fig6

Figure 6. Mechanical designs for 4D shape-changing structures. (A) A 4D printed shape memory hinge that can be repeatedly programmed and automatically deformed upon electric heating^[130]. (B) A 4D printed hydrogel flower that gradually closes due to swelling dynamics^[133]. (C) 4D printed reversible shape-changing soft structures based on the buckling of a non-Euclidean plate^[153]. (D) 4D printed soft actuators with programmable twisting and bending deformation^[155].