Multiprogrammable Anisotropic Soft Material via Magneto-Orientation of Ferromagnetic Nanoplates

Anisotropic materials featured with ordered arrangement of sub-structures are ubiquitous in living organisms, and possess rapidly increasing relevance to emerging technologies in smart materials, soft robotics, flexible displays, and biomedicines. However, the integration and programming of multiple properties into anisotropic materials, which endow themselves with extended intrinsic capabilities and utilities, still remain a challenge. Herein, we report a multi-programmable anisotropic material by embedding ferromagnetic two-dimensional nanoplates into hydrogel matrix. The nanoplate exhibits not only a disc-like non-isotropic shape, but also an intrinsic easy magnetization axis perpendicular to its basal plane. Using a directional external magnetic field, we can precisely control the orientation of nanoplates inside hydrogel precursor solution and then fix them via photolithographic polymerization, leading to the fabrication of anisotropic hydrogel with on-demand ordered alignment of nanoplates. Such deliberate arrangement of nanoplates brings in extraordinary optical properties due to birefringence, enabling us to encrypt pattern information into hydrogel materials that is only visible under polarized light. Soft actuators with programmable optical, mechanical and magnetic properties are engineered, which allow to encode diverse deformation and locomotion modes, determine the actuation sites, and monitor the sub-structural anisotropy all simultaneously, opening new avenues for the design of anisotropic soft materials.