Cellulose cuprophane

Fig. 5. Scanning electron micrographs of hoUow fiber dialysis membranes. Membranes in left panels are prepared from regenerated cellulose (Cuprophan) and those on the right from a copolymer of polyacrylonitrile. The ceUulosic materials are hydrogels and the synthetic thermoplastic forms a microreticulated open cell foam with a tight skin on the inner wall. Pictures at top are membrane cross sections those below are of the wall region. Dimensions as indicated.

Various membranes are in common use for the filtration of blood during dialysis. In this investigation cellulosic (Cuprophan) and synthetic (acryl nitrile, SPAN) capillary membranes were tested. The fluorine gas treatment was performed as described before. Three parameters are chosen for the assessment... 

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... 

The hollow fibre is the most crucial part of the microdialysis probe. It acts as a membrane, and its characteristics affect performance in the sampling step as well as the probe s suitability for the selected application. Hollow fibres are commercially available in different materials, the most common being polycarbonate (PC), regenerated cellulose (Cuprophan, CU), cellulose acetate (CA), polyacrylonitrile (PAN), polyethersulphone (PES), polysulphone (PE), and polyamide (PA). Generally, the fibres have an outer diameter between 200... 

The first hemodialysis devices utilized natural cellulose (cuprophan) membranes, which possessed predominantly small pores. These membranes permitted the removal of excess fluid, ions, and small molecules, but prohibited the removal of substances above approximately 1200 Da in size. Larger molecules, such as P2-microglogulin (P2M, ll.SkDa), accumulated in the blood and were thought to contribute to many of the additional health problems and high mortality of patients on dialysis. This idea, coined the middle molecule hypothesis by Bapp et al. [342], led to the development of new synthetic polysulfone or polyacrylonitrile dialysis membranes that possessed larger pores and, in combination with equipment to control transmembrane pressure, permitted more efficient elimination of middle molecules. 

Figure 7.18. A plot of K yiv cos 0 versus yiv obtained for eleven liquids by using three differently modified cellulose hollow fibres O, unmodified cellulose (CUPROPHAN) , chemically modified cellulose (Ml) chemically modified cellulose (M2) (from ref. (44)), reproduced with permission from Springer-Verlag...

Hollow Fiber with Sorbent Walls. A cellulose sorbent and dialy2ing membrane hoUow fiber was reported in 1977 by Enka Glan2stoff AG (41). This hoUow fiber, with an inside diameter of about 300 p.m, has a double-layer waU. The inner waU consists of Cuprophan ceUulose and is very thin, approximately 8 p.m. The outer waU, which is ca 40-p.m thick, consists mainly of sorbent substance bonded by ceUulose. The advantage of such a fiber is that it combines the principles of hemodialysis with those of hemoperfusion. Two such fibers have been made one with activated carbon in the fiber waU, and one with aluminum oxide, which is a phosphate binder (also see Dialysis). 

With either type of dialysis, studies suggest that recovery of renal function is decreased in ARF patients who undergo dialysis compared with those not requiring dialysis. Decreased recovery of renal function may be due to hemodialysis-induced hypotension causing additional ischemic injury to the kidney. Also, exposure of a patient s blood to bioincompatible dialysis membranes (cuprophane or cellulose acetate) results in complement and leukocyte activation which can lead to neutrophil infiltration into the kidney and release of vasoconstrictive substances that can prolong renal dysfunction.26 Synthetic membranes composed of substances such as polysulfone, polyacrylonitrile, and polymethylmethacrylate are considered to be more biocompatible and would be less likely to activate complement. Synthetic membranes are generally more expensive than cellulose-based membranes. Several recent meta-analyses found no difference in mortality between biocompatible and bioincompatible membranes. Whether biocompatible membranes lead to better patient outcomes continues to be debated. 

Figure 12.4 Solute permeability relative to the permeability of a film of water for various solutes in a regenerated cellulose membrane (Cuprophan 150). This type of membrane is still widely used in hemodialysis devices...

Fig. 18 a, b. Typical permeabilities of various hydrogels to water and various solutes (a) Water permeability at pressures less than 7 x 107 dyne/cm2 531 (1) = polyelectrolyte complex of poly-(sodium styrenesulfonate) (NaSS)-poly(4-vinylbenzyltrimethylammonium chloride) (PVBMA), (2) = crosslinked hydrogel of poly(2-hydroxyethyl methacrylate), (3) - cellulose (b) Dialytic permeability of a polyelectrolyte complex composed of NaSS-PVBMA to solutes with various molecular weights541 (1) Water, (2) neutral polyelectrolyte complex (water content = 70%), (3) anionic polyelectrolyte complex (water content = 61%), (4) cellophane and cuprophane (water content = 57%)... 

The membranes produced from polyelectrolyte complexes on the basis of weak polyelectrolytes, e.g. poly(carboxylic adds) (PAA and PMAA) and polyamines [poly(2-N,N-dimethylaminoethyl methacrylate), polyethylenepiperidine, polyethyl-enepyperasine, polyethylenimine] have been prepared140,141 and used in dialysis and ultrafiltration. Permeability coeffirients of membranes made from poly electrolyte complexes are much higher (4 and 20 times, resp.) in comparison with the cellulose-based membranes (Cuprophane, Film 1(M)). 

In dialysis, size exclusion is the main separation mechanism, while osmotic pressure and concentration difference drive the transport across two typically aqueous phases. While dialysis is used in some analytical separations, dialysis for the removal of toxins from blood (hemodialysis) is the most prominent application for hollow fiber technology in the biomedical field. The hemodialyzers are used to treat over one million people a year and have become a mass produced, disposable medical commodity. While the first hemodialyzers were developed from cellulosic material (Cuprophane, RC, etc.), synthetic polymers such as polyacrylonitrile, poly(ether) sulfone, and polyvinyl pyrrolidone are increasingly used to improve blood compatibility and flux. Hemodialyzer modules consist of thousands of extremely fine hollow fibers... 

A third possible complicating factor in rejection measurements, especially with protein solution, is physical Interaction of the solute with the membrane surface. Solute adsorption, for example, could alter the parameters L, a or P and cause anamo-lous rejection. An earlier search O for adsorption effects by a cellulosic membrane was negative. Although other investigators have reported such effects with non-cellulosic membranes, the effects with Cuprophan fibers were not observed, and adsorption parameters were not included in this transport model. 

Samples. Cuproammonium cellulose fibers made by Enka Glanzstoff AG were used in the study. The fibers designated Cuprophan HDE, (Table I) are Intended for application in hemofiltration and generally are characterized by having 5 to 10 times the hydraulic permeability of similar fibers made for hemodialysis. Fiber samples were tested in dog-bone shaped experimental dlalyzers having fiber lengths of 20.5 cm and filament numbers of 2940, 5870, and 8800. With a nominal inside fiber diameter of 0j0215 cm, surface areas of these devices were... 

Dialyzer membrane bioincompatibility, hence complement activation, is maximal with the first use of cuprophane membranes, is considerably less with cellulose acetate, and is negligible or absent with polyacrylonitrile and polymethacrylate membranes. With dialyzer reuse, complement activation is greatly attenuated (C2). The effects of dialysate and dialyzer on the induction of hypoxemia are additive, so that hypoxemia is greatest during the first use of a cuprophane membrane and acetate bath, but is much improved by the substitution of a bicarbonate bath. The use of a polyacrylonitrile or polymethacrylate membrane with a bicarbonate bath will not cause hypoxemia (D3). 

FIGURE 21-1 7 Membmae permeability P ( ) ned reflection coefficient ( ) versos sol me molecular weight for a regenerated cellulose membrane (Cuprophan 150 PM, Enks AG. Wuppertal, West Germany). Data From Ref. 36,... 

Sample preparation Dialyze 400 p.L plasma against 175 p.L acceptor solution through a 4 cm cuprophan (cellulose acetate, molecular mass cut-off 15000) membrane for 25 min at 20° and 10 min at 37°, inject 500 p-L acceptor solution (including the dialysis sample) onto column A at 0.5 mL/min, elute column A onto column B with mobile phase, remove column A from circuit and condition it with 1 mL acceptor solution, elute column B with mobile phase and monitor the effluent. Flush acceptor channel with 5 mL acceptor solution and plasma channel with 8 mL acceptor solution containing 50 p,g/mL Triton X-100. (Acceptor solution contained 5.9 g NaCl, 4.1 g sodium acetate, 0.3 g KCl, and 1.65 g sodium citrate in 1 L water, adjusted to pH 7.4 with citric add.)... 

To improve the delivery, 13-mm-diameter rate-controlling membranes held in a Swinnex filter chamber (Millipore Corp.) were inserted in the delivery line between the insulin reservoir and the micropump. The effective membrane area was 0.7 cm2. Membranes investigated were l- xm and 8- xm pore size polycarbonate filters (Nucle-pore Corp.), 0.45- xm cellulosic microporous filters (Amicon Corp.), Cuprophane PT-150 (from Ultra-Flow 145 Dialyser, Travenol Laboratories), and 0.2- xm and 1.2- xm pore size cellulose acetate filters (Schleicher and Schuell OE 66 and ST 69). 

Insulin deposition in the controlled-release micropump is not expected to be important. While it was significant in one of the prototypes (Figure 4), changing the rate-controlling membrane from a hydrophobic polycarbonate filter to a hydrophilic Cuprophane or cellulose acetate membrane has apparently eliminated the problem. Although the situation may be different as longer-term experiments are performed, presumably the problems that may arise may relate more to the biological stability of the insulin reservoir than to insulin deposition. 

Cellulose UF membranes are used in applications where low fouling characteristics are required. Cellulose has a very regular structure and is able to form strong intermolecular hydrogen bonds between the several hydroxy groups. As a result, cellulose is practically insoluble in almost all solvents. The only exceptions are dilute solutions in DM Ac or NMP with addition of lithium chloride. Cellulose membranes are prepared by methods that basically involve precipitation from a solution of chemically modified native cellulose (from cotton linters, etc.). Until some years ago the three main methods were based on cellophane, cuprophane and cuenophane. 

Pore-filling MIP composite membranes had been first prepared by Dzgoev and Haupt [100]. They casted the reaction mixture into the pores of a symmetric microfiltration membrane from polypropylene (cutoff pore size 0.2 pm) and performed a cross -linking copolymerization of a functional polyacrylate for imprinting protected tyrosine. Hattori et al. [101] had used a commercial cellulosic dialysis membrane (Cuprophan) as matrix and applied a two-step grafting procedure by, (i) activation of the cellulose by reaction with 3-methacryloxypropyl trimethoxysilane from toluene in order to introduce polymerizable groups into the outer surface layer, (ii) UV-initiation of an in situ copolymerization of a typical reaction mixture (MAA/EDMA, AIBN) for imprinting theophylline. 

Kasper et al. studied dialysis membranes made of Cuprophan (flat sheet) with AFM and observed differences between modified and immodified as well as between dry and wet membranes [34]. Modified membranes contained 5,10,15, 20,40, and 100% diethylaminoethylcellulose (DEAE). On the modified Cuprophan in air as well as under water. These strings maybe interpreted as cellulose fibrils, ordered more or less parallel to the membrane production process. 

Cellulose is a partially crystalline polysaccharide and is the chief constituent of plant fiber. Cotton is the purest natural form of cellulose, containing 90 percent cellulose. Cellulose decomposes before melting and therefore cannot be melt processed. It is insoluble in organics and water and can only be dissolved in strong basic solutions. Regenerated cellulose, also known as rayon, is cellulose that has been precipitated form a basic solution. Cellulose is used in bandages and sutures. Cuprophan is cellulose precipitated fix>m copper hydroxide solutions to form hemo alysis membranes. 

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