IMX Talks - Hierarchical structure and functionality of the mineralized tissue of shark vertebral centra

Shark vertebral bodies (centra) consist of cartilage which is reinforced by nanoparticles of bioapatite mineral. The centra possess remarkable resistance to millions of cycles of in vivo strains exceeding 4-8%. These strains are enormous for a mineralized tissue, and the centra have evolved to achieve this performance through a hierarchy of structures spanning dimensions from centimeters to nanometers. Since 2019, there has been significant progress in characterizing the various structures, and results will be presented from larger to smaller spatial dimensions, i.e., macro-, micro- and nano-scales. Laboratory microComputed Tomography (microCT) with 15-20 µm volume elements (voxels) revealed complex microstructure related to centra’s growth processes. Relatively low resolution, 3D energy dispersive diffraction mapping uncovered zones with different (mineral) crystallographic texture. At the one micrometer level, synchrotron microCT with 0.67 µm voxels quantified 3D centra microstructures: these consist of an interconnected array of 5-15 µm thick mineralized plates (trabeculae) separated by a similarly-sized continuous network of unmineralized soft tissue and fluid. Synchrotron microCT observation of in situ loading of small blocks demonstrated that the deformation is accommodated by rotation/deflection of the centra’s trabeculae. Synchrotron microbeam diffraction of small blocks during in situ loading revealed the mineral phase is carrying only small strains. Finally, prospects for continuing studies are discussed.