The Behavior of a Lipid Bilayer Vesicle in a Simple Shear Flow (1st Report, Validation of the Relationship Between Inclination Angle and Swelling Ratio)

Deformation and motion of lipid bilayer vesicles in a simple shear flow have been observed by phase contrast microscopy. We construct a rotating-cylinder apparatus, which can create a simple shear flow with steady shear rates. Vesicles are prepared from 1, 2-dioleoyl-sn-glycero-3-phosphocholine by the gentle hydration method. In our observation, vesicles are deformed to steady ellipsoidal shapes and show constant orientations with θi, which is the angle between the major axis and the flow direction. It is confirmed that the relationship between the θi and the swelling ratio (volume/surface ratio) Sw agrees quantitatively with the experimental result of Abkarian & Viallat [Biophys. J., Vol.89, 1055 (2005)], which is obtained with vesicles in wall bounded shear flows. It is also confirmed that our result agrees with a theoretical analysis of Keller & Skalak [J. Fluid Mech., Vol.120, 27 (1982)] and other numerical simulations. They are based on different membrane models, which are supposed to cause the different local behaviors of the membrane. This agreement indicates that the local membrane behavior does not have significant influence on θi.