Effect of Fg concentration on integrin cluster distance from cell center. The distance of each integrin cluster from the cell centroid is normalized by the average radius of that cell, which is defined as the mean of the distances from the cell centroid to the cell perimeter, as measured at each cluster location (see Figure 1d). Based on this normalization, most integrin clusters are located just inside the cell periphery at a normalized cluster location below 1; however, some clusters may reside at a normalized cluster location greater than 1 if they are located further from the cell centroid than the average distance to the cell periphery. (a) shows an example frequency distribution of normalized cluster locations in cells adhering to 2 μg/mL Fg. (b) shows that integrin cluster locations move closer to the cell periphery as ECM density increases.