Artificial Kidney Membrane

Although the data show a relationship between the ability of a surface to adsorb fibrinogen out of plasma, the plasma s inability to convert this fibrinogen, and the tendency of platelets to adhere, it does not confirm that adsorption of fibrinogen must precede adhesion of platelets to all kinds of surface, or that surfaces which adsorb fibrinogen under these conditions will be bad biomaterials in vivo as heart valves, blood vessels, or canulae, or ex vivo as artificial kidney membranes—even though the latter are most likely to be impeded by any adsorbate. 

Chitosan membranes have been proposed as an artificial kidney membrane because of their suitable permeability and high tensile strength. Chitosan and its same derivatives are used to prepare scaffolds for tissue engineering applications. It can also be used for designing artificial skin, treatment of brain-scalp damage, and in plastic skin surgery. Chitosan has replaced the synthetic polymers in ophthalmo-logical applications due to its characteristic properties such... 

Not only fibres can be produced with such technologies. Once the cellulose or its derivative is dissolved, this dope can be shaped into other bodies like hollow fibres for membrane applications (artificial kidney), membrane films, packaging films (e.g. Cellophane), self-adhesive tapes (Sellotape), or sponges. 

Dialyzer. One of the most successful products derived from membrane technology is the artificial kidney. Membranes are used to remove metabolites accumulated in the blood. 

From several hours to one day Fixation of a hydrophobic polymer Artificial kidney membrane... 

Artificial kidney membranes prepared from modified and albumin-blended chitosan membranes were found to be potential candidates for dialysis applications [135]. These membranes displayed a superior permeability properties for smaller molecules compared to the standard cellulose membranes, and interestingly showed maximum reduction in platelet adhesion in comparison to other membranes [136,137]. 

Wet spinning of this type of hoUow fiber is a weU-developed technology, especiaUy in the preparation of dialysis membranes for use in artificial kidneys. Systems that spin more than 100 fibers simultaneously on an around-the-clock basis are in operation. Wet-spun fibers are also used widely in ultrafiltration appUcations, in which the feed solution is forced down the bore of the fiber. Nitto, Asahi, Microgon, and Romicon aU produce this type of fiber, generaUy with diameters of 1—3 mm. 

Spira.1- Wound Modules. Spiral-wound modules were used originally for artificial kidneys, but were fuUy developed for reverse osmosis systems. This work, carried out by UOP under sponsorship of the Office of Saline Water (later the Office of Water Research and Technology) resulted in a number of spiral-wound designs (63—65). The design shown in Figure 21 is the simplest and most common, and consists of a membrane envelope wound around a perforated central coUection tube. The wound module is placed inside a tubular pressure vessel, and feed gas is circulated axiaUy down the module across the membrane envelope. A portion of the feed permeates into the membrane envelope, where it spirals toward the center and exits through the coUection tube. 

In terms of membrane area used and doUar value of the membrane produced, artificial kidneys are the single largest appHcation of membranes. Similar hoUow-fiber devices are being explored for other medical uses, including an artificial pancreas, in which islets of Langerhans supply insulin to diabetic patients, or an artificial Uver, in which adsorbent materials remove bUinibin and other toxins. 

One unique appHcation area for PSF is in membrane separation uses. Asymmetric PSF membranes are used in ultrafiltration, reverse osmosis, and ambulatory hemodialysis (artificial kidney) units. Gas-separation membrane technology was developed in the 1970s based on a polysulfone coating appHed to a hoUow-fiber support. The PRISM (Monsanto) gas-separation system based on this concept has been a significant breakthrough in gas-separation... 

Cellulose acetate films, specially cast to have a dense surface and a porous substmcture, are used in reverse osmosis to purify brackish water (138—141) in hollow fibers for purification of blood (artificial kidney) (142), and for purifying fmit juices (143,144) (see Membrane technology). 

While it would be difficult to enumerate all of the efforts in the area of implants where plastics are involved, some of the significant ones are (1) the implanted pacemaker, (2) the surgical prosthesis devices to replace lost limbs, (3) the use of plastic tubing to support damaged blood vessels, and (4) the work with the portable artificial kidney. The kidney application illustrates an area where more than the mechanical characteristics of the plastics are used. The kidney machine consists of large areas of a semi-permeable membrane, a cellulosic material in some machines, where the kidney toxins are removed from the body fluids by dialysis based on the semi-permeable characteristics of the plastic membrane. A number of other plastics are continually under study for use in this area, but the basic unit is a device to circulate the body fluid through the dialysis device to separate toxic substances from the blood. The mechanical aspects of the problem are minor but do involve supports for the large amount of membrane required. 

The evaluation of the apparent ionization constants (i) can indicate in partition experiments the extent to which a charged form of the drug partitions into the octanol or liposome bilayer domains, (ii) can indicate in solubility measurements, the presence of aggregates in saturated solutions and whether the aggregates are ionized or neutral and the extent to which salts of dmgs form, and (iii) can indicate in permeability measurements, whether the aqueous boundary layer adjacent to the membrane barrier, Umits the transport of drugs across artificial phospholipid membranes [parallel artificial membrane permeation assay (PAMPA)] or across monolayers of cultured cells [Caco-2, Madin-Darby canine kidney (MDCK), etc.]. 

Haemodialysis equipment parts, membranes for artificial kidneys, blood purification. .. 

Physical or physico-chemical capability (Table 1), including mechanical strength, permeation, or sieving characteristics, is another important requirement of biomaterials. Cuprammonium rayon, for instance, maintains its dominant position as the most popular material for hemodialysis (artificial kidney). Thanks to its good mechanical strength, cuprarayon can be fabricated into much thinner membranes than synthetic polymer membranes as a consequence, much better clearance of low-molecular-weight solutes is achieved. 

The main form of artificial kidney is the hemodialyzer, which uses semipermeable membranes to remove urea and other metabolic wastes, as well as some water... 

Grafting ethyleneimine onto cellophane followed by conventional heparinization yielded a product used in making the membranes for artificial kidney which displayed good thromboresistance 80). 

Liquid membranes of the water-in-oil emulsion type have been extensively investigated for their applications in separation and purification procedures [6.38]. They could also allow extraction of toxic species from biological fluids and regeneration of dialysates or ultrafiltrates, as required for artificial kidneys. The substrates would diffuse through the liquid membrane and be trapped in the dispersed aqueous phase of the emulsion. Thus, the selective elimination of phosphate ions in the presence of chloride was achieved using a bis-quaternary ammonium carrier dissolved in the membrane phase of an emulsion whose internal aqueous phase contained calcium chloride leading to phosphate-chloride exchange and internal precipitation of calcium phosphate [6.1]. 

Perhaps the most important medical use of dialysis is in artificial kidney machines, where hemodialysis is used to cleanse the blood of patients whose kidneys have malfunctioned. Blood is diverted from the body and pumped through a cellophane dialysis tube suspended in a solution formulated to contain many of the same components as blood plasma. These substances—glucose, NaCl, NaHC03, and KC1—have the same concentrations in the dialysis solution as they do in blood, so that they have no net passage through the cellophane membrane. 

Six developed and a number of developing and yet-to-be-developed industrial membrane technologies are discussed in this book. In addition, sections are included describing the use of membranes in medical applications such as the artificial kidney, blood oxygenation, and controlled drug delivery devices. The status of all of these processes is summarized in Table 1.1. 

Medical applications of membranes Artificial kidneys Artificial lungs Controlled drug delivery Well-established processes. Still the focus of research to improve performance, for example, improving biocompatibility... 

The membrane separation processes described above represent the bulk of the industrial membrane separation industry. Another process, dialysis, is not used industrially but is used on a large scale in medicine to remove toxic metabolites from blood in patients suffering from kidney failure. The first successful artificial kidney was based on cellophane (regenerated cellulose) dialysis membranes and was developed in 1945. Over the past 50 years, many changes have been made. Currently, most artificial kidneys are based on hollow-fiber membranes formed into modules having a membrane area of about 1 m2 the process is illustrated in Figure 1.7. Blood is circulated through the center of the fiber, while isotonic... 

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