Figure 1.

Bone at different hierarchical levels. At a macroscopic level, bone consists of the cortical and the trabecular bone compartments. On a microstructural level, the trabecular network and the Haversian system are observed, which are typically formed by bone lamellae. At a lower hierarchical level, bone ultrastructure comprises mineralized collagen fibrils, which are arranged randomly or in bundles. This review presents the methods that enable investigations of the organization of the ultrastructure. (a) Human femur cut in half and imaged using scanning electron microscopy (SEM). (Image from [1] with kind permission of the Royal Society of Chemistry.) (b) Trabecular network imaged using SEM in backscattered electron mode. (Image from [2] with kind permission of Humana Press, Inc.) (c) Haversian system imaged using synchrotron radiation-based computed tomography (SR-CT). (Image from [3] with kind permission of SPIE.) (d) Lamellar structure of trabecular bone imaged using polarized second harmonic generation (pSHG) imaging. (Image from [4] with kind permission of the Materials Research Society.) (e) Lamellar structure of cortical bone imaged using circularly polarized light microscopy. (Image from [5] with kind permission of John Wiley and Sons, Inc.) (f) Mineralized collagen fibril bundles imaged using transmission electron microscopy (TEM). (Image from [6] with kind permission of PLoS.) (g) Single mineralized collagen fibril and diffraction pattern (inset) showing the orientation of unit crystal cells imaged using TEM and electron diffraction, respectively. (Image from [7] with kind permission of ACS Publications.) (Online version in colour.)