Effects of different extremely low-frequency electromagnetic fields on osteoblasts

It is well known that the extremely low-frequency electromagnetic field (EMF) can promote the healing of bone fractures, but its mechanism remains poorly understood. The purpose of this study was to examine the response of neonatal rat calvarial bone cells to the rectangular electromagnetic field (REMF), triangular electromagnetic field (TEMF), sinusoidal electromagnetic field (SEMF), and pulsed electromagnetic field (PEMF). The stimulatory effects of EMF were evaluated by the proliferation (methyltetrazolium colorimetric assay), differentiation (alkaline phosphatase (ALP) activity), and mineralization (area of mineralized nodules of the cells). REMF treatment of osteoblasts increased cellular proliferation and decreased ALP activity (p < 0.05). TEMF had an accelerative effect on the cellular mineralized nodules (p < 0.05). SEMF treatment of osteoblasts decreased the cellular proliferation, increased ALP activity, and suppressed mineralized nodules formation (p < 0.05). PEMF promoted the proliferation of osteoblasts, inhibited their differentiation, and increased the mineralized nodules formation (p < 0.05). Moreover, the effects of PEMF on osteoblasts were concerned with the extracellular calcium, P2 receptor on the membrane, and PLC pathway, but the response of osteoblasts on SEMF was only related to PLC pathway. The results suggested that the waveforms of EMF were the crucial parameters to induce the response of osteoblasts.