Biomimetic Nonuniform, Dual-Stimuli Self-Morphing Enabled by Gradient Four-Dimensional Printing

Programmable non-uniform deformation is of great significance for self-shape morphing systems that are commonly seen in biological systems, and also has practical applications in drug delivery, biomedical devices and robotics, etc. Here we present a novel gradient 4D printing method towards biomimetic non-uniform, dual-stimuli self-morphing. By modeling and printing graded active materials with water-swelling properties, we can configure continuously smooth gradients of volume fraction of the active material in bilayer structures. The variation of swelling ratio mismatch between the two layers can be delicately regulated, which results in the programmable non-uniform shape transformation. The shape-shifting results can be predicted by the established mathematical model and computational simulations. Furthermore, we demonstrate dual-stimuli self-morphing structures by printing the graded water-responsive elastomer materials onto a heat-shrinkable shape memory polymer, which could produce different shape ch...