Objective      To evaluate the effects of the static magnetic field (SMF) on bone marrow mesenchymal stem cells (MSCs) osteogenic differentiation and explore the possible mechanism.       Methods      Density gradient centrifugation-isolated rat bone marrow mononuclear cells were cultured in vitro. MSCs of the 3rd and 4th passages were chosen as target cells. After osteogenic induction

the MSCs were exposed to SMF at 0

0.5

1.5

2 or 3 mT. The activity of alkaline phosphatase (ALP) was assayed with IFCC. The calcium nodes of MSCs were stained by alizarin red. The concentrations of osteocalcin (OCN) and type Ⅰ collagen were measured by radioimmunoassay. Western blotting was used to detect the phosphorylation of MAPK P38. Specific P38 inhibitor SB253580 was added into the culture media of MSCs to investigate the role of P38 in this process.       Results      SMF

especially at 1.5 and 2 mT

increased the activity of ALP

the number of calcium nodes and the concentrations of OCN and type Ⅰ collagen in MSCs. SMF activated MAPK P38 signaling molecule. Blocking the P38 signal pathway by SB253580 partially reversed the effects of SMF on osteogenic differentiation of MSCs.       Conclusion      SMF promotes the osteogenic differentiation of MSCs and the P38 MAPK pathway is involved in this process.