Shuyi Li,Zhengyi Song,Yuyan Fan,Dongsong Wei,Yan Liu
Liquid crystal elastomers (LCEs) are polymer networks that exhibit anisotropic liquid crystalline properties while maintaining the properties of elastomers, presenting reversible high-speed and large-scale actuation in response to external stimuli. Herein, we formulated a non-toxic, low-temperature liquid crystal (LC) ink for temperature-controlled direct ink writing 3D printing. The rheological properties of the LC ink were verified under different temperatures given the phase transition temperature of 63 °C measured by the DSC test. Afterwards, the effects of printing speed, printing temperature, and actuation temperature on the actuation strain of printed LCEs structures were investigated within adjustable ranges. In addition, it was demonstrated that the printing direction can modulate the LCEs to exhibit different actuation behaviors. Finally, by sequentially conforming structures and programming the printing parameters, it showed the deformation behavior of a variety of complex structures. By integrating with 4D printing and digital device architectures, this unique reversible deformation property will help LCEs presented here apply to mechanical actuators, smart surfaces, micro-robots, etc.Keywords:liquid crystal elastomers;temperature-responsive;programmable shape-changing;4D printing
Faced with complex and diverse tasks, researchers seek to introduce stimuli-responsive materials into the field of microrobots. Magnetic helical microrobots based on shape-memory polymers demonstrate excellent locomotion capability and programmable shape transformations. However, the stimulation method of shape changes is still dependent on the rising of ambient temperature and lacks the ability to address individuals among multiple microrobots. In this paper, magnetic helical microrobots were prepared based on polylactic acid and Fe3O4 nanoparticles, which demonstrated controlled locomotion under rotating magnetic fields and programmable shape changes in their length, diameter, and chirality. The transition temperature of shape recoveries was adjusted to a range above 37 °C. At 46 °C, helical microrobots had a fast shape change with a recovery ratio of 72% in a minute. The photothermal effect of Fe3O4 nanoparticles under near-infrared laser can actuate the shape recovery rapidly, with a recovery ratio of 77% in 15 s and 90% in a minute. The stimulation strategy also allows addressing among multiple microrobots, or even within a single microrobot, selectively stimulating one or a part to change its shape. Combined with the magnetic field, laser-addressed shape changes were used for precise deployment and individual control of microrobots. Multiple microrobots can be enriched at the targeted point, heating the ambient temperature over 46 °C. The shape changes of internal parts of microrobots help them to grasp and assemble objects. Such microrobots have great potential in biomedicine and micromanipulation.
Controllable tissue expansion is critical in regenerative medicine to address skin or mucosal defects. Tissue expanders based on isotropic water filling or swelling offer a clinical solution but face challenges in addressing individual anatomical complexities. Here, a 4D printing biocompatible hydrogel expander with customizable designs is reported. Water-swellable polymer sheets with non-swellable elastomer frameworks are synthesized via digital photocuring. The sheets buckle upon adsorption of tissue fluids to execute anisotropic and programmable morphing, forming predesigned 3D structures with time as the fourth dimension for the shape changing. With an initial thickness of 1.0 mm, which is remarkably thinner than previous devices (typically 3–5 mm), the expander enabled minimally invasive implantation in the rat scalp. After 5 days’ implantation, the skin area and weight respectively increase to two and three folds without tissue damage, illustrating that the buckling-based strategy provides a safer yet accelerated expansion effect over previous devices. RNA sequencing indicates that the buckling-induced regeneration involving epithelial-to-mesenchymal transition (EMT) may be affected by the PI3K-AKT pathway. This work provides an inspiring strategy for personalized regeneration medicine.
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