduced. Then, the fabrication of LCEs by 4D printing techniques and the advantages over conventional manufacturing methods are demonstrated. Finally, perspectives on the current challenges and potential development trends toward the 4D printing of LCEs are discussed, which may shed light on future research directions in this new field.
Liquid crystal elastomers (LCEs) exhibit attractive stimuli‐responsive properties, showing great application potential in soft robotics, biomedicine, optics, etc. The advent of 4D printing opens a new door for the design and fabrication of LCEs with programmable stimuli‐responsive properties and 3D geometries. The state‐of‐the‐art advances in 4D printing of LCEs are reviewed, with emphasis on both mechanisms and potential applications.
Growing demand in portable electronics raises a requirement to electronic devices being stretchable, deformable, and durable, for which functional polymers are ideal choices of materials. Here, the ...first transformable smart energy harvester and self‐powered mechanosensation sensor using shape memory polymers is demonstrated. The device is based on the mechanism of a flexible triboelectric nanogenerator using the thermally triggered shape transformation of organic materials for effectively harvesting mechanical energy. This work paves a new direction for functional polymers, especially in the field of mechanosensation for potential applications in areas such as soft robotics, biomedical devices, and wearable electronics.
A shape‐memory‐polymer‐based triboelectric nanogenerator (STENG) is developed to harvest biomechanical energy and detect biomechanical motion. The STENG is able to transform its shape according to different requirements and hold on to a temporary configuration, which can act as an energy harvester as well as a self‐powered, wearable, biomechanical sensor.
PDF
