Biomedical Engineering Reference
In-Depth Information
osteoblasts. The OPG expression was upregulated and the RANKL concen-
tration was downregulated, compared to the control group.
In another study [44], researchers investigated the effect of PEMF with
parameters modified by clinical bone stimulator devices and concluded that
OPG might be a potential intermediary involved in the interplay between
PEMF stimulation and osteoclastogenesis. Where appropriate, PEMF inten-
sities could either promote or suppress OPG expression in the osteoblastic
lineage. Moreover, the osteogenesis effect of PEMF was accompanied by a
decrease of RANKL. The research of Schwartz et al. [45] also demonstrated
that PEMF induces cells in the osteoblast lineage to express OPG.
Several further studies have demonstrated that PEMF causes osteoblasts to
produce other paracrine factors, including TGF-β1, prostaglandin E2 (PGE
2
),
and bone morphogenetic protein-2 [46-48]. Moreover, macrophage colony-
stimulating factor (M-CSF) has been shown to decrease after PEMF exposure
[44] and bone morphogenetic protein-2, -4, and -5 was found to increase in
osteoblasts after PEMF application [49,50]. However, these observations were
not consistent in the literature; as a result, they are not included in the effects
of PEMF on bone remodeling in the model in this study.
Unlike drug administration, PEMF stimulation can produce a local con-
centration of growth factor synthesis, without any systemic side effects.
It is important, however, to bear in mind that, as with a drug, the dosage of
physical stimulus is fundamental if positive effects on osteogenesis are to
be produced. The biological effects of PEMF stimulation depend not only
on the treatment time but also on signal characteristics such as intensity,
waveform, frequency, and length of the signal [51]. The work reported in
Zhang et al. [52] indicates that PEMF is the most responsive, compared with
other waveforms such as rectangular electromagnetic fields (REMFs), trian-
gular electromagnetic fields (TEMFs), and sinusoidal electromagnetic fields
(SEMFs), in terms of their effects on the proliferation and differentiation of
osteoblastic cells.
With regard to the different types of PEMF, Bassett, Mitchell, and Gaston
[53] proposed that single-pulse is better than burst pulsed PEMF stimulation
for osteoporosis prevention and nonunion fracture healing, whereas burst
pulsed PEMF stimulation has better effects on acceleration of bone fracture
healing. Hannay, Leavesley, and Pearcy [54] examined the response of osteo-
blast-like cells to a PEMF stimulus, mimicking that of a clinically available
device, using four protocols of the timing of the stimulus, each conducted
over 3 days. Protocol 1 stimulated the cells for 8 hours each day, protocol 2
stimulated the cells for 24 hours on the first day, protocol 3 stimulated the
cells for 24 hours on the second day, and protocol 4 stimulated the cells for
24 hours on the third day. In terms of proliferation and differentiation of the
cells compared with the control group, no clear trend was observed between
the four protocols.
Intensity of the PEMF is also an important factor, as data from Chang
et al. [44] demonstrated that PEMF with different intensities could regulate
