Surface forces in supported spherical lipid membranes

Schneider-Henriquez, Juan E.; Denicourt, Normand; Fendler, János H.

doi:10.1021/la00048a036

Cited by 3 publications

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“…Equation (3) is plotted in Figure 2a using the measured r. Fitting this equation to the data in Figure 2a gives a surface tension of 3.5 mNm -1 , well within the range of bifacial surface tensions observed for spherical lipid membranes by Schneider-Henriquez et al [15] The strong correspondence between the measured capacitance values and the capacitance values expected for a spherically bulging membrane indicates that, when not surrounded with a hydrogel, a membrane will respond to applied pressure gradients by bulging out from the substrate on which it has been formed. In fact, at pressures above about 12 Pa, the solvent annulus could be seen to leave the interior of the Teflon orifice completely, expanding the radius of the now hemispherical membrane beyond the orifice radius, as described by Antonov et al [16] (see Supporting Information).…”

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Long‐Lived Planar Lipid Bilayer Membranes Anchored to an In Situ Polymerized Hydrogel

2007

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Planar bilayer lipid membranes (BLMs) are important tools for studying isolated membrane channel and pore proteins in vitro. Recently, engineered pore proteins incorporated in BLMs have also been explored as chemical sensors [1] and as tools to sequence single molecules of DNA. [2] Unfortunately these applications all require freestanding BLMs, which suffer from short lifetimes (< 1 d) and are highly susceptible to mechanical vibrations. These shortcomings limit the scope of applications possible using channel proteins incorporated into BLMs. We recently described a system that addresses these shortcomings by encapsulating a BLM in situ within a poly(ethylene glycol)-based hydrogel.[3] These hydrogel encapsulated membranes (HEMs) are mechanically stabilized, showing extended lifetimes and resistance to mechanical perturbation, while supporting the measurement of incorporated pore proteins at single-channel resolution. This membrane platform has since been explored by other researchers, and has been demonstrated as a promising portable molecular sensing element. [4,5] In the current work, we extend this concept by covalently conjugating the headgroups of lipids in the membrane to the hydrogel during the hydrogel polymerization process. These conjugated hydrogel encapsulated membranes (cgHEMs) demonstrate superior longevity and stability, and they provide insight into the mechanism by which the process of in situ hydrogel encapsulation stabilizes lipid bilayer membranes.Freestanding membranes spread from a lipid-containing organic solvent solution (the Mueller-Rudin method [6] ) have a significant solvent component existing at the membrane/substrate boundary (the Plateau-Gibbs border), [7] which stabilizes the membrane and serves as a lipid reservoir [8] . By forming a hydrogel with strong covalent bonds to the membrane, we are able to provide support analogous to that of a solid surface. It is possible that the presence of the hydrogel in our HEMs also stabilizes the solvent at the membrane boundary, and that covalent conjugation of the hydrogel to the lipid at the organic/aqueous interface provides further stabilization of the solvent.In investigating the extraordinary stability of cgHEMs, we first confirmed attachment of the hydrogel to the bilayer by examining the various responses of HEMs, cgHEMs, and conventional unprotected membranes to applied pressure and by measuring lipid fluidity in fluorescence recovery after photobleaching (FRAP) experiments. Once the successful conjugation of the membrane to the hydrogel was established, we performed optical studies of the membranes, with a particular emphasis on observing the behavior of the solvent located at the membrane/orifice boundary. We used fluorescence microscopy to track this solvent with and without hydrogel encapsulation, and have found significant differences in this behavior, with important implications for engineering stable BLMs.Covalent conjugation of lipid bilayers to a supporting hydrogel also offers the possibility of building biomimetic struct...

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confidence: 70%