This paper presented a cohesive model of cell sorting using a mathematical model that considered different effective cell surface energies as the strength of cellular ligand/receptor interactions and with the surrounding media. However, I would be interested to see how this model could be adapted to include a 3rd component: that of 3D extracellular structures, such as collagen and fibrin. In particular, this consideration would be of great interest to a better understanding to how effector cells move to avoid scar tissues and disrupted lattice matrices in wound healing. The model considers the cases of a confined cell mass vs. an unconfined cell mass, but what of a caged cell mass with obstacles within? Cells can act, to a degree, as discrete particles in motion and therefore me somewhat analogous to a viscous fluid, but this does not preclude unique behavior in the above situations.