Bioinspired Twisted Artificial Muscles with Enhanced Performance for Underwater Applications

Twisted artificial muscles (TAMs) demonstrate great promise in robotic applications involving locomotion and manipulation. However, their functionality in underwater environments remains challenging due to limitations in deformation, output force, and heat dissipation especially for thermally driven TAMs. To address these challenges, a novel TAM configuration inspired by the twining structures of climbing plants that consists of braided and pre-twisted fiber bundles is proposed. This configuration achieves large deformation and high output force, reaching a contraction ratio of 40.0% under a load of 300 g. Meanwhile, a soft insulation layer inspired by the blubber layer of seals is applied to reduce heat dissipation in underwater environments, resulting in a 30.5 °C temperature difference. In addition, a rapid actuation unit is developed, which utilizes elastic energy storage and release to achieve an angular velocity of 180° s⁻¹ in water. Finally, a bionic ray driven by the proposed TAMs is developed as a demonstrator, achieving a displacement of 105 mm for straight motion and a turning angle of 30° within a single actuation cycle. These results highlight the strong potential of the proposed TAMs for underwater application.