Modified cellulose membranes

Modified carbon fibers, 13 383-385 Modified cellulosic membranes, in hemodialysis, 26 825, 826-828t Modified chemical vapor deposition (MCVD), in fiber optic fabrication, 11 136-137, 138, 139 Modified-Claus sulfur recovery process, 23 601, 602... 

There are three types of membranes based on the type of the polymer used in the membrane preparation. They are cellulosic, modified cellulosic and synthetic membranes (D. M. Ruthven, Encyclopedia of Separation Technology, John Wiley Sons, 1997). Here the authors only discuss cellulosic and modified cellulosic membranes. 

Hattori and coworkers exploited both the living characteristics and photoactivation mechanism of STIMP to create MIPs consisting of methacrylic acid (MAA) and ethyleneglycol dimethacrylate (EDMA) synthesized from iniferter-modified cellulose membranes in the presence of theophylline, which served as the template molecule [76]. In addition to the ability to control polymer architecture, they observed that the STIMP photoactivation mechanism avoids template-monomer complexation, which is highly undesirable but usually observed in MIPs synthesized by thermally activated polymerization methods [76]. The MAA and EDMA comonomer system has also been used to synthesize MIPs from iniferter-modified carbon nanotubes... 

Modified cellulose membranes Methyl vinyl United States 3,498,841 1970 Borden... 

Roeckel, A., Hertel, J., Fiegel, R, Abdelhamid, S., Panitz, N., and Walb, D. (1986). Permeability and secondary membrane formation of a high flux polysulfone membrane. Kidney Int. 30, 429. Sasaki, M., Hosoya, N., and Saruhashi, M. (2000). Vitamin E modified cellulose membrane. Artif. Organs 24(10), 779. 

Complement Activation Complement proteins are so-named because they complement antibody activity to eliminate pathogens. The alternate pathway of the complement cascade is normally activated by bacterial surface molecules. Complement activation during dialysis was first identified by the rapid drop in white blood cell counts (neutropenia) during the first 30 min of dialysis. Regenerated cellulose membranes activate complement through the alternate pathway (Chenoweth et al., 1983). Modified cellulose membranes approach the biocompatibility profile of synthetic materials in terms of neutropenia and complement activation. 

TABLE 19.1 Cellulose and Modified Cellulose Membranes Used in Hemodialyzers Today... 

Platelet adhesion tests on the modified cellulose membranes were done in the modified Baumgartner chamber under shear rates of 1050 sec" with citrated whole blood as described earlier Platelet adhesion tests with silicon tubes were done with citrated whole blood without any contact to unmodified surface. Luminal modified silicone tubes with regioselective modified heparin derivatives were prepared as earlier described The platelet adhesion has been measured before and after the test via percentage loss of platelets. ... 

The flow behavior in miniaturized hemodialyzer modules with two types of biocompatible membrane materials, SMC and SPAN, was investigated by using doubly distilled water as the flowing fluid in both compartments, subsequently termed membrane side (M) and dialysate side (D), respectively (Figure 4.6.1 (c, d)) [12], SMC stands for Synthetically Modified Cellulose and SPAN for Special PolyAcryloNitrile-based copolymer (Akzo Nobel, Membrana GmbH), both types representing standard membrane material. The capillaries made from this hollow... 

SPAN module. It was mentioned at the beginning that the special polyacrylonitrile fibers of SPAN have a wall thickness of 30 gm, which is considerably thicker than the 8 gm wall thickness of the SMC modules [19]. As a consequence, the presence of stronger capillary effects from the special porous fiber material of the SPAN module would be a reasonable conclusion. Furthermore, the texture of the special polyacrylonitrile fibers is expected to have better surface properties, supporting the permeation of molecules as compared with synthetically modified cellulose. In conclusion, both convection and diffusion effectively contribute to the filtration efficiency in a SPAN module, whereas for the SMC membrane, diffusion is the driving force for molecular exchange, the efficiency of which is also considerable and benefits from the large surface-to-volume ratio. 

The effect of casting solution composition on flux and rejection of formamide-modified cellulose acetate membranes is shown in Figure 1, illustrating the general capability of this membrane type as function of solvent concentration. Membranes of casting solution composition cellulose diacetate/acetone/ formamide 23/52/25 (solvent-to-polymer ratio 2.26) were used as reference membranes in this work. 

Figure 6. Low-pressure reverse osmosis performance of ammonia-modified cellulose diacetate membranes (IV) compared with formamide-modified reference membranes (I)...

Problems of desorption and loss of activity encountered with natural heparin have led numerous workers to explore synthetic heparin-like polymers or heparinoids, as reviewed by Gebelein and Murphy [475, 514, 515]. The blood compatibility of 5% blended polyelectrolyte/polyfvinly alcohol) membranes was studied by Aleyamma and Sharma [516,517]. The membranes were modified with synthetic heparinoid polyelectrolytes, and surface properties (platelet adhesion, water contact angle, protein adsorption) and bulk properties such as permeability and mechanical characteristics were evaluated. The blended membrane had a lower tendency to adhere platelets than standard cellulose membranes and were useful as dialysis grade materials. 

The Methocel matrix, formulation A, was further investigated using the hairless mouse skin as the diffusion barrier. Here the drug release was observed to be reduced significantly to 1.3mg/ (24h) compared with 11.75 mg/(24h) through the cellulose membrane. The formulation was further modified with the inclusion of... 

At high pH (10), Traut s reagent also is reactive with aliphatic and aromatic hydroxyl groups, although the rate of reaction with these groups is only about 0.01 that of primary amines. In the absence of amines, however, carbohydrates such as agarose or cellulose membranes can be modified to contain sulfhydryl residues (Alagon and... 

Dansylglycine-modified cyclodextrin (DnsC4-/i-CD) was found to be capable of being immobilised on a cellulose membrane and of acting as a fluorescence sensor for enantiomers [36]. DnsC4-/J-CD decreased its fluorescence intensity upon exposure to guest molecules. This result implicates a useful application of a cellulose membrane as a supporting material for various... 

Gunasingham H, Teo P, Lai Y, Tan S. Chemically modified cellulose acetate membrane for biosensor applications. Biosensors 1989, 4, 349-359. 

Later the same research group claimed that, in the first step of the in situ synthesis scheme, ionic functional groups as such are not necessary for the introduction of ferrous ions into a cellulose matrix [161,162], This suggestion was made based on a comparative study of ferrite synthesis between a case with anionically modified cellulose materials and the other case with non-ionic cellulose gels, which included a never-dried bacterial cellulose (BC) membrane and a never-dried cellulose wet-spun filament or cast film (Lyocell) using N-methylmorpholin-N-oxide as the solvent. SPM proper-... 

There are two types of membranes, cellulosic and synthetic or polymeric ones. Cellulosic membranes can be in regenerated cellulose (cuprophan, Bioflux from Membrana, Germany) or modified cellulose (cellulose acetate or diacetate, from Asahi, triacetate cellulose from Baxter and Nipro, which has a high hydraulic permeability or Hemophan from Membrana). Cuprophan was originally the most common one, because of its low cost, but is no longer produced because of its lower biocompatibility and hydraulic permeability. A wide variety of polymeric membranes are now available with both high and medium hydraulic permeabilities. Only the Eval... 

If not noted elsewhere, all data correspond to the preparation of a 10 x 12 cm cellulose membrane (96-well plate size). For larger membranes preparation of related amounts of reagents is required. If we write about the use of amino acids, it should always include the use of other organic building blocks (e.g., PNA monomers, peptoidic elements, heterocycles) (22,23), which can be used under spot synthesis conditions. Here we describe only the basic procedures for spot synthesis of linear peptides. For the synthesis of modified peptides, such as cyclization or side-chain modifications, see ref. (24). 

Hjartstam, J. (1998), Ethyl Cellulose Membranes Used in Modified Release Formulations, Chalmers University of Technology, Goteborg, Sweden. 

Cellulosic Membranes. The first asymmetric membrane for gas separation appeared in 1970 (Table II), and It was not surprising that this membrane was a modified CA membrane of the Loeb-Sourirajan type (17). Gelled CA membranes for water desalination must be stored wet In order to maintain their permeation performance. However, In gas permeation, wet, plasticized membranes tend to lose their properties with time due to plastic creep of the soft material under pressure and due to slow drying during which the microporous sublayer may collapse and thus increase the thickness of the dense skin-layer. Gantzel and Merten (17) dried CA membranes with an acetyl-content of 39.4% by quick-freezing and vacuum sublimation at... 

Modification of Polymers. One way to solve the problem of finding good polymers for membranes is to make modifications of the chemical structure of the polymer. Sulphonation for instance of polysulphone (19) is a well known example of how a hydrophobic polymer can be modified to a hydrophilic polymer with charged groups. Other attemps have been made, for instance to modify cellulose acetate by putting charged positive groups in the form of quaternary ammonium into the polymer (20). 

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