Effect of curvature on bilayer thickness of liposome suspensions in water

Abstract

The bilayer thickness of different sizes of SOPC lipid liposomes is measured using small-angle neutron scattering (SANS) at 30 °C and a model is developed to estimate the bilayer thickness of liposome based on its diameter. Three different sizes of liposome suspensions are prepared by extruding the suspension through 30 nm, 100 nm, and 200 nm membrane pore sizes. The bilayer thickness of liposomes is measured for these suspensions using small-angle neutron scattering and the results show a slight reduction in bilayer thickness as liposome size increases. The average diameter of liposomes in these extruded suspensions varies from 59 nm to 109 nm as measured by dynamic light scattering. A model is developed that calculates the bilayer thickness depending on the diameter of the liposome. The model shows a decrease in bilayer thickness as liposome size increases. However, the calculated bilayer thickness drops to a very small extent with the increase in liposome diameter. We also study the effect of the addition of ethanol on the bilayer thickness of liposomes. SANS measurements find that the bilayer thickness of liposomes decreases after adding ethanol to liposome suspensions. The decrease in bilayer thickness in ethanol is of similar extent for various sizes of liposomes and it reduces by 12%–15% at a concentration of 20 vol% ethanol.