Migration of blood cells and phospholipid vesicles induced by concentration gradients in microcavities.

Microcavities provide a well-controlled flow-free microenvironment and play an important role in many microfluidic systems, for example as cell-culturing microchambers. Here we show that transient concentration gradients that emerge during diffusive exchange of solutes in microcavities induce passive migration (diffusiophoresis) of blood cells and synthetic phospholipid vesicles. The passive migration is observed in various concentration gradients comprising non-electrolytes and electrolytes, i.e., glucose, sucrose, sodium chloride, potassium chloride, potassium benzoate, and potassium sulfate. The results add to prior reports, where gradients of non-electrolytes and monovalent salts, produced by micropipette injection, did not induce a noticeable migration of vesicles. The migration distances measured depended on the solution and the cell or vesicle type, and were in the range of several tens of micrometers. The results show that diffusiophoresis of cells and vesicles is a notable phenomenon in a flow-free environment and has to be taken into account when an accurate spatiotemporal control of cells or vesicles in microcavities is required.