Biomedical Engineering Reference
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such as lamellipodia [54] and finger-like filopodia [14] [69] or through transverse
membrane undulations [156] [203], thus inducing transient contacts between mem-
brane receptors and fixed ligands, which may provide a powerful way of rapidly
gathering information [158]. The outcome of interactions is heavily dependent on
the
kinetics
of bond formation between surface-attached ligands and receptors and
the
strength
of attachments. These phenomena are highly dependent on the kinet-
ics and mechanics of receptor-ligand interactions. Arguably, cells use DFS to probe
their environment (Figure 1.1).
Inflammation
is an ubiquitous process used by multicellular organisms to cope
with various forms of aggression, and particularly infection. A key step is the adhe-
sion of flowing blood leukocytes to the vessel walls, with subsequent transmigra-
tion through these walls and entry into tissues containing infectious agents or dam-
aged cells. Unraveling the mechanisms of leukocyte interaction with endothelial cells
coating the vessel walls was a major task during the last two decades, and this pro-
vided a model of prominent biophysical interest (Figure 1.2).
It has been known for more than a century that locally activated endothelial cells
areabletobindtoflowing leukocytes, which undergo a nearly 100-fold velocity
decrease (typically from 1 mm/s to 10
m/s). Leukocytes then display a charac-
teristically jerky motion called
rolling
. During the rolling phase, leukocytes remain
sufficiently close to the wall to detect specific molecules with a capacity to activate
µ
(a)
(b)
FIGURE 1.1
Cells probe their environment. (a) A monocytic THP-1 cell was deposited
on a surface coated with fibronectin and was examined with interference-reflection contrast
microscopy (IRM). Short filopodia (white arrow) appear as black lines. (b) The image shows
the underside of a lymphocyte falling on an activating surface, and tridimensional shape was
derived from IRM images. A dynamic study revealed undulations of a few nm amplitude and
Hz frequency. Horizontal bar length is 5
µ
m and vertical bar length is 100 nm. See reference
46 for details.
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