Advances and Applications of 4D-Printed High-Strength Shape Memory Polymers

"Life" represents a distinctive attribute inherent to organisms in nature, evident in their capacity to actively adapt to changes in their environment. In contrast to the static and intricate constructs of additive manufacturing (AM), the dynamic structure of 4D printing (4DP) adeptly integrates AM technology, responsive mechanisms, and external stimuli, imbuing it with a semblance of "life." This fusion significantly broadens its functional applications across biomedicine, actuators, and metamaterials. The escalating demand across diverse fields necessitates heightened criteria for 4DP, encompassing rapid response, multi-stimulus response, large shape change, and specific mechanical properties (e.g., high strength, high modulus) capable of accommodating varying environmental conditions. In recent years, shape memory polymers (SMPs) have garnered increasing attention among 4DP researchers due to their ease of design and preprogramming at the molecular level, facilitating controlled transformations along predictable pathways. However, 4DP of high-strength SMPs, as an indispensable part of the high-performance field, is full of challenges because the intrinsic properties of the raw materials are not well compatible with the printing principle and the printed configuration is not flexible enough. Consequently, this paper provides a concise overview of the response mechanisms and applications of five prominent high-strength SMPs utilized in 4DP: epoxy resin, poly(ether-ether-ketone), polyimide, polylactic acid, and polyurethane. Additionally, it delves into the associated challenges and prospects, offering researchers valuable insights into the potential value of high-strength SMPs within the domain of 4DP.