Inverse lipid–water phases such as cubic phases can form kinetically stable dispersions by fragmentation in water. Cubic lipid phases can be dispersed by polar lipids favoring lamellar phases or by block copolymers, which can close the bilayer at the surface so that the hydrocarbon chain core is not exposed to water. Monodisperse particles based on glycerol monooleate, with their bilayer curved as the P-, D- or G-minimal surface, have been prepared in this way. Their inner bilayer conformation and outer shape have been examined, mainly by X-ray diffraction and cryo transmission electron microscopy. There is also a different type of cubic lipid bilayer particles with a periodicity in the micrometer range, which have been identified in phospholipid–water dispersions and in cell membrane assemblies. The mechanism behind formation in vivo of such cubic membranes, which also follow the P-, D- and G-surfaces, is discussed. Other lipid–water dispersions with lower symmetry are finally considered; dispersions formed by the inverse hexagonal phase and the dispersed state of a tetragonal bilayer structure formed by lung surfactants.

Aqueous dispersions of cubic lipid–water phases

Effective conductivities and elastic moduli of novel foams with triply periodic minimal surfaces

Micromechanical finite element predictions of a reduced coefficient of thermal expansion for 3D periodic architectured interpenetrating phase composites

Multilayers formed by polyelectrolyte-surfactant and related mixtures at the air-water interface.

Among the unsolved mysteries of modern biology is the nature of a lining of blood vessels called the 'endothelial surface layer' or ESL. In venous micro-vessels, it is half a micron in thickness. The ESL is 10 times thicker than the endothelial glycocalyx (eGC) at its base, has been presumed to be comprised mainly of water, yet is rigid enough to exclude red blood cells. How is this possible? Developments in physical chemistry suggest that the venous ESL is actually comprised of nanobubbles of CO2, generated from tissue metabolism, in a foam nucleated in the eGC. For arteries, the ESL is dominated by nanobubbles of O2 and N2 from inspired air. The bubbles of the foam are separated and stabilized by thin layers of serum electrolyte and proteins, and a palisade of charged polymer strands of the eGC. The ESL seems to be a respiratory organ contiguous with the flowing blood, an extension of, and a 'lung' in miniature. This interpretation may have far-reaching consequences for physiology.

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Structure and function of the endothelial surface layer: unraveling the nanoarchitecture of biological surfaces

The conformation of the lung surfactant lipid bilayer (termed tubular myelin) is shown to fit an infinite periodic surface, which is free from self-intersections and with zero or close to zero average curvature. A single lipid bilayer is curved in space, forming a tetragonal structure (CLP) with tubular units, the walls of which are close to planar and parallel to two orthogonal directions. A cryo transmission electron microscopy (cryo-TEM) study of the alveolar surface layer from rabbit was performed. Direct deposition of the surface layer on the microscopy grid indicates that the surface zone consists of a homogeneous phase. The cryo-TEM texture of the bilayer is consistent with earlier reported electron microscopy observations of dispersed aggregates in lung washings. It is shown how the interface towards air can be formed by opening up the phase along lipid methyl end groups. The model is fundamentally different from earlier proposals, involving a “free” lipid-protein monolayer at the air/wat...

P. Wollmer

Papers

The alveolar surface structure: transformation from a liposome-like dispersion into a tetragonal clp bilayer phase