Entrapment membrane

Characteristic Physical adsorption Ionic binding Chelation Covalent bonding Cross-linking Physical entrapment Membrane entrapment Whole cells... 

Centonze, D., C. Malitesta, F. Palmisano, and P.G. Zambonin. 1994. Permeation of solutes through an electropolymerized ultra thin poly-o-phenylenediamine film used as an enzyme-entrapped membrane. Electroanalysis 6 423. 

Characteristics Adsorption Covaient binding Entrapment Membrane confinement... 

The influence of membranes modification with IIO2 on their permeability is a complex issue. The permeability strongly depends on the membrane porosity and pore structure, which was discussed above. In most cases when the amount of the entrapped I1O2 is low, an improvement of pure water flux compared to the flux measured for neat membranes is observed. At higher T1O2 concentration the pure water flux of H02-entrapped membranes... 

With the aim to develop a drug delivery system with thermal stimuli respons-ing, Nozawa et al. have been investigated liquid crystal (LC)-entrapped membranes, polymer alloyed membranes and LC-adsorbed membranes for the transport and release of indomethacin. Polymer alloyed membranes were obtained by polymerizing aaylic monomers in presence of LC and LC-adsorbed membrane were obtained by adsorbing LC into porous hydrophobic polymer membrane. Permeation experiments showed that below and above the gel-liquid crystal phase transition tanperature of the LC, the extent of thermo-sensitivity for LC-adsorbed... 

Films or membranes of silkworm silk have been produced by air-drying aqueous solutions prepared from the concentrated salts, followed by dialysis (11,28). The films, which are water soluble, generally contain silk in the silk I conformation with a significant content of random coil. Many different treatments have been used to modify these films to decrease their water solubiUty by converting silk I to silk II in a process found usehil for enzyme entrapment (28). Silk membranes have also been cast from fibroin solutions and characterized for permeation properties. Oxygen and water vapor transmission rates were dependent on the exposure conditions to methanol to faciUtate the conversion to silk II (29). Thin monolayer films have been formed from solubilized silkworm silk using Langmuir techniques to faciUtate stmctural characterization of the protein (30). ResolubiLized silkworm cocoon silk has been spun into fibers (31), as have recombinant silkworm silks (32). 

Because enzymes can be intraceUularly associated with cell membranes, whole microbial cells, viable or nonviable, can be used to exploit the activity of one or more types of enzyme and cofactor regeneration, eg, alcohol production from sugar with yeast cells. Viable cells may be further stabilized by entrapment in aqueous gel beads or attached to the surface of spherical particles. Otherwise cells are usually homogenized and cross-linked with glutaraldehyde [111-30-8] to form an insoluble yet penetrable matrix. This is the method upon which the principal industrial appHcations of immobilized enzymes is based. 

Erythrocyte Entrapment of Enzymes. Erythrocytes have been used as carriers for therapeutic enzymes in the treatment of inborn errors (249). Exogenous enzymes encapsulated in erythrocytes may be useful both for dehvery of a given enzyme to the site of its intended function and for the degradation of pathologically elevated, diffusible substances in the plasma. In the use of this approach, it is important to determine that the enzyme is completely internalized without adsorption to the erythrocyte membrane. Since exposed protein on the erythrocyte surface may ehcit an immune response following repeated sensitization with enzyme loaded erythrocytes, an immunologic assessment of each potential system in animal models is required prior to human trials (250). 

Carbon dioxide devices were originally developed by Severinghaus and Bradley (59) to measure the partial pressure of carbon dioxide in blood. This electrode, still in use today (in various automated systems for blood gas analysis), consists of an ordinary glass pH electrode covered by a carbon dioxide membrane, usually silicone, with an electrolyte (sodium bicarbonate-sodium chloride) solution entrapped between them (Figure 6-17). When carbon dioxide from the outer sample diffuses through the semipermeable membrane, it lowers the pH of the inner solution ... 

Apart from the passive encapsulation methods, different active entrapment techniques are described in the literature. Nichols and Deamer (1976) prepared liposomes with a pH gradient across the membrane (acidic interior with respect to the external buffer). These liposomes efficiently incorporated several catecholamines added to the external buffer. The same technique has been used to concentrate doxorubicin (DXR) in pH gradient liposomes (Mayer et al., 1986b). 

Fig. 6 Method of (salen)MnCl entrapment into polysiloxane membranes...

The most important physical methods are physical and ionic adsorption on a water-insoluble matrix, inclusion and gel entrapment, and microencapsulation with a liquid or a solid membrane. The most important chemical methods include covalent attachment to a water-insoluble matrix, cross-hnking with the use of a multifunctional, low-molecular weight reagent, and co-cross-linking with other neutral substances, for example proteins. 

Concerning the mechanism of action of catechins, studies carried out on S. aureus and E. coli cells by Ikigai et al. [72] reported that their bactericidal effect is primarily involved in the damage of bacterial membranes catechins induce a rapid leakage of small molecules entrapped in the intraliposomal space, determining the aggregation of the liposomes. These actions cause damage in the membrane lipid bilayer and cell death (Table 1). 

Flux Decline Plugging, Fouling, Polarization Membranes operated in NFF mode tend to show a steady flux decline while those operated in TFF mode tend to show a more stable flux after a short initial decline. Irreversible flux decline can occur by membrane compression or retentate channel spacers blinding off the membrane. Flux decline by fouling mechanisms (molecular adsorption, precipitation on the membrane surface, entrapment within the membrane structure) are amenable to chemical cleaning between batches. Flux decline amenable to mechanical disturbance (such as TFF operation) includes the formation of a secondary structure on the membrane surface such as a static cake or a fluid region of high component concentration called a polarization layer. 

Scale prevention methods include operating at low conversion and chemical pretreatment. Acid injection to convert COs to CO2 is commonly used, but cellulosic membranes require operation at pH 4 to 7 to prevent hydrolysis. Sulfuric acid is commonly used at a dosing of 0.24 mg/L while hydrochloric acid is to be avoided to minimize corrosion. Acid addition will precipitate aluminum hydroxide. Water softening upstream of the RO By using lime and sodium zeolites will precipitate calcium and magnesium hydroxides and entrap some silica. Antisealant compounds such as sodium hexametaphosphate, EDTA, and polymers are also commonly added to encapsulate potential precipitants. Oxidant addition precipitates metal oxides for particle removal (converting soluble ferrous Fe ions to insoluble ferric Fe ions). 

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