FN fibril in vitro morphometrical and force measurements. (A) Raw (top) and analyzed (bottom) FN fibril images at different time points. Scale bars, 100 μm. (B) Two analyzed FN fibrils, in which custom image processing measures fibril image outline (red), skeleton (yellow), and end points (blue). Fibril length is quantified as the maximum end-to-end distance of the image skeleton. Scale bars, 5 μm. (C) Composite image of a cell on mPADs, used to quantify cell-generated traction forces. (Red) Actin; (white) mPAD posts; (green) FN. Scale bars, 50 μm. (D) Comparison of in silico (red) and in vitro (black) FN fibril length. Standard error bars too small to be visible. (E) Comparison of in silico and in vitro normalized force data. In silico and in vitro measurements normalized to a maximum of 155.7 and 6.2 pN, respectively. In (D) and (E), error bars denote the standard error. To see this figure in color, go online.