Biocompatibility of the polyamide membranes

Formation of Thrombin-Antithrombin III Complex Using Polyamide and Hemophan Dialyzers

The recently developed ELISA for the thrombin-antithrombin III complex (TAT) is a sensitive, specific, and simplified means of detecting intravascular coagulation. For further evaluation of the thrombogenicity of a polyamide (P) and a Hemophan (H) hollow-fibre dialyzer a cross-over study was done in ten stable patients on maintenance hemodialysis. At the same doses of heparin (mean bolus of 30 U/kg bw and maintenance doses of 86 U/kg bw), thrombin time and partial thromboplastin time were significantly lower using H. At the end of dialysis TAT was significantly higher in H (mean ± SEM before HD 3.57 ± .56, at 240 min 14.9 ± 6.5 ng/ml, p < 0.05, Wilcoxon-test) than in P (before HD 4.36 ± .98, at 240 min 8.95 ± 3.0 ng/ml, p ± 0.05 H 240 vs. P 240, Wilcoxon-test). Visible clotting was more pronounced in the H filter. Among other favourable features of blood compatibility the polyamide/polyvinylpyrrolidone copolymer with a hydrophilic/hydrophobic microdomain structure has less thrombogenicity. The modified cellulosic membrane H has advantages in complement activation and leukocyte depression, but thrombogenicity seems less favourable since the incorporated diethyl-amino-ethyl groups with their positive charge bind and inactivate negatively charged heparin.

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 hydroxylgroups, 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.

Does convective dialysis therapy applied daily approach renal blood purification?

Outcome studies in dialysis have generally failed to show an impact of changes in membrane flux or biocompatibility, and only dose increases up to a certain level have been shown to improve survival significantly. However, to see an effect of a potentially improved dialysis treatment, all available factors that make dialysis more physiological may need to be combined. A membrane that mimics the glomerular basement membrane in being hemocompatible, having a high hydraulic permeability and a generous sieving, yet not leading to albumin loss could be used. The dialysis fluid composition could be individualized, and the quality and volume appropriate for the selected application. The new system of online-prepared ultrapure dialysis fluid and sterile infusion solutions, as integral parts of the treatment, are cost effective and labor saving as well as biocompatible. Ideally, we should select a blood purification method that covers the same range of solutes as the kidney. Convection is equally effective for all solutes that can pass through the membrane, and the corresponding renal therapy is hemofiltration. For enhanced small solute removal, convection can be combined with diffusion as in hemodiafiltration, which has the potential to achieve the largest solute removal over a wide molecular weight spectrum among all forms of dialysis. Finally, the dialysis treatment should be applied as often as is practically possible-preferably daily-in order to reduce the peaks caused by uremic toxins, the exposure to acidosis and alkalosis, and the burden on the cardiovascular system by overhydration. While the designed therapy is already technically feasible today, a positive result from outcome studies will be needed to bring about the political and economic decisions required to change conventional dialysis into a treatment approaching true renal blood purification.

Surface modification of the polymers present in a polysulfone hollow fiber hemodialyser by covalent binding of heparin or endothelial cell surface heparan sulfate: flow characteristics and platelet adhesion

The present study addresses the problem of simultaneous surface modification of various polymers, i.e. polysulfone (PSU), polycarbonate (PC), and polyurethane (PU), which constitute the Ultraflux AV 600 S hollow fibre hemodialyser. An investigation was first made into six different chemical routes aimed at introducing carboxyl groups onto the surface of PSU, PC, and PU model polymers to which heparin (HE) or endothelial cell surface heparan sulfate (ESHS) was covalently bound via the reaction of residual amino groups and a coupling reagent. Carboxyl groups were introduced using three specific reactions based on their nucleophilic or electrophilic introduction into aromatic repeating units of the polymers and three non-specific carboxylation reactions, i.e. UV, heat or redoxactivation via nitrene or radical species. Concentrations of 1-20 nmol COOH groups per cm(-2) led to HE or ESHS surface concentrations corresponding to one or several layers. Two nonspecific carboxylation reactions followed by HE- or ESHS-coupling provided the lowest change in membrane pore structure according to cut off, clearance (urea, phosphate, maltose), ultrafiltration, and diafiltration assessments. In some cases the introduction of excess negatively-charged carboxyl groups and HE improved the flux properties of the modified membranes. The various methods were applied to the dialysis module. Platelet adhesion was not observed in the case of the ESHS-coating of PSU membrane at shear rates of 1050 s(-1), whereas HE and subendothelial matrix showed 56 and 100% coverage, respectively, under similar conditions. The coating of PSU or of other high-flux membranes by ESHS appears a promising method for improving membrane properties and to generate biocompatibility characteristics similar to those of natural blood vessels, i.e. inertness to platelet adhesion and no level effects for complement and intrinsic coagulation cascade activation. The ESHS coating may be used without anticoagulants.

Effect of hemofiltration on hemodynamics and systemic concentrations of anaphylatoxins and cytokines in human sepsis

OBJECTIVE

To determine whether hemofiltration (HF) can eliminate cytokines and complement components and alter systemic hemodynamics in patients with severe sepsis.

DESIGN

Prospective observation study.

SETTING

Surgical intensive care unit of a university hospital.

PATIENTS

16 patients with severe sepsis.

INTERVENTIONS

Continuous zero-balanced HF without dialysis (ultrafiltrate rate 2 l/h) was performed in addition to pulmonary artery catheterization, arterial cannulation, and standard intensive care treatment.

MEASUREMENTS AND MAIN RESULTS

Plasma and ultrafiltrate concentrations of cytokines (the interleukins IL-1 beta, IL-6, IL-8, and tumor necrosis factor alpha) and of complement components (C3adesArg, C5adesArg) were measured after starting HF (t0) and 4 h (t4) and 12 h later (t12). Hemodynamic variables including mean arterial pressure (MAP), mean central venous pressure, mean pulmonary artery pressure, pulmonary capillary wedge pressure, and cardiac output were serially determined. During HF, cytokine plasma concentrations remained constant. However, C3adesArg and C5adesArg plasma concentrations showed a significant decline during 12-h HF (C3adesArg: t0 = 676.9 +/- 99.7 ng/ml vs t12 = 467.8 +/- 71, p < 0.01; C5adesArg: 26.6 +/- 4.7 ng/ml vs 17.6 +/- 6.2, p < 0.01). HF resulted in a significant increase over time in systemic vascular resistance (SVR) and MAP (SVR at t0: 669 +/- 85 dyne.s/cm5 vs SVR at t12: 864 +/- 75, p < 0.01; MAP at t0: 69.9 +/- 3.5 mmHg vs MAP at t12: 82.2 +/- 3.7, p < 0.01).

CONCLUSIONS

HF effectively eliminated the anaphylatoxins C3adesArg and C5adesArg during sepsis. There was also a significant rise in SVR and MAP during high volume HF. Therefore, HF may represent a new modality for removal of anaphylatoxins and may, thereby, deserve clinical testing in patients with severe sepsis.

Granulocyte activation and adhesion molecules during hemodialysis with cuprophane and a high-flux biocompatible membrane

Hemodialysis with complement-activating membranes, such as cuprophane, induces neutropenia and expression of the granulocyte adhesion receptor Mac-1 (CD11b/CD18), while hemodialysis with noncomplement-activating membranes does not. Increased expression of CD11b by neutrophils may mediate cuprophane-induced leukopenia. However, the rebound granulocytosis that follows leukopenia is not fully understood. Ten patients on regular hemodialysis were included in a cross-over study. Hemodialysis was performed for 2 weeks with cuprophane and 2 weeks with polyamide, a high-flux noncomplement-activating membrane. At the end of each period, the following parameters were determined during a hemodialysis session: C5a concentration by enzyme immunoassay and the neutrophil expression of CD11b, LFA-1 (CD11a/CD18), and the antigen recognized by MoF11 (MoF11 Ag), a monoclonal antibody that recognizes activated neutrophils, by immunofluorescence flow cytometry. Hemodialysis with cuprophane induced an increase in C5a concentration and in the expression of CD11b and MoF11 Ag, which were maximal after 15 minutes of hemodialysis, at the nadir of neutropenia. CD11b expression was maintained throughout hemodialysis, despite the reversal of neutropenia. Conversely, after peak expression, C5a and MoF11 Ag decreased as the neutrophil count increased to baseline values. Polyamide hemodialysis did not induce variations in C5a concentration, nor in CD11b and MoF11 Ag expression. CD11a/CD18 expression remained stable during hemodialysis with both membrane types. Neutrophil activation, as determined by MoF11 Ag expression, was correlated with the evolution of neutrophil count and C5a concentration during cuprophane hemodialysis, while CD11b expression was not correlated with neutrophil count throughout dialysis. A decrease in neutrophil activation could explain in part the detachment of neutrophils previously bound to endothelium and, therefore, the reversal of neutropenia.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical evaluation of a new dialyzer, FLX-12 GW, with a polyester-polymer alloy membrane

The performance of a membrane in renal failure therapy is determined by its structure, its overall mass transfer properties, and its blood compatibility. In this regard, removal of beta 2-microglobulin (beta 2M) has become a major objective of dialysis therapy. In the present study, a newly developed high-flux membrane composed of a polyester-polymer alloy (PEPA) with the components of polyarylate and polyethersulfone (dialyzer FLX-12 GW; Nikkiso Co., Japan) has been evaluated with regard to both biocompatibility and elimination capacity for beta 2M during hemodialysis of 8 stable chronic uremic patients. The clearance values of low molecular weight solutes were in the same range as those reported for high-flux dialyzers of comparable surface area. There was no drop in leukocyte counts and only a minimal fall in platelet counts nearly in the same range as has been observed by other investigators using polyamide membrane. C3a Des Arg generation was low, and C5a Des Arg formation was not significantly influenced. There was a sharp drop in the serum beta 2M level (-35%) during dialysis with a clearance between 59.7 +/- 5.6 ml/min (QB 200 ml/min) and 70.1 +/- 9.7 ml/min (QB 300 ml/min), respectively. Accordingly, the sieving coefficient was calculated to be 0.2 at 30 min after start of dialysis and 0.6 1 h later. The membrane was able to remove 184.0 +/- 22.3 mg/4 h due to an apparent rate of adsorption during the first hour of treatment in combination with high transmembrane transfer in the following time.