  Inertial effects should be considered for micro- and nano-swimmers moving in
a low-density medium confined by irregular structures that create entropic
barriers, where viscous effects are no longer paramount. Here, we present a
separation mechanism of self-propelled particles in a two-dimensional
asymmetric channel, which leads to the drift of particles of different masses
in opposite directions. In particular, this mechanism is based on the combined
action of the spatial asymmetry of the channel structure, the temporal
asymmetry inherent in particles dynamics, and an external static force. This
work is relevant for potential applications that can be found in the
development of lab-on-a-chip devices and artificial channels for separating
particles of different masses.
