Twisted String Actuators in Wearable Robotics: Review and Perspective across Rehabilitation, Assistance,...

Twisted String Actuators (TSAs) have emerged as a compelling soft actuation paradigm for wearable robotic systems, offering high force output within a compact, lightweight, and mechanically compliant form factor. This systematic review provides a comprehensive analysis of TSA-based wearable devices reported in the literature between 2013 and 2026, synthesizing 34 functional prototypes identified through a structured search of Scopus and Google Scholar databases. Devices are categorized according to two orthogonal frameworks: anatomical target segment and primary application domain. The review examines the biomimetic foundations of TSA operation, its analogy to the human musculoskeletal system, and the key mechanical design decisions governing actuator configuration, force transmission strategy, degrees of freedom, structural substrate, and sensing modality. A progressive shift from rigid toward soft and hybrid architectures is identified across the review period, consistent with user acceptance requirements in clinical and industrial settings. Intent-driven control strategies fusing surface electromyography and inertial measurement units have emerged as the dominant paradigm for assistive and augmentation devices. Persistent open challenges include the non-linear kinematics of TSA force-displacement relationships, the near-total absence of long-term mechanical durability data, and the lack of real-world clinical validation. Notable anatomical gaps, particularly at the shoulder and cervical complex, are identified as high-priority directions for future development. Collectively, the findings position TSA-based wearables as a rapidly maturing technology with strong potential for translation into mainstream rehabilitation and human augmentation platforms.