Membrane Permeability and Stability of Liposomes Suspended in Shear Flow

Abstract

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.

Keywords:

• Adsorption
• cone-and-plate geometry
• liposomes
• membrane permeability
• shear flow

Acknowledgments

The authors are grateful to Mr. Kentaro Tsutsumi (Faculty of Engineering, Yamaguchi University) for performing preliminary experiments on fluorescence measurements. This work was supported in part by the Grant-in-Aid for Young Scientists (B) (No. 23760751) from the Japan Society for the Promotion of Science (JSPS).