Fig. 6

Differences in the ultrastructure between BMSC cultured in osteogenic (a, c, e) and non-osteogenic (b, d, f) conditions, revealed by FIB milling and observed with SEM as block-face low voltage imaging. In osteogenic group the organelles were not visible, and whole cell interior was filled with electron-heavy hydroxyapatite crystals (a), the vesicular structures were filled with hydroxyapatite deposits (c), and small vesicles with hydroxyapatite crystals on their membranes were clearly visible (e); arrows show the regions of crystalizing hydroxyapatite, V shows the mineralizing vesicle, white arrowheads show small vesicles without the hydroxyapatite. In non-osteogenic group, cells have all typical organelles (b, d), including the nucleus, mitochondria and rough endoplasmic reticulum, the microvesicles released by them were complex but did not contain any electron-heavy crystals (f); N nucleus, arrows alginate fibers, V membrane microvesicle; scale bars 1 µm (a, b), 400 nm (c, d), 200 nm (e, f)