Preparation of patterned hydrogels for anti-counterfeiting and directional actuation by shear-induced orientation of cellulose nanocrystals

Hydrogels with anisotropic structures are of great interest in the fields of bionic actuators, sensing and anti-counterfeiting due to their unique optical and stimulus response properties. Here we report an anisotropic cellulose nanocrystals/polyacrylamide (CNC/PAM) hydrogel with a patterned structure obtained by shear-induced orientation of CNC in precursor solution. Due to the difference in affinity between different slider surfaces and the precursor, patterned structures with different interference colors were realized by adhering the polypropylene (PP) film with a specific pattern to the bottom glass slider, which leads to differences in CNC orientation in different areas. These interfere color patterns can only be observed between crossed polarization, allowing the hydrogel to be used in applications of anti-counterfeiting and information encryption. Moreover, a complex and controllable 3D deformation is realized by introducing “zebra crossing” structure in the hydrogel. The opening and closing processes of flowers are vividly mimicked using the reversible swelling and shrinking properties of hydrogels in water and salt solutions, making the hydrogel promising for soft actuators.