Technical characterization of dialysis fluid flow and mass transfer rate in dialyzers with various filtration coefficients using dimensionless correlation equation.

The objective of the present study is to evaluate the effect of filtration coefficient and internal filtration on dialysis fluid flow and mass transfer coefficient in dialyzers using dimensionless mass transfer correlation equations. Aqueous solution of vitamin B12 clearances were obtained for REXEED-15L as a low flux dialyzer, and APS-15EA and APS-15UA as high flux dialyzers. All the other design specifications were identical for these dialyzers except for filtration coefficient. The overall mass transfer coefficient was calculated, moreover, the exponents of Reynolds number (Re) and film mass transfer coefficient of the dialysis-side fluid (k D) for each flow rate were derived from the Wilson plot and dimensionless correlation equation. The exponents of Re were 0.4 for the low flux dialyzer whereas 0.5 for the high flux dialyzers. Dialysis fluid of the low flux dialyzer was close to laminar flow because of its low filtration coefficient. On the other hand, dialysis fluid of the high flux dialyzers was assumed to be orthogonal flow. Higher filtration coefficient was associated with higher k D influenced by mass transfer rate through diffusion and internal filtration. Higher filtration coefficient of dialyzers and internal filtration affect orthogonal flow of dialysis fluid.

Poly(N-vinyl-2-pyrrolidone) elution from polysulfone dialysis membranes by varying solvent and wall shear stress.

Some dialysis patients are treated with post-hemodiafiltration (HDF); the blood viscosity of the patients who undergo post-HDF is higher than that of the patients who undergo conventional hemodialysis. This study aims to evaluate poly(N-vinyl-2-pyrrolidone) (PVP) elution from PSf dialysis membranes by varying solvents and high wall shear stress caused by blood viscosity. We tested three commercial membranes: APS-15SA (Asahi Kasei Kuraray), CX-1.6U (Toray) and FX140 (Fresenius). Dialysate and blood sides of the dialyzers were primed with reverse osmosis (RO) water and saline. RO water, saline and dextran solution (2.9 and 5.8 mPa s) were circulated in the blood side. The amount of eluted PVP was determined by 0.02 N iodometry. The hardness and adsorption force of human serum albumin (HSA) on the membrane surfaces were measured by the atomic force microscope. When wall shear stress was increased using dextran, the amount of PVP eluted by the 2.9 mPa s solution equaled that eluted by the 5.8 mPa s solution with APS-15SA and CX-1.6U sterilized by gamma rays. The amount of PVP eluted by the 5.8 mPa s solution was higher than that eluted by the 2.9 mPa s solution with FX140 sterilized by autoclaving. The wall shear stress increased the PVP elution from the surface, hardness and adsorption force of HSA. Sufficient gamma-ray irradiation is effective in decreasing PVP elution.

Longer storage of dialyzers increases elution of poly(N-vinyl-2-pyrrolidone) from polysulfone-group dialysis membranes.

The objective of this study was to evaluate the effect of protracted storage of dialyzers on the amount of poly(N-vinyl-2-pyrrolidone) (PVP) eluted from polysulfone-group dialysis membranes. We tested five dialysis membranes: APS-15SA (Asahi Kasei Kuraray, wet), CX-1.6U (Toray, moist), FX140 (Fresenius, dry), PES-15Sα (Nipro, dry), and FDX-150GW (Nikkiso, wet). Each dialyzer was stored for 1, 3, 14, and 18 months after sterilization. The dialysis-fluid side compartment was primed with reverse osmosis (RO) water at 500 mL/min for 5 min at 310 K. The blood side compartment was primed with RO water at 200 mL/min for 5 min at 310 K. Finally, 1 L RO water was circulated through the blood side compartment at 200 mL/min for 4 h at 310 K. Eluted PVP was determined by use of the iodine method, using 0.02 N: iodine solution. PVP was mainly eluted from wet-type dialyzers during priming. Thus, the standard 5 min priming of the wet-type dialyzer according to the maker manual inhibits PVP elution during circulation. PVP was eluted in the dialysis-fluid side of the moist-type dialyzer during priming but no PVP was eluted in the blood side. PVP was mainly eluted from dry-type dialyzers during circulation. We recommend more than the standard 5 min priming, particularly for dry-type dialyzers stored for protracted periods, because 5 min insufficient to inhibit PVP elution during circulation.

Fabrication of zeolite-polymer composite nanofibers for removal of uremic toxins from kidney failure patients.

There is a need to develop a simple, cheap, and accessible method of treating patients with kidney failure, especially in resource-limited environments such as disaster areas and the developing world due to the inaccessibility of conventional hemodialysis treatments. In this study, we develop a zeolite-polymer composite nanofiber mesh to remove uremic toxins for blood purification. The nanofiber is composed of blood compatible poly(ethylene-co-vinyl alcohol) (EVOH) as the primary matrix polymer and zeolites which are capable of selectively adsorbing uremic toxins such as creatinine. The composite fiber meshes were produced by a cost-effective electrospinning method: electrospinning composite solutions of EVOH and zeolites. Scanning electron microscope (SEM) images revealed that the 7 w/v% EVOH solution produced non-woven fibers with a continuous and smooth morphology. The SEM also showed that over 90% of zeolites in the solution were successfully incorporated into the EVOH nanofibers. Although the barrier properties of the EVOH matrix lowered the creatinine adsorption capacity of the zeolites in the fiber when compared with adsorption to free zeolites, their adsorption capacity was still 67% of the free zeolites. The proposed composite fibers have the potential to be utilized as a new approach to removing nitrogenous waste products from the bloodstream without the requirement of specialized equipment.

Nanotechnological characterization of human serum albumin adsorption on wet synthetic polymer dialysis membrane surfaces.

The objective of the present study was to evaluate the characteristics of protein adsorption on the inner surface of various dialysis membranes, to develop protein adsorption-resistant biocompatible dialysis membranes. The adsorption force of human serum albumin (HSA) on the inner surface of a dialysis membrane and the smoothness of the membrane were evaluated from a nanoscale perspective by atomic force microscopy. The content ratio of the hydrophilic polymer, polyvinylpyrrolidone (PVP), was determined by attenuated total reflection Fourier transform infrared spectroscopy. Nine synthetic-polymer dialysis membranes on the market made of polysulfone (PSF), polyethersulfone (PES), polyester polymer-alloy (PEPA), and ethylene vinylalcohol (EVAL) were used in the present study. The HSA adsorption force on the surface of the hydrophobic polymer PEPA membrane was higher than that on the hydrophilic polymer EVAL membrane surface. It has been considered beneficial, for decreasing the HSA adsorption force, to cover a hydrophobic polymer membrane surface with PVP. However, there were some areas on PVP-containing membrane surfaces at which much higher HSA adsorption forces were observed. The HSA adsorption force gave a nearly linear correlation with the surface roughness on the PSF membrane surface. However, the HSA adsorption force was uncorrelated with the PVP content ratio for any of the PSF membrane surfaces tested. In conclusion, protein adsorption can be minimized by the use of dialysis membranes made of hydrophobic polymers containing PVP with a smooth surface.