Carbon Nanotube Artificial Muscles Multistimuli Actuation Mechanisms and Emerging Applications

Carbon nanotube (CNT)-based artificial muscles are transformative soft actuators with exceptional mechanical properties and versatile stimulus-response capabilities, making them strong candidates for next-generation applications in soft robotics, biomedical devices, and smart textiles. This Review maps the design space from simple sheets to twisted and coiled yarns, core-sheath architectures, and guest-integrated hybrids that enable precise control of tensile and torsional strokes as well as stimulus selectivity. It organizes actuation mechanisms by driving stimulus-voltage-driven electrochemical actuation and non-voltage routes including thermal, photothermal, and solvent-assisted swelling-and summarizes their working principles, performance trade-offs, and routes to multifunctional operation. Key breakthrough strategies such as unipolar actuation via polystyrene sulfonate coatings, solid-state designs eliminating liquid electrolytes, and core-sheath architectures enabling multimodal response, as well as emerging applications ranging from wearable biomedical devices to adaptive building facades are highlighted. Despite remarkable progress, challenges persist in scalable manufacturing, long-term stability, and biocompatibility. The review concludes by identifying underexplored opportunities in nanoscale parameter optimization and alternative stimuli development that could unlock unprecedented performance. As the field advances toward commercial viability, CNT-based artificial muscles are poised to bridge the gap between synthetic actuators and biological muscle, enabling a new generation of adaptive, intelligent soft systems.