Fig. 1
Trajectories of cancer cell motions on linear microtracks. a Scheme of substrate fabrication using the Wet Etching technique40, 48, 49. b Optical micrographs showing a cell migrating on a microtrack (scale bar = 20 µm). The cell moves along the etched, optically transparent microtrack, and not across cell-adhesion-resistant dark regions. The definition of step persistence length/time is the distance/time the cell travels in one direction before it reverts the direction of motion. The arrows labeled L1, L2, and L3 indicate three consecutive “steps” of the cell (here, to the right, to the left, and to the right again). c A representative trajectory of a metastatic cell comprised of clusters of “small” steps (shown in gray) interspersed with “large” steps (color denotes elapsed time and each long step is in different color) is characteristic of a Lévy walk (see also Supplementary Figure 2 for long-term trajectories). Scale bar is 100 μm for Lévy trajectory and 20 μm for the inset. This can be contrasted with a trajectory of a non-metastatic cell exhibiting diffusive motion (all steps are small and shown in gray, scale bar is 20 μm). Note that while cell motions in experiments are in 1D (along microtracks), the vertical axis in the trajectories shown here corresponds to time (from top to bottom). Total length of each trajectory is 960 min with each point 3 min apart. See also Supplementary Movies 1–6. The distinction between “small” and “large” steps is best appreciated by viewing long-term Supplementary Movies 13–15
