Investigating

the role of hierarchy on th evidence of a crucial synergy between h Pu hit ar f tre is, tio e n te b ine ’ ’ a pr nano-fibers or platelets, which are typically embedded within divided into six major hierarchical levels, from collagen fibrils n strands), to collagen fibers collagen fibers, to secondary cles’ ’ of bundles, to groups of don itself. At all hierarchical er by sheaths of stabilizing has an exterior sheath of n. Hierarchy and functional properties of natural materials ength scales, i.e. the overall cture rarely reflect the bulk ting it, and rather they depend grading architecture.1,16 Virtually all stiff biological materials are composites with the Dynamic Article LinksC<Nanoscale Cite this: Nanoscale, 2012, 4, 1200 www.rsc.org/nanoscalebLaboratory of Bio-Inspired Nanomechanics ‘‘Giuseppe Maria Pugno’’,the inner architecture, the porosity and the shape of the bone. The mechanical properties of bone are well known to strongly depend on all these parameters.7–11 The same behavior is found in other natural materials, e.g. wood,12 nacre,13,14 spider silk,15 etc. smallest components mostly in the size-range of nanometres.17 In some cases (plants or insect cuticles, for example), a polymeric matrix is reinforced by stiff polymer fibers, such as cellulose or keratin.12 Even stiffer structures are obtained when a (fibrous) polymeric matrix is reinforced by hard particles, such as carbonated hydroxyapatite in the case of bone or dentin.18 The general mechanical performance of these composites is quite remarkable. In particular, they combine two properties which ar