The effects of exposure to 15-nm, 30-nm SiO
and micro-sized SiO
particles on cell cycle of HaCaT cells. A shows the representative images of cell cycle of HaCaT cells after 24-h exposure to 15-nm, 30-nm or micro-sized SiO2particles at the dosages of 2.5 μg/mL, 5 μg/mL, 10 μg/mL or 15 μg/mL. B shows the results of the quantitative cell cycle analysis. Values were mean ± SD from three independent experiments. *p < 0.05, **p < 0.01 vs control cells; #p < 0.05 vs cells exposed to 30-nm SiO2 particles; &p < 0.05 vs cells exposed to micro-sized SiO2 particles.