Electrohydrodynamic size stratification and flow separation of giant vesicles
Original Entry by Michelle Borkin, AP225 Fall 2009
S. Lecuyer, W. D. Ristenpart, O. Vincent, and H. A. Stone, Appl. Phys. Lett., 92, 104105, 2008
electrohydrodynamics, Vesicle, suspensions
An electrohydrodynamic (EHD) method for separating small from giant unilamellar vesicles (GUVs) is presented in this paper. GUVs are fragile and common suspension separation techniques (e.g. centrifugation) are ineffective. Thus having an effective way to separate them is desirable. GUVs are of particular interest due to their ability to model biophysical systems since GUVs have similar sizes and structures (e.g. lipid bilayers, membranes) as living cells. There is also interest in using GUVs for new technology including nanoreactors and designable drug carriers. In summary, the process for separating the vesicles involves applying an oscillatory electric field which generates an EHD flow around each vesicle close to an electrode. The result is that the smaller vesicles are pulled underneath the larger ones thus lifting the larger ones off the electrode and shielding them. A brief spike in the electric field is applied to keep the smaller vesicles on the bottom while a flow is applied to push the larger vesicles into a separate container. The result is the removal of >90% of the small vesicles from the GUVs.
The unilamellar vesicles studied in this paper are self-assembled phospholipid vesicles in which spherical molecular bilayers separate a specific internal volume from the external environment. The giant unilamellar vesicles (GUVs) that the researchers are attempting to isolate are on the order of tens of micrometers in diameter. When an external electric field is applied, a dipole field is induced around each vesicle and this field distorts the charge polarization layer near the electrode thus giving rise to an electrohydrodynamic (EHD) flow. A schematic of this experimental set-up and a sketch of the EHD streamlines can be seen in Figure 1.