OBJECTIVETo investigate the effect of exposure to static magnetic fields (SMFs) of 3.9 mT on proliferation and differentiation of osteoblasts in vitro.

METHODSThe newborn rat calvarial osteoblasts were isolated by enzyme digestion and randomly divided into 9 groups after one passage. The intensity of the SMFs was 3.9 mT. The cells were exposed in the SMFs for 0 (control group), 0.5, 1.0, 1.5, 2.0, 2.5, 3, 3.5 and 4.0 h groups respectively. They were observed under the contrast phase microscope each day. After 48 h, cell proliferation was assayed by MTT method. The alkaline phosphatase (Alkaline Phosphatase, ALP) activities and calcium content were measured after 3, 6, 9, and 12 days exposed with SMFs. The ALP positive colonies were histochemically stained after 8 days and the calcified nodules were stained by Alizarin Bordeaux after 10 days; BMP-2, Runx-2 and Opg mRNA expression were measured after SMFs treatment in 0, 24, 48 and 72 h.

RESULTSContrast with control group, all SMFs groups enhanced cell proliferation (P < 0.01 or P < 0.05), and they promoted maturation and mineralization of the osteoblasts. The results showed that SMFs improved the ALP activity, promoted calcium content, boost BMP-2, Runx -2 and Opg mRNA expression.

CONCLUSIONThe cells exposed to the SMFs of 3.9 mT at 2.5 h apparently promote proliferation and differentiation of osteoblasts in vitro.