Hemodialysis membranes materials

In hemodialysis, blood from the patient flows on one side of a membrane and a specially prepared dialysis solution is fed to the other side. Waste material in the blood such as urea, excess acids, and electrolytes diffuse into the dialysate the blood is then returned to the patient, as shown in Fig. 48. A patient typically undergoes dialysis three times per week in sessions lasting several hours each. Modern dialysis systems combine sophisticated monitoring and control functions to ensure safe operation. Regenerated cellulose was the first material used in hemodialysis membranes because of its biocompatibility and low cost it remains the most popular choice. Subsequently, high-permeability dialysis membranes derived from cellulose esters, modified polysulfone, or polyacrylonitrile copolymers have also gained wide acceptance because of the shorter sessions they make possible. 

Polyethylene-co-vlnylaloohol/polyethylene-co-vinylacetate (PVA) polymers have been fabricated into membranes for both hemodialysis and microfiltration. The fabrication procedure and physical properties of the finished membrane material have not been published. Both the PMMA and PVA membranes have been developed in Japan, where most of the application studies have been performed. 

One aspect of RRT that is overlooked by most clinicians is which hemodialyzer or hemofilter is used during the treatment. The material used to make the membranes of hemodialyzers (for hemodialysis) and hemofilters (for hemofiltration) varies by manufacturer, and recent evidence suggests that which membrane material is used may influence the outcomes of patients with ARF. When blood comes into contact with these membranes, the complement cascade is activated, resulting in an immune reaction. Each type of membrane induces complement to a different degree. Those that cause less of a complement cascade are termed biocompatible, while membranes that induce a large reaction are considered bioincompatible. Bio-... 

In 1968, Ontario Research Foundation developed a series of segmented polyether polyurethanes as polymer membrane materials for reverse cosmosis, ultrafiltration and hemodialysis. The elastomers of recent implant studies are polyurea-urethanes( .) with modification of the synthesis limited to only one variable— the chain length of the polyether component. 

Several classes of polymeric materials are found to perform adequately for blood processing, including cellulose and cellulose esters, polyamides, polysulfone, and some acrylic and polycarbonate copolymers. However, commercial cellulose, used for the first membranes in the late 1940 s, remains the principal material in which hemodialysis membranes are made. Membranes are obtained by casting or spinning a dope mixture of cellulose dissolved in cuprammonium solution or by deacetylating cellulose acetate hollow fibers [121]. However, polycarbonate-polyether (PC-PE) block copolymers, in which the ratio between hydrophobic PC and hydrophilic PE blocks can be varied to modulate the mechanical properties as well as the diffusivity and permeability of the membrane, compete with cellulose in the hemodialysis market. 

This chapter deals with CS or its derivatives as a membrane material in the field of membrane technology. This covers the brief history of membranes, qualities of CS as a good membrane material, methods to prepare CS-based membranes, cross-linking agents and its effects, and modification of CS and its applications in the various fields like wastewater purification, pervaporation, fuel cells, and hemodialysis. 

For hemodialysis membranes, biocompatibility is the primary requirement. It is known that surface properties such as surface roughness play important roles in determining membrane biocompatibihty. It has also been reported that for a given material, smoother surfaces are more biocompatible [64]. Hence, the sinfaces of three different commercial hollow fibers were studied by AFM to compare their roughness parameters. Figures 4.42 and 4.43 show AFM images of inner and outer surfaces, re-... 

Hemodialysis units are usually hoUow-fibre devices with a membrane area of 0.5-1.5 m. The classical membrane material is regenerated cellulose, closest to the natural material. Other membranes include polyether sulphone (PES) and polysulphone (PS), which are made somewhat hydrophilic by blending with PVP, a necessary requirement to address the problems of biocompatibUity and fouhng by proteins [39]. The membranes are asymmetric (10—100 pm thick) with a narrow pore size distribution and the pore diameter less than 10 nm [17]. 

Although fairly distinct in their capabilities, these processes have several features in common. The membrane materials used are generally polymeric in origin and are extensions, both in mode of preparation and in composition, of the cellulose acetate membranes pioneered by Loeb and Sourirajan. Another common feature shared by most of the processes bsted is the use of pressure as the driving force the exceptions are the different forms of dialysis. Thus, in hemodialysis, concentration replaces pressure as the driving force, while electrodialysis is driven by an electrical potential. 

Extracorporeal artificial organs provide mass-transfer operations to support failing or impaired organ systems [126]. Common examples include kidney substitute, hemodialysis, cardiopulmonary bypass (CPB), apheresis therapy, peritoneal dialysis, lung substitute and assist, and plasma separation. A critical component involved in the extracorporeal artificial organ is the membrane, which serves to separate the undesired substance from the blood or plasma. Ideally, materials used as the membrane in these particular applications should have appropriate cellular and molecular permeability, as well as blood compatibility (i.e., hemocompatibility). Over the years, both natural and synthetic polymers have been used as membrane materials. 

Cellulosic hollow fibers, 16 18-20 Cellulosic materials, in ethanol fermentation, 10 535—536 Cellulosic membranes, in hemodialysis,... 

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. 

DNA has been used to modify the PSf membrane by blending and immobilizing DNA onto its surface [123,124]. PSf is one of the most important polymeric materials and is widely used in artificial and medical devices. However, when used as a hemodialysis hollow fiber, the blood compatibility of the PSf membrane is not adequate. The hydrophilicity of the DNA-modified surface increased, but the amount of adsorbed protein did not decrease significantly, which indicates that the DNA-modified membrane might have a better blood compatibility. 

Application Qearly one important application of microporous materials in which the effectiveness is critically dependent on the monodispersity of the pores is the sieving of proteins. In order that an ultrafiltration membrane have high selectivity for proteins on the basis of size, the pore dimensions must first of all be on the order of 25 - ioOA, which is the size range provided by typical cubic phases. In addition to this, one important goal in the field of microporous matmals is the attainment of the narrowest possible pore size distribution, enabling isloation of proteins of a very specific molecular weight, for example. Applications in which separation of proteins by molecular weight are of proven or potential importance are immunoadsorption process, hemodialysis, purification of proteins, and microencapsulation of functionally-specific cells. 

These membranes are used for the ultrafiltration of biological liquids (blood and urine), for hemodialysis in an artificial kidneys and for hemooxygenation in an artifidal lung The extraordinarily hi water permeability allows us to use the polyionic complexes as the additives to usual film-forming resins for preparing materials with a high coefficient of permeability to water vapor ... 

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