Research on giant vesicles is becoming increasingly popular. Giant vesicles provide model biomembrane systems for systematic measurements of mechanical and rheological properties of bilayers as a function of membrane composition and temperature, as well as hydrodynamic interactions. Membrane response to external factors (for example electric fields, ions and amphiphilic molecules) can be directly visualized under the microscope. In this paper we review our current understanding of lipid bilayers as obtained from studies on giant unilamellar vesicles. Because research on giant vesicles increasingly attracts the interest of scientists from various backgrounds, we also try to provide a concise introduction for newcomers in the field. Finally, we summarize some recent developments on curvature effects induced by polymers, domain formation in membranes and shape transitions induced by electric fields.

This review is dedicated to electric field effects on giant unilamellar vesicles, a cell-size membrane system. We summarize various types of behavior observed when vesicles are subjected either to weak AC fields at various frequency, or to strong DC pulses. Different processes such as electrodeformation, -poration and -fusion of giant vesicles are considered. We describe some recent developments, which allowed us to detect the dynamics of the vesicle response with a resolution below milliseconds for all of these processes. Novel aspects on electric field effects on vesicles in the gel phase are introduced.

When subjected to alternating electric fields in the frequency range 10(2)-10(8) Hz, giant lipid vesicles attain oblate, prolate, and spherical shapes and undergo morphological transitions between these shapes as one varies the field frequency and/or the conductivities lambda(in) and lambda(ex) of the aqueous solution inside and outside the vesicles. Four different transitions are observed with characteristic frequencies that depend primarily on the conductivity ratio lambda(in)/lambda(ex). The theoretical models that have been described in the literature are not able to describe all of these morphological transitions.

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