Biomedical Engineering Reference
In-Depth Information
guidance.
10
Because cells establish contacts along the elevated
features offibersubstrates,
1
thediminishedspreading onrandomly
electrospun meshes may be a consequence of the spatially lim-
ited adhesive features. In contrast, when fibers are aligned they
guide adherent cells to extend lamellipodia outward along parallel
fibers, resulting in cell alignment parallel to fiber alignment. The
second explanation is related to the mechanical properties of the
meshes. Because spreading of mammalian cells is reduced on less
rigid materials,
16
,
17
and electrospun substrates can be more than
an order of magnitude more compliant than the bulk polymer,
18
the projected cell area on random electrospun meshes should be
less than that on cast films of the same polymer. However, when
the fibers are aligned the mechanical properties of the electro-
spun meshes are anisotropic and stiffer in the direction of fiber
alignment.
18
-
20
Consequently, cells may preferentially align par-
allel to the more rigid axis. A similar effect has been observed
when cells are seeded into anisotropic gels that are uniaxially con-
fined: the cells will align parallel to the confined (more rigid)
axis.
21
15.2.2
Effect of Fiber Diameter on Cell Morphology
Cell behavior can also be influenced by the diameter of electro-
spun fibers, and this can be varied by adjusting a number of elec-
trospinning parameters, including the concentration of the polymer
solution, the voltage potential, and needle diameter (see Subbiah
et al
.
22
for a review). The effect of fiber diameter on cell morphol-
ogy appears to vary with cell type. For example, both the projected
area and the aspect ratio of adherent fibroblasts are increased with
increasesinfiberdiameter.
23
Incontrast,neuralstemcellshavebeen
shown to extend significantly longer neurites on aligned meshes of
300nmfibersthanonalignedmeshesof1.5
μ
m.
24
Theeffectoffiber
diameteroncelladhesionandproliferationisambiguous.Somedata
has suggested that larger fibers support modestly better cell adhe-
sion and proliferation,
1
while other data suggests the opposite.
11
,
25
(Thelatter,however,maybeaconsequenceofresidualsolventinthe
fibers.)
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