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1. Photothermally Reconfigurable Shape Memory Magnetic Cilia

   https://doi.org/10.1002/admt.202000147  

   Liu, Jessica A. ‐C.; Evans, Benjamin A.; Tracy, Joseph B. (May 2020, Advanced Materials Technologies)

   Abstract Stimulus‐responsive polymers are attractive for microactuators because they can be easily miniaturized and remotely actuated, enabling untethered operation. In this work, magnetic Fe microparticles are dispersed in a thermoplastic polyurethane shape memory polymer matrix and formed into artificial, magnetic cilia by solvent casting within the vertical magnetic field in the gap between two permanent magnets. Interactions of the magnetic moments of the microparticles, aligned by the applied magnetic field, drive self‐assembly of magnetic cilia along the field direction. The resulting magnetic cilia are reconfigurable using light and magnetic fields as remote stimuli. Temporary shapes obtained through combined magnetic actuation and photothermal heating can be locked by switching off the light and magnetic field. Subsequently turning on the light without the magnetic field drives recovery of the permanent shape. The permanent shape can also be reprogrammed after preparing the cilia by applying mechanical constraints and annealing at high temperature. Spatially controlled actuation is demonstrated by applying a mask for optical pattern transfer into the array of magnetic cilia. A theoretical model is developed for predicting the response of shape memory magnetic cilia and elucidates physical mechanisms behind observed phenomena, enabling the design and optimization of ciliary systems for specific applications. 

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2. 3D‐Printed Photoresponsive Liquid Crystal Elastomer Composites for Free‐Form Actuation

   https://doi.org/10.1002/adfm.202210614  

   Wang, Yuchen; Yin, Rui; Jin, Lishuai; Liu, Mingzhu; Gao, Yuchong; Raney, Jordan; Yang, Shu (November 2022, Advanced Functional Materials)

   Abstract Direct ink writing of liquid crystal elastomers (LCEs) offers a new opportunity to program geometries for a wide variety of shape transformation modes toward applications such as soft robotics. So far, most 3D‐printed LCEs are thermally actuated. Herein, a 3D‐printable photoresponsive gold nanorod (AuNR)/LCE composite ink is developed, allowing for photothermal actuation of the 3D‐printed structures with AuNR as low as 0.1 wt.%. It is shown that the printed filament has a superior photothermal response with 27% actuation strain upon irradiation to near‐infrared (NIR) light (808 nm) at 1.4 W cm⁻²(corresponding to 160 °C) under optimal printing conditions. The 3D‐printed composite structures can be globally or locally actuated into different shapes by controlling the area exposed to the NIR laser. Taking advantage of the customized structures enabled by 3D printing and the ability to control locally exposed light, a light‐responsive soft robot is demonstrated that can climb on a ratchet surface with a maximum speed of 0.284 mm s⁻¹(on a flat surface) and 0.216 mm s⁻¹(on a 30° titled surface), respectively, corresponding to 0.428 and 0.324 body length per min, respectively, with a large body mass (0.23 g) and thickness (1 mm). 

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3. Repeatable and Reprogrammable Shape Morphing from Photoresponsive Gold Nanorod/Liquid Crystal Elastomers

   https://doi.org/10.1002/adma.202004270  

   Wang, Yuchen; Dang, Alei; Zhang, Zhifeng; Yin, Rui; Gao, Yuchong; Feng, Liang; Yang, Shu (October 2020, Advanced Materials)

   Abstract Liquid crystal elastomers (LCEs) are of interest for applications such as soft robotics and shape‐morphing devices. Among the different actuation mechanisms, light offers advantages such as spatial and local control of actuation via the photothermal effect. However, the unwanted aggregation of the light‐absorbing nanoparticles in the LCE matrix will limit the photothermal response speed, actuation performance, and repeatability. Herein, a near‐infrared‐responsive LCE composite consisting of up to 0.20 wt% poly(ethylene glycol)‐modified gold nanorods (AuNRs) without apparent aggregation is demonstrated. The high Young's modulus, 20.3 MPa, and excellent photothermal performance render repeated and fast actuation of the films (actuation within 5 s and recovery in 2 s) when exposed to 800 nm light at an average output power of ≈1.0 W cm⁻², while maintaining a large actuation strain (56%). Further, it is shown that the same sheet of AuNR/LCE film (100 µm thick) can be morphed into different shapes simply by varying the motifs of the photomasks. 

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4. Laser reprogramming magnetic anisotropy in soft composites for reconfigurable 3D shaping

   https://doi.org/10.1038/s41467-020-20229-6  

   Deng, Heng; Sattari, Kianoosh; Xie, Yunchao; Liao, Ping; Yan, Zheng; Lin, Jian (December 2020, Nature Communications)

   Abstract Responsive soft materials capable of exhibiting various three-dimensional (3D) shapes under the same stimulus are desirable for promising applications including adaptive and reconfigurable soft robots. Here, we report a laser rewritable magnetic composite film, whose responsive shape-morphing behaviors induced by a magnetic field can be digitally and repeatedly reprogrammed by a facile method of direct laser writing. The composite film is made from an elastomer and magnetic particles encapsulated by a phase change polymer. Once the phase change polymer is temporarily melted by transient laser heating, the orientation of the magnetic particles can be re-aligned upon change of a programming magnetic field. By the digital laser writing on selective areas, magnetic anisotropies can be encoded in the composite film and then reprogrammed by repeating the same procedure, thus leading to multimodal 3D shaping under the same actuation magnetic field. Furthermore, we demonstrated their functional applications in assembling multistate 3D structures driven by the magnetic force-induced buckling, fabricating multistate electrical switches for electronics, and constructing reconfigurable magnetic soft robots with locomotion modes of peristalsis, crawling, and rolling. 

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5. 3D Structuring of Magnetoelastomers for Anisotropic Actuation Properties

   Atescan, Yagmur; Yamamoto, Namiko. (January 2020, AIAA paper)

   Smart structures with actuation function are desired for aerospace applications, including morphing airfoils, deployable structures and more. While shape memory alloys and piezoelectric ceramics and polymers are currently a popular smart material options for such applications, magnetoelastomers (MEs) can be uniquely actuated with application of non-contact magnetic field. Magnetoelastomers (MEs), composite materials made of magnetic particles and soft, non-magnetic matrix, can potentially contribute to such smart structures as a light-weight, smart material option with large strain change, fast response time (milliseconds) and anisotropic actuation properties. Other than aerospace applications, MEs, as soft actuators, have been investigated for flexible electronics, soft robotics, and biomedical applications. Anisotropic actuation properties of MEs can be controlled with particle organization within the elastomer. To provide this control, parametric studies on fabrication of MEs need to be performed. This study presents experimental work on nanoparticle organization within MEs using uniaxial, biaxial and triaxial magnetic fields and on the structure-property relationships of MEs. Iron oxide nanoparticles were used as a model nanofillers, and their surfaces were treated with silane coupling agent to improve dispersion and suspension within a polydimethylsiloxane (PDMS) elastomer. The fabricated MEs were inspected using microCT, and their anisotropic susceptibilities are being measured. 

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