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    • To date there have not

    2018-11-06

    To date, there have not been a consistent set of EMF stimulus parameters used among research groups reported in the literature; however, results suggest that EMF promotion of bone ECM deposition in vitro is more far more efficient in osteoblasts differentiated from hBMSCs than from γ-Secretase inhibitor IX of other tissues (Bianco et al., 2013). Sun et al. have investigated the effect of PEMF on the proliferation and differentiation potential of human hBMSCs. EMF stimulus was administered to cells for 8h per day during the culture period. The EMF applied consisted of 4.5ms bursts repeating at 15Hz, and each burst contained 20 pulses. Results showed 59% more viable hBMSCs were obtained in the EMF-exposed cultures at 24h after plating and 20–60% higher cell densities were achieved during the exponentially expanding stage. Many newly divided cells appeared from 12 to 16h after the EMF treatment; however, cytochemical assays and immunofluorescence analysis showed multilineage differentiation of EMF-exposed hBMSCs to be similar to that of the control group, which used only standard growth media (Sun et al., 2009). Bone tissue engineering typically uses biomaterial scaffolds, osteoblasts, or cells that can become osteoblasts, and biophysical stimulation to promote cell attachment and differentiation. Saino et al. tested the effects of EMF on hBMSCs seeded on gelatin cryogel disks and compared with control conditions without EMF stimulus. Treatment with EMF (at 2mT intensity and 75Hz frequency) increased the cell proliferation and differentiation, as well as enhanced the biomaterial surface coating with bone ECM proteins (Saino et al., 2011). Using this approach, the gelatin biomaterial, coated with differentiated cells and their ECM proteins, has the potential to be used in clinical applications as an implant for bone defect repair. For example, under the appropriate culture conditions, PEMF enhances the osteogenic effects of BMP-2 on hBMSCs. Thus, PEMF could potentially be used clinically to stimulate bone formation from transplanted hBMSCs. Specific studies investigating whether the effects of PEMF on osteogenic cells were substrate dependent, and could also regulate osteoclastic bone resorption. Schwartz et al. treated hBMSCs and human osteosarcoma cell lines (MG63 cells, SaOS-2 cells) capable of osteoblastic differentiation with BMP-2, then cultured them on calcium phosphate (CaP) or tricalcium phosphate (TCP) to test their response to a 15Hz PEMF at either 4.5ms bursts or 20 pulses repeated for 8h/day. Outcomes were determined to be a function of the decoy receptor, osteoprotegerin (OPG), and RANK ligand (RANKL) production, both of which are associated with the regulation of osteoclast differentiation. Results suggested that when osteogenic cells were cultured on CaP, PEMF decreased cell number and increased production of paracrine factors associated with reduced bone resorption such as OPG (Schwartz et al., 2009). RANKL was unaffected, indicating that the OPG/RANKL ratio was increased, further supporting a surface-dependent osteogenic effect of PEMF. Moreover, effects of estrogen were surface-dependent and enhanced by PEMF, demonstrating that PEMF can modulate osteogenic responses to anabolic regulators of osteoblast function. Therefore, PEMF shows promising results when used in conjunction with complex 3-D cell culture systems as a strategy for tissue engineering approaches.
    Influence of EMF on chondrogenic differentiation of hBMSCs Chondrogenesis is initiated by condensation of embryonic mesenchyme, which induces differentiation of mesenchyme into chondrocytes, and the subsequent secretion of the molecules that form the ECM (Charbord et al., 2011). EMF has been shown to exert beneficial effects on cartilage tissue, and differentiated hBMSCs are being investigated as an alternative approach for cartilage repair. Repair, replacement or regeneration of cartilage tissue is challenging due to the fact that injured articular cartilage is not easily able to repair itself and often the repair of articular cartilage fails because there is a lack of an abundant source of cells to accelerate the healing process and promote host tissue. Research has demonstrated that it is not easy to obtain a sufficient number of hBMSCs for therapeutic use after expansion in vitro, because after thirty population doublings (PDs), hBMSCs exhibit replicative senescence, which blocks their ability to differentiate. However, in vivo studies have shown that PEMF can be used to promote proliferation of endogenous chondroblasts (Fitzsimmons et al., 2008), and suppress inflammatory reactions induced by the repair treatment, thereby enhancing cartilage regeneration (Fini et al., 2013). Successful articular cartilage tissue engineering relies largely on identifying appropriate cell sources, designing the proper formulations of 3D scaffolding matrix, bioactive agents, differentiation stimulants and safe gene delivery (Ahmed and Hincke, 2014).