Studying the Effect of Shape in Fast Biological Springs

Michael Rosario, University of Massachusetts, Amherst

Although biomechanical analyses of elastic mechanisms demonstrate the role of elasticity in extremely fast movements, many studies overlook the details of how the shapes of these mechanisms can impact their performance. Often, these studies measure either the mechanical response or the material composition of these springs. However, experiments that attempt to understand the effect of shape in these mechanisms are scarce. In this study, we ask two main questions: 1) How can we use measures of cross-sectional shape to understand the effect of morphology on elastic function, and 2) can the morphology of a biological spring explain its mechanical response? In order to answer these questions, we created cross-sectional models from microcomputed tomography scans of the appendages of mantis shrimp. These crustaceans use elastic energy to generate strikes with over 500 N of force and with accelerations over 100 km/s². In previous studies, the spring stiffness was measured for species of different body sizes and showed no statistical relationship between stiffness and body size. Additionally, experimental work suggested that the saddle, a single component of the multicomponent spring in mantis shrimp, functions more as structural support in species with more dorsally positioned saddles than in species with medially positioned saddles. Here, we measure the stiffness efficiency of the cross-sections of different species, and assess the functional consequence of having dorsally positioned saddles. Cross-sectional efficiency is similar for all species in this study, which is consistent with previously published data. Additionally, dorsally positioned saddles are predicted to contain the highest stressed point in spring compression, supporting the hypothesis that dorsally positioned saddles play a larger role in structural support than in elastic energy storage. These findings highlight the potential importance of understanding the effect of spring shape on elastic function.

Abstract Author(s): Rosario, M.V., Patek, S.N.