Transforming nanoscopic dynamic molecular motions into the macroscopic scale in a predictable manner is of great interest for the advancement of smart materials. When these dynamic molecular systems are integrated with 3D printing technology, i.e. the extrusion-based direct ink writing, their micro- and macroscale properties are unleashed cooperatively as a result of the controlled assembly and complex 3D geometry. By (1) synchronizing the molecular motions, (2) hierarchically controlling materials’ nano- and mesoscale super-structures, and (3) fabricating their macroscale features into complex three-dimensional (3D) , actuators with dynamic motions have been developed successfully.1 Herein, we report the design and synthesis of 3D printable polypseudorotaxane hydrogels (PRHs), which are composed of α-cyclodextrins (α-CDs) and polymer backbones. The hydrogen-bonding interactions between the CDs and formed crystalline domains allow PRHs to possess appropriate shear-thinning and self-healing properties to facilitate their 3D printability. The PRHs are fabricated into woodpile-lattice cubes, and photo-crosslinked to afford polyrotaxane monoliths (PMs). Through solvent exchange and pH switching induced hydrogen-bonding deformation/formation, the CD rings on the polymer axles switch between the shuttling and stationary states. These PMs are capable of lifting objects vertically against gravity, thus converting the chemical energy input into mechanical work. Our work demonstrates a general approach to control the macroscopic motions through molecular motions in response to environmental stimuli, which is another example of 4D printing.
1. Q. Lin, X. Hou, and C. Ke, Angew. Chem. Int. Ed., 2017, 56, 4452.