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Hechingen, Germany

Majeed S.,Helmholtz Center Geesthacht | Fierro D.,Helmholtz Center Geesthacht | Fierro D.,Reutlingen University | Buhr K.,Helmholtz Center Geesthacht | And 5 more authors.
Journal of Membrane Science | Year: 2012

Hydroxyl functionalized multi-walled carbon nanotubes (MWCNTs) were blended with polyacrylonitrile (PAN) to prepare ultrafiltration membranes by a phase inversion process. Three different concentrations of MWCNTs were used in PAN, i.e. 0.5, 1 and 2. wt%. The water flux of the membranes increased by 63% at 0.5. wt% loading of MWCNTs compared to neat PAN membranes. The water flux decreased upon further increase in the concentration of MWCNTs, but at 2. wt% loading it was still higher compared to pure PAN membranes. The surface hydrophilicity of the membranes was enhanced upon the addition of MWCNTs, as observed by contact angle measurements. The increased hydrophilicity might have an impact on the improved water flux. All the membranes showed a molecular weight cut off (MWCO) of approximately 50. kg/mol. Surface pore size analysis by scanning electron microscopy (SEM) showed no significant difference in the mean pore size of the nanocomposite membranes compared to the neat membranes. The cross section morphology was influenced by the introduction of MWCNTs where less but enlarged macrovoids were observed, particularly prominent at a loading of 2. wt% MWCNTs. The membranes containing 2. wt% MWCNTs showed 36% improvement in resistance against compaction compared to neat membranes. Furthermore, the tensile strength of the membranes at 2. wt% MWCNTs loading increased over 97% compared to neat ones. © 2012 Elsevier B.V. Source

Axelsson J.,Lund University | oberg C.M.,Lund University | Rippe A.,Lund University | Krause B.,Gambro Dialysatoren GmbH | Rippe B.,Lund University
Journal of Membrane Science | Year: 2012

The aim of the present study was to investigate the size-selectivity of two different synthetic dialyzing membranes, having widely differing sieving properties, with respect to their handling of polydispersed fluorescein isothiocyanate (FITC)-Ficoll, FITC-dextran and of proteins, i.e. 125I-human serum albumin (RISA) and 125I-myoglobin (Myo). Are Ficoll and dextran, compared to proteins, " hyperpermeable" across synthetic dialyzing membranes, similar to their behavior across the glomerular filtration barrier (GFB)? A high-flux membrane (HF-Revaclear ®; n=12) and a high cut-off membrane (HCO; n=14) in capillary mini-dialyzers were perfused with diluted horse serum. The perfusate contained polydisperse FITC-Ficoll 70/400 or FITC-dextran (molradius 13-80Å), FITC-Inulin, and, in some experiments, RISA/Myo. After a priming period, sampling of filtrate occurred, and a midpoint plasma sample taken. Filtrate-to-plasma concentration ratios (θ) vs. molecular radius (a e) were assessed using HPLC for Ficoll and dextran. Size-selectivity for Ficoll increased in the order: HF-Revaclear ® Source

Fierro D.,Helmholtz Center Geesthacht | Fierro D.,Reutlingen University | Boschetti-de-Fierro A.,Helmholtz Center Geesthacht | Boschetti-de-Fierro A.,Gambro Dialysatoren GmbH | Abetz V.,Helmholtz Center Geesthacht
Journal of Membrane Science | Year: 2012

The solution-diffusion with imperfections model has been used together with diffusion models such as the Vrentas & Duda diffusion theory and the Wesselingh & Bollen multicomponent diffusion model as a tool to successfully describe the permeation behavior of mixtures of ketones and glycols through polydimethylsiloxane composite membranes in a cross-flow membrane cell for pressures varying from 10 to 40. bar. The model has shown the great importance of an accurate determination of the diffusion coefficients and the average concentration of permeants inside the membrane into the successful modeling of nanofiltration experiments. © 2012 Elsevier B.V. Source

Sakota R.,Gambro | Lodi C.A.,Gambro | Sconziano S.A.,Gambro | Beck W.,Gambro Dialysatoren GmbH | Bosch J.P.,Gambro
Artificial Organs | Year: 2015

Gradual deterioration of red blood cells (RBCs) due to mechanical stress (chronic hemolysis) is unavoidable during treatments that involve extracorporeal blood circulation, such as hemodialysis (HD). This effect is generally undetectable and does not generate any acute symptoms, but it leads to an increase in plasma free hemoglobin (fHb). There are no absolute safety levels for fHb increase, indicating the need for an empirical evaluation using comparative testing. The increase in fHb levels was investigated in vitro by applying double-needle double-pump HD (HD-DNDP), a new modality in which arterial and venous pumps both run continuously. fHb was measured during typical and worst-case simulated dialysis treatments (double-needle single-pump HD [HD-DNSP], hemodiafiltration [HDF-DN], single-needle double-pump HD [HD-SNDP], and HD-DNDP) performed in vitro using bovine blood for 4 h. Hemolysis-related indices (fHb%; index of hemolysis, IH; and normalized IH) were calculated and used for comparison. The increase in fHb during either HDF-DN or HD-SNDP with Artis and AK200 dialysis machines was similar, while the fHb at the maximum real blood flow rate (Qbreal) at the completion of the HD-DNDP treatment on Artis was higher than that for HD-DNSP using a Phoenix dialysis machine (fHb%=1.24±0.13 and 0.92±0.12 for the Artis machine with HD-DNDP at Qbreal=450mL/min and Phoenix with HD-DNSP at Qbreal=500 mL/min, respectively). However, the fHb levels increased linearly, and no steep changes were observed. The increases observed during HD-DNDP were the same order of magnitude as those for widely used bloodlines and treatment modes for delivering dialysis treatments. The observed results matched literature findings, and thus the measured fHb trends are not predicted to have clinical side effects. HD-DNDP treatment with Artis does not merit any additional concern regarding mechanical stress to RBCs compared with that observed for routinely used dialysis treatments, bloodlines and machines. Although the in vitro measurement of the fHb increase in bovine blood does not allow a prediction of the absolute level of blood mechanical damage or the possible effects in humans, such measurements are valuable for assessing hemolytic harm by performing tests comparing the proposed treatment with existing devices. © 2015 The Authors. Source

Louis Chakkalakal G.,Helmholtz Center Geesthacht | Alexandre M.,Helmholtz Center Geesthacht | Alexandre M.,University of Liege | Abetz C.,Helmholtz Center Geesthacht | And 3 more authors.
Macromolecular Chemistry and Physics | Year: 2012

The surface of silica nanoparticles is modified using the "grafting from" technique. A multi-step reaction is conducted to modify their surface properties. (3-glycidoxypropyl) trimethoxysilane (GPS) is used as the coupling agent for the fixation of atom transfer radical polymerization (ATRP) initiator. The grafting efficiency of GPS mixed with aqueous suspension of silica nanoparticles is studied, followed by the coupling efficiency towards ATRP initiator. The bromide concentration of ATRP initiator is kept constant for comparative kinetic studies of styrene and MMA polymerizations. The consequences at high conversions and the particle size distribution are studied. The behaviour of the glass transition temperature of either polymer-modified particles and the nature of dispersion of polymer-coated silica particles are analyzed. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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