One Leader of Smart Materials: Two‐Way Shape Memory Polymers

ABSTRACT In the field of smart materials, an increasing demand is being observed for shape memory materials that exhibit advanced stimuli‐sensing and responsive capabilities. Two‐way shape memory polymers (2 W‐SMPs), as a novel type of smart shape memory material, offer numerous advantages over traditional one‐way shape memory polymers (1 W‐SMPs), particularly the fully reversible shape memory effect (SME), where the two‐way process (low‐temperature shape fixation and high‐temperature recovery to the original shape) occurs without the need for external energy input. These polymers are lightweight and exhibit remarkable deformation abilities, reversible changes in modulus, and multiple actuation modes. Additionally, they feature a high elastic modulus and increased response stress, making them particularly suitable and indispensable in fields ranging from medical devices and robotics to aerospace engineering and smart textiles. This review focuses on 2 W‐SMPs, detailing the underlying mechanisms of both 1 W‐SMPs and 2 W‐SMPs, as well as the various driving modes. We further discuss quasi‐2 W‐SMPs (with applied load force σ ≠ 0) and 2 W‐SMPs (with applied load force σ = 0) across different cross‐linking strategies. It also covers the broad applications of SMP materials and outlines the current challenges and potential avenues for future research.