Biomedical Engineering Reference

In-Depth Information

Fig. 8.7
The normalized

pull-off force as a function of

the normalized surface

undulation amplitude under

different values of the SCI

and wave numbers. Other

selected parameters are

g ¼
2,
l ¼
2.576, and
b ¼
1

0.7

α=0.1, 2πa/l=1

α=0.1, 2πa/l=2

α=0.1, 2πa/l=4

α=5, 2πa/l=1

α=5, 2πa/l=2

α=5, 2πa/l=4

0.6

0.5

0.4

0.3

0.2

1

0

0.2

0.4

0.6

0.8

h
0
/a

uniform at
a ¼
0.1 for different shapes. This analysis of specific adhesion via

receptor-ligand bond clusters demonstrates that optimal adhesion can be achieved

at any length scale by designing the shape of the contact surfaces. However, the

robustness of optimal adhesion against random shape variations can only be

achieved at sufficiently small contact size or for a small SCI,
a
.

In order to investigate the specific adhesion of a soft elastic body on a wavy

surface via a patch of molecular bonds, we consider a wavy surface profile,
hðxÞ

¼ h
0
½
1
þ
cos
ð
2
px=lÞ
. By solving (
8.15
) and (
8.17
) at steady state, Fig.
8.7
shows

the normalized pull-off force as a function of the amplitude of surface undulation

for different magnitudes of surface wavelength and SCI,
a
. It can be seen from

Fig.
8.7
that for relatively small adhesion size or SCI, the adhesion strength tends to

decrease monotonically as the surface amplitude increases. This can be understood

from the point of view that increasing surface amplitude leads to more non-uniform

stress distribution within the contact patch. For relatively large adhesion size or

SCI, there exists an optimal surface topography with a finite undulating amplitude

and an optimal wavelength on the same scale as the adhesion patch size for the

maximum adhesion strength.

8.5.5 Active Control of Focal Adhesions

Analysis of the SCI has shown that, depending on system parameters, there is a

transition between uniform stress (equal load sharing) and crack-like singular stress

distribution along the contact interface. It seems that an important parameter under

control by the cell is the stiffness of the cell body, as contractile forces can stiffen or

soften the actin network of the cytoskeleton, allowing the cell to modulate stress

distribution along the cell-substrate interface and, in so doing, control the stability

and growth/shrinkage of FAs.

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