Reversible shape‐shifting in polymeric materials

In recent years, significant progress has been made in polymeric materials, which alter shape upon external stimuli, suggesting potential applications in robotics, biomedical engineering, and optical devices. These stimuli‐responsive materials may be categorized into two classes: (i) shape‐changing materials in which a specific type of shape‐shifting is encoded in the original material structure and (ii) shape‐memory materials, which do not possess any predetermined shape‐shifting as prepared, yet allow programming of complex shape transformations on demand. While shape alterations in shape‐changing materials are intrinsically reversible, shape memory is usually a one‐way transformation from a metastable (programmed) to an equilibrium (original) state. Recently, different principles for both one‐way reversible and two‐way reversible shape memory have been developed. These offer a powerful combination of reversibility and programmability, which significantly expands the range of potential applications. The goal of this review is to highlight recent developments in reversible shape‐shifting by introducing novel mechanisms, materials, and applications.