ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

600 nm 2 /molecule. Furthermore, the cell size was varied in another set of simulations
where bcell = 25, 35, and 55 µm, and fcell = 1. Both the cases where the adhesion
coefficient was insensitive to bcell or increased with bcell were considered.
Simulations were performed using the Solid Mechanics Module in COMSOL
Multiphysics 4.2. Linear elastic material properties were assumed for the cellular
domain. Time-dependent analyses were run with 1,000 time points from t = 0 to 600 s,
which is in the range of one cell contraction cycle [13]. Results were then compared at
the final time point.
4. RESULTS
Shown in Fig. 2(a) is a plot of the cell migration speed as a function of the ECM
degradation coefficient for different values of fcell. For this case, the adhesion coefficient
was independent of bcell and fixed at 600 nm 2 /molecule. As discussed in [9], the cell
speed exhibits a biphasic relationship with respect to α since high ECM densities can
impede movement whereas low densities do not provide enough mechanical support for
the cell to exert tractions on. Note that as fcell was increased, the maximum cell speed
increased in magnitude and occurred at a lower degradation coefficient as well. Since the
traction was kept normal to boundary when the cell shape was altered, there was less
traction in the direction of cell movement for the cells with the higher aspect ratios. As a
result, these cells required higher ECM densities (lower degradation coefficients) to
compensate. For the case where fcell = 2 in the simulations, the matrix density never
approached a high enough value to impede cell movement. Thus, the speed did not drop
to zero as the degradation coefficient was lowered.
Figure 2. Plot of the average migration speed as a function of the ECM degradation coefficient for an
aspect ratio of 2, 1.5, 1, 0.75, and 0.5 where the adhesion coefficient was (a) independent of bcell or (b)
increased with bcell. (c) Plot of the dependency of the maximum traction on the degradation coefficient for
the same case as part (b).