Comparison of the new polyethersulfone high-flux membrane DIAPES(R) HF800 with conventional high-flux membranes during on-line haemodiafiltration

Polyethersulfone Polymer for Biomedical Applications and Biotechnology

Polymers stand out as promising materials extensively employed in biomedicine and biotechnology. Their versatile applications owe much to the field of tissue engineering, which seamlessly integrates materials engineering with medical science. In medicine, biomaterials serve as prototypes for organ development and as implants or scaffolds to facilitate body regeneration. With the growing demand for innovative solutions, synthetic and hybrid polymer materials, such as polyethersulfone, are gaining traction. This article offers a concise characterization of polyethersulfone followed by an exploration of its diverse applications in medical and biotechnological realms. It concludes by summarizing the significant roles of polyethersulfone in advancing both medicine and biotechnology, as outlined in the accompanying table.

Biocompatibility evaluation of polyethersulfone-pyrolytic carbon composite membrane in artificial pancreas

Polyethersulfone (PES) membranes are widely used in medical devices, especially intravascular devices such as intravascular bioartificial pancreases. In the current work, the pure PES and PES-pyrolytic carbon (PyC) composite membranes were synthesized and permeability studies were conducted. In addition, the cytocompatibility and hemocompatibility of the pure PES and PES-PyC membranes were investigated. These materials were characterized using peripheral blood mononuclear cell (PBMC) activation, platelet activation, platelet adhesion, ß-cell viability and proliferation, and ß-cell response to hyperglycemia. The results showed that platelet activation decreased from 87.3% to 27.8%. Any alteration in the morphology of sticking platelets was prevented, and the number of attached platelets decreased by modification with PyC. The 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay corroborated that PBMC activation was encouraged by the PyC-modified PES membrane surface. It can be concluded that PES-modified membranes show higher hemocompatibility than pure PES membranes. ß-cells cultured on all the three membranes displayed a lower rate of proliferation although the cells on the PES-PyC (0.1 wt. %) membrane indicated a slightly higher viability and proliferation than those on the pure PES and PES-PyC (0.05 wt. %) membranes. It shows that the PES-PyC (0.1 wt. %) membrane possesses superior cytocompatibility over the other membranes.

Improving the In Vitro Removal of Indoxyl Sulfate and p-Cresyl Sulfate by Coating Diatomaceous Earth (DE) and Poly-vinyl-pyrrolidone-co-styrene (PVP-co-S) with Polydopamine

Polydopamine (PDA) is a synthetic eumelanin polymer mimicking the biopolymer secreted by mussels to attach to surfaces with a high binding strength. It exhibits unique adhesive properties and has recently attracted considerable interest as a multifunctional thin film coating. In this study, we demonstrate that a PDA coating on silica- and polymer-based materials improves the entrapment and retention of uremic toxins produced in specific diseases. The low-cost natural nanotextured fossil diatomaceous earth (DE), an abundant source of mesoporous silica, and polyvinylpyrrolidone-co-Styrene (PVP-co-S), a commercial absorbent comprising polymeric particles, were easily coated with a PDA layer by oxidative polymerization of dopamine at mild basic aqueous conditions. An in-depth chemical-physical investigation of both the resulting PDA-coated materials was performed by SEM, AFM, UV-visible, Raman spectroscopy and spectroscopic ellipsometry. Finally, the obtained hybrid systems were successfully tested for the removal of two uremic toxins (indoxyl sulfate and p-cresyl sulfate) directly from patients' sera.

In vivo transcriptomic profiling using cell encapsulation identifieseffector pathways of systemic aging

Sustained exposure to a young systemic environment rejuvenates aged organisms and promotes cellular function. However, due to the intrinsic complexity of tissues it remains challenging to pinpoint niche-independent effects of circulating factors on specific cell populations. Here, we describe a method for the encapsulation of human and mouse skeletal muscle progenitors in diffusible polyethersulfone hollow fiber capsules that can be used to profile systemic aging in vivo independent of heterogeneous short-range tissue interactions. We observed that circulating long-range signaling factors in the old systemic environment lead to an activation of Myc and E2F transcription factors, induce senescence, and suppress myogenic differentiation. Importantly, in vitro profiling using young and old serum in 2D culture does not capture all pathways deregulated in encapsulated cells in aged mice. Thus, in vivo transcriptomic profiling using cell encapsulation allows for the characterization of effector pathways of systemic aging with unparalleled accuracy.

Effects of Expanded Hemodialysis with Medium Cut-Off Membranes on Maintenance Hemodialysis Patients: A Review

Kidney failure is associated with high morbidity and mortality. Hemodialysis, the most prevalent modality of renal replacement therapy, uses the principle of semipermeable membranes to remove solutes and water in the plasma of patients with kidney failure. With the evolution of hemodialysis technology over the last half century, the clearance of small water-soluble molecules in such patients is adequate. However, middle molecules uremic toxins are still retained in the plasma and cause cardiovascular events, anemia, and malnutrition, which significantly contribute to poor quality of life and high mortality in maintenance hemodialysis patients. A new class of membrane, defined as a medium cut-off (MCO) membrane, has emerged in recent years. Expanded hemodialysis with MCO membranes is now recognized as the artificial kidney model closest to natural kidney physiology. This review summarizes the unique morphological characteristics and internal filtration–backfiltration mechanism of MCO membranes, and describes their effects on removing uremic toxins, alleviating inflammation and cardiovascular risk, and improving quality of life in maintenance hemodialysis patients.

Randomized controlled trial of medium cut-off versus high-flux dialyzers on quality of life outcomes in maintenance hemodialysis patients

Medium cut-off (MCO) dialyzers help remove larger middle molecules associated with symptoms related to the accumulation of uremic retention solutes. We investigated the effect of an MCO dialyzer on the improvement of quality of life (QOL) in maintenance hemodialysis (HD) patients. Forty-nine HD patients with high-flux dialysis were randomly assigned to either an MCO (Theranova 400, Baxter) or a high-flux (FX CorDiax 80 or 60, Fresenius Medical Care) dialyzer and completed the study. QOL was assessed at baseline and after 12 weeks of treatment using the Kidney Disease Quality of Life Short Form-36, and pruritus was assessed using a questionnaire and visual analog scale. The reduction ratios of middle molecules were also evaluated. Laboratory markers, including serum albumin, did not differ between the two groups after 12 weeks. Removals of kappa and lambda free light chains were greater for MCO dialyzer than high-flux dialyzer. The MCO group had higher scores than the high-flux group in the domains of physical functioning and physical role (75.2 ± 20.8 vs. 59.8 ± 30.1, P = 0.042; 61.5 ± 37.6 vs. 39.0 ± 39.6, P = 0.047, respectively), and the MCO group had lower mean scores for morning pruritus distribution and the frequency of scratching during sleep (1.29 ± 0.46 vs. 1.64 ± 0.64, P = 0.034; 0.25 ± 0.53 vs. 1.00 ± 1.47, P = 0.023, respectively). MCO dialyzers may improve patient-reported outcomes, particularly the physical components of QOL and uremic pruritus, in patients with high-flux dialyzers.

Hypoalbuminemia: a price worth paying for improved dialytic removal of middle-molecular-weight uremic toxins?

Hemodiafiltration (HDF) increases the removal of middle-molecular-weight uremic toxins and may improve outcomes in patients with end-stage kidney disease (ESKD), but it requires complex equipment and comes with risks associated with infusion of large volumes of substitution solution. New high-flux hemodialysis membranes with improved diffusive permeability profiles do not have these limitations and offer an attractive alternative to HDF. However, both strategies are associated with increased albumin loss into the dialysate, raising concerns about the potential for decreased serum albumin concentrations that have been associated with poor outcomes in ESKD. Many factors can contribute to hypoalbuminemia in ESKD, including protein energy wasting, inflammation, volume expansion, renal loss and loss into the dialysate; of these factors, loss into the dialysate is not necessarily the most important. Furthermore, recent studies suggest that mild hypoalbuminemia per se is not an independent predictor of increased mortality in dialysis patients, but in combination with inflammation it is a poor prognostic sign. Thus, whether hypoalbuminemia predisposes to increased morbidity and mortality may depend on the presence or absence of inflammation. In this review we summarize recent findings on the role of dialysate losses in hypoalbuminemia and the importance of concomitant inflammation on outcomes in patients with ESKD. Based on these findings, we discuss whether hypoalbuminemia may be a price worth paying for increased dialytic removal of middle-molecular-weight uremic toxins.

Membrane innovation: closer to native kidneys

Modern methods in analytical biochemistry have established that uraemia is associated with the retention of proteins, both in their native state and post-translationally modified, over a wide range of molecular weights up to 60 kDa. Evidence is accumulating that these higher molecular weight retention solutes are important uraemic toxins, and therapies such as online haemodiafiltration (HDF), which enhance their removal, are associated with improved outcomes. However, HDF has limitations regarding cost, clinical implementation and the need for an external source of sterile substitution solution to maintain fluid balance. New membranes that have a solute removal profile more closely approaching that of the glomerular filtration barrier when used for conventional haemodialysis, while at the same time not allowing the passage of clinically significant amounts of beneficial proteins, are needed to address these limitations. Tighter control of the molecular characteristics of the polymers used for membrane fabrication, along with the introduction of additives and improvements in the manufacturing process, has led to membranes with a tighter pore size distribution that allows the use of an increased absolute pore size without leaking substantial amounts of albumin. At the same time, the wall thickness and internal diameter of membrane fibres have been decreased, enhancing convective transport within the dialyser without the need for an external source of substitution solution. These new expanded range membranes provide a solute removal profile more like that of the native kidney than currently available membranes when used in conventional haemodialysis.

Albumin handling in different hemodialysis modalities

Hypoalbuminemia is a major risk factor for morbidity and mortality in dialysis patients. With increasing interest in highly permeable membranes and convective therapies to improve removal of middle molecules, transmembrane albumin loss increases accordingly. Currently, the acceptable upper limit of albumin loss for extracorporeal renal replacement therapies is unknown. In theory, any additional albumin loss should be minimized because it may contribute to hypoalbuminemia and adversely affect the patient's prognosis. However, hypoalbuminemia-associated mortality may be a consequence of inflammation and malnutrition, rather than low albumin levels per se. The purpose of this review is to give an overview of albumin handling with different extracorporeal renal replacement strategies. We conclude that the acceptable upper limit of dialysis-related albumin loss remains unknown. Whether enhanced middle molecule removal outweighs the potential adverse effects of increased albumin loss with novel highly permeable membranes and convective therapies is yet to be determined.

Precise Quantitative Assessment of the Clinical Performances of Two High-Flux Polysulfone Hemodialyzers in Hemodialysis: Validation of a Blood-Based Simple Kinetic Model Versus Direct Dialysis Quantification

Highly permeable dialysis membranes with better design filters have contributed to improved solute removal and dialysis efficacy. However, solute membrane permeability needs to be well controlled to avoid increased loss of albumin that is considered to be detrimental for dialysis patients. A novel high-flux dialyzer type (FX CorDiax; Fresenius Medical Care) incorporating an advanced polysulfone membrane modified with nano-controlled spinning technology to enhance the elimination of a broader spectrum of uremic toxins has been released. The aim of this study was to compare in the clinical setting two dialyzer types having the same surface area, the current (FX dialyzer) and the new dialyzer generation (FX CorDiax), with respect to solute removal capacity over a broad spectrum of markers, including assessment of albumin loss based on a direct dialysis quantification method. We performed a crossover study following an A1-B-A2 design involving 10 patients. Phase A1 was 1 week of thrice-weekly bicarbonate hemodialysis with the FX dialyzer, 4 h per treatment; phase B was performed with a similar treatment regimen but with a new FX CorDiax dialyzer and finally the phase A2 was repeated with FX dialyzer as the former phase. Solute removal markers of interest were assessed from blood samples taken before and after treatment and from total spent dialysate collection (direct dialysis quantification) permitting a mass transfer calculation (mg/session into total spent dialysate/ultrafiltrate). On the blood side, there were no significant differences in the solute percent reduction between FX CorDiax 80 and FX 80. On the dialysate side, no difference was observed regarding eliminated mass of different solutes including β₂ -microglobulin (143.1 ± 33.6 vs. 138.3 ± 41.9 mg, P = 0.8), while the solute mass removal of total protein (1.65 ± 0.51 vs. 2.14 ± 0.75 g, P = 0.04), and albumin (0.41 ± 0.21 vs. 1.22 ± 0.51 g, P < 0.001) were significantly less for FX CorDiax 80 compared to the FX 80 dialyzer. The results of this cross-over study indicate that the new FX CorDiax dialyzer has highly effective removal of middle molecules, without any concomitant increase in total protein and albumin loss. The clinical relevance and potential benefit of this finding needs to be determined.

Performance of hemodialysis with novel medium cut-off dialyzers

Background. Compared to high-flux dialysis membranes, novel medium cut-off (MCO) membranes show greater permeability for larger middle molecules.

Methods. In two prospective, open-label, controlled, randomized, crossover pilot studies, 39 prevalent hemodialysis (HD) patients were studied in four dialysis treatments as follows: study 1, three MCO prototype dialyzers (AA, BB and CC with increasing permeability) and one high-flux dialyzer in HD; and study 2, two MCO prototype dialyzers (AA and BB) in HD and high-flux dialyzers in HD and hemodiafiltration (HDF). Primary outcome was lambda free light chain (λFLC) overall clearance. Secondary outcomes included overall clearances and pre-to-post-reduction ratios of middle and small molecules, and safety of MCO HD treatments.

Results. MCO HD provided greater λFLC overall clearance [least square mean (standard error)] as follows: study 1: MCO AA 8.5 (0.54), MCO BB 11.3 (0.51), MCO CC 15.0 (0.53) versus high-flux HD 3.6 (0.51) mL/min; study 2: MCO AA 10.0 (0.58), MCO BB 12.5 (0.57) versus high-flux HD 4.4 (0.57) and HDF 6.2 (0.58) mL/min. Differences between MCO and high-flux dialyzers were consistently significant in mixed model analysis (each P < 0.001). Reduction ratios of λFLC were greater for MCO. Clearances of α1-microglobulin, complement factor D, kappa FLC (κFLC) and myoglobin were generally greater with MCO than with high-flux HD and similar to or greater than clearances with HDF. Albumin loss was moderate with MCO, but greater than with high-flux HD and HDF.

Conclusions. MCO HD removes a wide range of middle molecules more effectively than high-flux HD and even exceeds the performance of high-volume HDF for large solutes, particularly λFLC.

Pancreatic islet macroencapsulation using microwell porous membranes

Allogeneic islet transplantation into the liver in combination with immune suppressive drug therapy is widely regarded as a potential cure for type 1 diabetes. However, the intrahepatic system is suboptimal as the concentration of drugs and nutrients there is higher compared to pancreas, which negatively affects islet function. Islet encapsulation within semipermeable membranes is a promising strategy that allows for the islet transplantation outside the suboptimal liver portal system and provides environment, where islets can perform their endocrine function. In this study, we develop a macroencapsulation device based on thin microwell membranes. The islets are seeded in separate microwells to avoid aggregation, whereas the membrane porosity is tailored to achieve sufficient transport of nutrients, glucose and insulin. The non-degradable, microwell membranes are composed of poly (ether sulfone)/polyvinylpyrrolidone and manufactured via phase separation micro molding. Our results show that the device prevents aggregation and preserves the islet’s native morphology. Moreover, the encapsulated islets maintain their glucose responsiveness and function after 7 days of culture (stimulation index above 2 for high glucose stimulation), demonstrating the potential of this novel device for islet transplantation.

Factors Associated with Albumin Loss in Post-Dilution Hemodiafiltration and Nutritional Consequences

Introduction

Hemodiafiltration is currently one of the most effective techniques of extra-renal purification but results in an increase of albumin loss in dialysate. We aimed to determine the factors associated with albumin loss during post-dilution hemodiafiltration, compare an “automatic” mode of infusate flow control versus a “manual” control, and assess the potential nutritional impact.

Methods

This prospective observational study included all hemodialysis patients in our institution who underwent post-dilution hemodiafiltration 3 times a week on a Fresenius 5008 for at least 2 months. At each session, albumin content was measured in a representative effluent dialysate volume. The automatic mode of the Fresenius 5008 was used for automatic infusate flow control.

Results

In all, 18 patients (mean age 60.7 ± 15 years) underwent 85 post-dilution hemodiafiltration sessions. The mean albumin loss was 3134 ± 2450 mg/session. Albumin loss was significantly affected by infusate flow, infusate volume, transmembrane pressure and ultrafiltration volume. The loss was greater with Toraysulfone and FX 1000 membranes rather than FX 80 or FX 100 membranes. With AutoSub rather than manual control, infusate flow was greater ( P<.001), transmembrane pressure was higher (P = .004), and the albumin loss was greater (P = .010). However, there was no correlation between albumin loss and nutritional variables.

Conclusions

Albumin loss during post-dilution hemodiafiltration was correlated with increased transmembrane pressure and infusate flow, especially AutoSub flow control, and type of membrane. However, this loss, when moderate, did not seem to affect nutritional aspects and should not limit the use of hemodiafiltration.

Antithrombogenicity of Fluorinated Diamond-Like Carbon Films Coated Nano Porous Polyethersulfone (PES) Membrane

A nano porous polyethersulfone (PES) membrane is widely used for aspects of nanofiltration, such as purification, fractionation and dialysis. However, the low-blood-compatibility characteristic of PES membrane causes platelets and blood cells to stick to the surface of the membrane and degrades ions diffusion through membrane, which further limits its application for dialysis systems. In this study, we deposited the fluorinated-diamond-like-carbon (F-DLC) onto the finger like structure layer of the PES membrane. By doing this, we have the F-DLC films coating the membrane surface without sacrificing the membrane permeability. In addition, we examined antithrombogenicity of the F-DLC/PES membranes using a microfluidic device, and experimentally found that F-DLC drastically reduced the amount of blood cells attached to the surface. We have also conducted long-term experiments for 24 days and the diffusion characteristics were found to be deteriorated due to fouling without any surface modification. On the other hand, the membranes coated by F-DLC film gave a consistent diffusion coefficient of ions transfer through a membrane porous. Therefore, F-DLC films can be a great candidate to improve the antithrombogenic characteristics of the membrane surfaces in hemodialysis systems.

Biocompatibility of modified polyethersulfone membranes by blending an amphiphilic triblock co-polymer of poly(vinyl pyrrolidone)-b-poly(methyl methacrylate)-b-poly(vinyl pyrrolidone)

An amphiphilic triblock co-polymer of poly(vinyl pyrrolidone)-b-poly(methyl methacrylate)-b-poly(vinyl pyrrolidone) (PVP-b-PMMA-b-PVP) was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The block co-polymer can be directly blended with polyethersulfone (PES) using dimethylacetamide (DMAC) as the solvent to prepare flat sheet and hollow fiber membranes using a liquid-liquid phase separation technique. The PVP block formed a brush on the surface of the blended membrane, while the PMMA block mingled with the PES macromolecules, which endowed the membrane with permanent hydrophilicity. After adding the as-prepared block co-polymer the modified membranes showed lower protein (bovine serum albumin) adsorption, suppressed platelet adhesion, and a prolonged blood coagulation time, and thereby the blood compatibility was improved. Furthermore, the modified PES membranes showed good cytocompatibility, ultrafiltration and protein anti-fouling properties. These results suggest that surface modification of PES membranes by blending with the amphiphilic triblock co-polymer PVP-b-PMMA-b-PVP allows practical application of these membranes with good biocompatibility in the field of blood purification, such as hemodialysis and bioartificial liver support.

Immobilization of silver nanoparticles onto sulfonated polyethersulfone membranes as antibacterial materials

By using the interaction between the sulfonated groups and silver ions, silver nanoparticles were successfully introduced onto the surface of sulfonated polyethersulfone (SPES) membranes by using vitamin C as reducing agent. The presence of silver nanoparticles on the surface of the PES/SPES hybrid membranes was characterized by UV spectrophotometer, scanning electron microscopy and transmission electron microscopy. Detailed studies on the antibacterial activity of the (PES/SPES)-Ag composites were carried out for Staphylococcus aureus, Staphylococcus albus, and Escherichia coli, for which, the composites exhibited significantly inhibition capacity. Cytocompatibility of the (PES/SPES)-Ag composites were also investigated by cell cytotoxicity and cell adhesion tests. The results indicated that after immobilizing with silver nanoparticles, the (PES/SPES)-Ag was still within the safe use range. To our knowledge, this is the first time that PES membranes have been prepared with antibacterial capacity. We anticipate that this novel and green method might lead to an expanded usage of PES with antibacterial properties in medical instruments and food processing industries in the future, and might also make a potential contribution to the fields of antibacterial chemistry.

Clinical evaluation of plasma insulin and C-peptide levels with 3 different high-flux dialyzers in diabetic patients on hemodialysis

AIM

Changes in plasma immunoreactive insulin (IRI) and connecting-peptide immunoreactivity (CPR) concentrations during hemodialysis (HD) were evaluated in diabetic HD patients with 3 different high-flux membranes. The removal properties of the membranes were compared.

METHOD

In this prospective controlled study, 15 stable diabetic patients on HD were randomly selected for 6 HD sessions with 3 different membranes: polysulfone (PS), cellulose triacetate (CTA), and polymethylmethacrylate (PMMA). Blood samples were obtained from the blood tubing at the arterial (A) site at the beginning and end of the sixth HD session. At 60 minutes after dialysis initiation, blood samples were obtained from both the A and venous (V) sites of the dialyzer to investigate the clearance and removal properties of the membranes.

RESULTS

The plasma IRI and CPR levels decreased significantly at each time point with all 3 membranes. IRI clearance with the PS membrane was significantly higher than that with the CTA and PMMA membranes. No difference was observed in the IRI reduction rate between the 3 membranes. CPR clearance and reduction rate with the PMMA membrane were lower than with the PS and CTA membranes. No significant difference was observed in serum creatinine clearance and reduction rates between the 3 membranes; however, serum urea nitrogen clearance was significantly lower with the PMMA membrane compared with the PS and CTA membranes. A significantly high beta2-microglobulin clearance and reduction rate was achieved in the order PS > CTA > PMMA.

CONCLUSION

Plasma IRI and CPR are cleared by HD; their clearance rates differ with the dialyzer membranes. Plasma IRI clearance with the PS membrane is higher than that with the CTA and PMMA membranes.

New Ligand Coupling Procedure for Formation of an Immunoadsorption Wall

To prevent the occurrence of dialysis-related amyloidosis, an immunoadsorption wall based on polyacrylamide has been manufactured by a recently developed, partially incomplete, two-stage polymerization method. During the preparation process, efficient utilization of coupling antibodies is the key to large-scale production of such a toxin removal modality. In this study, we attempted to carry out the ligand coupling procedure after formation of a cyanogen bromide (CNBr)-activated stationary phase, using anti-beta2-microglobulin (beta-2M) antibodies. In vitro immunoadsorption tests show that the levels of beta-2M decrease rapidly within the first 2 hours for all the immunoadsorption tests. After that, nearly blank values were reached for tests of initial levels of c. 30 microg/mL and c. 82 microg/mL, whereas a relatively constant level of c. 10 microg/mL was maintained for the test of initial levels of c. 185 microg/mL. The maximum surface binding capacity of the prepared immunoadsorption walls is estimated by fitting experimental data, using a mathematical model of saturation kinetics. The present comparative investigation also suggests the manufacturing process for an immunoadsorption wall could be improved and facilitated by this new ligand coupling procedure without compromising the resulting binding capacity. Furthermore, the experimental protocols as well as the present methodology could be helpful for development of a clinically applicable immunoadsorption wall.

In vitro hemocompatibility of albumin-heparin multilayer coatings on polyethersulfone prepared by the layer-by-layer technique

Polyethersulfone foils (PES)--a unique material for blood purification membranes--were coated with a multilayer assembly of heparin (unfractionated or high anticoagulant activity fraction heparin) and albumin (albumin-heparin coatings), or with a multilayer of albumin (albumin coating), using the layer-by-layer technique. The coatings combine advantages of albumin (reduction of nonspecific interactions) and heparin (specific interactions with blood coagulation proteins). The differences between the two heparins, while significant for their biological activity, had only a minor effect on the multilayer assembly with albumin monitored in situ by reflection infrared spectroscopy (FTIR MIRS). Uncoated as well as modified PES surfaces were evaluated using an in vitro assay with freshly drawn, slightly heparinized (1.5 IU heparin/mL) human whole blood. The blood was circulated with a roller pump over the sample surfaces in shear flow across rectangular slit channels ( app. 6 mL/min and 120 s(-1)) for 1.5 h at 37 degrees C. All coatings effectively reduced platelet adhesion and activation according to the PF4 release. The activation of coagulation evaluated as TAT generation was significantly lowered for the coating composed of albumin and high activity heparin. A further beneficial effect of the heparin containing coatings was reduced complement activation as determined by different complement fragments.

Beta2-microglobulin removal by extracorporeal renal replacement therapies

There is increasing evidence that end-stage renal disease patients with lower beta(2)-microglobulin plasma levels and patients on convective renal replacement therapy are at lower mortality risk. Therefore, an enhanced beta(2)-microglobulin removal by renal replacement procedures has to be regarded as a contribution to a more adequate dialysis therapy. In contrast to high-flux dialysis, low-flux hemodialysis is not qualified to eliminate substantial amounts of beta(2)-microglobulin. In hemodialysis using modern high-flux dialysis membranes, a beta(2)-microglobulin removal similar to that obtained in hemofiltration or hemodiafiltration can be achieved. Several of these high-flux membranes are protein-leaking, making them suitable only for hemodialysis due to a high albumin loss when used in more convective therapy procedures. On-line hemodiafiltration infusing large substitution fluid volumes represents the most efficient and innovative renal replacement therapy form. To maximize beta(2)-microglobulin removal, modifications of this procedure have been proposed. These modifications ensure safer operating conditions, such as mixed hemodiafiltration, or control albumin loss at maximum purification from beta(2)-microglobulin, such as mid-dilution hemodiafiltration, push/pull hemodiafiltration or programmed filtration. Whether these innovative hemodiafiltration options will become accepted in clinical routine use needs to be proven in future.

Protein-Leaking Membranes for Hemodialysis: A New Class of Membranes in Search of an Application?

A new class of membranes that leak protein has been developed for hemodialysis. These membranes provide greater clearances of low molecular weight proteins and small protein-bound solutes than do conventional high-flux dialysis membranes but at the cost of some albumin loss into the dialysate. Protein-leaking membranes have been used in a small number of clinical trials. The results of these trials suggest that protein-leaking membranes improve anemia correction, decrease plasma total homocysteine concentrations, and reduce plasma concentrations of glycosylated and oxidized proteins. However, it is not clear yet that routine use of protein-leaking membranes is warranted. Specific uremic toxins that are removed by protein-leaking membranes but not conventional high-flux membranes have not been identified. It is also unclear whether protein-leaking membranes offer benefits beyond those obtained with conventional high-flux membranes used in convective therapies, such as hemofiltration and hemodiafiltration. Finally, the amount of albumin loss that can be tolerated by hemodialysis patients in a long-term therapy has yet to be determined. Protein-leaking membranes offer a new approach to improving outcomes in hemodialysis, but whether their benefits will outweigh their disadvantages will require more basic and clinical research.