Polymethylmethacrylate membranes

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. 

Hollow membrane fibers are required for many medical application, e.g. for disposable dialysis. Such fibers are made by usmg an appropriate fiber spinning technique with a special inlet in the center of the spinneret through which the fiber core forming medium (liquid or gas) is injected. The membrane material may be made by melt-spinning, chemical activated spinning or phase separation. The thin wall (15-500 xm thickness) acts as a semi-permeable membrane. Commonly, such fibers are made of cellulose-based membrane materials such as cellulose nitrate, or polyacrylonitrile, polymethylmethacrylate, polyamide and polypropylene (van Stone, 1985). 

Figure 3.15. A two-step molding process for fabricating a microporous metal membrane by using polymethylmethacrylate (PMMA) as an intermediate template [Masuda et al., 1993]...

Blends of isotactic and atactic polymethylmethacrylate (PMMA) in solution have been used to form semipermeable membranes, for both hemodialysis and hemofiltration. Details of the polymer properties are not available (18). 

For hip surgeries, the protection of the acetabulum is provided by a deposit on the metal of the prosthesis of a layer of polyethylene with a very high cross-linked mass using y radiation. Inguinal hernias are treated by the introduction of a polypropylene membrane. Cataracts are treated by the extraction of the natural crystalline lens, and replacing it with a substitute in polymethylmethacrylate. 

A promising technique for residual monomer removal is pervaporation, as no additional chemicals are needed for this membrane process and the energy costs are typically low. It has been shown that pervaporation can remove a considerable amount of acryhc monomer from polymethylmethacrylate (PMMA) latexes [15]. Apparently, the Hmiting factor for mass transfer does not occur in the polymer particles, mainly because of the high specific area of the polymer-water interface as compared to the membrane area. Although the high initial costs, as well as fouling of the membrane surface with the polymer particles, are potential drawbacks, pervaporation may thus be expected to provide a viable alternative. 

As of 1995, more than 30 different polymer blends were being used in the manufacture of membranes for hemodialysis and hemofiltration (Klinkmann and Vienken, 1995). The various membrane types used for renal replacement therapy can be divided into membranes derived from cellulose (83 percent of 1991 worldwide total) and from synthetic materials (the remaining 17 percent) (Klinkmann and Vienken, 1995). Synthetic membranes have been constructed from such materials as polyacrylonitrile (PAN), polysulfone, polyamide, polymethylmethacrylate, polycarbonate, and ethyl-vinylalchohol copolymer (Klinkmann and Vienken, 1995). In the United States, use of cellulosic materials for membrane construction predominates at around 95 percent of the total number of membranes used (Klinkmann and Vienken, 1995). 

The first electrode of this type was based on the Ca-dodecylphos-phate/dioctylphenyl phosphonate system [71]. A mixture of 5% PVC in cyclohexanone and 0.1 M calcium dodecylphosphate in dioctylphenyl phosphonate was dried on the end of a platinum wire. This electrode exhibits greater selectivity for Ca-" over other divalent cations, as compared to traditional i.s.e.s, with the exception of Pb-" and. Its response relies upon the complexation of aqueous Ca by dodecylphosphate dispersed in the organic (membrane) phase. Anion-selective CWEs can be prepared in a similar manner, e.g., by the incorporation of methyltricaprylammonium salts into a polymer membrane placed on a copper wire [72]. Other mediators, including particularly neutral carriers, show promise for utilization in CWE construction. In some cases, polymethylmethacrylate or epoxy resin could be substituted for PVC with retention of response. 

Since flat membranes are relatively simple to prepare, they are very useful for testing on a laboratory scale. For very small membrane surface areas (less than 1000 cm ), the membranes are cast mostly by hand or semi-automadcally, not on a non-woven polyester but often on a glass plate (other materials can also be used, e. g. metals, and polymers such as polytetrafluoroethylene, polymethylmethacrylate etc.). The same procedure is followed as that depicted in figure HI - 5. 

The essential feature of the pressurized ultramicro chamber system is that the sorbent layer is completely covered with a flexible membrane under an external pressure so that the vapor phase above the layer is virtually eliminated (20-22). In this chamber system it is possible to optimize the flow velocity of the eluent by means of a pump. The principle of pressurized ultramicro chamber made of polymethylmethacrylate and used mainly for circular separation is illustrated in Fig. 11. 

Fig. 13.1 Polymers used for medical devices for dialysis and peritoneal dialysis. Polyurethane (PUR) is applied as potting material for capillary membranes, silicone tings guarantee a leak-age-free system, polycarbonate and polypropylene are used for casings, and a series of polymers are incorporated as membrane materials (P5M-polysulfone, P S-polyether-sulfone, PA-polyamide, PAAf-polyacrylonitrile, PMMA-polymethylmethacrylate, CIA-cellulose-tri-acetate). PUC-polyvinylchloride as a biomaterial for tubing needs plasticizers for its flexibility, such as D 7/P/DOP-di-ethyl-hexylphthalate/di-octyl-phthalate, TOTM-tn-octyl trimeUitate, DWCif-di-isononyl-cyclohexane...

Various polymers have been successfully electrospun from solution, sol-gel suspension, or melt into ultrafine nanotibers. For example, as listed in Table 13.2, these polymers included nylon-6 [20, 21], polyacrylonitrile (PAN) [22, 23], polyethylene terephthalate (PET) [24], polyvinyl alcohol (PVA) [25], polystyrene (PS) [26, 27], polyvinylidene fluoride (PVDF) [28, 29], polyethersulfone (PES) [30], polyimides (PI) [31, 32], polyethylene oxide (PEO) [33], polyurethanes (PU) [34], polycarbonates (PC) [35], polycaprolactone (PCL) [36], polybenzimidazole (PBI) [37, 38], polyvinylpyrrolidone (PVP) [39], polytrimethylene terephthalate (PTT) [40], polyvinyl chloride (PVC) [41], polymethylmethacrylate (PMMA) [42], hydrox-ypropyl cellulose (HPC) [43], polyglycolic acid (PGA) [44], polyhydroxybutyrate (PHB) [45], cellulose acetate (CA) [46,47] and many more. To be used as filtration membranes, nanoflbers made of water-soluble polymers have to be further cross-linked after the electrospinning process. As polymers having different physical and... 

Capillary membranes (microporous hollow fibers) are an integral part of artificial lungs and kidneys. They represent extracorporeal applications where both the fibers and the textile structure are in direct contact with biood. For hemodialysis, mainly fibers made from cellulose, polysulfone, polymethylmethacrylate, and polyacrylonitrile are used. In oxygenators, mainly microporous hollow fibers made from polymethylpentene and silicone are used. Microporous hollow fibers can be... 

Hoenich, N. A. (1998). Platelet and leukoc3de betiaviour during hemodialysis. In C. Ronco (Ed.), Contribution in Nephrology, Vol. 125, Polymethylmethacrylate. A Flexible Membrane for a Tailored Dialysis. Karger, Basel, p. 76. 

Noncellulosic Synthetic Membranes In the dialysis field, the term synthetic membrane is used to denote all polymeric membranes that are not cellulose based. Table 19.2 lists the various synthetic membranes that are commercially available. Polymers such as polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), and ethylene vinyl alcohol (EVAL) copolymer were adapted from the textile industry, while polymers such as polysulfone, polycarbonate, and polyurethane were developed as engineering plastics. Synthetic membranes with high water permeability were developed in the 1960s... 

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