Osmophoresis of lipid vesicles in solute gradients

Lipid membranes are semipermeable, allowing for water transport across the membrane but rejecting polar solutes and large molecules. Differences in solute concentrations across a lipid membrane lead to differences in the osmotic pressure Δπ causing water to flow towards regions of higher osmotic pressure (higher solute concentration) at speeds of v=-LpΔπ , where Lp is the hydraulic conductivity of the membrane. When a lipid vesicle is placed in a concentration gradient, it is predicted to move to regions of lower concentration due to osmotic flows across the membrane. John Anderson labeled this motion "osmophoresis'' and proposed a theory that predicts the vesicle velocity as U = -½𝛼LpRTG, where 𝛼 is the vesicle radius, RT is the thermal energy, and G=∇C is the imposed concentration gradient. The first experimental demonstration of osmophoresis reported a 1 μm/s migration velocity of DMPC vesicles in a 10 mM/mm sucrose gradient created between two dialysis tubes. However, Anderson's theory predicts that osmophoretic velocity should be four order of magnitude smaller than the observed velocity. A central goal of this Dissertation is to resolve this discrepancy either by validating