Hierarchically self-morphing structure through 4D printing

Hierarchical self-morphing refers to the concurrent global and local changes in shape or structure. Previous research works have demonstrated 3D printed self-morphing structures and the sequential folding/unfolding behaviours. However, the shape change events occurred mainly at the global level in a water environment either through absorbing moisture or through heating. Concurrent global and local shape changes in an ambient environment have not been reported. In this paper, we report a hierarchically blooming flower that blossoms in an ambient environment. Our design considers the strain limit through understanding the effect of thickness on the local strain to avoid fracture and the appropriate allocation of multiple materials to achieve predefined global and local shape changes. This design approach of hierarchical 4D printing may be useful for a variety of applications that involve controlled self-morphing structures with complex geometries.