Direct-write fabrication of 4D active shape-changing structures based on a shape memory polymer and its nanocomposite

Four-dimensional (4D) active shape-changing structures based on shape memory polymers (SMPs) and shape memory nanocomposites (SMNCs) are able to be controlled in both space and time and have attracted increasing attention worldwide. However, conventional processing approaches have restricted the design space of such smart structures. Herein, 4D active shape-changing architectures in custom-defined geometries exhibiting thermally and remotely actuated behaviors are achieved by directwrite printing of ultraviolet (UV) cross-linking poly(lactic acid)-based inks. The results reveal that, by the introduction of a UV cross-linking agent, the printed objects present excellent shape memory behavior, which enables three-dimensional (3D)-onedimensional (1D)-3D, 3D-two-dimensional (2D)-3D, and 3D-3D-3D configuration transformations. More importantly, the addition of iron oxide successfully integrates 4D shape-changing objects with fast remotely actuated and magnetically guidable properties. This research realizes the printing of both SMPs and SMNCs, which present an effective strategy to design 4D active shape-changing architectures with multifunctional properties. This paves the way for the further development of 4D printing, soft robotics, flexible electronics, minimally invasive medicine, etc.