Pulsed electromagnetic field may accelerate in vitro endochondral ossification.

Recapitulation of embryonic endochondral bone formation is a promising alternative approach to bone tissue engineering. However, the time-consuming process is one of the reasons the approach is unpractical. Here, we aimed at accelerating the in vitro endochondral ossification process of tissue engineering by using a pulsed electromagnetic field (PEMF). The rat bone marrow-derived stem cells were chondrogenic or hypertrophic differentiated in a three-dimensional pellet culture system, and treated with different intensities of PEMF (1, 2, and 5 mT with modulation frequency 750 Hz, carrier frequency 75 Hz and a duty ratio of 0.8, 3 h/day for 4 weeks). The effects of PEMF on hypertrophy and endochondral ossification were assessed by safranin O staining, immunohistochemistry, and quantitative real-time polymerase chain reaction. The results suggest that PEMF at 1, 2, and 5 mT may inhibit the maintenance of the cartilaginous phenotype and increase cartilage-specific extracellular matrix degradation in the late stage of chondrogenic differentiation. In addition, among the three different intensities, only PEMF at 1 mT directed the differentiation of chondrogenic-induced stem cell pellets to the hypertrophic stage and promoted osteogenic differentiation. Our findings provide the feasibility to optimize the process of in vitro endochondral ossification with PEMF stimulation.