Fig. 6.

Hierarchical Levels 9, 10 and 11 of bone mineral organization: stacks, plates and needles. (A) STEM tomography of a FIB-milled foil of lamellar bone. The contrast originates from the crystallites’ electron density, and all the crystallites are segmented (using a deep neural network), volume-rendered, and color-coded following a watershed transformation. (B) Twenty digitally separable crystallite aggregates are shown in situ (in unmodified orientations) within the same STEM tomographic volume as in A. The remaining tomogram volume is rendered transparent. The yellow inset in the bottom right corner of panel B schematically illustrates the orientation of collagen fibrils within the tomogram rendered in panels A and B. (C) A gallery of 20 digitally separable crystallite aggregates ranging in size between 10⁶ nm³ and 10⁵ nm³ (in a descending order). Individual aggregates are intentionally shown in re-orientations different from those orientations observed in situ.