Mutual adhesion of lecithin membranes at ultralow tensions

Abstract

2014 On présente une étude par microscopie optique de l'adhésion mutuelle de doubles couches de lécithine d'0153uf ou dimyristoyl dans des échantillons très gonflés. Les tensions latérales permettant l'adhésion, en dessous de 3 x 10-4 dyn cm-1, sont déterminées à partir de la courbure de la membrane à proximité de la zone de contact. L'angle de contact maximal des deux membranes soumises à des tensions égales à une valeur maximale de 45°. En dépit de quelque dispersion, cet angle ne semble pas dépendre de la tension jusqu'à sa valeur observable la plus faible, 3 x 10-6 dyn cm-1. L'angle de contact maximal d'une membrane isolée adhérant à un ensemble de membranes est proche de 70°. Les données indiquent que l'adhésion mutuelle est toujours induite par la tension latérale. La valeur constante des angles de contact semble compatible avec la théorie des ondulations, mais cette valeur nous pousse à postuler une rugosité de la membrane, non détectable optiquement, qui servirait de réserve d'aire. Abstract. 2014 We present an extensive light-microscopic study of mutual adhesion of egg (and dimyristoyl) lecithin bilayers in highly swollen samples, including adhesion brought about by osmotic inflation of vesicles. The lateral tensions associated with adhesion, if below ca. 3 x 10-4 dyn cm-1, could be read from a rounding of the membrane next to the contact area. The contact angle of symmetric adhesion, i.e. of two membranes under equal tension, had a maximum of 45°. While showing some scatter, it did not seem to depend on tension down to 3 x 10-6 dyn cm-1, the lowest tension observed. The maximum contact angle of single membranes adhering to bundles of membranes was near 70°. The data indicate that mutual adhesion of lecithin membranes is always induced by lateral tension. The constancy of the contact angles appears to be compatible with undulation theory, but their magnitude compels us to postulate an unknown, optically unresolvable roughness of lecithin membranes which serves as an area reservoir.

Effects of Surfactants and Polyelectrolytes on the Interaction between a Negatively Charged Surface and a Hydrophobic Polymer Surface

“…For surfactant concentrations above the CMC, a fluid MTAB bilayer adsorbs on the mica and a densely packed MTAB monolayer adsorbs into the PDMS layer. The interaction forces now resemble the interactions measured between two fusing lipid bilayers, 33,38,39 as shown in Figure 3B. The adsorbed layers first approach each other and interact through a long-range electrostatic interaction ( Figure 3B(i)).…”

Imaging optical thicknesses and separation distances of phospholipid vesicles at solid surfaces

“…Two cases are studied : strong and weak adhesion. Adhesion of vesicles to surfaces has been studied experimentally and theoretically [14][15][16]. In the case of strong adhesion the vesicle takes the shape of a spherical cap.…”

“…In this case pronounced thermal undulations of the membrane are visible which, in the former examples, were suppressed by lateral tension induced by osmotic pressure or by strong adhesion [15]. To measure the fluctuating Separation distance of the membrane directly we followed the phase shift technique described in section 1.7.…”

Analytical characterization of adhering vesicles

“…The shape of this region has been determined in Refs. [16,17] using an open membrane description, i.e., no volume constraint and an externally imposed tension acting along a fixed direction mimicking the asymptotic contact angle. Imposing explicitly the volume constraint, we recover the same shape for the contact angle region.…”