Vesicles as osmotic motors

We report on a quantitative study of the motion of model osmotic motors-lip id vesicles in a solute concentration gradient. The vesicles move through r ecoil produced by osmotic pumping, but the transformation of entropic osmot ic energy into mechanical motion is found to be unexpectedly efficient: The drift velocity is more than 3 orders of magnitude faster than predicted by linearized nonequilibrium thermodynamics.