FIGURE 8.

Effect of external versus internal force for the experimental adhesion geometry from Fig. 5. (a–c) External force with a threshold value for detachment of F_c = 6 nN. Because the cell is elliptically elongated, a morphology arises which is typical for a migrating fibroblast. (d–f) Exactly the same morphology can be obtained by using internally generated force only. To this purpose, contracting fibers (represented by the thick red lines) are attached between the FAs at the left boundary and the circular area at the center. Their respective contractility is then adjusted in such a way that rupture at the left boundary is avoided, while at the center area, the same overall force is achieved as in panels a–c.