Dynamic control of shape can bring multifunctionality to devices. Soft materials capable of programmable shape change require localized control of the magnitude and directionality of a mechanical ...response. We report the preparation of soft, ordered materials referred to as liquid crystal elastomers.The direction of molecular order, known as the director, is written within local volume elements (voxels) as small as 0.0005 cubic millimeters. Locally, the director controls the inherent mechanical response (55% strain) within the material. In monoliths with spatially patterned director, thermal or chemical stimuli transform flat sheets into three-dimensional objects through controlled bending and stretching. The programmable mechanical response of these materials could yield monolithic multifunctional devices or serve as reconfigurable substrates for flexible devices in aerospace, medicine, or consumer goods.
Stimuli-responsive materials are able to undergo controllable changes in materials properties in response to external cues. Increasing efforts have been directed towards building materials that mimic ...the responsive nature of biological systems. Nevertheless, limitations remain surrounding the way these synthetic materials interact and respond to their environment. In particular, it is difficult to synthesize synthetic materials that respond with specificity to poorly differentiated (bio)chemical and weak physical stimuli. The emerging area of engineered living materials (ELMs) includes composites that combine living cells and synthetic materials. ELMs have yielded promising advances in the creation of stimuli-responsive materials that respond with diverse outputs in response to a broad array of biochemical and physical stimuli. This review describes advances made in the genetic engineering of the living component and the processing-property relationships of stimuli-responsive ELMs. Finally, the implementation of stimuli-responsive ELMs as environmental sensors, biomedical sensors, drug delivery vehicles, and soft robots is discussed.
Engineered living materials integrate genetic engineering and synthetic materials to program stimuli responses that enable the fabrication of devices for diverse applications.
Three‐dimensional structures that undergo reversible shape changes in response to mild stimuli enable a wide range of smart devices, such as soft robots or implantable medical devices. Herein, a dual ...thiol‐ene reaction scheme is used to synthesize a class of liquid crystal (LC) elastomers that can be 3D printed into complex shapes and subsequently undergo controlled shape change. Through controlling the phase transition temperature of polymerizable LC inks, morphing 3D structures with tunable actuation temperature (28 ± 2 to 105 ± 1 °C) are fabricated. Finally, multiple LC inks are 3D printed into single structures to allow for the production of untethered, thermo‐responsive structures that sequentially and reversibly undergo multiple shape changes.
Novel inks for printable liquid crystal elastomers (LCEs) are reported herein. The 3D‐printed LCE structures undergo controlled and reversible shape change upon heating. By controlling the reaction parameters (e.g., reaction type, mesogen concentration, or crosslinking density), a wide range of LCEs are synthesized and characterized for their use as soft actuators.
4D‐Printing of Photoswitchable Actuators Lu, Xili; Ambulo, Cedric P.; Wang, Suitu ...
Angewandte Chemie International Edition,
March 1, 2021, Letnik:
60, Številka:
10
Journal Article
Recenzirano
Shape‐switching behavior, where a transient stimulus induces an indefinitely stable deformation that can be recovered on exposure to another transient stimulus, is critical to building smart ...structures from responsive polymers as continue power is not needed to maintain deformations. Herein, we 4D‐print shape‐switching liquid crystalline elastomers (LCEs) functionalized with supramolecular crosslinks, dynamic covalent crosslinks, and azobenzene. The salient property of shape‐switching LCEs is that light induces long‐lived, deformation that can be recovered on‐demand by heating. UV‐light isomerizes azobenzene from trans to cis, and temporarily breaks the supramolecular crosslinks, resulting in a programmed deformation. After UV, the shape‐switching LCEs fix more than 90 % of the deformation over 3 days by the reformed supramolecular crosslinks. Using the shape‐switching properties, we print Braille‐like actuators that can be photoswitched to display different letters. This new class of photoswitchable actuators may impact applications such as deployable devices where continuous application of power is impractical.
Shape‐switching liquid crystal elastomers are formulated where light is used to trigger a shape change which is then stable indefinitely. The original shape can be recovered on heating. These materials can be 4D printed into reconfigurable Braille‐like actuators capable of displaying letters “L”, “C” and “E” by switching the shape‐morphing of the Archimedean chord patterns with UV light and heating.
This randomized trial showed no effect of early adenotonsillectomy, as compared with watchful waiting, on the primary outcome of attention and executive functioning in children with obstructive sleep ...apnea. Many secondary outcomes favored early surgery.
The childhood obstructive sleep apnea syndrome is associated with numerous adverse health outcomes, including cognitive and behavioral deficits.
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The most commonly identified risk factor for the childhood obstructive sleep apnea syndrome is adenotonsillar hypertrophy. Thus, the primary treatment is adenotonsillectomy, which accounts for more than 500,000 procedures annually in the United States alone.
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Nevertheless, there has been no controlled study evaluating the benefits and risks of adenotonsillectomy, as compared with watchful waiting, for the management of the obstructive sleep apnea syndrome.
The Childhood Adenotonsillectomy Trial (CHAT) was designed to evaluate the efficacy of early adenotonsillectomy versus watchful waiting with supportive . . .
Synthetic approaches to prepare designer materials that localize deformation, by combining rigidity and compliance in a single material, have been widely sought. Bottom-up approaches, such as the ...self-organization of liquid crystals, offer potential advantages over top-down patterning methods such as photolithographic control of crosslink density, relating to the ease of preparation and fidelity of resolution. Here, we report on the directed self-assembly of materials with spatial and hierarchical variation in mechanical anisotropy. The highly nonlinear mechanical properties of the liquid crystalline elastomers examined here enables strain to be locally reduced >15-fold without introducing compositional variation or other heterogeneities. Each domain (⩾0.01 mm(2)) exhibits anisotropic nonlinear response to load based on the alignment of the molecular orientation with the loading axis. Accordingly, we design monoliths that localize deformation in uniaxial and biaxial tension, shear, bending and crack propagation, and subsequently demonstrate substrates for globally deformable yet locally stiff electronics.
The ability to pattern material response, voxel by voxel, to direct actuation and manipulation in macroscopic structures can enable devices that utilize ambient stimuli to produce functional ...responses at length scales ranging from the micro- to the macroscopic. Fabricating liquid crystalline polymers (LCPs), where the molecular director is indexably defined in three-dimensional (3D) freeforms, can be a key enabler. Here, the combination of anisotropic magnetic susceptibility of the liquid crystalline monomers in a reorientable magnetic field and spatially selective photopolymerization using a digital micromirror device to independently define molecular orientation in light and/or heat-responsive multimaterial elements, which are additively incorporated into 3D freeforms, is exploited. This is shown to enable structural complexity across length scales in nontrivial geometries, including re-entrant shapes, which are responsive to either heat or light. A range of monomer compositions are optimized to include photoinitiators, light absorbers, and polymerization inhibitors to modulate the polymerization characteristics while simultaneously retaining the tailorability of the nematic alignment. The versatility of this framework is illustrated in an array of examples, including (i) thermomechanical generation of Gaussian-curved structures from flat geometries, (ii) light-responsive freeform topographies, and (iii) multiresponsive manipulators, which can be powered along independent axes using heat and/or light. The ability to integrate responses to multiple stimuli, where the principal directions of the mechanical output are arbitrarily tailored in a 3D freeform, enables new design spaces in soft robotics, micromechanical/fluidic systems, and optomechanical systems.
Soft actuators that undergo programmable shape change in response to a stimulus are enabling components of future soft robots and other soft machines. Strategies to power these actuators often ...require the incorporation of rigid, electrically conductive materials into the soft actuator, thus limiting the compliance and shape change of the material. In this study, we develop a 4D-printable composite composed of liquid crystal elastomer (LCE) matrix with dispersed droplets of eutectic gallium indium alloy (EGaIn). Using deformable EGaIn droplets in place of rigid conductive fillers preserves the compliance and shape-morphing properties of the LCE. The process enables 4D-printed LCE actuators capable of photothermal and electrothermal actuation. At low liquid metal (LM) concentrations (71 wt %), the composite actuator exhibits a photothermal response upon irradiation of near-IR light. Printed actuators with a twisted nematic configuration are capable of bending angles of 150° at 800 mW cm–2. At higher LM concentrations (88 wt %), the embedded LM droplets can form percolating networks that conduct electricity and enable electrical Joule heating of the LCE. Actuation strain ranging from 5 to 12% is controlled by the amount of electrical power that is delivered to the composite. We also introduce a method for multimaterial printing of monolithic structures where the LM filler loading is spatially varied. These multifunctional materials exhibit innate responsivity where the actuator behaves as an electrical switch and can report one of two states (on/off). These multiresponsive, 4D-printable composites enable multifunctional, mechanically active structures that can be powered with IR light or low DC voltages.
Natural soft tissue achieves a rich variety of functionality through a hierarchy of molecular, microscale, and mesoscale structures and ordering. Inspired by such architectures, we introduce a soft, ...multifunctional composite capable of a unique combination of sensing, mechanically robust electronic connectivity, and active shape morphing. The material is composed of a compliant and deformable liquid crystal elastomer (LCE) matrix that can achieve macroscopic shape change through a liquid crystal phase transition. The matrix is dispersed with liquid metal (LM) microparticles that are used to tailor the thermal and electrical conductivity of the LCE without detrimentally altering its mechanical or shape-morphing properties. Demonstrations of this composite for sensing, actuation, circuitry, and soft robot locomotion suggest the potential for versatile, tissue-like multifunctionality.
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