Blood Membrane Interface

Brain vascular endothelial cells are linked by tight junction proteins creating high-resistance junctions between cells that effectively prevent the movement of hydrophilic substances, including electrolytes, such as Na and K+. Water moves across the lipid bilayer of endothelial cells through simple diffusion and vesicular transport (Tait et al., 2008). However, specialized water channels are formed by molecules called aquaporins (AQPs), which are highly expressed in blood-brain interfaces to facilitate the transport of water across cell membranes. 

Membrane filtration can be used in sample preparation for liquid chromatography, e.g., in the ion-chromatographic determination of various inorganic anions and cations in water samples. Tubular membrane interfaces have been used for sample introduction in capillary zone electrophoresis to separate the low-molecular mass organic constituents of blood plasma. 

Fig. 18-3. The GE DuaLung employs a plastics membrane. Interposed between the sweep gas and blood is a membrane which prevents the blood from interfacing with the gas. (Courtesy General Electric Medical Systems Division)...

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... 

The structural analysis of membrane-associated peptides comprises two steps (a) the elucidation of the three-dimensional fold of the peptide and (b) the determination of the membrane-peptide interface. We will use our results gained for the 36 amino acid residue neuropeptide Y (NPY) [83] to demonstrate the approaches that can be used. NPY regulates important pharmacological functions such as blood pressure, food intake or memory retention and hence has been subject of many investigations (for a review see Ref. [84]). It targets the so-called Y receptors that belong to the class of seven transmembrane receptors coupled to G-proteins (GPCRs). 

At the most fundamental level, monolayers of surfactants at an air-liquid interface serve as model systems to examine condensed matter phenomena. As we see briefly in Section 7.4, a rich variety of phases and structures occurs in such films, and phenomena such as nucleation, dendritic growth, and crystallization can be studied by a number of methods. Moreover, monolayers and bilayers of lipids can be used to model biological membranes and to produce vesicles and liposomes for potential applications in artificial blood substitutes and drug delivery systems (see, for example, Vignette 1.3 on liposomes in Chapter 1). 

Recently developed blood oxygenators are disposable, used only once, and can be presterilized and coated with anticoagulant (e.g., heparin) when they are constructed. Normally, membranes with high gas permeabilities, such as silicone rubber membranes, are used. In the case of microporous membranes, which are also used widely, the membrane materials themselves are not gas permeable, but gas-liquid interfaces are formed in the pores of the membrane. The blood does not leak from the pores for at least several hours, due to its surface tension. Composite membranes consisting of microporous polypropylene and silicone rubber have also been developed. 

Although the cells of the arachnoid membrane have tight junctions (TJ) between them, due to its avascular nature and relatively small surface area, the arachnoid membrane does not represent a significant potential interface for exchange between the blood and the CNS (Figure 27.1) [6],... 

Both microdialysis and ultrafiltration collection obtain analytes from a sample in the reverse direction regardless of how a normal hemodialysis membrane is used. In hemodialysis, the blood is passed through the inner fiber lumen and filtrate is then collected on the outside of the hollow fiber. When these fibers are used as microdialysis or ultrafiltration devices for collection of samples, the outside of the fiber is interfaced with the sample and the analyte is collected into the inner fiber lumen of the hollow fiber. This is important particularly for the asymmetric membranes that have their large porous support layer on the outside facing the tissue sample. 

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