Biomedical Engineering Reference
In-Depth Information
complex interplaying mechanisms include strain-related potentials, activation
of ion channels, membrane tension, cytoskeleton deformation, and mechanical
lever (primary cilium) [14]. For example, osteocytes, which are believed to play
an important role as mechanosensing elements in bone tissues, in particular
respond strongly to fluid flow by a rapid release of nitric oxide (NO) and
prostaglandins [15]. Apart from NO and prostaglandins, others such as Ca
2
+
and adenosine 5
-triphosphate (ATP) are also released as molecular signals
in mechanotransduction cascades, which ultimately causes bone formation.
Recent studies have shown that several molecular, cellular, and extracellular
components and structures play important roles in the mediation of cellular
mechanotransduction. These mechanotransduction elements include extra-
cellular matrix (ECM), cell-cell and cell-ECM adhesion, cytoskeleton structures
(namely, microfilaments, microtubules, and intermediate filaments), specialized
surface processes (e.g., ion channels and surface receptors), and nuclear structures
[16].
7.2.4
Mechanical Influences on Stem Cell
Stem cell is a cell from which other types of cells, such as bone, cardiac, and
cartilages are developed. Recently, researches on stem cells have become increas-
ingly important for developing new techniques for bone regeneration [17]. Much
research effort has been directed to study how biochemical environments may alter
the gene expression of stem cells. However, very limited studies have been done
to elucidate how mechanical force/stimulation influences the differentiation and
proliferation of stem cells in order to form bone cells. Figure 7.3 simply shows the
progenic cascade of stem cell.
Mechanical forces affect bone regeneration which can be significantly found in
osteogenic differentiation of mesenchymal stem cells (MSCs) [19]. In this study, a
short period of cyclic mechanical strains (2000 microstrains for 40min) was applied
to rat MSCs through stretching an MSCs-seeded elastic membrane. The results
showed that mechanical strains can promote proliferation of MSCs. Moreover, a
more recent study shows that dynamic compression on human mesenchymal stem
cells (hMSCs) cultured in a bioreactor for 24 h will lead to a significant increase
(about fivefold) in osteopontin, which is a major noncollagenous bone matrix
protein [20]. This result also implies that dynamic compression is an important
factor for modulating progenitor cell differentiation after mechanical instability
caused by a fracture.
In addition to compressive stimulation, it has also been found that marrow
stromal osteoblasts exposed to shear stress in the range of 0.01-0.03 Pa in a
transverse flow will increase their mineral deposition. When shear stress was
in the range of 0.5-1.5 Pa in 2D planar plates, the expansion and differential
phenotype of osteoblasts grown in bioreactor systems were enhanced [21, 22].
However, it was also found that an average surface stress of 5
10
−
5
Pa in 3D
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