Medical artificial kidney

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. 

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... 

In this chapter, the use of membranes in medical devices is reviewed briefly. In terms of total membrane area produced, medical applications are at least equivalent to all industrial membrane applications combined. In terms of dollar value of the products, the market is far larger. In spite of this, little communication between these two membrane areas has occurred over the years. Medical and industrial membrane developers each have their own journals, societies and meetings, and rarely look over the fence to see what the other is doing. This book cannot reverse 50 years of history, but every industrial membrane technologist should at least be aware of the main features of medical applications of membranes. Therefore, in this chapter, the three most important applications—hemodialysis (the artificial kidney), blood oxygenation (the artificial lung) and controlled release pharmaceuticals—are briefly reviewed. 

This membrane industry is very fragmented. Industrial applications are divided into six main sub-groups reverse osmosis ultrafiltration microfiltration gas separation pervaporation and electrodialysis. Medical applications are divided into three more artificial kidneys blood oxygenators and controlled release pharmaceuticals. Few companies are involved in more than one sub-group of the industry. Because of these divisions it is difficult to obtain an overview of membrane science and technology this book is an attempt to give such an overview. 

Selective separation and concentration of both cations and anions using water-soluble polymer solutions LM as carriers and hoUow-fiber units (artificial kidneys) as membrane barrier were tested. The authors termed the process as affinity dialysis [74]. Hollow fiber units of Spectrum Medical Industries, Inc. with fibers of 5000 molecular weight cutoff and 150 cm surface area from Spectrapor were used in the experiments. 

This handbook emphasizes the use of synthetic membranes for separations involving industrial or municipal process streams. Little will be said concerning the use of membranes in medical applications as in artificial kidneys or for controlled drug release. 

Extracorporeal medical machines (e.g., artificial kidney, pump-oxygenator) perfused with blood have been an effective part of the therapeutic armamentarium for many years. These devices all rely on systemic heparinization to provide blood compatibility. Despite continuous efforts to improve anticoagulation techniques, many patients still develop coagulation abnormalities with the use of these devices (1-3). Even longer perfusion times may occur with machines such as the membrane oxygenator. In such cases, the drawbacks of systemic heparinization are multiplied (4). A number of ap-... 

Treatment consists of providing supportive medical care in a hospital setting. Blood transfusions and intravenous fluids (that is, fluids injected directly into a vein) may be needed. Some people may require hemodialysis (artificial kidneys) for kidney failure. No antidotes are available for arsine. 

A very common commercial device for hemodialysis is the C-DAK 4000 artificial kidney of Althin CD Medical, Inc. (acquired by Baxter International, Inc. in March, 2000). This disposable, sterilized membrane module, shown in Figure 19.5, resembles a shell-and-tube heat exchanger. The tubes, which number 10,000, are hollow fibers, 200 microns i.d. by 10 microns wall thickness by 22 cm long, made of hydrophilic microporous cellulose acetate of 15 to 100 A pore diameter. Alternatively, fibers of polycarbonate, polysulfone, and other poly-... 

Of medical and biotechnical importance are the thicker homogeneous gel membranes, such as Cuprophane , which are used in the artificial kidney and/or concentration dialysis. With the Cuprophane membranes, diffosional nugration, driven by concentration differences across the membrane, effects flie transport of the various species across the membrane and little, if any, pressure differential is applied. 

Enzymes may also be immobilized by microencapsulation. In this technique, which has medical applications, enzymes are enclosed by various types of semi-permeable membrane, e.g. polyamide, polyurethane, polyphenyl esters and phospholipids. Microcapsules of phospholipids are also called liposomes. The micro-encapsulated enzymes and proteins inside the micro-capsule cannot pass the membrane envelope, but low M, substrates can pass into it, and products can leave. Such encapsulated proteins do not elicit an antigenic response, and they are not attacked by proteases outside the microcapsule. They are therefore suitable for the delivery of enzymes for therapeutic purposes. This area of application is still at an early stage of development, but positive results have been reported from animal experiments and clinical studies, e.g. treatment of inherited catalase deficiency with encapsulated catalase. There are various methods of administration intramuscular, subcutaneous or intraperito-neal injection. However, their major area of application is outside the body. For example, microencapsulated urease can be employed as an artificial kidney in hemodiffusion (Rg.2). 

Medical Syringes, blood aspirators, intravenous connectors and valves, petri dishes, and artificial kidney devices... 

A microcontroller is a self-contained computing system with peripherals, memory, and central processing unit. Mostly the system is embedded into any products/systems for which its used. For this reason, it is also referred to as embedded controller. The largest single use for microcontrollers is in the automobile industry, but it finds its application in almost all day-to-day use devices such as ovens, toasters, and clock systems. Also it has a number of applications in medical units viz. an artificial kidney or heart. Even in sophisticated spacecraft, microcontrollers are used. In instrumentation, there has been extensive use of microcontrollers, viz. sensor, field controller, positions, etc. Naturally some knowledge about the same is essential for studying SIS. 

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