Membranes for dialysis: can we do without them?

Haemocompatibility and ion exchange capability of nanocellulose polypyrrole membranes intended for blood purification

Composites of nanocellulose and the conductive polymer polypyrrole (PPy) are presented as candidates for a new generation of haemodialysis membranes. The composites may combine active ion exchange with passive ultrafiltration, and the large surface area (about 80 m(2) g(-1)) could potentially provide compact dialysers. Herein, the haemocompatibility of the novel membranes and the feasibility of effectively removing small uraemic toxins by potential-controlled ion exchange were studied. The thrombogenic properties of the composites were improved by applying a stable heparin coating. In terms of platelet adhesion and thrombin generation, the composites were comparable with haemocompatible polymer polysulphone, and regarding complement activation, the composites were more biocompatible than commercially available membranes. It was possible to extract phosphate and oxalate ions from solutions with physiological pH and the same tonicity as that of the blood. The exchange capacity of the materials was found to be 600 ± 26 and 706 ± 31 μmol g(-1) in a 0.1 M solution (pH 7.4) and in an isotonic solution of phosphate, respectively. The corresponding values with oxalate were 523 ± 5 in a 0.1 M solution (pH 7.4) and 610 ± 1 μmol g(-1) in an isotonic solution. The heparinized PPy-cellulose composite is consequently a promising haemodialysis material, with respect to both potential-controlled extraction of small uraemic toxins and haemocompatibility.

Introduction: beyond toxins removal, towards high-quality dialysis

The choice of dialyzer may affect the dialysis process more than any other single component of the dialysis system. Over the past five decades, membranes used for the treatment of chronic kidney disease have continuously evolved, and the use of classical non-modified cellulose membranes has declined in favor of cellulose-based membranes in which the basic structure has been modified to improve the biocompatibility profile of the material as well as membranes based on synthetic polymers. Dialysis membranes with the best biological properties should be biocompatible, exclude impurities in the dialysate and have a large pore size. A high adsorptive capacity, a main feature of the polymethylmetacrylate (PMMA) membranes, is high helpful and may both increase the total amount of solutes removed and removes different kinds of solutes. Moreover, PMMA dialyzer membrane has a good chance to obtain an optimal rather than an adequate dialysis in the field of biocompatibility, immune regulation and inflammation.

Complement anaphylatoxin C5a contributes to hemodialysis-associated thrombosis

Thrombosis is a common complication of end-stage renal disease, particularly in patients on hemodialysis. Although substantial progress has been made in preventing thrombotic complications in various other groups of patients, the mechanisms of thrombosis during hemodialysis require clarification. In this report, we demonstrate that complement activation triggered by hemodialysis biomaterials, and the subsequent generation of the complement anaphylatoxin C5a, results in the expression of functionally active tissue factor (TF) in peripheral blood neutrophils. Because TF is a key initiator of coagulation in vivo, we postulate that the recurring complement activation that occurs during long-term hemodialysis contributes to thrombosis in dialyzed end-stage renal disease patients. Furthermore, we found that complement contributed to the induction of granulocyte colony-stimulating factor, which has been implicated in the pathogenesis of thrombosis in patients treated with the recombinant form of this molecule. Importantly, the inhibition of complement activation attenuated the TF expression and granulocyte colony-stimulating factor induction in blood passing through a hemodialysis circuit, suggesting that the complement system could become a new therapeutic target for preventing thrombosis in patients with chronic renal failure who are maintained on hemodialysis.