Rolling microshuttles: trapping and shipping colloids by pure hydrodynamics

Trapping and transporting materials within nano to micrometer length scales is crucial in living systems. Molecular motors translate along proteins and carry organelles to proper locations. While white blood cells deform and travel in confined channels, trapping and engulfing bacteria. These and many other biological processes consist in the controlled and precise transport of objects within thermalized complex fluids like blood or in the interior of cells. In order to replicate this artificially, possibly for a localized delivery of medicine in the body, a shuttle particle must be employed. This shuttle particle must attract to a targeted cargo to deliver the cargo to a specific location. It is normally the case that the attraction between the shuttle and cargo be mediated by electrostatic interactions, however, an alternative mechanism relies on advective flow created by the motion of the shuttles. When these shuttles translate they generate closed streamlines known as microvortices, it is in these regions where the cargo is trapped and thus orbits around the shuttle. One benefit of this mechanism is that it does not rely on adding a specific interaction between the shuttles and the cargoes. In this talk, we experimentally demonstrate how micron sized rollers can efficiently transport cargo of various sizes and masses by purely hydrodynamic means within a thermalized fluid, effectively acting as microshuttles. These microrollers can pick up particles three times its size due to microvortices, and we are able transport the cargo to desired locations by manipulating the external driving field. In addition, we use Stokesian dynamics simulations to understand the cargo mechanism, and show that it is possible to selectively pick the desired size/density of the particles from a cluster even when the fluid is thermalized.