Leveraging Inter-Bundle Anchoring Effect to Induce Static and Dynamic Twist-Stability in Multifunctional Carbon Nanotube Coiled Yarn Hydro-Actuators

Carbon nanotube (CNT) coiled yarns have revolutionized 1D yarn actuators. However, their intrinsic twist-instability poses significant challenges, limiting their practical applicability. In this study, static and dynamic twist-stability are imparted to CNT coiled-yarn hydro-actuators by leveraging the inter-bundle anchoring effect. An inter-bundle anchor (IBA) is embedded within the coiled yarn by continuously twisting CNT sheets coated with a polymer agent. This integration enhances the inter-bundle connectivity within the yarns, ensuring twist retention of 97.5% in static mode. In dynamic mode, the IBA functions as an internal return spring, providing high actuation reversibility with torsional elasticity above 0.8 across repeated cycles. Furthermore, electrothermal recovery via Joule heating improves the actuation frequency to 0.039 Hz, and the pseudocapacitive properties of the polymer agent enable energy storage with an areal capacitance of 79.0 mF cm⁻². These advancements underscore the potential of CNT-coiled yarn hydro-actuators for use in humidity monitoring, adaptive electronics, and various wearable and implantable applications.