Variable Stiffness Structures in Biomimetic Robotic Fish: A Review of Mechanisms, Applications, and Challenges. - Shao, Hua; Lin, Cong; Yang, Zhoukun; Deng, Luanjiao; Yang, Jinfeng; He, Xianhong; Xie, Fengran (Biomimetics (2313-7673), 2026)