Biomedical Engineering Reference
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FIGURE 7.6: (See color insert.) Time-evolution of VEGF-induced intracel-
lular calcium dynamics. Calcium signals are clearly detectable at the early
stages of tumor capillary-like formation, while they are downregulated in the
final phases of the process, when the network is more structured. Scale bar is
100 m long.
see again [360]). Moreover, they are biologically functional and instrumental
for an optimal metabolic exchange: a coarser capillary pattern would be in
fact unable to differentiate to form the lumen, while an immature and finer
structure would be obviously useless (refer to [82, 175]).
Similarly to the experimental pictures in [360] for HUVECs, we now fo-
cus on the trajectories of single cells. Figure 7.5 shows that their motion is
directed towards zones of higher concentrations of morphogen, displaying a
directional persistence. A random component is of course present, however it
is not predominant. Such a characteristic migration, which is the combination
of chemotaxis and persistence, has been experimentally demonstrated to be
fundamental to produce capillary chords in physiological cases as well. On
the opposite, the slower sideaway fluctuations of cells have been shown to be
instead responsible of pattern coarsening, when single branches connect each
other forming a structured network [261, 360].
Figure 7.5 also captures the elongation process of TECs, which undergo
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