Effects of fluid flow on elution of hydrophilic modifier from dialysis membrane surfaces

Comparative Study on Elution of Polyvinylpyrrolidone on Dialyzers Using Ultraviolet Analysis and Iodine Method

It is known that poly(arylethersulfone)-based dialyzers can elute poly( N -vinyl-2-pyrrolidone) (PVP). With regard to chronic renal replacement therapy, this is a burden for the patient, because PVP is deposited in different organs and cannot be degraded or released from there; so elutable PVP has to be minimized. Usually, the iodine method is used for quantification of extractable PVP. To overcome the chain length dependency of this method, we used an ultraviolet method that is independent from the PVP chain lengths; so the absolute amount of eluted PVP can be quantified. The current study shows the amount of eluted PVP on differently sterilized low flux dialyzers (1.6 m 2 , similar storage time, n = 12)-PS160 (Allmed, Egypt), F7HPS (Fresenius Medical Care, Germany), F16 (Wego, China), and B-16P (Bain, China). Using the ultraviolet method, the irradiated filters show a sum total of approximately 9 mg more eluted PVP compared with the steam-sterilized ones, whereas the iodine method shows a value about three times lower between different types of sterilization. The boundary conditions during the radiation sterilization could lead to PVP degradation instead of cross-linking. The resulting shorter PVP chains can be more easily rinsed out and can falsely decrease the calculated eluted PVP amount by using the iodine complexation method.

Impact of Hydrophilic Modification of Synthetic Dialysis Membranes on Hemocompatibility and Performance

The dialyzer is the core element in the hemodialysis treatment of patients with end-stage kidney disease (ESKD). During hemodialysis treatment, the dialyzer replaces the function of the kidney by removing small and middle-molecular weight uremic toxins, while retaining essential proteins. Meanwhile, a dialyzer should have the best possible hemocompatibility profile as the perpetuated contact of blood with artificial surfaces triggers complement activation, coagulation and immune cell activation, and even low-level activation repeated chronically over years may lead to undesired effects. During hemodialysis, the adsorption of plasma proteins to the dialyzer membrane leads to a formation of a secondary membrane, which can compromise both the uremic toxin removal and hemocompatibility of the dialyzer. Hydrophilic modifications of novel dialysis membranes have been shown to reduce protein adsorption, leading to better hemocompatibility profile and performance stability during dialysis treatments. This review article focuses on the importance of performance and hemocompatibility of dialysis membranes for the treatment of dialysis patients and summarizes recent studies on the impact of protein adsorption and hydrophilic modifications of membranes on these two core elements of a dialyzer.

A porcine model of hemodialyzer reactions: roles of complement activation and rinsing back of extracorporeal blood

Hemodialysis reactions (HDRs) resemble complement-activation-related pseudoallergy (CARPA) to certain i.v. drugs, for which pigs provide a sensitive model. On this basis, to better understand the mechanism of human HDRs, we subjected pigs to hemodialysis using polysulfone (FX CorDiax 40, Fresenius) or cellulose triacetate (SureFlux-15UX, Nipro) dialyzers, or Dialysis exchange-set without membranes, as control. Experimental endpoints included typical biomarkers of porcine CARPA; pulmonary arterial pressure (PAP), blood cell counts, plasma sC5b-9 and thromboxane-B2 levels. Hemodialysis (60 min) was followed by reinfusion of extracorporeal blood into the circulation, and finally, an intravenous bolus injection of the complement activator zymosan. The data indicated low-extent steady rise of sC5b-9 along with transient leukopenia, secondary leukocytosis and thrombocytopenia in the two dialyzer groups, consistent with moderate complement activation. Surprisingly, small changes in baseline PAP and plasma thromboxane-B2 levels during hemodialysis switched into 30%-70% sharp rises in all three groups resulting in synchronous spikes within minutes after blood reinfusion. These observations suggest limited complement activation by dialyzer membranes, on which a membrane-independent second immune stimulus was superimposed, and caused pathophysiological changes also characteristic of HDRs. Thus, the porcine CARPA model raises the hypothesis that a second "hit" on anaphylatoxin-sensitized immune cells may be a key contributor to HDRs.

Recent advances in dialysis membranes

PURPOSE OF REVIEW

Improvement in hemodialysis treatment and membrane technology are focused on two aims: the first one is to achieve a better control of circulating uremic solutes by enhancing removal capacity and by broadening molecular weight spectrum of solutes cleared; the second one is to prevent inflammation by improving hemocompatibility of the global dialysis system.

RECENT FINDINGS

Despite impressive progresses in polymers chemistry few hazards are still remaining associated with leaching or sensitization to polymer additives. Research has focused on developing more stable polymers by means of additives or processes aiming to minimize such risks. Membrane engineering manufacturing with support of nanocontrolled spinning technology has opened up membrane to middle and large molecular weight substances, while preserving albumin losses. Combination of diffusive and enhanced convective fluxes in the same hemodialyzer module, namely hemodiafiltration, provides today the highest solute removal capacity over a broad spectrum of solutes.

SUMMARY

Dialysis membrane is a crucial component of the hemodialysis system to optimize solute removal efficacy and to minimize blood membrane biological reactions. Hemodialyzer is much more than a membrane. Dialysis membrane and hemodialyzer choice are parts of a treatment chain that should be operated in optimized conditions and adjusted to patient needs and tolerance, to improve patient outcomes.

Polyvinylpyrrolidone in hemodialysis membranes: Impact on platelet loss during hemodialysis

INTRODUCTION

Hydrophilic modification with polyvinylpyrrolidone (PVP) increases the biocompatibility profile of synthetic dialysis membranes. However, PVP may be eluted into the patient's blood, which has been discussed as a possible cause for adverse reactions rarely occurring with synthetic membranes. We investigated the content of PVP and its elution from the blood-side surface from commercially available dialyzers, including the novel FX CorAL, with PVP-enriched and α-tocopherol-stabilized membrane, and link the results to the level of platelet loss during dialysis as a maker of biocompatibility.

METHODS

Six synthetic, PVP containing, dialyzers (FX CorAL, FX CorDiax [Fresenius Medical Care]; Polyflux, THERANOVA [Baxter]; ELISIO [Nipro]; xevonta [B. Braun]) were investigated in the present study. The content of PVP on blood-side surface was determined with X-ray photoelectron spectroscopy (XPS). The amount of elutable PVP was measured photometrically after 5 h recirculation. The level of platelet loss was evaluated in an ex vivo recirculation model with human blood.

FINDINGS

Highest PVP content on the blood-side surface was found for the polysulfone-based FX CorAL (26.3%), while the polyethersulfone-based THERANOVA (15.6%) had the lowest PVP content. Elution of PVP was highest for the autoclave steam-sterilized THERANOVA (9.1 mg/1.6 m² dialyzer) and Polyflux (9.0 mg/1.6 m² dialyzer), while the lowest PVP elution was found for the INLINE steam sterilized FX CorAL and FX CorDiax (<0.5 mg/1.6 m² dialyzer, for both). Highest platelet loss was found for xevonta (+164.4% compared to the reference) and the lowest for the FX CorAL (-225.2%) among the polysulfone-based dialyzers; among the polyethersulfone-based dialyzers, THERANOVA (+95.5%) had the highest and ELISIO (-52.1%) the lowest platelet loss.

DISCUSSION

Polyvinylpyrrolidone content and elution differ between commercially available dialyzers and were found to be linked to the membrane material and sterilization method. The amount of non-eluted PVP on the blood-side surface may be an important determinant for the biocompatibility of dialyzers.

Highly Permeable Polyamide Nanofiltration Membrane Mediated by an Upscalable Wet-Laid EVOH Nanofibrous Scaffold

For energy-saving purposes, the pursuit of ultrahigh permeance nanofiltration membranes without sacrificing selectivity is never-ending in desalination, wastewater treatment, and industrial product separation. Herein, we reported a novel facile route to engineer a highly porous and superhydrophilic nanofibrous substrate to mediate the interfacial polymerization between trimesoyl chloride and piperazine, generating an ultrathin PA active layer (∼13 nm) with a hierarchical crumpled surface. The wet laying process and subsequent plasma treatment endowed a rougher and more hydrophilic surface for ethylene vinyl alcohol copolymer (EVOH) nanofibers in the thin compact nanofibrous scaffold (∼9 μm) with a mean pore size of 210 nm, radically different from the nanofibrous membrane by other methods. Nanofibrous scaffold with these features provide abundant thin-thick alternative continuous water layers between nanofibers and organic phase, facilitating the formation of the abovementioned PA layer. As a result, an ultrahigh permeance of 42.25 L·m^-2 h^-1 bar^-1 and a reasonably high rejection of 95.97% to 1000 ppm Na₂SO₄ feed solution were obtained, superior to most state-of-the-art NF membranes reported so far. Our work provides an easy and scalable method to fabricate advanced PA NF membranes with outstanding performance, highlighting its great potential in liquid separation.

Real-Time Measurement of Polyvinylpyrrolidone Eluted from Polysulfone Membrane Dialyzers Based on the Ultraviolet Spectrum

The objective of this study was to develop a new method for measuring polyvinylpyrrolidone (PVP) eluted from polysulfone (PSu) membrane dialyzers. The Müller method is generally used for the measurement of PVP, in which the PVP concentration is determined by measuring the absorbance after a red color is generated by the formation of PVP-iodine complexes when iodine is added to a sample. In contrast, our method does not require any reagents and allows real-time measurement of PVP by the ultraviolet absorption spectrum (UV-s method). In this study, the UV-s method and the Müller method were used to measure PVP eluted from two types of PSu membrane dialyzer (PS-1.6UW sterilized by autoclaving [n = 10] and APS-15SA sterilized by gamma radiation [n = 10]). Polyvinylpyrrolidone concentrations measured by the two methods showed a significant positive correlation (rs = 0.99, p = 0.0006). The PVP concentration (median [25th-75th percentiles]) in PS-1.6UW dialyzer washings obtained by rinsing with physiologic saline was 2.0 (1.18-4.85) mg/L with the Müller method and 3.35 (2.38-4.23) mg/L with the UV-s method, showing no significant difference. However, the PVP concentration in APS-15SA dialyzer washings was 0 (0-0.35) mg/L by the Müller method and 0.95 (0.45-2.58) mg/L by the UV-s method, and there was a significant difference between the two methods. In conclusion, the low concentration of PVP eluted from a PSu dialyzer sterilized by gamma radiation was hardly detected by the Müller method but could be clearly detected by the new UV-s method. These findings suggest that the UV-s method could be used for real-time measurement of PVP eluted from PSu membrane dialyzers.

High-Performance Membrane Dialyzers and Mortality in Hemodialysis Patients: A 2-Year Cohort Study from the Annual Survey of the Japanese Renal Data Registry

BACKGROUND

Little information is available regarding the type of dialyzer which results in good prognosis. This study is aimed at investigating the association between 7 types of dialyzers and 2-year mortality.

METHODS

We conducted a cohort study using data from a nationwide registry of the Japanese Society for Dialysis Therapy. Subjects were 136,676 patients on maintenance hemodialysis (HD) between 2009 and 2011 who underwent maintenance HD for at least 2 years and were treated with one of the following 7 types of high-performance membrane dialyzers: cellulose triacetate (CTA), ethylene vinyl alcohol (EVAL), polyacrylonitrile (PAN), polyester polymer alloy (PEPA), polyethersulfone (PES), polymethylmethacrylate (PMMA), and polysulfone (PS). Cox regression was used to estimate the association between baseline dialyzers and all-cause 2-year mortality, adjusting for potential confounders.

RESULTS

Data were adjusted using basic factors, with PS as a reference group, and the hazard ratio (HR) was significantly higher in CTA, PMMA, PAN, and EVAL groups. Further data adjustment for Kt/V yielded the same results as were obtained from data adjusted for basic factors. After further adjustment for nutrition- and inflammation-related factors, HR was significantly lowered for the PES and PMMA groups compared with the PS group (HR 0.88; 95% CI 0.82-0.94 and HR 0.84 95% CI 0.76-0.93, respectively). After propensity score matching, HR for the PES and PMMA groups was significantly lowered compared with the PS group.

CONCLUSIONS

The use of different membrane types may affect mortality. Further long-term prospective studies are needed to clarify whether the PES and PMMA membranes can improve prognosis.

Differences in the adsorption of nafamostat mesilate between polyester-polymer alloy and polysulfone membranes

We previously experienced severe clot formation in a polyester-polymer alloy (PEPA) dialyzer and hemodialysis (HD) circuit with nafamostat mesilate (NM) as an anticoagulant. The possibility of NM adsorption to the PEPA membrane was taken into consideration, but there was not enough information. In the present study, we evaluated differences in the adsorption of NM between a PEPA membrane (FDX-120 GW, Nikkiso, Tokyo, Japan) and two different polysulfone membranes (FX-140, Fresenius Medical Care, Tokyo, Japan; NV-15U, Toray Medical, Tokyo, Japan). We calculated the NM concentration by measuring absorbance at 241 nm using a spectrometer. NM adsorption was evaluated in three ways. First, we evaluated NM adsorption to hollow fibers. Then, we passed an NM solution through dialyzers and evaluated its adsorption in a single-pass examination. Finally, we circulated an NM solution in an HD circuit using a blood pump and evaluated NM adsorption. In all the experiments, NM adsorption to the PEPA membrane was greater than that to the polysulfone membranes examined. In the blood pump experiment, the estimated adsorption quantities of NM to the PEPA membrane and the FX-140 and NV-15U polysulfone membranes were 12.0 ± 0.1, 1.0 ± 0.1, and 4.1 ± 0.4 mg/m², respectively. NM adsorption was confirmed, especially in the early phase, and the PEPA membrane adsorbed greater amounts of NM than the polysulfone membranes. We should pay attention to the choice of dialyzer as well as the appropriate dose of NM administration during the preparation of HD circuits.

The blood compatibilities of blood purification membranes and other materials developed in Japan

The biocompatibilities in blood purification therapy are defined as "a concept to stipulate safety of blood purification therapy by an index based on interaction in the body arising from blood purification therapy itself." The biocompatibilities are associated with not only materials to be used but also many factors such as sterilization method and eluted substance. It is often evaluated based on impacts on cellular pathways and on humoral pathways. Since the biocompatibilities of blood purification therapy in particular hemodialysis are not just a prognostic factor for dialysis patients but a contributory factor for long-term complications, it should be considered with adequate attention. It is important that blood purification therapy should be performed by consistently evaluating not only risks associated with these biocompatibilities but also the other advantages obtained from treatments. In this paper, the biocompatibilities of membrane and adsorption material based on Japanese original which are used for blood purification therapy are described.

Anaphylactic reaction induced by a polysulfone/polyvinylpyrrolidone membrane in the 10th session of hemodialysis with the same dialyzer

The majority of severe hypersensitivity reactions in hemodialysis patients have occurred due to sensitization to ethylene oxide or to nonbiocompatible membrane dialyzers. The use of polysulfone dialyzers rarely causes hypersensitivity reactions. In the present study, we describe a case of severe life-threatening reactions induced by polysulfone dialyzers (from different manufacturers subjected to a variety of sterilization methods), which occurred after 9 sessions of hemodialysis with the same prescription, exemplifying the complexity of such reactions.

Improvement of blood compatibility on polysulfone-polyvinylpyrrolidone blend films as a model membrane of dialyzer by physical adsorption of recombinant soluble human thrombomodulin (ART-123)

ART-123 is a recombinant soluble human thrombomodulin (hTM) with potent anticoagulant activity, and is available for developing antithrombogenic surfaces by immobilization. We focused on improving blood compatibility on the dialyzer surface by the physical adsorption of ART-123 as a safe yet simple method without using chemical reagents. The physical adsorption mechanism and anticoagulant activities of adsorbed hTM on the surface of a polysulfone (PSF) membrane containing polyvinylpyrrolidone (PVP) as a model dialyzer were investigated in detail. The PVP content of the PSF-PVP films was saturated at 20 wt% after immersion in Tris-HCl buffer, even with the addition of over 20 wt% PVP. The surface morphology of the PSF-PVP films was strongly influenced by the PVP content, because PVP covered the outermost surface of the PSF-PVP films. The adsorption speed of hTM slowed dramatically with increasing PVP content up to 10 wt%, but the maximum adsorption amount of hTM onto the PSF-PVP film surface was almost the same, regardless of the PVP content. The PSF-PVP film with the physically adsorbed hTM showed higher protein C activity as compared to the PSF film, it showed excellent blood compatibility due to the protein C activity and the inhibition properties of platelet adhesion. The physical adsorption of hTM can be useful as a safe yet simple method to improve the blood compatibility of a dialyzer surface.