Dynamics of 3D Axisymmetric Multicomponent Vesicles in A Viscous Fluid

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Multicomponent vesicles are hollow, closed biomembranes with a lipid bilayer membrane containing different types of lipids and cholesterol. Recent experiments on giant unilamellar vesicles demonstrate that there exists a variety of behavior of multicomponent vesicles. Under this understanding, we develop and investigate numerically a thermodynamically consistent model of three dimensional axisymmetric multicomponent vesicles in an incompressible viscous fluid. The model is derived using an energy variation approach that accounts for different lipid surface phases, the excess energy (line energy) associated with surface phase domain boundaries, bending energy, spontaneous curvature, Gaussian bending energy, local inextensibility and fluid flow via the Stokes equations. The equations are high-order (fourth order)nonlinear and nonlocal due to incompressibility of the fluid and the local inextensibility of the vesicle membrane. To solve the equations numerically, we develop a nonstiff, pseudo-spectral boundary integral method that relies on an analysis of the equations at small scales. We present simulations of multicomponent vesicles in a quiescent and an extensional flow and investigate the effect of varying the average surface concentration of an initially unstable mixture of lipid phases. The phases then redistribute and alter the morphology of the vesicle and its dynamics. A comparison of results with experimental vesicle morphologies yields good agreement.