A brief review on mechanical designs for 4D printing

Abstract

4D printing is a fast-developing technique which enables the transformation of shape, property, and function after a structure is manufactured. Here the ’fourth dimension’ refers to a time-dependent deformation, and thus 4D printing technique is closely related to the mechanical design strategies of materials and structures. This review concentrates on the recent progress of fundamental mechanical theories, analytical methods, and designing tools, for three categories of designing principles in 4D printing. The first type of 4D printing relies on active materials that respond to external stimuli. The second type includes a wide range of 4D-printed innovative structures, where the automatic actuation mainly comes from a combination of different deformation mechanisms. The third type of 4D printing focuses on mechanical designs related to the manufacturing process. The classification bridges the gaps between materials, microarchitectures, and large-scale structures, while some 4D printing strategies might involve more than one aforementioned design principle. This review provides reference and guidance for future 4D printings with customized deformation modes and multiple functionalities.