Morphology and dynamic scaling analysis of cell colonies with linear growth fronts

The growth of linear cell colony fronts is investigated from the morphology of cell monolayer colonies, the cell size and shape distribution, the front displacement velocity, and the dynamic scaling analysis of front roughness fluctuations. At the early growth stages, colony patterns consist of rather ordered compact domains of small cells, whereas at advanced stages, an uneven distribution of cells sets in, and some large cells and cells exhibiting large filopodia are produced. Colony front profiles exhibit overhangs and behave as fractals with the dimension D-F=1.25 +/- 0.05. The colony fronts shift at 0.22 +/- 0.02 mu m min(-1) average constant linear velocity and their roughness (w) increases with time (t). Dynamic scaling analysis of experimental and overhang-corrected growth profile data shows that w versus system width l log-log plots collapse to a single curve when l exceeds a certain threshold value l(o), a width corresponding to the average diameter of few cells. Then, the influence of overhangs on the roughness dynamics becomes negligible, and a growth exponent beta=0.33 +/- 0.02 is derived. From the structure factor analysis of overhang-corrected profiles, a global roughness exponent alpha(s)=0.50 +/- 0.05 is obtained. For l>200 mu m, this set of exponents fulfills the Family-Vicsek relationship. It is consistent with the predictions of the continuous Kardar-Parisi-Zhang model.