Semi-Quantitative Evaluation of Asymmetricity of Dialysis Membrane Using Forward and Backward Ultrafiltration.

Performance of the dialysis membrane is strongly dependent upon the physicochemical structure of the membrane. The objective of this study is to devise a new in vitro evaluation technique to quantify the physicochemical structures of the membrane. Three commercial dialyzers with cellulose triacetate (CTA), asymmetric CTA (termed ATA®), and polyether sulfone (PES) membranes (Nipro Co., Osaka, Japan) were employed for investigation. Forward and backward ultrafiltration experiments were performed separately with aqueous vitamin B12 (MW 1355), α-chymotrypsin (MW 25,000), albumin (MW 66,000) and dextran solutions, introducing the test solution inside or outside the hollow fiber (HF), respectively. Sieving coefficients (s.c.) for these solutes were measured under the test solution flow rate of 200 mL/min and the ultrafiltration rate of 10 mL/min at 310 K, according to the guidelines provided by Japanese academic societies. We defined the ratio of s.c. in the backward ultrafiltration to that in the forward ultrafiltration and termed it the index for asymmetricity (IA). The IA values were unity for vitamin B12 and α-chymotrypsin in all three of the dialyzers. The IA values for albumin, however, were 1.0 in CTA, 1.9 in ATA®, and 3.9 in PES membranes, respectively, which corresponded well with the fact that CTA is homogeneous, whereas ATA® and PES are asymmetrical in structure. Moreover, the asymmetricity of ATA® and PES may be different by twofold. This fact was verified in continuous basis by employing dextran solution before and after being fouled with albumin. These findings may contribute to the development of a novel membrane for improved success of dialysis therapy.

Effects of Plasma Proteins on the Transport and Surface Characteristics of Polysulfone/Polyethersulfone and Asymmetric Cellulose Triacetate High Flux Dialyzers.

Blood-membrane interactions can have a large impact on the performance of hemodialysis membranes, particularly for high flux membranes in which the membrane itself provides very low resistance to solute transport. The objective of this study was to examine the effects of exposure to serum on the solute clearance and convective sieving characteristics of high flux polysulfone (Optiflux F250NR), polyethersulfone (ELISIO-25H), and asymmetric cellulose triacetate (SOLACEA-25H) hemodialyzers using both vitamin B12 and a range of polydisperse dextrans. Zeta potential measurements were used to obtain additional insights into the changes in membrane surface properties. Exposure to serum in a simulated dialysis session caused a significant reduction in both solute clearance and sieving coefficients for the polysulfone/polyethersulfone dialyzers, particularly for the larger molecular weight solutes. In contrast, the transport characteristics of the asymmetric cellulose triacetate dialyzers were almost unchanged after exposure to serum. The zeta potential of the cellulose triacetate membrane became slightly more negative after exposure to serum, consistent with an adsorbed protein layer composed largely of albumin. The net result is that the asymmetric cellulose triacetate dialyzer had dramatically higher clearance of the larger dextrans after exposure to serum, with the clearance and sieving coefficient for a 10 kDa molecular weight dextran being more than an order of magnitude greater than that of the polysulfone/polyethersulfone membranes. These results provide important insights into the expected clinical performance of these high flux dialyzers.

Transport Characteristics of Asymmetric Cellulose Triacetate Hemodialysis Membranes.

AIMS: The objective of this study was to compare the transport characteristics of highly asymmetric cellulose triacetate (ATA™) membranes with that of both symmetric cellulose triacetate and asymmetric polysulfone membranes. METHODS: Data were obtained for solute clearance and sieving coefficients of vitamin B12 and a range of polydisperse dextrans using ATA™ SOLACEA-25H and Optiflux F250NR polysulfone dialyzers. Results for these, and the CT190 symmetric cellulose triacetate dialyzer, were analyzed using available membrane transport models. RESULTS: The ATA™ had the largest solute clearance, although the homogeneous CT190 dialyzer had the highest sieving coefficients. These differences were a direct result of the differences in the underlying membrane morphology, with the asymmetric ATA™ membrane providing much higher diffusive transport rates (and thus higher solute clearance). CONCLUSIONS: These results demonstrate the importance of membrane morphology on dialyzer transport and provide important insights into the effective clinical performance observed with the highly asymmetric ATA™ dialyzers.

Evaluation of blood adsorption onto dialysis membranes by time-of-flight secondary ion mass spectrometry and near-field infrared microscopy.

Blood adsorption onto the inside surface of hollow fiber dialysis membranes was investigated by means of time-of-flight secondary ion mass spectrometry (TOF-SIMS) and near-field infrared microscopy (NFIR) in order to evaluate the biocompatibility and permeability of dialysis membranes. TOF-SIMS is useful for the imaging of particular molecules with a high spatial resolution of approximately 100 nm. In contrast, infrared spectra provide quantitative information and NFIR enables analysis with a high spatial resolution of less than 1 µm, which is close to the resolution of TOF-SIMS. A comparison was made of one of the most widely used dialysis membranes made of polysulfone (PSf), that has an asymmetric and inhomogeneous pore structure, and a newly developed asymmetric cellulose triacetate (ATA) membrane that also has an asymmetric pore structure, even though the conventional cellulose triacetate membrane has a symmetric and homogeneous pore structure. As a result, it was demonstrated that blood adsorption on the inside surface of the ATA membrane is more reduced than that on the PSf membrane. Graphical abstract Analysis of blood adsorption on inside surface of hollow fiber membrane.

Fundamental Characteristics of the Newly Developed ATA™ Membrane Dialyzer.

BACKGROUND: Dialysis membranes are often made from synthetic polymers, such as polysulfone. However, membranes made from cellulose triacetate have superior biocompatibility and have been used since the 1980s. On-line hemodiafiltration treatment accompanied by massive fluid replacement is increasingly being used in Europe and Japan, but cellulose triacetate is not suitable for this treatment. SUMMARY: Our newly developed asymmetric triacetate membrane, the ATA™ membrane, substantially improved the filtration properties and blood compatibility because of the asymmetric structure and smooth surface of this cellulose acetate membrane. Key Message: The ATA membrane maintains its high permeability even after massive filtration and shows less temporal variation in its permeation performance, lower protein adsorption, and superior biocompatibility compared with conventional membranes.

Cellulose triacetate as a high-performance membrane.

The cellulose triacetate membrane is one of the typical high-performance membranes. Cellulose triacetate is a plastic material manufactured from cellulose. The hydroxyl group of cellulose is chemically substituted for the carboxyl group. Therefore, its characteristics are quite different from cellulose. The cellulose triacetate membrane has a homogeneous membrane structure. It can be produced with a wide range of permeability, from low-flux performance to super high-flux performance. Because the thickness of the membrane is thin, and flow distribution of the dialysate (due to the moiré structure) is uniform, this enables the development of a dialyzer with high diffusive efficiency. Recently, this new product, improved through a sieving process, produced a uniform pore size distribution. As for the dialyzer, through sterilization by γ-rays with the absence of oxygen, now enables long-term safety of the product. Several clinical improvements have been reported, such as high antithrombus, the improvement of lipid metabolism and the reduction of biomarkers. Thus, continuous membrane development is desired, made of safe and stable cellulose triacetate material.