Figure 2. Simulated fibronectin fiber tension and stress compared to in vitro data.

The tension of in silico fibers with 4 domains initially unfolded was scaled by the Fn concentration measured by UV microscopy. The model output is shown with experimental data from Klotzsch, 2009 [4]. The equal loading configuration (A) is shown scaled to the density determined by the UV microscope measurements (B) with wavelengths 280 nm (blue, 1.65e5 fibrils), 260 nm (green, 2.52e5 fibrils) and 220 nm (red, 1.49e5 fibrils), with the experimental data (blue dots). The tension along the equally loaded fiber (B) rises more quickly than the experiment before module unfolding begins to dominate the fiber mechanics slowing the rise in tension. Panel C shows the ratio of the model scaled by the 280 nm UV measurement to the experimental data. In the disparate loading case (E), the unequal distribution of forces causes the onset of unfolding at lower forces, smoothing the initial rise in tension (F). The ratio of force in the disparate simulation to the in vitro force reached was lower than in the equal fiber (G). The disparate loading case more closely matched the fiber tension of the experiment. The fiber stress was calculated for concentrations measured with each wavelength assuming a constant fiber volume and a fiber diameter of 3.0 µm at 0% strain (D, H). In the disparate loading condition (E) the force was scaled by the number of disparately loaded fibers (280 nm 5.50e4 fibrils; 260 nm 8.39e4 fibrils; 220 nm 4.98e4 fibrils).