Programmable carbon nanotube/shape memory polymer composite fibers with both high actuation strain and stress

Shape memory composite fiber actuators have been extensively studied due to their excellent flexibility, weavability, actuation performance, and low-cost continuous fabrication. However, integrating both high actuation strain and high actuation stress within a single fiber-based material system remains a key challenge. In this study, we developed a high-performance shape memory composite fiber using a scalable wet-spinning process. The fiber exhibited 15 MPa actuation stress and up to 76% actuation strain within 1 s during thermal shrinkage, along with a high work capacity of 1339 J kg^-1. The electrical actuation achieved through efficient Joule heating also demonstrated 13 MPa actuation stress. Mechanistic analysis revealed excellent interfacial bonding between carbon nanotubes (CNTs) and the polymer (polyurethane) matrix. Furthermore, the combined effect of CNTs and crystalline regions promoted tensile alignment of polymer chains, leading to improved mechanical and actuation properties of the fiber. This study demonstrated that the fiber structure enabled integrated actuation and programmed deformation in various 2D/3D configurations, with promising applications in future intelligent soft robotics, wearable devices, and smart textiles.