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Liquid crystal elastomers (LCEs) are stimuli-responsive materials capable of reversible and programmable shape change in response to an environmental stimulus. Despite the highly responsive nature of these materials, the modest elastic modulus and blocking stress exhibited by these actuating materials can be limiting in some engineering applications. Here, we engineer a semicrystalline LCE, where the incorporation of semicrystallinity in a lightly cross-linked liquid crystalline network yields tough and highly responsive materials. Directed self-assembly can be employed to program director profiles through the thickness of the semicrystalline LCE. In short, we use the alignment of a liquid crystal monomer phase to pattern the anisotropy of a semicrystalline polymer network. Both the semicrystalline-liquid crystalline and liquid crystalline-isotropic phase transition temperatures provide controllable shape transformations. A planarly aligned sample's normalized dimension parallel to the nematic director decreases from 1 at room temperature to 0.42 at 250 °C. The introduction of the semicrystalline nature also enhances the mechanical properties exhibited by the semicrystalline LCE. Semicrystalline LCEs have a storage modulus of 390 MPa at room temperature, and monodomain samples are capable of generating a contractile stress of 2.7 MPa on heating from 25 to 50 °C, far below the nematic to isotropic transition temperature. The robust mechanical properties of this material combined with the high actuation strain can be leveraged for applications such as soft robotics and actuators capable of doing significant work.

Optically tunable and switchable reflection grating LC gels can be used in anti-counterfeiting materials for optical security and encryption. Reflection colors and patterns appear by applying an AC field and a DC field controls the holographic color of the samples.

Stress urinary incontinence (SUI) is characterized by the involuntary loss of urine due to increased intra-abdominal pressure during coughing, sneezing, or exercising. SUI affects 20-40% of the female population and is exacerbated by aging. Severe SUI is commonly treated with surgical implantation of an autologous or a synthetic sling underneath the urethra for support. These slings, however, are static, and their tension cannot be non-invasively adjusted, if needed, after implantation. This study reports the fabrication of a novel device based on liquid crystal elastomers (LCEs) capable of changing shape in response to temperature increase induced by transcutaneous IR light. The shape change of the LCE-based device was characterized in a scar tissue phantom model. An in vitro urinary tract model was designed to study the efficacy of the LCE-based device to support continence and adjust sling tension with IR illumination. Finally, the device was acutely implanted and tested for induced tension changes in female multiparous New Zealand white rabbits. The LCE device achieved 5.6% ± 1.1% actuation when embedded in an agar gel with an elastic modulus of 100 kPa. The corresponding device temperature was 44.9 °C ± 0.4 °C, and the surrounding agar temperature stayed at 42.1 °C ± 0.4 °C. Leaking time in the in vitro urinary tract model significantly decreased (p 0.0001) when an LCE-based cuff was sutured around the model urethra from 5.2min ± 1min to 2min ±0.5min when the cuff was illuminated with IR light. Normalized leak point force (LPF) increased significantly (p = 0.01) with the implantation of an LCE-CB cuff around the bladder neck of multiparous rabbits. It decreased significantly (p = 0.023) when the device was actuated via IR light illumination. These results demonstrate that LCE material could be used to fabricate a dynamic device for treating SUI in women.

Cholesteric liquid crystals (CLC) are molecules that can self-assemble into helicoidal superstructures exhibiting circularly polarized reflection. The facile self-assembly and resulting optical properties makes CLCs a promising technology for an array of industrial applications, including reflective displays, tunable mirror-less lasers, optical storage, tunable color filters, and smart windows. The helicoidal structure of CLC can be stabilized via in situ photopolymerization of liquid crystal monomers in a CLC mixture, resulting in polymer-stabilized CLCs (PSCLCs). PSCLCs exhibit a dynamic optical response that can be induced by external stimuli, including electric fields, heat, and light. In this review, we discuss the electro-optic response and potential mechanism of PSCLCs reported over the past decade. Multiple electro-optic responses in PSCLCs with negative or positive dielectric anisotropy have been identified, including bandwidth broadening, red and blue tuning, and switching the reflection notch when an electric field is applied. The reconfigurable optical response of PSCLCs with positive dielectric anisotropy is also discussed. That is, red tuning (or broadening) by applying a DC field and switching by applying an AC field were both observed for the first time in a PSCLC sample. Finally, we discuss the potential mechanism for the dynamic response in PSCLCs.

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.

In this research, we have developed a novel temperature sensor to be utilized in the Cold-Supply-Chain (CSC) for perishable items. This sensor conveys temperature threshold crossings by switching operation between two individual RFID ICs, i.e., two individual Electronic Product Codes (EPCs). The advantage of this sensor compared to other existing technologies is that it can operate passively (i.e., battery-free) through multiple room-to-cold and cold-to-room temperature cycles, in real-time, without requiring any form of resetting. This design utilizes innovative cold-responsive liquid crystal elastomers (LCEs), which change shape when stimulated by cold temperatures and returns to a relaxed state when the stimulus is removed. In fact, this is the first temperature sensor that conveys temperature threshold crossings by switching between two RFID ICs using LCEs. The correct operation of the sensor is validated by RFID measurements. ANSYS HFSS and ANSYS Circuit Designer were used for the simulation analysis. The performance of the proposed design was validated using simulations and measurements.

An autonomous and continuously operating Radio Frequency Identification (RFID) temperature sensor is designed, manufactured, and tested. This sensor is battery-free and can detect temperature threshold crossings for multiple (room-to-cold and cold-to-room) temperature cycles, respectively. The proposed sensor conveys temperature threshold crossings through the controlled switching of its operating frequency within the 902-928 MHz Ultra High Frequency (UHF) RFID band. For the first time, shape morphing cold-temperature reactive Liquid Crystal Elastomers (LCEs), which provide reversible actuation, are utilized. The proposed sensor design consists of a patch antenna with a customized slot. A passive mechanical switch is connected across this slot and provides the frequency switching as it is activated and deactivated. The integration of this switch with the antenna is achieved using a co-simulation method. Furthermore, the cold-temperature reactive LCE triggers the switch when a temperature violation has occurred, thereby switching the operating frequency of the sensor based on temperature changes. Additionally, a high-dielectric constant substrate and a single matching network that operates at two discrete frequencies are used to design our compact frequency-domain temperature sensor. Moreover, based on the RFID platform, this sensor operates effectively in close-proximity to other sensors. Also, is provides identification and temperature information through an autonomous, continuous, and cost-effective design. Therefore, the proposed sensor has the potential for operation in the Internet of Things (IoTs) applications, where large amounts of data is collected from numerous sensors to extract valuable information for the benefit of users, manufacturers, and delivery companies in the virtual domain of the internet. Finally, ANSYS HFSS and Circuit Designer are used for the simulation modeling. The performance of our sensor is validated using measurements and simulations that agree very well.

Significance Research in soft robotics and wearable technologies has led to increasing demand for shape-changing materials that can be powered with portable electronics. Liquid crystal elastomers (LCEs) are a promising functional material for these applications but lack the electrical and thermal conductivity required for electrically stimulated shape-memory activation. To address this, LCEs are typically embedded with rigid fillers that enhance conductivity. However, these particles degrade the mechanical properties and shape-morphing capabilities of the LCE matrix. Here, we overcome these limitations with an advanced material architecture in which rigid filler is replaced with deformable liquid metal inclusions. This results in LCE composites that exhibit a combination of high electrical conductivity, high thermal conductivity, and actuation capabilities unlike any other soft composite.

A new passive radio frequency identification (RFID) temperature sensor is presented for monitoring the temperature of the surrounding environment of perishable goods, such as foods and medicines, in the cold supply chain. Specifically, this sensor self-tunes between 902 and 928 MHz, operating in the RFID UHF band, as the temperature rises or falls beyond a certain threshold. The novelty of this passive sensor is its ability to operate through multiple high-/low-temperature cycles. The design consists of a planar dipole antenna with a customized integrated T-match network (ITMN) that is actuated above a ground plane. The actuation shifts the operating frequency and is controlled by liquid crystal elastomers (LCEs), which are programmable and reversible temperature-dependent polymers. As a result, our design can be reconfigured to operate at various temperature ranges for which the LCE is designed to operate. The analysis is performed to examine the performance of the proposed sensor near practical items and when it is in close-proximity to an additional sensor with varying orientation. Finally, the sensor’s performance was validated through full-wave simulations using ANSYS HFSS and measurements. Both the simulation and measurements agreed well with theory.

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.

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.

Composites of liquid crystal elastomer (LCE) that are electrically conductive have the potential to function as soft "artificial muscle" actuators that can be reversibly stimulated with electrical Joule-heating. Conductivity can be achieved by embedding the LCE with droplets of an alloy of gallium and indium that is liquid at room temperature. These soft artificial muscles are capable of >50% reversible actuation with an applied load. The key to actuation at high loadings of liquid metal (LM) is that the droplets deform with the surrounding matrix. By controlling the size of LM droplets through simple processing techniques, we show that the actuator properties of the LM-LCE muscle can be tuned. For example, composites with smaller liquid metal particles (ca. 10 μm or less) are stiffer than those with larger liquid metal particles (ca. >100 μm) and are capable of greater force output. However, smaller particles reduce actuation strain and composites with large particles exhibit significantly greater stroke length. Such tunability in actuation properties permits the fabrication of specialized soft artificial muscles, where processing of the composite controls actuation strain and actuation force.

Three-dimensional structures capable of reversible changes in shape, i.e., four-dimensional-printed structures, may enable new generations of soft robotics, implantable medical devices, and consumer products. Here, thermally responsive liquid crystal elastomers (LCEs) are direct-write printed into 3D structures with a controlled molecular order. Molecular order is locally programmed by controlling the print path used to build the 3D object, and this order controls the stimulus response. Each aligned LCE filament undergoes 40% reversible contraction along the print direction on heating. By printing objects with controlled geometry and stimulus response, magnified shape transformations, for example, volumetric contractions or rapid, repetitive snap-through transitions, are realized.

The antenna design presented here supports a new generation of battery-free RFID sensing technology in which the antenna element dynamically conforms to the changing environment in a controlled manner. Specifically, we propose a sensing antenna that reversibly and repeatedly switches operating frequencies from 905MHz to 923.5 MHz based on a temperature threshold crossing. The developed antenna is a patch antenna matched to an RFID IC and integrated with a customized slot. The antenna shifts its operating frequency by using a novel thermal responsive polymer or Liquid Crystal Elastomer (LCE) which is programmable and operates reversibly. Furthermore, 4D printed LCE structures are to be coupled with an Ultra Subminiature Mechanical Switch (USMS) which shorts the slot when the LCE is activated. Finally, as the thermal excitation is removed, the switch returns to the open state. The short and open states of the switch will enable the frequency shift of the antenna structure. In this paper, the methodology of the frequency shift in the patch antenna and the novel LCE switch mechanism are described through simulation and measurements.

INTRODUCTION AND OBJECTIVES:Current sling materials placed around the urethra are permanently fixed and do not adapt to the patient's continence needs. We report on the design of a novel, shape-cha...

Liquid crystal elastomers (LCEs) are a class of stimuli-responsive polymers that undergo reversible shape-change in response to environmental changes. The shape change of LCEs can be programmed during processing by orienting the liquid crystal phase prior to crosslinking. The suite of processing techniques that has been developed has resulted in a myriad of LCEs with different shape-changing behavior and mechanical properties. Aligning LCEs via mechanical straining yields large uniaxial actuators capable of a moderate force output. Magnetic fields are utilized to control the alignment within LCE microstructures. The generation of out-of-plane deformations such as bending, twisting, and coning is enabled by surface alignment techniques within thin films. 4D printing processes have emerged that enable the fabrication of centimeter-scale, 3D LCE structures with a complex alignment. The processing technique also determines, to a large extent, the potential applications of the LCE. For example, 4D printing enables the fabrication of LCE actuators capable of replicating the forces generated by human muscles. Employing surface alignment techniques, LCE films can be designed for use as coatings or as substrates for stretchable electronics. The growth of new processes and strategies opens and strengthens the path for LCEs to be applicable within biomedical device designs.

Stimuli-responsive materials that exhibit a mechanical response to specific biological conditions are of considerable interest for responsive, implantable medical devices. Herein, we report the synthesis, processing and characterization of oxidation-responsive liquid crystal elastomers that demonstrate programmable shape changes in response to reactive oxygen species. Direct ink writing (DIW) is used to fabricate Liquid Crystal Elastomers (LCEs) with programmed molecular orientation and anisotropic mechanical properties. LCE structures were immersed in different media (oxidative, basic and saline) at body temperature to measure in vitro degradation. Oxidation-sensitive hydrophobic thioether linkages transition to hydrophilic sulfoxide and sulfone groups. The introduction of these polar moieties brings about anisotropic swelling of the polymer network in an aqueous environment, inducing complex shape changes. 3D-printed uniaxial strips exhibit 8% contraction along the nematic director and 16% orthogonal expansion in oxidative media, while printed LCEs azimuthally deform into cones 19 times their original thickness. Ultimately, these LCEs degrade completely. In contrast, LCEs subjected to basic and saline solutions showed no apparent response. These oxidation-responsive LCEs with programmable shape changes may enable a wide range of applications in target specific drug delivery systems and other diagnostic and therapeutic tools.

A novel passive RFID temperature sensor is proposed in this paper. The sensor utilizes an integrated T -match network (TMN) for matching the antenna to the RFID IC. Furthermore., the sensor detects changes in temperature by shifting its operating frequency. The frequency shifts are accomplished by a 3D printed liquid crystal elastomer (LCE) array that can reversibly actuate depending on the temperature to move the antenna and change its distance from the ground plane.

A passive RFID temperature sensor is presented. This sensor design utilizes a patch antenna integrated with a customized slot. Using a novel Liquid Crystal Elastomer (LCE) switch, the slot is shorted when the temperature reaches a specified threshold. When the temperature decreases below this threshold, the switch retracts to the original position. As a result, the antenna operates at one of two states corresponding to a controlled shift in frequency within the RFID band. Additionally, a single impedance matching network is designed to accommodate a favorable match between the two antenna states and the RFID IC.