Composite model of the shark's skeleton in bending: A novel architecture for biomimetic design of functional compression bias

Much of the skeleton of sharks, skate and rays (Elasmobranchii) is characterized by a tessellated structure, composed of a shell of small, mineralized plates (tesserae) joined by intertesseral ligaments overlaying a soft cartilage core. Although tessellated cartilage is a defining feature of this group of fishes and has been maintained for millions of years, the significance of this skeletal tissue type - particularly from a mechanical perspective - is unknown. A cross-sectional model, based on empirical material property and morphological data, was developed in the present work to analyze the function of intertesseral joints in regulating the stress distribution within the skeletal tissue during bending. The results indicate that this structure distributes more stress to the tesserae loaded in compression when compared to those loaded in tension. A functional bias towards compression has also been observed for bone, but with the formation of microcracks in the region under greatest tension. The present model demonstrates how functional compression bias can also be achieved in tessellated cartilage structures but in the absence of microcracking. This behavior provides possible advantages including increasing the resistance to fatigue damage as well as mitigating the risk of tearing under excessive bending loads. (C) 2010 Elsevier B.V. All rights reserved.