Dialysis membranes biocompatibility

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. 

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. 

Another issue relating to dialysis membranes is their ability to stimulate the immune system. If the dialysis filter membrane does not activate the complement system (C3a and C5a) when it comes in contact with the patient s blood, it is considered biocompatible. In the acute setting, the incidence of hypotension, fever, bronchoconstric-tion, and thrombocytopenia are lower in patients dialyzed with biocompatible filters. The most biocompatible dialyzers use a synthetic membrane of PS, PAN, or PMMA. Although not definitive, biocompatible membranes may be associated with fewer adverse events during dialysis, lower rates of hospitalization, reduced death rates, and slower declines in residual renal function. ... 

Biocompatibility of dialysis membranes. In Nissenson AR, Fine RN, eds. Dialysis Therapy. Philadelphia, Hanley Belfus, 2002 110-115. 

M.V. Risbud, R.R. Bhonde, Suitability of cellulose molecular dialysis membrane for bioartificial pancreas in vitro biocompatibility studies, J. Biomed. Mater. Res. 54 (3) (2001) 436 44. 

The selection of the polymer material for the production of dialysis membranes has significant implications on the quality of hemodialysis therapy. Only a limited number of polymers are suitable for the spinning and extrusion process involved in the manufacture of capillary membranes. The selection was originally based on experiences from textile fiber production. Further, biochemical and physical properties that may result from the membrane formation process, determine the selection of a polymer. The ideal polymer family should allow the production of biocompatible dialysis membranes and possess a stable physical stability. The latter guarantees an easy production process and sterilization without problems. 

Baurmeister, U., Brodowski, W., Diamantoglou, M., Dunweg, G., Henne, W., Pelger, M., and Schulze, H. (1987). Dialysis membrane of modified cellulose with improved biocompatibility. U.S. Patent 4,668,396. 

Vienken, J., Diamantoglou, M., Hahn, C., Kamusewitz, H., and Paul, D. (1995). Considerations on developmental aspects of biocompatible dialysis membranes. Artif. Organs 19, 398. 

Many industrial yams have specific surface function requirements. For technical yams the market share for composites or coated fabrics is almost 70%. Furthermore, textile applications also can benefit from a special surface treatment in order to improve the water repellency. Capillary membranes for dialysis, however, have totally different requirements enhanced biocompatibility of the membranes is needed.4-6... 

In a hollow fiber dialyzer the blood flows down the bore of the fiber, providing good fluid flow hydrodynamics. An advantage of the hollow fiber design is that only 60-100 mL of blood is required to fill the dialyzer. At the end of a dialysis procedure hollow fiber dialyzers can also be easily drained, flushed with sterilizing agent, and reused. Dialyzer reuse is widely practiced, in part for economic reasons, but also because the biocompatibility of the membrane appears to improve after exposure to blood. 

Figure 11.6 Dialysis capillary setup that could be used to employ the SWNT sensing system in vivo. The dextran-SWNT and Con A mixture is retained in the capillary while glucose is free to diffuse across the membrane. A biocompatible hydrogel, filled with VEGF, can be used to coat the capillary. Such a system could be implanted beneath the skin, with SWNT excitation from a laser photodiode and fluorescence detection from a CCD camera. Adapted with permission from Ref. 17.

Adsorbents are used in medicine mainly for the treatment of acute poisoning, whereas other extracorporeal techniques based on physico-chemical principles, such as dialysis and ultrafiltration, currently have much wider clinical applications [1]. Nevertheless, there are medical conditions, such as acute inflammation, hepatic and multi-organ failure and sepsis, for which mortality rates have not improved in the last forty years. These conditions are usually associated with the presence of endotoxin - lipopolysaccharide (LPS) or inflammatory cytokines - molecules of peptide/protein nature [2]. Advantages of adsorption over other extracorporeal techniques include ability to adsorb high molecular mass (HMM) metabolites and toxins. Conventional adsorbents, however, have poor biocompatibility. They are used coated with a semipermeable membrane of a more biocompatible material to allow for a direct contact with blood. Respectively, ability of coated adsorbents to remove HMM solutes is dramatically reduced. In this paper, preliminary results on adsorption of LPS and one of the most common inflammatory cytokines, TNF-a, on uncoated porous polymers and activated carbons, are presented. The aim of this work is to estimate the potential of extracorporeal adsorption technique to remove these substances and to relate it to the porous structure of adsorbents. 

Cellulose acetate (CA), the acetate ester of cellulose, is one of the most commonly used biocompatible materials for the preparation of semi-permeable membranes to be used for dialysis, ultrafiltration, and reverse osmosis. CA membranes have very low absorption characteristics and thermal stability with high flow rates. Cellulose-based materials are also widely used in the bio-pharmaceutical industry as the matrix for adsorbent beads and membranes. Moreover, CA nanofibers can be used as carrier for delivery of vitamins or pharmaceutical products [15]. 

While transport properties play an important role in the selection of a dialyzer membrane, an equally important consideration in the evolution of the dialyzer technology has been biocompatibility, or the compatibility of the dialyzer with blood. Three aspects of biocompatibility that are important in dialysis are clotting, activation of the complement cascade, and cytokine generation. 

Complement Activation Complement proteins are so-named because they complement antibody activity to eliminate pathogens. The alternate pathway of the complement cascade is normally activated by bacterial surface molecules. Complement activation during dialysis was first identified by the rapid drop in white blood cell counts (neutropenia) during the first 30 min of dialysis. Regenerated cellulose membranes activate complement through the alternate pathway (Chenoweth et al., 1983). Modified cellulose membranes approach the biocompatibility profile of synthetic materials in terms of neutropenia and complement activation. 

Siheone has been shown to have excellent biocompatibility, hemocompatibihty and desired permeability properties. These properties make it ideal for use as silicone tubing and membranes used in kidney dialysis and heart bypass machines with high oxygen diffusivity and ions. It has also found application in several mechanical heart valves. 

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