Design Strategies for Flexible Skeletons of Underwater Bionic Robots

Underwater bionic robots, by mimicking the efficient promotion mechanism of aquatic animals, have significantly overcome the mobility and noise limitations of the traditional rigid submersibles, which demonstrate unique value in resource exploration and ecological monitoring. As the core carrier for realizing the bionic implementation, the flexible skeleton not only determines the efficiency of the transmission between deformation and driving force but also directly relates to the degree of integration of structure, perception, and actuation. This paper focuses on flexible skeletons, first systematically outlining two major technical routes: purely soft continuous skeletons and hinge-hybrid joint skeletons. Based on this, it proposes a third, entirely new technical route: an integrated smart material skeleton. Subsequently, popular examples were selected and analyzed in accordance with the above routes and methods to evaluate their performance. Ultimately, the key challenges currently faced in terms of collaboration, environmental tolerance, and large-scale manufacturing are summarized. Furthermore, targeted improvement strategies are proposed, including multi-material hybrid printing, gradient stiffness topology, and distributed intelligent material-driven systems, with a vision for the next generation of flexible skeletons where “structure is the actuation mechanism and the skeleton is the sensing mechanism.