Is there a need for plasticizer-free biomaterials in dialysis therapy?

The impact of plasticizers on general health is an extremely controversial subject. Most of the results in this area, especially those related to di-ethylhexyl-phthalate, are collected from animal studies and the extrapolation to humans is still controversial and difficult. This review of research findings explores the science of using soft polyvinyl(chloride). With particular reference to dialysis, it explains why some companies now offer products made of plasticizer-free biomaterials.

Membranes for endotoxin removal from dialysate: considerations on feasibility of commercial ceramic membranes

As the quality of water in dialysis fluid varies considerably, dialysate is often contaminated by large amounts of bacteria and endotoxins. Membrane properties and operating pressures are acknowledged to give high-flux dialysis with bicarbonate the bacteriological potential to favor passage of endotoxin fragments from the dialysate into the blood stream. Therefore, a sterile dialysate will have to become a standard. Ultrafiltration across hydrophobic synthetic membranes was shown to remove endotoxins (and their fragments) from dialysis water by the combined effect of filtration and adsorption. However, each module can be used for a limited time only. Ceramic membranes may represent an alternative to polymeric membranes for endotoxin removal. In this article, we tested the capacity of different commercial ceramic membranes with nominal molecular weight cut-off down to 1,000 to retain endotoxins from Ps. aeruginosa. The tested membranes did not generally produce dialysate meeting the Association for the Advancement of Medical Instrumentation standard. When using aluminum-containing membranes, we detected aluminum leaking into the dialysate that could possibly be transported into the blood stream.

Artificial dialysis membranes: from concept to large scale production

The development of hemodialysis from an experimental concept to a routine medical therapy is closely related to research, manufacturing and availability of dialysis membranes. Collodion, a cellulose-trinitrate derivative, was the first polymer to be used as an artificial membrane and played a central role in further investigations and applications. Basic studies on the mechanism of solute transport through membranes, like diffusion, were done by A. Fick and T. Graham using collodion as a membrane material. In vivo dialysis in animals and humans was performed with collodion by J. Abel in the USA and G. Haas in Germany. Cellophane and Cuprophan membranes replaced collodion later, because of their better performance and mechanical stability. However, due to its alleged lack of hemocompatibility, membranes made from unmodified cellulose lost their market share. They have been replaced by modified cellulosic and synthetic dialysis membranes which show a better hemocompatibility than unmodified cellulose membranes. Most of the new membrane materials are also available in high-flux modifications and for this reason suitable as well for more effective therapy modes, such as hemodiafiltration and hemofiltration. The success of hemodialysis as a routine therapy is also the success of membrane development, because both, a reproducible membrane production and an unlimited availability of dialysis membranes have increased the number of dialyzed patients to about 1 million patients worldwide in 1999.

Cellulose carbamates and derivatives as hemocompatible membrane materials for hemodialysis

Dialysis membranes made from regenerated cellulose are under dispute because of their alleged lack of hemocompatibility. The introduction of membranes from synthetically modified cellulose, like cellulose acetate or Hemophan, has proven, however, that hemocompatible membranes can be fabricated from cellulose by means of chemical surface modifications. In addition to membranes made from modified cellulose like ethers or esters, which were investigated in earlier experiments, we looked for further cellulose modifications to be assessed for their hemocompatibility. For this purpose, we synthesized a series of cellulose carbamate derivatives to profit from the excellent hemocompatibility pattern of the urethane family. In vitro investigations on membranes made from these cellulose modifications proved a direct relationship between the degree of modification and hemocompatibility. This was proven for the following 3 representative hemocompatibility parameters: complement C5a generation, thrombin-antithrombin (TAT) III formation, and platelet count (PC). As already shown for modifications made from cellulose esters, a direct dependency between improved hemocompatibility and the degree of substitution (DS) in the cellulose molecule could be found. In our experiments, a degree of substitution below a value of 0.1 led to a nearly complete suppression of complement activation for all cellulose carbamates under investigation. In contrast to data on cellulose esters, we observed that molecular weight or molecular conformation of chemical substituents exerted only a minor effect on the hemocompatibility pattern. In addition, data on cellulose carbamate esters (e.g., cellulose succinate-phenyl-carbamate) show that a simultaneous but balanced substitution with hydrophilic and hydrophobic groups at the surface of the cellulose polymer is a further prerequisite for optimal hemocompatibility. It seems that the carbamate configuration per se has a positive effect on the hemocompatibility pattern of synthetically modified cellulose membranes.

Ex vivo complement protein adsorption on positively and negatively charged cellulose dialyser membranes

An ex vivo test system was used to measure complement protein C3 and factor B adsorption onto small dialyser modules made from regenerated and modified cellulosic hollow fibre membranes in which positive diethylaminoethyl (DEAE) or negative carboxymethyl (CM) groups were introduced into the cellulose matrix. The extracorporeal system, which included test-dialysers and the dialysis environment, allowed the use of labelled proteins without contaminating the blood donors which were connected in an open-loop fashion to the extracorporeal test system. The modules were removed at selected time points from the extracorporeal system for radioactivity counting. The results were used to evaluate the mechanisms involved in complement reactions to foreign surfaces. The system therefore allowed the analysis of complement protein adsorption occurring in the dialyser modules and its relationship to the complement generation rate in the extracorporeal system to be evaluated. It was possible to demonstrate that significant complement C3 and factor B adsorption occurred in the test modules made of cellulosic membranes. Complement adsorption as a function of the pH and the release reaction of the adsorbed C3 and factor B after membrane blood perfusion were therefore found to be variable according to the cellulosic membrane type and the presence of positive or negative charged groups within the cellulose matrix. The data obtained from the ex vivo model therefore provided additional evidence on the discussion of the mechanisms involved in the increased complement activation by regenerated cellulose and in its attenuation by DEAE- or CM-modified cellulose.

Comparison of hollow fibre membranes for hepatocyte immobilisation in bioreactors

Various hollow fibre membranes of polyamide, cellulose and polypropylene were investigated as potential substrata for hepatocyte immobilisation in bioreactors for hybrid liver support systems. Membranes were subjected to a cytocompatibility test in which the attachment and morphology of primary hepatocytes were evaluated. The effect of coating with collagen and fibronectin was also studied. Adequate cell immobilisation was possible on polypropylene and polyamide membranes even without coating. The flattening process of the cells was dependent on the material and the coating. The incorporation of porous polypropylene hollow fibres in hybrid liver cell bioreactors and their specific permeability properties could also offer means for cell oxygenation, metabolite distribution and immuno-isolation purposes.

Dilemma of membrane biocompatibility and reuse

Numerous articles have been published on the multiple use of dialyzers and on the effect of different reprocessing chemicals and techniques on the dialyzer biocompatibility and performance. The results often appear contradictory, especially those comparing standard biocompatibility parameters. Despite this confusion, a discerning review of the published works allows certain limited conclusions to be drawn. Reprocessing of used hemodialyzers changes the biocompatibility profile of a dialyzer as defined by the parameters complement activation, leukopenia, and cytokine release. The effect of reprocessing depends on the chemicals and reprocessing technique applied and also on the type of membrane polymer being subjected to the reprocessing procedure. Reports of pyrogenic reactions indicate that the flux of the membrane also influences how suitable it is for safe reuse. An increased risk of allergic and pyrogenic reactions appears to be associated with dialyzer reuse. Furthermore, there has been a lack of investigations into the immunologic effect of the layer of adsorbed and chemically altered proteins that remains on the inner surface of reprocessed dialyzers. We conclude that the clinical benefit of dialyzer reuse cannot be generally accepted from a biocompatibility point of view.

Determination of contact phase activation by the measurement of the activity of supernatant and membrane surface-adsorbed factor XII (FXII): its relevance as a useful parameter for the in vitro assessment of haemodialysis membranes

We investigated hemodialysis membrane biocompatibility with respect to contact phase activation by determination of FXII-like activity (FXIIA) on the membrane surface and in the supernatant phase, during plasma contact with various hemodialysis membranes using an in vitro incubation test cell. The results were compared to the influence of these membranes on the activation of purified FXII. A time course for the generation of activated FXII using purified FXII solution at physiologic concentrations on two similar negatively charged polymers was performed. The membranes assessed were regenerated cellulose (Cuprophan; Akzo Faser AG, Germany), modified cellulosic (Hemophan; Akzo Faser AG), acrylonitrile-sodium methallyl copolymer-based membrane AN69S (Hospal, France), and SPAN, a new polyacrylonitrile-based copolymer (akzo Nobel AG). The plasma FXIIA at the membranes surface was significantly different between the membranes, while the supernatant phase FXIIA exhibited no significant differences. In contrast, activation of purified FXII in a plasma-free system with respect to supernatant activity indicated significant differences between the materials. A similar finding for the membrane-bound factor XIIA was also observed when purified factor XII was used. The membrane-bound FXIIA values observed in the plasma system containing heparin were significantly greater than in citrated plasma. This demonstrated the strong influence of heparin and the interaction of other plasma components to the membrane surface on the activation of contact phase of coagulation.

In vitro contact phase activation with haemodialysis membranes: role of pharmaceutical agents

Contact phase activation was investigated in vitro using flat sheet type of haemodialysis membranes, Cuprophan (Akzo, Faser, Germany) and AN69S (Hospal, France), and a negatively charged polyamide Ultipor NR 14225 membrane as a control. The investigation focussed on the determination of factor XII-like activity (FXIIA) as an indicator of contact phase activation in the supernatant phase and at the membrane surface after plasma-membrane contact using an incubation test cell. The findings were compared with the observations from a plasma-free system utilizing purified unactivated factor XII. The plasma FXIIA bound to the membrane surface was significantly different between the membranes, while the supernatant phase FXIIA exhibited no significant differences. In contrast, the plasma-free system exhibited significant differences in the supernatant FXIIA and membrane-bound FXIIA for all the materials used and the magnitude of the activity was significantly greater for negatively charged materials. This finding demonstrated the strong influence of the interaction of other plasma constituents on the membrane surface and as such the binding and subsequent activation of factor XII may be altered possibly due to competitive binding and steric hindrance. On the addition of anticoagulants such as heparin, low-molecular-weight heparin, citrate and hirudin, no significant differences were observed in plasma supernatant phase FXIIA. However, each anticoagulant appears to have a distinct influence on the magnitude of plasma membrane-bound FXIIA. On the addition of aprotinin (a kallikrein inhibitor), no significant differences were observed in the plasma supernatant FXIIA. In contrast, aprotinin appears to significantly reduce membrane-bound FXIIA on Cuprophan and polyamide NR, but significantly increase the magnitude of the membrane-bound FXIIA on AN69S.

Considerations on developmental aspects of biocompatible dialysis membranes

Modern strategies in developing new polymers for dialysis membranes aim to improve their blood compatibility. To achieve such a goal, two approaches have been successfully applied: existing cellulosic polymers were modified, either by introducing functional groups through ester or ether bonds, by mixing synthetic polymers with bulk additives, or by using copolymerization techniques. As a detailed example, the first synthetically modified cellulose membrane, Hemophan, was prepared by substituting some hydrogen atoms in the cellulosic glucose unit by diethyl-amino-ethyl groups with the modification having a considerable impact on the membrane's hemocompatibility. It is further known that the hemocompatibility of hydrophobic synthetic membranes is improved by rendering these materials partially hydrophilic. We tested the hypothesis, whether the hemocompatibility of a material, which is hydrophilic per se, such as unmodified cellulose, is changed after the introduction of hydrophobic substituents. For this purpose, the number and nature of substituents have been systematically varied in order to alter surface properties, and these variations have been subsequently related to blood compatibility parameters. As expected, thrombin generation as well as complement- and cell-activation depend on the number and nature of the substituents whereby some of the substituents show a very narrow optimum if their hemocompatibility is related to the degree of substitution. Changes in hemocompatibility can be followed by physical methods, such as surface angle analyses and zeta potential determinations. Data show that alterations in the lipophilic/hydrophilic balance on the polymer surface may explain substituent-related changes in polymer hemocompatibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatibility of membranes used in the treatment of renal failure

Haemodialysis membranes with a wide range of solute and hydraulic permeabilities are used clinically. Such membranes are manufactured from either cellulose or synthetic co-polymers and their biocompatibility is commonly characterized by the complement activation and white cell changes observed during their use. The cellobiosic unit may be modified by the partial or total replacement of the hydroxyl groups by diethylaminoethyl (Hemophan), acetate (cellulose acetate), triacetate (cellulose triacetate) or 2,5-acetate (Diaphan). We have undertaken a prospective study in which such renal membranes have been studied in terms of the complement activation and neutropenia produced with the aim of investigating the relationship between modification of the cellobiosic unit and the magnitude of neutropenia and complement activation, and the extent to which membrane base material influences these parameters, by comparing the changes observed in modified cellulose membranes with that for a synthetic membrane (polysulphone). Our findings show that, while the degree of substitution varies between < 1% and total substitution, there is no correlation between the numbers of hydroxyl groups replaced and alteration of complement activation and neutropenia. However, by modification of the cellobiosic unit it is possible to produce a membrane whose biocompatibility is similar to that of a membrane manufactured from a synthetic co-polymer such as polysulphone.

Membranes for dialysis

Today, more than 30 different polymers or polymer blends are used as materials for dialysis membranes. They can be categorized following the scheme of a family tree of haemodialysis membranes. The trunk represents membranes from regenerated cellulose, major branches show either synthetically modified cellulose membranes or membranes manufactured from synthetic polymers. As the latter are standardly hydrophobic, small branches elucidate the technique on how these materials have been rendered partially or completely hydrophilic. Complications may arise, when comparing membranes only following their polymer names, such as polysulfone, polyacrylonitrile or polyamide. Due to varying polymer compositions, membranes with the same polymer names may differ in their haemocompatibility, flux properties and adsorption characteristics. Adsorption of proteins like beta 2-microglobulin, fibrinogen and coagulation factors, complement proteins, or hormones like parathormon and erythropoietin are differently adsorbed by dialysis membranes and thus adsorption contributes to the removal characteristics. Of central interest for membrane development and application is the question of how these membranes can be sterilized, as a series of patient adverse reactions has been attributed to the dialyser sterilization procedures. Apart from the cellulosic membranes Cuprophan and Hemophan, the majority of membranes cannot be sterilized by steam, as these materials degrade when exposed to above their class-point temperature. Finally, future aspects of modern membrane development should not neglect the needs of patient populations with specific blood properties, such as diabetics.

Contamination of dialysis water and dialysate. A survey of 30 centers

The concentration of bacteria and endotoxin in dialysis water and dialysate of 30 dialysis centers in western Germany was examined. Water samples were obtained after treatment by reverse osmosis or other processing methods. Collection of dialysis samples for bacterial, fungal, and endotoxin analysis was conducted before and 2 hours after start of hemodialysis. In 17.8% of all water samples analyzed, the AAMI standard was exceeded and bacterial and fungal counts greater than 200 colony forming units/ml were found. In 11.7% of all dialysate samples, higher contamination than the recommendations for dialysate of 2000 colony forming units/ml were found. The concentration of endotoxin in water and dialysate varied between 0 and 95 endotoxin units in the water samples and 0 and 487 endotoxin units/ml in the dialysate samples. In 12.2% of all water sampled, and 27.5% of all dialysate samples, values of 5 endotoxin units/ml were found. No correlation was found between the level of contamination of either water or dialysate in a specific center and the following factors: water processing method (reverse osmosis or others), type of dialysate (acetate of bicarbonate), type of dialysate machine, or method of machine disinfection. In view of these results it is suggested that endotoxin testing, especially in the dialysate, be a part of regular quality control in dialysis.

Cellulose-ester as membrane materials for hemodialysis

The majority of dialysis membranes are fabricated from regenerated unmodified cellulose. This standard type of cellulosic membrane is frequently under attack because of its alleged lack of biocompatibility. Recent developments, however, have proven that a chemical modification of the reactive surface groups of regenerated cellulose, the hydroxyl-groups, limits the complement-activating potential of these materials and thus improves its blood-compatibility. We extended the idea of modifying cellulose for improved blood-compatibility to a series of different cellulose esters. Special focus was directed towards the question whether a variation of the type of substituent and degree of substitution could influence the blood-compatibility pattern of these materials: the analysis of blood-compatibility profiles showed a direct dependency on the type of substituent and the degree of substitution (DS). As an example, it was found that the DS, necessary for a complete reduction of complement activation, decreases with increasing chain lengths of aliphatic substituents. Optimal degrees of substitution are characteristic of the type of substituents and enable us to tailor materials specifically for optimized blood compatibility.

Membranes for dialysis

In the submitted review the authors give an account of contemporary problems of membranes for dialysis available at present. Although the authors mention also cellulose based membranes (membranes made from unmodified regenerated cellulose, synthetic modified cellulose membranes produced by chemical transformation of cellobiose), the main attention is paid to polymer membranes--typical synthetic polymers, i.e. polysulphone (PSu), polyacrinon nitrate (PAN), polyamide (PA), ethyl vinyl alcohol polymers (EVAL), polyester mixtures formed by polyacrylonitrile and polyether sulphone (PEPA). The authors describe their adsorption capacity, possibility of sterilization and specific problems of interaction with different drugs. In the conclusion the authors outline demands on the development of modern membranes and their problems in future.

Bacteria- and endotoxin-free dialysis fluid for use in chronic hemodialysis

As the quality of water in the dialysis fluid varies considerably, dialysis fluid is contaminated with a high percentage of bacteria and endotoxins. The bacterial populations contained in the dialysis fluid are as heterogeneous as the chemical structure of the endotoxins that result. The latter can pass through the dialysis membrane whereby high-flux membranes permit a larger number of retransportable molecules than low-flux membranes. A central aim toward a future, safe dialysis process should, therefore, be the production of a dialysate that is free of bacteria and endotoxins. As we were able to demonstrate in various examinations, this goal is most likely to be achieved with the aid of sterile filtration using hollow fiber modules of polyamid. To avoid disinfection of the polyamid membrane, as this would only reach bacteria but not endotoxins, the filter was changed after at most 10 h. The achieved dialysis fluid was free of bacteria and endotoxins. We were also able to show that the release of interleukin-1 was reduced. In addition, side-effects, such as a drop in blood pressure, headaches, muscular cramps, and nausea, were reduced.

Side effects of hybrid liver support therapy: TNF-alpha liberation in pigs, associated with extracorporeal bioreactors

During acute liver failure, hybrid liver support therapy could serve as a bridge to liver transplantation. In this desired temporary use, immune competent cell responses, such as the production of cytokines, might be of limiting relevance. We have investigated the Tumor Necrosis Factor-alpha (TNF) liberation in two models using pigs, connected with an extracorporeal bioreactor with homologous hepatocytes: TNF liberation was measured in arterial plasma during a 4 day perfusion time in untreated animals, model (i), and during short term perfusion of hepatectomized pigs in model (ii). Animals four days after catheter implantation in model (i) had TNF values of < 5 pg/ml. After connecting the system without hepatocytes, TNF rose to 9.7 +/- 2 within 120 min and rose further to 32.6 +/- 6 pg/ml within 4 hours after filling the system with the homologous hepatocytes. After 24 hours of continuous perfusion and during four days of perfusion, the TNF levels were lowered to baseline levels. In model (ii), TNF rose to 220 +/- 130 pg/ml within 180 min and decreased to 110 +/- 10 pg/ml within six hours, whereas controls without hepatocytes showed mean levels with a maximum of 120 +/- 20 pg/ml. In both models, there was no correlation between TNF levels and clinical abnormalities such as fever or shock symptoms. There is evidence for an activation of blood cells during experimental extracorporeal hybrid support. No typical side effects were, however, observed. Thus, TNF mediated extracorporeal cell activation does not appear to limit the application of homologous hybrid liver support therapy.

Membranes and polymer structures--biocompatibility aspects with respect to production limits

Plasmapheresis can be performed by centrifugation and by use of membrane technology. With the latter technique we receive a plasma which is absolutely free from platelets. This is why membranes are gaining market shares in this particular field of medical application. Today plasmapheresis membranes are mostly fabricated from synthetic polymers, such as polypropylene (e.g. PLASMAPHAN), polysulfone, polyacrylonitrile, polymethylmethacrylate, polyvinylalcohol and others, the only exception being cellulose acetate. Parameters determining the biocompatibility of plasmapheresis membranes are generation of complement C3a or C5a, hemolysis and possible thrombus formation. These parameters depend on various properties of the membrane polymer: e.g. the nature of the molecular end/side-groups, the distribution of electrical charges on the polymer surface and the different chemical structures and conformation of the polymer. In addition, membrane properties like pore distribution and geometry or the flow characteristics of a particular device-design may trigger cell activation or influence biocompatibility through the adsorption of various plasmacomponents. Most of the polymers which are used today for manufacturing plasmapheresis membranes have not been developed for this purpose. They were originally selected to be used as textile fibers. Further, no present membrane polymer has been specifically developed to achieve high biocompatibility. The membrane profile was designed in such a way that pheresis properties were met rather than optimizing biochemical blood/polymer interactions. One reason for this decision may be that the market volume of plasmapheresis technology is too small in order to justify specific and high-cost developments of polymers for this purpose. Polymer selection to achieve excellent biocompatibility profiles is determined by polymer-availability, costs, membrane-forming processes and environmental aspects related to possible pollution during the manufacturing process. The production of PLASMAPHAN by the unique Accurel-process combines several of these parameters. The main membrane production processes and especially the Accurel-process are described here. The influence of polymer-surface properties, membrane structure and module-design on the biocompatibility of plasmapheresis treatments are discussed and explained by appropriate examples.

Systemic levels of tumor necrosis factor alpha during hemodialysis with cellulosic membranes: no effect of the sterilization procedure

Extractable constituents of dialyzer membranes (e.g., monomers and beta-glucans) may induce the production of cytokines in vitro. We therefore studied circulating tumor necrosis factor alpha (TNF alpha) levels in 23 stable hemodialysis patients during treatment with dry Cuprophan membranes (ETO-sterilized n = 10, steam-sterilized n = 13) longitudinally over a period of 4 weeks. After 4 weeks, those 5 patients of each group showing the highest TNF alpha levels were switched to steam-sterilized, wet Cuprophan membranes. No significant increase in plasma TNF alpha was observed during hemodialysis with either ETO- or steam-sterilized dry Cuprophan membranes. A substantial TNF alpha increase (> or = 100% compared to pre-HD values), however, was observed during 14 of 84 treatment sessions. In 5 selected patients with ETO-sterilized, dry Cuprophan dialyzers, TNF alpha rose from (mean +/- SEM) 17.2 +/- 3.0 (pre-HD) to 20.9 +/- 6.2 (120 min) and 21.9 +/- 4.5 pg/ml (240 min). Corresponding levels in patients with steam-sterilized, dry Cuprophan were 16.2 +/- 5.4 (pre-HD), 21.9 +/- 6.8 (120 min), and 16.0 +/- 3.7 pg/ml (240 min), respectively. There was no difference between ETO- and steam-sterilized dialyzers. No significant reduction in mean TNF alpha plasma levels or in frequency of elevated peak levels was achieved when these patients were switched to wet Cuprophan dialyzers for another 4 weeks. It is suggested that an induction of elevated TNF alpha levels during hemodialysis is possible but is not observed regularly during treatment with Cuprophan membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Variables associated with the assessment of systemic tumor necrosis factor alpha levels during hemodialysis

Conflicting results have been published concerning the systemic induction of the cytokine tumor necrosis factor alpha (TNF alpha) during hemodialysis (HD). We therefore evaluated in vitro TNF alpha production in whole blood as well as in vivo variability of TNF alpha levels in patients on long-term HD. Whole blood was incubated at room temperature (RT) with or without exogenously added endotoxin (ET), and plasma-TNF alpha was measured after 5, 30, 120, 240, and 960 min by specific enzyme immunoassay. Additionally, plasma-TNF alpha before and after 120 and 240 min HD was studied longitudinally once a week over a period of 4 weeks in 36 patients on Cuprophan (CU, n = 23) or polysulfone-F60 (PSu, n = 13) HD. Mean plasma TNF alpha levels in vitro rose from (mean) 8 pg/ml after 5 min to 12 pg/ml (120') and 32 pg/ml (960') even without ET addition, and to 18 pg/ml (after 120') and 88 pg/ml (after 960') when 0.1 microgram/ml ET were added. Pre-dialytic as well as intra-dialytic TNF alpha levels in patients showed high intra-individual variability. A substantial (> 100%) increase in plasma TNF alpha was observed during only 14 out of 84 treatments with CU and 20 out of 47 with PSu, however, the increase in TNF alpha was not statistically significant in either group. We conclude that the sampling procedure, if not carefully standardized, is a potential source of artifacts with regard to "systemic" TNF alpha levels. The high intra and inter-individual variability of plasma TNF alpha suggests that results of cross-sectional studies are questionable.

[Clinical study of biocompatibility of dialysis membranes made from non-modified and modified cellulose]

Basic biocompatibility parameters of dialysis membranes made of non-substituted regenerated cellulose (NRC) and cellulose membranes with hydroxyl groups substituted, to a higher (H) or lower (L) degree, by dl-ethyl-amino-ethyl groups (DEAE), or by acetate (CA) were investigated in a 16-week clinical study, involving 10 long-term haemodialysis patients. In the 15th minute of dialysis, the decrease in blood leukocyte count, while using NRC (0.24 +/- 0.03 of baseline value, arithmetic mean +/- SEM) was deeper compared with that seen in DEAE-L (0.88 +/- 0.10, p < 0.001), in DEAE-H (0.79 +/- 0.10, p < 0.01), and in CA (0.73 +/- 0.05. p < 0.05). In the 15th minute of the procedure, C5a concentrations, reflecting complement activation, were higher in NRC (4.4 +/- 0.51 micrograms/L) than in DEAE-L (1.41 +/- 0.22, p < 0.001), in DEAE-H (1.68 +/- 0.47, p < 0.01), and in CA (1.68 +/- 0.22, p < 0.01). Activated clotting times were, in the 10th minute of the procedure, significantly longer in NRC (2.94 +/- 0.37 of baseline value) than in DEAE-H (1.74 +/- 0.10, p < 0.05) and, by the end of dialysis, the difference between these membranes (NRC: 1.47 +/- 0.21, DEAE-H: 0.85 +/- 0.08, p = 0.07) was close to the level of statistical significance. The authors conclude: 1. Substitution of the hydroxyl groups of regenerated cellulose reduces the decrease in leukocyte count and complement activation in the initial phase of haemodialysis. 2. At the same time, substitution by DEAE groups may raise thrombogenicity, as indicated by the shorter activated clotting times.(ABSTRACT TRUNCATED AT 250 WORDS)