scholarly journals Degradation-Induced Actuation in Oxidation-Responsive Liquid Crystal Elastomers

Crystals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 420 ◽  
Author(s):  
Mahjabeen Javed ◽  
Seelay Tasmim ◽  
Mustafa K. Abdelrahman ◽  
Cedric P. Ambulo ◽  
Taylor H. Ware
Keyword(s):  
Liquid Crystal ◽  
Mechanical Response ◽  
Polymer Network ◽  
Orthogonal Expansion ◽  
Aqueous Environment ◽  
Wide Range ◽  
Anisotropic Mechanical Properties ◽  
Liquid Crystal Elastomers ◽  
Shape Changes

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.

scholarly journals Effect of Crosslinkers on Optical and Mechanical Behavior of Chiral Nematic Liquid Crystal Elastomers

Molecules ◽  
2021 ◽  
Vol 26 (20) ◽  
pp. 6193
Author(s):  
Kyosun Ku ◽  
Kyohei Hisano ◽  
Kyoko Yuasa ◽  
Tomoki Shigeyama ◽  
Norihisa Akamatsu ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Polymer Network ◽  
Molar Ratio ◽  
Stimuli Responsive ◽  
Breaking Strain ◽  
Responsive Materials ◽  
Sensor Applications ◽  
Color Changes ◽  
Chiral Nematic ◽  
Liquid Crystal Elastomers

Chiral nematic (N*) liquid crystal elastomers (LCEs) are suitable for fabricating stimuli-responsive materials. As crosslinkers considerably affect the N*LCE network, we investigated the effects of crosslinking units on the physical properties of N*LCEs. The N*LCEs were synthesized with different types of crosslinkers, and the relationship between the N*LC polymeric system and the crosslinking unit was investigated. The N*LCEs emit color by selective reflection, in which the color changes in response to mechanical deformation. The LC-type crosslinker decreases the helical twisting power of the N*LCE by increasing the total molar ratio of the mesogenic compound. The N*LCE exhibits mechano-responsive color changes by coupling the N*LC orientation and the polymer network, where the N*LCEs exhibit different degrees of pitch variation depending on the crosslinker. Moreover, the LC-type crosslinker increases the Young’s modulus of N*LCEs, and the long methylene chains increase the breaking strain. An analysis of experimental results verified the effect of the crosslinkers, providing a design rationale for N*LCE materials in mechano-optical sensor applications.

Shape changes in chemoresponsive liquid crystal elastomers

2017 ◽  
Vol 240 ◽  
pp. 511-518 ◽  
Author(s):  
Jennifer M. Boothby ◽  
Hyun Kim ◽  
Taylor H. Ware
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystal Elastomers ◽  
Shape Changes

scholarly journals An Interpenetrating Alginate/Gelatin Network for Three-Dimensional (3D) Cell Cultures and Organ Bioprinting

Molecules ◽  
2020 ◽  
Vol 25 (3) ◽  
pp. 756 ◽  
Author(s):  
Qiuhong Chen ◽  
Xiaohong Tian ◽  
Jun Fan ◽  
Hao Tong ◽  
Qiang Ao ◽  
...  
Keyword(s):  
Cell Cultures ◽  
Structural Integrity ◽  
Polymer Network ◽  
Three Dimensional ◽  
Biochemical Properties ◽  
Interpenetrating Polymer Network ◽  
3D Cell Cultures ◽  
Wide Range ◽  
The Individual

Crosslinking is an effective way to improve the physiochemical and biochemical properties of hydrogels. In this study, we describe an interpenetrating polymer network (IPN) of alginate/gelatin hydrogels (i.e., A-G-IPN) in which cells can be encapsulated for in vitro three-dimensional (3D) cultures and organ bioprinting. A double crosslinking model, i.e., using Ca2+ to crosslink alginate molecules and transglutaminase (TG) to crosslink gelatin molecules, is exploited to improve the physiochemical, such as water holding capacity, hardness and structural integrity, and biochemical properties, such as cytocompatibility, of the alginate/gelatin hydrogels. For the sake of convenience, the individual ionic (i.e., only treatment with Ca2+) or enzymatic (i.e., only treatment with TG) crosslinked alginate/gelatin hydrogels are referred as alginate-semi-IPN (i.e., A-semi-IPN) or gelatin-semi-IPN (i.e., G-semi-IPN), respectively. Tunable physiochemical and biochemical properties of the hydrogels have been obtained by changing the crosslinking sequences and polymer concentrations. Cytocompatibilities of the obtained hydrogels are evaluated through in vitro 3D cell cultures and bioprinting. The double crosslinked A-G-IPN hydrogel is a promising candidate for a wide range of biomedical applications, including bioartificial organ manufacturing, high-throughput drug screening, and pathological mechanism analyses.

Polydopamine nanoparticles doped in liquid crystal elastomers for producing dynamic 3D structures

2017 ◽  
Vol 5 (14) ◽  
pp. 6740-6746 ◽  
Author(s):  
Zhen Li ◽  
Yang Yang ◽  
Zhenhua Wang ◽  
Xiaoyong Zhang ◽  
Qiaomei Chen ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Polymer Films ◽  
Smart Materials ◽  
Mechanical Response ◽  
External Stimulus ◽  
3D Structures ◽  
Liquid Crystal Elastomers ◽  
2D Polymer

Achieving 3D structures that can be reversibly formed from dry 2D polymer films is useful for the development of suitable smart materials capable of converting an external stimulus into a mechanical response.

scholarly journals Influence of Liquid Crystallinity and Mechanical Deformation on the Molecular Relaxations of an Auxetic Liquid Crystal Elastomer

Molecules ◽  
2021 ◽  
Vol 26 (23) ◽  
pp. 7313
Author(s):  
Thomas Raistrick ◽  
Matthew Reynolds ◽  
Helen F. Gleeson ◽  
Johan Mattsson
Keyword(s):  
Liquid Crystal ◽  
Mechanical Response ◽  
Relaxation Times ◽  
Dielectric Relaxation Spectroscopy ◽  
Relaxation Dynamics ◽  
Liquid Crystal Elastomer ◽  
Nematic State ◽  
Out Of Plane ◽  
Liquid Crystal Elastomers ◽  
Polymer Configurations

Liquid Crystal Elastomers (LCEs) combine the anisotropic ordering of liquid crystals with the elastic properties of elastomers, providing unique physical properties, such as stimuli responsiveness and a recently discovered molecular auxetic response. Here, we determine how the molecular relaxation dynamics in an acrylate LCE are affected by its phase using broadband dielectric relaxation spectroscopy, calorimetry and rheology. Our LCE is an excellent model system since it exhibits a molecular auxetic response in its nematic state, and chemically identical nematic or isotropic samples can be prepared by cross-linking. We find that the glass transition temperatures (Tg) and dynamic fragilities are similar in both phases, and the T-dependence of the α relaxation shows a crossover at the same T* for both phases. However, for T>T*, the behavior becomes Arrhenius for the nematic LCE, but only more Arrhenius-like for the isotropic sample. We provide evidence that the latter behavior is related to the existence of pre-transitional nematic fluctuations in the isotropic LCE, which are locked in by polymerization. The role of applied strain on the relaxation dynamics and mechanical response of the LCE is investigated; this is particularly important since the molecular auxetic response is linked to a mechanical Fréedericksz transition that is not fully understood. We demonstrate that the complex Young’s modulus and the α relaxation time remain relatively unchanged for small deformations, whereas for strains for which the auxetic response is achieved, significant increases are observed. We suggest that the observed molecular auxetic response is coupled to the strain-induced out-of-plane rotation of the mesogen units, in turn driven by the increasing constraints on polymer configurations, as reflected in increasing elastic moduli and α relaxation times; this is consistent with our recent results showing that the auxetic response coincides with the emergence of biaxial order.

Sample preparation affects the nematic–isotropic transition in liquid crystal elastomers: insights from molecular simulation

Soft Matter ◽  
2018 ◽  
Vol 14 (8) ◽  
pp. 1408-1416 ◽  
Author(s):  
Gregor Skačej
Keyword(s):  
Liquid Crystal ◽  
Sample Preparation ◽  
Molecular Simulation ◽  
Polymer Network ◽  
Molecular Simulations ◽  
Liquid Crystal Elastomers

Molecular simulations elucidate how sample preparation—polymer network irregularity and swelling—affects the nematic–isotropic transition in liquid crystal elastomers.

scholarly journals Mechanical adaptability of artificial muscles from nanoscale molecular action

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Federico Lancia ◽  
Alexander Ryabchun ◽  
Anne-Déborah Nguindjel ◽  
Supaporn Kwangmettatam ◽  
Nathalie Katsonis
Keyword(s):  
Liquid Crystal ◽  
Mechanical Response ◽  
Polymer Network ◽  
Soft Materials ◽  
Molecular Switches ◽  
Polymer Materials ◽  
Artificial Muscles ◽  
Shape Transformation ◽  
Crystal Polymer ◽  
Molecular Action

Abstract The motion of artificial molecular machines has been amplified into the shape transformation of polymer materials that have been compared to muscles, where mechanically active molecules work together to produce a contraction. In spite of this progress, harnessing cooperative molecular motion remains a challenge in this field. Here, we show how the light-induced action of artificial molecular switches modifies not only the shape but also, simultaneously, the stiffness of soft materials. The heterogeneous design of these materials features inclusions of free liquid crystal in a liquid crystal polymer network. When the magnitude of the intrinsic interfacial tension is modified by the action of the switches, photo-stiffening is observed, in analogy with the mechanical response of activated muscle fibers, and in contrast to melting mechanisms reported so far. Mechanoadaptive materials that are capable of active tuning of rigidity will likely contribute to a bottom-up approach towards human-friendly and soft robotics.

scholarly journals Numerical Methods in Studies of Liquid Crystal Elastomers

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1650
Author(s):  
Madjid Soltani ◽  
Kaamran Raahemifar ◽  
Arman Nokhosteen ◽  
Farshad Moradi Kashkooli ◽  
Elham L. Zoudani
Keyword(s):  
Liquid Crystal ◽  
Numerical Models ◽  
Future Research ◽  
Artificial Muscles ◽  
Suitable Candidate ◽  
Numerical Studies ◽  
Wide Range ◽  
Electric And Magnetic Fields ◽  
Liquid Crystal Elastomers ◽  
External Stimuli

Liquid crystal elastomers (LCEs) are a type of material with specific features of polymers and of liquid crystals. They exhibit interesting behaviors, i.e., they are able to change their physical properties when met with external stimuli, including heat, light, electric, and magnetic fields. This behavior makes LCEs a suitable candidate for a variety of applications, including, but not limited to, artificial muscles, optical devices, microscopy and imaging systems, biosensor devices, and optimization of solar energy collectors. Due to the wide range of applicability, numerical models are needed not only to further our understanding of the underlining mechanics governing LCE behavior, but also to enable the predictive modeling of their behavior under different circumstances for different applications. Given that several mainstream methods are used for LCE modeling, viz. finite element method, Monte Carlo and molecular dynamics, and the growing interest and reliance on computer modeling for predicting the opto-mechanical behavior of complex structures in real world applications, there is a need to gain a better understanding regarding their strengths and weaknesses so that the best method can be utilized for the specific application at hand. Therefore, this investigation aims to not only to present a multitude of examples on numerical studies conducted on LCEs, but also attempts at offering a concise categorization of different methods based on the desired application to act as a guide for current and future research in this field.

scholarly journals Nanocapillary electrokinetic tracking for monitoring charge fluctuations on a single nanoparticle

2016 ◽  
Vol 193 ◽  
pp. 447-458 ◽  
Author(s):  
Sanli Faez ◽  
Sela Samin ◽  
Dashdeleg Baasanjav ◽  
Stefan Weidlich ◽  
Markus Schmidt ◽  
...  
Keyword(s):  
Electrophoretic Mobility ◽  
Medical Diagnostics ◽  
Catalytic Reactions ◽  
Aqueous Environment ◽  
Elastic Light Scattering ◽  
Colloid Science ◽  
Wide Range ◽  
Daunting Challenge ◽  
Measurement Capabilities

We introduce nanoCapillary Electrokinetic Tracking (nanoCET), an optofluidic platform for continuously measuring the electrophoretic mobility of a single colloidal nanoparticle or macromolecule in vitro with millisecond time resolution and high charge sensitivity. This platform is based on using a nanocapillary optical fiber in which liquids may flow inside a channel embedded inside the light-guiding core and nanoparticles are tracked using elastic light scattering. Using this platform we have experimentally measured the electrophoretic mobility of 60 nm gold nanoparticles in an aqueous environment. Further, using numerical simulations, we demonstrate the underlying electrokinetic dynamics inside the nanocapillary and the necessary steps for extending this method to probing single biomolecules, which can be achieved with existing technologies. This achievement will immensely facilitate the daunting challenge of monitoring biochemical or catalytic reactions on a single entity over a wide range of timescales. The unique measurement capabilities of this platform pave the way for a wide range of discoveries in colloid science, analytical biochemistry, and medical diagnostics.

scholarly journals Photo-Mechanical Response Dynamics of Liquid Crystal Elastomer Linear Actuators

Materials ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 2933
Author(s):  
Przemysław Grabowski ◽  
Jakub Haberko ◽  
Piotr Wasylczyk
Keyword(s):  
Liquid Crystal ◽  
Mechanical Response ◽  
Nanometer Scale ◽  
Response Dynamics ◽  
Responsive Materials ◽  
Liquid Crystal Elastomer ◽  
Power Pulse ◽  
Liquid Crystal Elastomers ◽  
Further Development ◽  
Simple Behavior

With continuous miniaturization of many technologies, robotics seems to be lagging behind. While the semiconductor technologies operate confidently at the nanometer scale and micro-mechanics of simple structures (MEMS) in micrometers, autonomous devices are struggling to break the centimeter barrier and have hardly colonized smaller scales. One way towards miniaturization of robots involves remotely powered, light-driven soft mechanisms based on photo-responsive materials, such as liquid crystal elastomers (LCEs). While several simple devices have been demonstrated with contracting, bending, twisting, or other, more complex LCE actuators, only their simple behavior in response to light has been studied. Here we characterize the photo-mechanical response of a linear light-driven LCE actuator by measuring its response to laser beams with varying power, pulse duration, pulse energy, and the energy spatial distribution. Light absorption decrease in the actuator over time is also measured. These results are at the foundation of further development of soft, light-driven miniature mechanisms and micro-robots.

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