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. 2020 Jul 8;21(14):4820. doi: 10.3390/ijms21144820

Figure 4.

Figure 4

Electron micrographs depict two types of amorphous calcium phosphate (ACP) precursors. (A) Large spherical particles (50–100 nm) with remarkable electron-dense areas (inset, yellow arrows) are typical of chemically synthetized nanoparticles (scale bar = 50 nm). (B–D) Biologically synthetized agglomerates of much smaller granules composed of hydroxyapatite (HAP) crystallites (5–10 nm; blue arrow) produced by human cells grown for 7 days in MEMα/10% FBS with αGP (2 mM) and CIP (1 U/mL). Scale bars: (B) = 100 nm; (C) = 20 nm; (D) = 2 nm. (E) Boundaries (green arrows) formed between HAP grains (scale bar = 5 nm).