Hemodialyzer mass transfer-area coefficients for urea increase at high dialysate flow rates

Hemodialyzer mass transfer-area coefficients for urea increase at high dialysate flow rates. The dialyzer mass transfer-area coefficient (KoA) for urea is an important determinant of urea removal during hemodialysis and is considered to be constant for a given dialyzer. We determined urea clearance for 22 different models of commercial hollow fiber dialyzers (N = ~5/model, total N = 107) in vitro at 37°C for three countercurrent blood (Qb) and dialysate (Qd) flow rate combinations. A standard bicarbonate dialysis solution was used in both the blood and dialysate flow pathways, and clearances were calculated from urea concentrations in the input and output flows on both the blood and dialysate sides. Urea KoA values, calculated from the mean of the blood and dialysate side clearances, varied between 520 and 1230ml/min depending on the dialyzer model, but the effect of blood and dialysate flow rate on urea KoA was similar for each. Urea KoA did not change (690 ± 160 vs. 680 ± 140 ml/min, P = NS) when Qb increased from 306 ± 7 to 459 ± 10ml/min at a nominal Qd of 500ml/min. When Qd increased from 504 ± 6 to 819 ± 8ml/min at a nominal Qb of 450ml/min, however, urea KoA increased (P < 0.001) by 14 ± 7% (range 3 to 33%, depending on the dialyzer model) to 780 ± 150ml/min. These data demonstrate that increasing nominal Qd from 500 to 800ml/min alters the mass transfer characteristics of hollow fiber hemodialyzers and results in a larger increase in urea clearance than predicted assuming a constant KoA

Modelling Complex Flows in Porous Media by Means of Upscaling Procedures

We review a series of problems arising in the field of flows through porous media and that are highly nontrivial either because of the presence of mass exchange between the fluid and the porous matrix (or other concurrent phenomena of physical or chemical nature), or because of a particularly complex structure of the medium. In all these cases there is a small parameter $\varepsilon$, representing the ratio between the microscopic and the macroscopic space scale. Our attention is focussed on a modelling technique (upscaling) which start from the governing equations written at the pore scale, introduces an expansion in power series of $\varepsilon$of all the relevant quantities and eventually leads to the formulation of the macroscopic governing equations at the various orders in $\varepsilon$ by a matching procedure, followed by suitable averaging. Two problems will be analyzed with some detail: soil erosion and the dynamics of water ultrafiltration devices. Moreover other problems will be occasionally discussed and open questions will be proposed

In-situ monitoring techniques for membrane fouling and local filtration characteristics in hollow fiber membrane processes: A critical review

© 2017 Elsevier B.V. Membrane fouling is the most serious challenge in the hollow fiber microfiltration (MF) and ultrafiltration (UF) processes. A number of in-situ monitoring techniques including optical and non-optical probes have been developed so that membrane fouling is better understood and controlled. This will help advance the membrane technology. In addition, the local filtration hydrodynamics wield a great influence on the membrane fouling formation and system operation stability. State-of-the-art in-situ monitoring techniques for membrane fouling and local filtration characteristics in hollow fiber MF/UF processes are critically reviewed. The principles and applications of these techniques are addressed in order to assess their strengths. This study demonstrated that the real-time observation techniques mainly focus on idealized laboratory apparatus and little on commercial membrane modules. Consequently, more attention should be paid to the development of simple and effective methods or integrated detecting technology so as to satisfy the real status of hollow fiber filtration processes and the optimization of membrane module. On the basis of this review, future analyses considering practical requirements are suggested as R&D priorities

Sodium Flux during Haemodialysis

Dialysis is aimed at the removal of charged ionic species in the blood that arise from complications in kidney disease. Although the process for the removal of urea and other unwanted charged species is understood, the effect of this removal on the net sodium concentration in the blood after treatment is not clear. In this report, we focus on formulating a fundamentally-based model to address this question. We consider the formulation near the membrane at the pore scale in order to determine effective jump conditions in ionic concentrations, electric potential and flow rate based on the membrane properties, and in order to determine whether electroneutrality holds within the pore. Secondly, we consider the local blood-cell concentration within one of the fibres and how this varies axially within the dialysis cartridge. Lastly, we consider a simple one-dimensional model of the charged species problem and find that advection transport through the membrane is important for sodium transport, but less pertinent for transport of other cation species

Design and modeling of a portable hemodialysis system

Research to improve artificial renal replacement therapies is varied across the many different parts of a hemodialysis system. Work largely focuses on developing a better dialyzer - the component that is directly responsible for removing wastes from the blood - but less study is devoted to the entire hemodialysis system. This work seeks to improve hemodialysis in two ways: by proposing a new renal replacement therapy that does not rely on traditional hemodialysis components, and by investigating the feasibility of adapting current hemodialysis practices to a portable format. While an alternative renal replacement therapy may be the best solution to today's dialysis problems, this work further focuses on reducing hemodialysis to a portable format through systematic engineering design. In that process, a detailed system model is made in Simulink that can account for the large number of inputs of such a system - the blood flow rate, dialyzer size, treatment time, etc. - allowing for detailed exploration of the design space. Once the model is completed, it is verified through in vitro experiments carried out with porcine blood. Additionally, the model is verified against published human hemodialysis data. After model verification, hemodialysis concepts are generated that allow for maximum portability under different patient conditions.M.S.Committee Chair: Rosen, David; Committee Member: Ku, David; Committee Member: Paredis, Chri

A Novel Approach to Synthesize Helix Wave Hollow Fiber Membranes for Separation Applications

Helix wave hollow fiber membranes are promising candidate to mitigate fouling and polarization effects in membrane operations. Current study describes a novel but simple approach to synthesize hollow fiber membranes with helix wave configuration. Poly(ether sulfone) (PES) based helix-waved hollow fiber membranes have been fabricated by dry-wet phase inversion process by using asymmetric coagulation conditions. Frequencies of the wave cycle have been observed approximately 20 and the wave length 7.1-7.6mm under the specifically required operating conditions defined by dope solution extrudate rate of 1g/min through 4cm of air-gap heights with 8.6m/min of winding speeds. On the other hand, simple hollow fibers are formed when the elongation force exerted by the winder is much higher than the surface tension of the external coagulant. The process can be useful for making polymer fibers for other applications as well

Severe dialyzer dysfunction undetectable by standard reprocessing validation tests

Severe dialyzer dysfunction undetectable by standard reprocessing validation tests. It is generally accepted that careful monitoring of total cell volume and ultrafiltration rates will ensure adequate function of reprocessed dialyzers. During routine urea kinetic measurements we noted that the percent of patients with clearances less than 200ml/min increased from 5% to 48% despite adherence to these validation tests. As these patients did not have evidence of recirculation in the vascular access, possible causes of dialyzer dysfunction were investigated. Injection of methylene blue into the dialysate port revealed non-uniform flow of dialysate in dialyzers from patients with markedly reduced clearances. In vitro studies of dialyzers subjected to sequential daily reprocessing, without patient exposure, demonstrated that in vitro clearances declined in one lot but not another. The initial clearances of 218 ± 4ml/min fell progressively to 112 ± 18 (P < 0.001) after 15 reuses. No effects of reprocessing were found in a different lot (230 ± 2 vs. 226 ± 4 ml/min). Soaking the dialyzers from the affected lot in either the disinfectant or dialysate solution caused a decline in the clearances which was less than that of serial reuse. Although the magnitude of the problem of dialyzer malfunction with reuse is unknown, careful attention to dialyzer function is warranted in patients treated with reprocessed dialyzers

STUDY OF DIALYZER MEMBRANE (POLYFLUX 210H) AND EFFECTS OF DIFFERENT PARAMETERS ON HEMODIALYSIS PERFORMANCE

Renal failure or kidney failure is a medical condition when the kidneys fail to filter toxins and waste products from the blood. Most of the time, problems encountered in kidney malfunction include abnormal fluid levels in the body, increased acid levels and abnormal levels of Urea, Glucose, Endothelin, β2-Microglobulin, Complement Factor D. In medicine, dialysis is a method that is used to remove waste products from blood when the kidneys are in a state of renal failure. Parameters characterizing the structure of dialyzers are very important because they decide overall clearance of toxin molecules and at the same time should allow retaining useful molecules in the blood. It is however not clear how the changes of dialyzer parameters will affect the clearance. This can be found out by doing simulation of a dialysis process. In this thesis, a numerical model was developed to simulate the process that goes on inside a dialyzer to determine which parameters are important for getting better clearance of toxin molecules and how the changes of those parameters can improve the performance of dialysis. In order to do that, a model of dialyzer membrane with details of the porosity is necessary. The dialyzer membrane that was considered in this research was Polyflux 210H. Here the cross sectional images of Polyflux 210H dialyzer membrane were taken by FESEM (Field Emission Scanning Electron Microscope) to obtain the porosity values of different layers. Using these porosity values, a multilayered membrane model was developed in Finite Element Software- COMSOL Multiphysics 4.3. Then a blood flow containing - Urea, Glucose, Endothelin, β2-Microglobulin, Complement Factor D and Albumin was introduced. For a certain blood flow rate the toxins diffuse through the membrane and on the other side of the membrane a dialysate flow was introduced to remove the toxins. Two different definitions of effective diffusivity were considered for the phenomenon of the diffusion of the molecules in the membrane. Between the two, the better definition was found out by comparing the results with experimental data of the manufacturer of Polyflux 210H. Then for the chosen definition, further analysis was done and the results were compared with another set of experimental data to validate the model. Then different parameters - magnitude and direction of both blood and dialysate flow, length and diameter of the fiber, pore sizes were changed to simulate how these changes affect toxin clearance and the removal of useful molecules. The results suggest some very interesting points to achieve better dialysis performance. First of all, the clearance rate of both Urea and Glucose increase rapidly with the increasing blood flow rate. When a maximum allowable blood flow rate is attained, increasing the dialysate flow rate can ensure better clearance rate for Urea and Glucose. In both the cases of increasing radius or length of the dialyzer fiber, the clearance rate of Glucose increases more rapidly than the clearance rate of Urea. For Endothelin and β2-Microglobulin the clearance rate increases twice compared to the initial condition. Meanwhile, the clearance rate of Albumin does not change that much. Also increasing the pore diameter up to 20 nm (but not more than that) can ensure higher clearance rate of Urea and Glucose, moderate clearance rate of middle molecules and minimum loss of Albumin