  In the absence of environmental cues, a migrating cell performs an isotropic
random motion. Recently, the breaking of this isotropy has been observed when
cells move in the presence of asymmetric adhesive patterns. However, up to now
the mechanisms at work to direct cell migration in such environments remain
unknown. Here, we show that a non-adhesive surface with asymmetric
micro-geometry consisting of dense arrays of tilted micro-pillars can direct
cell motion. Our analysis reveals that most features of cell trajectories,
including the bias, can be reproduced by a simple model of active Brownian
particle in a ratchet potential, which we suggest originates from a generic
elastic interaction of the cell body with the environment. The observed guiding
effect, independent of adhesion, is therefore robust and could be used to
direct cell migration both in vitro and in vivo.
