Timing of Pulsed Electromagnetic Field Stimulation Does Not Affect the Promotion of Bone Cell Development

Pulsed electromagnetic field (PEMF) devices have been used clinically to promote the healing of surgically resistant fractures in vivo. However, there is a sparsity of data on how the timing of an applied pulsed electromagnetic field effects the osteogenic cells that would be present within the fracture gap. The purpose of this study was to examine the response of osteoblast-like cells to a PEMF stimulus, mimicking that of a clinically available device, using four protocols for the timing of the stimulus. The PEMF signal consisted of a 5ms pulse burst (containing 20 pulses) repeated at 15Hz. Cultures of a human osteosarcoma cell line, SaOS-2, were exposed to the four timing protocols, each conducted over three days. Protocol one stimulated the cells for eight hours each day, protocol two stimulated the cells for 24 hours on the first day, protocol three stimulated the cells for 24 hours on the second day and protocol four stimulated the cells for 24 hours on the third day. Cells were seeded with either 25,000 or 50,000 cells/well (24 well cell culture plates). All assays showed reduced proliferation and increased differentiation (alkaline phosphatase activity) in the PEMF stimulated cultures compared with the control cultures, except for protocol four alkaline phosphatase measurements. No clear trend was observed between the four protocols, however this may be due to cell density. The results indicated that an osteoblast-like cell line is responsive to a 15Hz PEMF stimulus, which will stimulate the cell line to into an increasing state of maturity.