Quantification of MSC cooperativity during type I collagen fibrillogenesis.

<p>The distribution of the angles between the gradient vectors and cell-graph edges are plotted for untreated and treated (shown as PD) samples at each time point imaged. Histograms plot the frequency of each angle found within the corresponding set of images weighted according to the gradient magnitudes. The area under the curve between 60 and 120 degrees (red shaded area) is assigned as the Collagen Alignment Index for that sample and shown in the middle of the curve. This metric attains its maximum value at day 2 in the untreated tissue sample whereas in the treated tissue samples this value takes its maximum value as early as hour 12. Using these distributions, the samples were clustered into three groups by k-means algorithm. The first and the last tissue samples of both the untreated and treated tissues grouped in one cluster, day 2 of untreated and hour 12 of treated example were grouped in the second cluster and all the other samples clustered as a third. This analysis was performed on distinct biological samples, n = 3.