Meeting Abstract
The cartilaginous skeleton of sharks and rays (elasmobranchs) comprises an unmineralized hyaline-like cartilage core sheathed in a tessellated layer of calcified cartilage, wrapped in a fibrous perichondrium. The tessellated layer is a composite, composed of minute, mineralized tiles (tesserae), anchored to one another and the surrounding tissue by a collagenous network. This tiled calcified layer allows for skeletal growth, but also provides rigidity to an otherwise flexible skeleton. However, our understanding of the mechanics of the macroscopic tiled composite is limited by the lack of knowledge of the structural interactions between tesserae. We use high-resolution SR-µCT, novel shape-based analysis algorithms and 3D printing to characterize the articulations between tesserae in round stingray Urobatis halleri. Although tesserae begin as isolated elements, they grow into contact as animals age: the resultant intertesseral joint is a complex architecture of unmineralized fibrous zones (where fibers connect adjacent tesserae) surrounded by flat regions of close contact, where tesserae are typically <2µm apart. Tesserae, unlike other natural tilings, neither overlap nor exhibit macroscopic interdigitations; we note, however, that subtle topographic features of contact zone surfaces are mirrored in adjacent tesserae. Coupled with the extreme proximity of neighboring tesserae, this creates an interlocking effect, which we verified with 3D printed tesserae. To further characterize this effect, we developed a mesh-based shape analysis protocol to evaluate local and global interlocking of adjacent tesseral edges, defining variables relevant to skeletal mineralization, as well as to the mechanics of tessellated cartilage and future bio-inspired tessellations.
