FIG. 3.

Scanning electron microscopy (SEM) observation of MSCs during osteogenic differentiation. (A–C) Day 10. (A) Many cytoplasmic processes (arrowheads) and punctate globular vesicle structures (arrows) were observed in the extracellular spaces of long spindle-shaped MSCs (asterisks). Scale bar: 20 μm. (B) Magnification of the dotted square in (A). The globular vesicles (arrows) were intertwined with collagen fibrils. Scale bar: 5 μm. (D–F) Day 30. (D) MSCs showed a planar and solid structure. Scale bar: 10 μm. (E) Magnification of the dotted square in (D). Fibrous and vesicle structures were rarely observed. The remaining vesicle (asterisk) was almost embedded within the solid structure. Scale bar: 1 μm. (C, F) energy-dispersive X-ray spectroscopy (EDX) analyses of the areas shown in SEM images (A) and (D), respectively. Energy peaks in the EDX graph correspond to elemental phosphorous (P), calcium (Ca), carbon (C), and oxygen (O). Insets: The yellow and blue dots represent the elemental distribution of calcium and phosphorous, respectively. (C) Elemental calcium and phosphorous accumulated in the fibril and vesicle structures in the intracellular spaces by day 10. (F) The surface of the solid structure was covered with elemental calcium and phosphorous on day 30. Color images available online at www.liebertpub.com/scd