Review of Thermally Activated Twisted Coiled Polymer Actuators: A Materials Science Perspective

ABSTRACT Twisted and Coiled Polymer Actuator (TCPAs) are recognized as a promising class of soft actuators due to their high energy efficiency, low weight, and actuation performance. These actuators are typically based on thermally or electrothermally responsive polymer fibers and combine high strain and force output with tunable stiffness. As a result, they are considered for applications in robotics, prosthetics, and wearable systems. This article provides a comprehensive overview of the principles, fabrication strategies, and materials characterization methods of TCPAs, including thermomechanical, structural, and morphological analysis at different length scales. It further correlates polymer microstructure, processing history, and actuator geometry with key performance metrics such as stroke, blocking force, and cyclic stability. Furthermore, recent advances in performance optimization are discussed, covering approaches to accelerate thermal management, mitigate creep and fatigue, and improve controllability through integrated sensing and modeling. The application landscape of TCPAs in biomedical engineering, soft robotics, and adaptive textile structures is highlighted, followed by a critical assessment of current challenges and future research directions in materials design, scalable manufacturing, and standardized characterization protocols. The present work serves as a resource for researchers seeking a materials science perspective on the design, characterization, and application of twisted coiled polymer actuators.