Applications of DIC in the mechanics of collective cell migration

During wound repair, embryonic development, and cancer invasion, cells migrate in cooperative groups and clusters. Collective migration has been studied for decades, for example with experiments to determine how quickly a sheet of cells migrates to close a wound. Until recently, those experiments have been limited to investigating molecular mechanisms due to a lack of experimental tools to quantify the kinematics and forces. Now that digital image correlation has gained wide acceptance in engineering, physics, and biology, new possibilities exist to reveal quantitative understanding of the connections between signaling, motions, and forces. Here we review applications of digital image correlation in measuring cell velocities, cell-to-substrate tractions, and cell-to-cell stresses. The data show that forces and motions follow no typical constitutive relationship such as that of an elastic solid or a viscous fluid; in many cases even the orientations of force and motion are misaligned. Ongoing research is seeking to connect force and motion, often by modeling the active processes associated with cell signaling. While it remains unclear how to reduce the complicated and numerous signaling pathways into a physical picture of collective cell migration, the experimental tools now available offer a useful place to start.