Membrane blood interface, liquid

High-surface activity at the liquid membrane-blood interface— so that a liquid membrane can form around each gas bubble... 

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. 

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. 

Membrane oxygenators use a porous/microporous hydro-phobic membrane (Figure 3.4.10) on one side of the membrane, the blood from the patient flows, while on the other side air flows. The blood side pressure is maintained slightly above the air pressure to prevent air from bubbling into the blood (Callahan, 1988 Sirkar, 1992). Since the membrane is hydrophobic, most aqueous solutions, including blood, do not wet the pores, which remain filled with air. A gas-liquid interface is created at the mouth of every pore in the porous/microporous hydrophobic membrane the membrane facilitates the gas-liquid contact. Oxygen is absorbed from the gas into blood and CO2 is stripped from blood into the gas through such an interface. Unless the liquid pressure exceeds a... 

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