On the mechanistic origins of toughness in bone

On the mechanistic origins of toughness in bone Maximilien E. Launey 1 , Markus J. Buehler 2 , and Robert O. Ritchie 1,3 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94709; email: MELauney@lbl.gov Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139; email: mbuehler@MIT.EDU Department of Materials Science and Engineering, University of California, Berkeley, California 94720, email: RORitchie@lbl.gov Abstract: One of the most intriguing protein materials found in Nature is bone, a material composed out of assemblies of tropocollagen molecules and tiny hydroxyapatite mineral crystals, forming an extremely tough, yet lightweight, adaptive and multi‐functional material. Bone has evolved to provide structural support to organisms, and therefore, its mechanical properties are of great physiological relevance. In this article, we review the structure and properties of bone, focusing on mechanical deformation and fracture behavior from the perspective of the multi‐dimensional hierarchical nature of its structure. In fact, bone derives its resistance to fracture with a multitude of deformation and toughening mechanisms at many of these size‐scales, ranging from the nanoscale structure of its protein molecules to its macroscopic physiological scale.