Membranes cushioned

The exterior of the brain and spinal cord is cushioned within the skull and backbone by the cerebral-spinal fluid (CSF). The CSF is kept from direct contact with the brain by the arachnoid membrane covering the surface and the choroid plexus, tissue which selectively interacts with the contents of the CSF. An injection into the spinal cord or through the skull can put a drug directly into contact with the choroid plexus and the brain. For more on this subject you can read "The Mammalian Choroid Plexus" by Spector and Johanson Scientific American November 1989. 

SURFACE TENSION. Fluid surfaces exhibit certain features resembhng the properties of a stretched elastic membrane hence the term surface tension. Thus, one may lay a needle or a safety-razor blade upon the surface of water, and it will lie at rest in a shallow depression caused by its weight, much as if it were on a rubber air-cushion. A soap bubble, likewise, tends to contract, and actually creates a pressure inside, somewhat after the manner of a rubber balloon. The analogy is imperfect, however, since the tension in the rubber increases with the radius of the balloon, and the pressure inside, which would otherwise decrease, remains approximately constant while the liquid film tension remains constant and the pressure in the bubble falls off as the bubble is blown. 

Other types of cell membrane interaction have also been examined. For example Wang et al. have used an electrochemical SPR sensor to monitor peroxidase enzyme activity within the plasma membrane [77]. As a means of improving stability and creating a closer approximation of a true cell membrane, interlayer structures between the lower phospholipid leaf and the solid supports have been tested. Cushion layers based on PEG to enable transmembrane protein insertion were tested by Munro et al. [78], while Schuster et al. have reviewed the use of S-layer proteins as a construction element [79, 80]. 

Wagner ML, Tamm LK (2000) Tethered polymer-supported planar lipid bilayers for reconstitution of integral membrane proteins Silane-polyethyleneglycol-lipid as a cushion and covalent linker. Biophys J 79 1400-1414... 

Adhesion of different immune cells to one another or to epithelial cells has also been studied using planar bilayer models. For example, lymphocyte function-associated protein-1 (LFA-1) promotes cell adhesion in inflammation [i.e., a reaction that can be mimicked by binding to purified ICAM-1 in supported membranes (70)]. Similarly, purified LFA-3 reconstituted into supported bilayers mediates efficient CD2-dependent adhesion and differentiation of lymphoblasts (71). This work was followed by a study in which transmembrane domain-anchored and GPl-anchored isoforms of LFA-3 were compared (72). Because this research occurred before the introduction of polymer cushions and because the bilayers were formed by the simple vesicle fusion technique, the transmembrane domain isoform was immobile, whereas the GPl isoform was partially mobile. By comparing results with these two isoforms at different protein densities in the supported bilayer, the authors showed that diffusible proteins at a sufficient minimal density in the supported membrane were required to form strong cell adhesion contacts in this system. 

With only a few exceptions, metal-supported biomimetic membranes consist of a more or less complex architecture that includes a lipid bilayer. In order of increasing complexity, they can be classified into solid-supported bilayer lipid membranes (sBLMs), tethered bilayer lipid membranes (tBLMs), polymer-cushioned bilayer lipid membranes (pBLMs), S-layer stabilized bilayer lipid membranes (ssBLMs), and protein-tethered bilayer hpid membranes (ptBLMs). 

And finally, the very promising application of hydrogels as cushions but also as protective coatings for the tethered membrane architectures, eventually allowing even for operations in air, is presented and discussed. 

Keywords Tethered lipid bilayer membrane Polymer cushion Lipopolymer... 

Plasma-Polymer Layers as Cushions for Lipid Membrane Architectures. 105... 

Fig. 2 The construction of a polymer-cushioned lipid bilayer membrane. (A) Architecture constructed in a sequential way first, onto the functionalized substrate a polymer layer (cushion) is deposited by adsorption from solution and covalent binding, followed by the (partial) covalent attachment of a lipid monolayer containing some anchor lipids as reactive elements (B) able to couple the whole monolayer to the polymer cushion. (C) Alternatively, a lipopolymer monolayer, organized, e.g., at the water-air interface can be co-spread with regular low-mass amphiphiles and then transferred as a mixed monolayer onto a solid support, prefunctionalized with reactive groups, able to bind covalently to the polymer chains of the lipopolymer molecules, (B). (D) By a fusion step (or a Langmuir Schaefer transfer) the distal lipid monolayer completes the polymer-tethered membrane architecture...

Among the various strategies for the construction of polymer-tethered model membranes, the concept of simply using electrostatic interactions between the membrane with its partially charged lipids and a polyelectrolyte layer as cushion... 

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