Session E22: Biological Fluid Dynamics: Flows involving Vesicles

Electrodeformation and transport of sub-micron vesicles in a microfluidic device

Viral infection changes cell morphology and mechanical properties. Thus, mechanical characteristics of cells and other sub-micron vesicles, such as virus and neurotransmitters can be used to identify the extent of infection. In recent years, electrodeformation of vesicles suspended in a fluid medium has opened the way to study the deformation at a very small scale. The response of the vesicle is strongly influenced by the conductivity of surrounding fluid, vesicle size and shape, and the inherent charge of the vesicle. We studied the electrodeformation and transport of charged vesicles in a microfluidic device under a DC electric field. The electric field, flow field, and associated vesicle deformation are resolved with a hybrid immersed resolved technique. Force analysis on the membrane surface reveals linear scaling with vesicle size, but non-linear influence on initial shape of vesicles. Modeling results reveals that area averaged conductivity can be used to track the location and deformation of vesicles at any time. Moreover, electrodeformation of vesicles can be used to create unique external flows depending on the vesicle size, shape, and charge as well as electrical characteristics of the microchannel wall.   

Transient electrodeformation of giant unilamellar vesicles

The electrodeformation of giant vesicles provides fundamental insights into the electro-mechanical coupling of transmembrane potential and membrane shapes. The steady shape of a giant vesicle (~ 10-50 micron in radius) in a uniform AC field is widely used to measure membrane elastic properties such as bending rigidity and tension. We utilize the time dependent vesicle shape to extract dynamic properties such as membrane viscosity and capacitance. The method is applied to characterize membranes made of lipids and block-copolymers (polymersomes). We study the vesicle shape in a uniform AC electric field after change in field strength at a fixed frequency or after frequency change at a fixed field. Theoretical analysis and experimental quantification are provided for the deformation and relaxation of vesicles. Agreement allows for a robust measurement of membrane viscosity for different types and phases.   

The effect of AC electric field on the dynamics of a vesicle under shear flow in the small deformation regime

In this work, the dynamics of a vesicle subjected to simultaneous shear and uniform alternating current electric field is investigated. The coupled equation for vesicle orientation and shape evolution are derived theoretically and the resulting nonlinear equations are handled numerically to generate relevant phase diagrams that demonstrate the effect of electrical parameters on the different dynamic regimes such as tank-treading, trembling, and tumbling. It is found that while electric Mason number which represents the relative strength of the electrical forces to the shear forces, promotes tank-treading regime, the response itself is found to be sensitive to the applied frequency as well as the conductivity ratio. While higher outer conductivity promotes orientation along the flow axis, orientation along the field is favored when the inner conductivity is higher. Interestingly, in some cases, a coupling between electric field induced deformation and shear can result in the system admitting an intermediate tumbling regime while attaining the TT regime at high Mn. The results could enable designing better dielectrophoretic device.