A practical guide to giant vesicles. Probing the membrane nanoregime via optical microscopy

Abstract

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.

Membrane heterogeneity – from lipid domains to curvature effects

“…To that end, giant unilamellar vesicles (GUVs) have proven to be one of the most versatile model membrane system. These closed, spherical single lipid bilayers of 10-100 µm diameter can be produced from a broad range of lipid compositions in physiologically relevant buffer conditions (59). They are free-standing and can be produced in sizes that are comparable to cells.…”

Electroformation in a flow chamber with solution exchange as a means of preparation of flaccid giant vesicles

“…While it was customary in earlier works (e.g., [5]) to perform experiments in the same chamber where the electroformation was done, researchers have lately become aware of the fact that the vesicles in the electroformation chamber are attached to the substrate as a rule [30], and thus a comparision with theoretical models valid for free vesicles is doubtful. Instead, they adopted a technique where the vesicles are drained from the electroformation chamber and stored separately.…”

Confined Bilayers Passively Regulate Shape and Stress

“…We idealize (c) Corresponding model idealizations as a uniform membrane disc with radius R; or discs with a tubular (radius r t , length L) or a spherical protrusion (radius r s , contact angle c ). The free energy of these three families of shapes includes the contributions shown in (d), with the corresponding material properties; K s ¼ 0:12 J=m 2 is the elastic compressibility modulus of each monolayer; ¼ 10 À19 J is the bending modulus [29]; for U, we adopt the functional form proposed in Ref. [11] with an equilibrium separation t 0 ¼ 3 nm and set the adhesion energy to ¼ Uðþ1Þ À Uðt 0 Þ ¼ 2 mJ=m 2 estimated from the lysis of shallow caps (see text).…”