MSC viability, differentiation, and proliferation after labeling with I-fSiO4@SPIOs or (125)I-fSiO4@SPIOs. A) CCK-8 analysis of cell viability after labeling with 0.1 m m Fe I-fSiO4@SPIOs for different periods of time (a) or with different concentrations of I-fSiO4@SPIOs for 60 min (b). c) Cell viability after labeling with different doses of (125)I-fSiO4@SPIOs (0, 2, 10, 20, and 100 μCi/million cells). Data are presented as mean ± SD, n = 3 per group. B) Oil red and Alizarian Red S staining showed that I-fSiO4@SPIO- and (125)I-fSiO4@SPIO-labeled MSCs differentiated into adipocytes (a–c, arrows) and osteoblasts (d–f, arrows). Bar = 50 μm. C) Anti-BrdU staining of I-fSiO4@SPIO- and (125)I-fSiO4@ SPIO-labeled MSCs (b,c). d–f) 3D confocal images of the proliferation of MSCs. Scale bar = 20 μm.