Membrane Permeability and Stability of Liposomes Suspended in Shear Flow

The 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposome has been characterized in its stability and membrane permeability to 5(6)-carboxyfluorescein (CF) in the shear flow generated in the cone-and-plate geometry. The CF-containing liposomes (CFLs) were 101–323 nm in the mean diameter D P as measured with the dynamic light scattering (DLS) method. Adsorption of lipids to the cone-and-plate was observed, which clearly depended on the shear stress applied at the shear rate γ up to 1.5 × 103 s−1. The permeability of CFLs with D P of 101 and 117 nm definitely increased at the maximum γ value where the adsorption was negligible. The permeability coefficient of CF at 40°C in the shear flow was 5.7 times larger than that in the static liquid system. The DLS measurements revealed that the size distribution of CFLs with D P of 101–189 nm was practically unchanged under the shear stress even at 55°C. The results obtained show that the shear stress can permeabilize the CFL membranes with neither structural collapse nor coalescence.