Directing cell motions on micropatterned ratchets

Cell motility is a process deriving from the synchronized dynamics of the cytoskeleton. In several important physiological processes—notably, cancer metastasis—the randomly moving cells can acquire a directional motility phenotype and bias their motions in response to environmental cues. Despite intense research, however, the current understanding of directional cell migration is incomplete and there is a growing need to develop systems that would enable the study and control of this process. This article demonstrates that random motions of motile cells can be rectified by asymmetric (‘ratchet’) microgeometries. Interactions between the cells and the imposed geometrical cues guide cell polarization and give rise to directional motility. Depending on the ratchet design, cells of different types can move either in the same or in opposite directions on the same imposed pattern. In the latter case, it is possible to partially sort mixed cell populations into different collecting reservoirs. It is not surprising that a microfluidic channel whose walls have a ratchet-like structure can preferentially direct the flow of large particles in one direction. But a study of the movement of living cells through such channels provides the remarkable observation that the direction of preferred motion can be different for different species of cell.