Unmodified Cellulosic Membrane

In order to solve the problems that occurred with unmodified cellulosic membranes, synthetic membranes were developed. The first synthetic polymeric membrane was produced in the early 1970s. Since that time, various synthetic polymers such as poly-sulfone, polyamide, poly(methyl methacrylate), polyethersulfone, polyethersulfone/ polyamide have been used in the production of synthetic hemodialysis membranes [20,21]. Synthetic membranes have large mean pore size and thick wall structure. These properties provide high ultrafiltration rate, which is necessary for hemodialysis to be achieved with relatively low transmembrane pressures [20]. The main difference in synthetic and cellulosic membranes is the chemical composition of the membrane. Synthetic membranes are made from manufactured thermoplastics, while both modified and unmodified cellulosic membranes are prepared from natural polymers [20]. 

Cellulosic membranes have dominated the market for many years. The discussion about the alleged lack of blood compatibility has finally provoked the end of their production of regenerated unmodified cellulose membranes... 

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. ... 

Much work has been done with polymers to create biocompatible surfaces that resist protein fouling, i.e., non specific adsorption. A membrane composed of modified polyethersulfone (PES) (Omega Membrane) resisted albumin (ALB) absorption 24 times better than unmodified PES, and three times better than regenerated cellulose, a material known to resist biofouling. We compared porous SiC, both n-type and p-type, to the Omega Membrane [14] and found a very similar resistance to ALB absorption (Figure 12.3). 

The reverse osmosis properties of the grafted films are presented in Tables I and II and in Figures 3 and 4. The results are most interesting in that the flux could be increased considerably, up to ten fold in the best case, while maintaining the salt rejection at a similar level to that of unmodified dense cellulose acetate. This was accomplished by the copolymerization of 2-vinyl pyridine and styrene or methyl methacrylate followed by quatemization. The full development of these findings would need the additional development of assymetric or ultra thin membranes from these materials. 

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