Fig. 3.

Hierarchical structure of bone. a Collagen molecules, connected by crosslinks, and embedded mineral particles. b Collagen fibrils connected by an extrafibrillar matrix rich in proteoglycans and non-collagenous proteins. c Lamellar units form (f) osteonal and (e) fibrolamellar bone. The dashed line in f indicates a cement line around the osteon. d Woven bone lacks such highly organized fibril arrangement. g–i Corresponding cell networks to images d–f. All images show sections of long bones (j) in different species (woven: murine; fibrolamellar: ovine; osteonal: equine). Different bone types and different size levels exhibit varying interfaces. The red arrows indicate the sequence of hierarchical levels (from the smallest to largest) for the different bone types (Color figure online)