Figure 7.

Bone is a hierarchically structure composite, composed of roughly equal volume fractions of organic and inorganic phases, along with around 10% water from the hydrated collagen matrix (or ~65:25:10 wt% of HA:collagen:H₂O). (a) The microstructure of bone consists of concentric lamellae of mineralized collagen which wrap around the vasculature and nerves, referred to as osteons. (b) The focus of the discussion in this report is on bone’s nanostructured architecture, which can be seen via TEM to consist of nanocrystals of hydroxyapatite embedded within the collagen fibril. (inset) Selected area electron diffraction shows that the HA crystals are crystallographically oriented with their [001] axes roughly parallel to the long axis of the collagen fibril (indicated with arrow), and provide the dark striated contrast seen in this mineralized fibril extracted from equine cortical bone. The native banding pattern of type-I collagen can be observed due to the infiltration of the electron dense mineral, and staining was not used. Bar = 100 nm. (Reprinted with permission from ref 160. Copyright 2007 Elsevier B.V..)