Dual-Functionality, Bio-Friendly Artificial Muscles for Actuation and Motion Sensing in Smart Wearable Systems

Herein, we report a biofriendly, air-operating electrochemical platform based on a unipolar coiled carbon nanotube (CNT) yarn artificial muscle that can operate either as an ionic actuator or as an ionotronic strain sensor. The device comprises two coiled CNT yarn electrodes coated with complementary ion-selective eutectogels, consisting of fixed-charge polymer networks swollen with a diluted deep eutectic solvent (DES), enabling selective ion transport. Under an applied potential difference, the complementary electrochemical responses of both electrodes produce synchronized unipolar contraction, whereas in sensing mode the device generates a strain-dependent open-circuit voltage (OCV) variation. In actuation mode, the device achieves a maximal reversible contractile stroke of 2.9% under a 90 mN pre-load. In sensing mode, it operates as a self-powered strain sensor with a sensitivity of 0.5 mV.%^-1. Poisson-Nernst-Planck modelling is consistent with the proposed mechanism of strain-induced ion redistribution within the quasi-solid-state matrix. Two yarn artificial muscles were woven into a custom-made, bi-stretch auxetic structure with a folded zigzag geometry, enabling parallel actuation and strain monitoring, delivering peak-to-peak OCV signals of 4 mV at 10% extension. Finally, we demonstrate a wireless wearable armband for real-time motion monitoring, highlighting the potential of this platform for smart fabrics, wearable electronics, and adaptive soft robotics.