Mechanical Tensile–Shear Coupling of Liquid Crystal Elastomer Fiber Enables Precise Control Topological Deformation of Helical Knots

In liquid crystal polymers, constructing helical mesogenic orientation is a key strategy for achieving complex deformations. Besides self-assembled cholesteric structures, mechanical external forces can also induce helical structures. However, quantitative tools for precisely describing and regulating the on-demand deformation of these mechanically induced helical structures are still lacking. Herein, we present a tensile–shear coupling method for precise programming of helical mesogenic orientation in liquid crystal elastomer twist fibers (LCETFs). By leveraging the preservation of the topological invariant linking number in knot-based devices, multiple characteristics throughout the deformation can be quantitatively characterized, and deformation complexity can be enhanced. Furthermore, by controlling whether the helicity of LCETFs aligns with the handedness of the trefoil knots, devices can achieve both continuous and snap deformations. Finally, microdevices for motion control in complex fluid media have been developed. This research offers a creative design approach for complex 3D deformations in responsive materials, holding great promise for their practical applications in systems with complex mesogenic orientation.