Segmentations in fins enable large morphing amplitudes combined with high flexural stiffness for fish-inspired...

Fish fins do not contain muscles, yet fish can change their shape with high precision and speed to produce large and complex hydrodynamic forces-a combination of high morphing efficiency and high flexural stiffness that is rare in modern morphing and robotic materials. These "flexo-morphing" capabilities are rare in modern morphing and robotic materials. The thin rays that stiffen the fins and transmit actuation include mineral segments, a prominent feature whose mechanics and function are not fully understood. Here, we use mechanical modeling and mechanical testing on 3D-printed ray models to show that the function of the segmentation is to provide combinations of high flexural stiffness and high morphing amplitude that are critical to the performance of the fins and would not be possible with rays made of a continuous material. Fish fin-inspired designs that combine very soft materials and very stiff segments can provide robotic materials with large morphing amplitudes and strong grasping forces.