Kinetics-Induced Morphing of Three-Dimensional-Printed Gel Structures Based on Geometric Asymmetry

Emerging three-dimensional (3D) printing techniques for soft active materials have demonstrated fascinating applications in various areas including programmable and reconfigurable structures, tissue engineering, and soft robotics. For example, polymeric gels, which consist of polymer networks swollen with solvent molecules, are capable of deforming and swelling/deswelling in response to external stimuli. Although polymeric gels are used to print structures, little attention has been paid to the effect of printing parameters on the cross-sectional shape of 3D-printed gel filaments or further to the dynamic responses of the printed structures. Due to the flow of the precursor solution before fully cured, the cross section of a printed gel filament is usually asymmetric. When immersed in water, the asymmetry in the cross section causes the printed filament to bend, and the interdiffusion of the two solvents leads to the alternation in bending direction. The bending curvature and response rate can be adjusted by turning printing parameters. As applications of this mechanism, we demonstrated various types of gel structures, capable of deforming from 1D strips to 2D spiral or sinusoidal shapes, warping from 2D flat sheet to 3D cylindrical helix when swollen, or wrapping and manipulating objects under external stimuli.