Biomechanical Design of the Mantis Shrimp Saddle: A Biomineralized Spring Used for Rapid Raptorial Strikes

Stomatopods deliver one of the fastest strikes in the animal kingdom using their powerful "dactyl clubs." This kinematic performance is enabled by a power amplification device whereby elastic energy is stored in a saddle-shape mineralized bilayer structure. We combined a set of comprehensive micro-mechanical measurements with finite element modeling (FEM) to quantitatively elucidate the saddle biomechanical design. Dynamic nano-scale testing reveals that viscoelastic dissipation is minimized in the highly mineralized layer, whereas micro-bending experiments on miniature cantilevers highlight the critical role of the bilayer arrangement in optimizing storage of elastic energy. FEM shows that the saddle shape prevents stress concentration and the stresses remain well within the elastic range during loading, while the neutral surface coincides with the bilayer interface to prevent interfacial delamination. The study unveils the multi-scale design behind the intriguing ability of the saddle to store a high density of elastic energy using stiff but intrinsically brittle materials.