Photomechanical response under physiological conditions of azobenzene-containing 4D-printed liquid crystal elastomer actuators

Abstract

This work analyses the photomechanical work performance of 4D-printed liquid crystal elastomers under physiological conditions in PBS media.

Photoswitches in Order: One-Pot Synthesis of Azobenzene Main-Chain and Segmented Copolymers

“…In analogy with other azobenzene polymers, during UV light (365 nm) irradiation, , a photoinduced trans – cis isomerization occurs and is detected by variation of the absorption spectrum, as shown in Figure a. In particular, the absorbance decreased in the first band and increased in the second one.…”

Multimodal and Multistimuli 4D-Printed Magnetic Composite Liquid Crystal Elastomer Actuators

“…The POM observations are compatible with a mesogen orientation parallel to the printing direction, as previously described in the literature. 23,37,40,42 Once the material is extruded and deposited, the printed element is UV-exposed to activate the photoinitiator and cross-link the free acrylate groups at the chain ends leading to LCE elements. The alignment imparted during processing is retained after the curing process as checked by POM (Figure 1C) even if photoexposure is carried out tens of minutes after deposition.…”

“…The direction, speed, and extruding rate are dictated by computer numerical control (CNC) via custom-made g-code, generated from a CAD drawing. It is known that shear and elongational forces during filament extrusion and deposition in main chain LC polymers can lead to alignment of mesogens parallel to the movement direction of the nozzle. ,,, In this manner, the LC alignment can be digitally defined during the printing process (Figure B). This is also seen for the composite precursor system including MMPs, Figure C shows polarized optical microscope (POM) images at 0° (Figure C1) and 45° (Figure C2) with respect to the first polarizer transmission direction, for a 10 wt % MPs content uniaxial actuator.…”

“…Their mechanical response comes from the loss of order of the LC molecules, known as mesogens, due to the energy input of stimuli. ,− This process causes the polymer network to contract along the direction of the preferential orientation of the long molecular axes of the mesogens, known as the director n , and to expand along the perpendicular directions. − Given this anisotropic mechanical response, it is crucial in these materials to have precise control of the director. ,− Recently, four-dimensional (4D) printing emerged as a powerful tool to accurately define the director in LCE constructs. ,− Mesogen alignment induced during ink extrusion and deposition by rheological means, combined with the digital control over the path of the extruding nozzle during three-dimensional (3D) printing, allows a precise definition of the final LCE morphology via computer-aided design (CAD). ,, The resulting LCE objects are dynamic over time when a stimulus is applied. These actuators are capable of producing large strains upon the application of different stimuli, like heat, ,, humidity, or light. ,, …”

“…These actuators are capable of producing large strains upon the application of different stimuli, like heat, 23,33,37 humidity, 41 or light. 34,40,42 Despite their ability to undergo significant and reversible anisotropic mechanical deformations, 21,22,27,29 which sets them apart from other matrix materials, LCEs have not received extensive attention as matrix materials for MEs or magnetically actuated soft robots. 7,9,12,43−47 Only a few examples in the literature 48−51 make use of magnetic LCEs composites to provide shape-changing capabilities.…”