One of the most promising features of active systems is that they can extract
energy from their environment and convert it to mechanical work. Self propelled
particles enable rectification when in contact with rigid boundaries. They can
rectify their own motion when confined in asymmetric channels and that of
microgears. In this paper, we study the shape fluctuations of two dimensional
flexible vesicles containing active Brownian particles. We show how these
fluctuations not only are capable of easily squeezing a vesicle through narrow
openings, but are also responsible for its rectification when placed within
asymmetric confining channels (ratchetaxis). We detail the conditions under
which this process can be optimized, and sort out the complex interplay between
elastic and active forces responsible for the directed motion of the vesicle
across these channels.Comment: 8 pages, 8 figure