ure 2, cells stimulated with the electromagnetic field had a higher proliferation rate compared to unstimulated MSCs. Thus PEMF treatment for 14 days did not have any negative effect on MSC proliferation; rather, it enhanced the proliferative activity of these cells.

![Results of the MTT assay on mesenchymal stem cells (MSCs) exposed to an electromagnetic field (0.2 mT, 15 Hz, 6 hours/day) to estimate the number of cells after 5, 10 and 14 days. Unstimulated cells cultured for 5, 10, and 14 days were used as the control groups (P\<0.05).\
PEMF; Pulsed electromagnetic field.](Cell-J-19-34-g02){#F2}

Effects of electromagnetic field intensity
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We conducted real-time PCR analysis of the effects of field intensity on gene expression. MSCs from two separate groups were exposed to 0.1 mTor 0.2 mT-intensity fields with similar field parameters of 15 Hz frequency and 6 hours application of PEMF per day for 10 consecutive days. As shown in Figure 3, the 0.2 mT intensity field resulted in a greater increase in expression of osteoblastic genes compared to the 0.1 mT field.

![The effects of two different electromagnetic field intensity levels (0.1 mT and 0.2 mT) at 15 Hz, 6 hours/day for 10 consecutive days on the expressions of *Runx2* and *Ocn* according to realtime polymerase chain reaction (PCR). UMR-106 was the positive control. As shown, 0.2 mT intensity was more influential in stimulating mesenchymal stem cells (MSCs) to express osteogenic markers (P\<0.05).](Cell-J-19-34-g03){#F3}

Effects of electromagnetic field exposure duration
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We tested three different durations of daily exposure in order to find the most influential duration. Stem cells were stimulated with PEMF (0.2 mT and 15 Hz) for 10 consecutive days with daily exposure durations of 2, 4, or 6 hours. We observed the highest expression levels of *Runx2* and *Ocn* in the group that received 6 hours of daily exposure to PEMF ([Fig.4](#F4){ref-type="fig"}).

![The e