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Membrane Pore Size (membrane + pore_size)
Selected AbstractsThe membrane emulsification process,a reviewJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2004C Charcosset Abstract Membrane emulsification has received increasing attention over the last 10 years, with potential applications in many fields. In the membrane emulsification process, a liquid phase is pressed through the membrane pores to form droplets at the permeate side of a membrane; the droplets are then carried away by a continuous phase flowing across the membrane surface. Under specific conditions, monodispersed emulsions can be produced using this technique. The purpose of the present paper is to provide a review on the membrane emulsification process including: principles of membrane emulsification, influence of process parameters and industrial applications. Small-scale applications such as drug delivery systems, food emulsions, and the production of monodispersed microspheres are also included. Compared with conventional techniques for emulsification, membrane processes offer advantages such as control of average droplet diameter by average membrane pore size and lower energy input. Copyright © 2004 Society of Chemical Industry [source] Diffusional properties of chitosan hydrogel membranesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2001Barbara Krajewska Abstract Chitosan membranes were prepared by a solvent evaporation technique, followed by crosslinking with glutaraldehyde and coating with BSA. The effects of crosslinking and BSA coating on the pore structure of such prepared hydrogel chitosan membranes were determined. The diffusion rates of 12 non-electrolytes ranging in molecular radius between 2.5 and 14,Å through the membranes were measured, and the results were interpreted in terms of the capillary pore model and free volume model of solute diffusional transport through hydrogel membranes. Glutaraldehyde crosslinking was found to reduce the membrane water content and consequently the membrane pore size and surface porosity, whereas further BSA coating brought about the opposite effect. The latter effect lessened with an increase in glutaraldehyde pretreatment of the membranes. The optimal chitosan membrane preparation, compromising between the solute flux and membrane stability and durability was obtained when the membranes were crosslinked with glutaraldehyde at concentrations between 0.01 and 0.1% (w/w). The knowledge of transport properties and of physical strength of the membranes is of importance for the development of chitosan-based controlled release systems. © 2001 Society of Chemical Industry [source] A fine match between the stereoselective ligands and membrane pore size for enhanced chiral separationAICHE JOURNAL, Issue 9 2009Honglei Wang Abstract A D,L -tryptophan separation factor of 12,15 and D -tryptophan yield of >95% have been successfully achieved through using human serum albumin (HSA) as the stereoselective ligand in an affinity ultrafiltration (UF) system. The obtained separation factor in this work is even higher than the intrinsic value of 8.5 of HSA. This synergism may arise from the fact that a fine match between the regular crystalline structure of HSA molecules and suitable pore size of membranes makes some HSA molecules be retained within the membrane cross-section, thus offering a second-stage binding opportunity for L -tryptophan molecules. Therefore, a simultaneous enhancement in separation factor and D -tryptophan yield has been fulfilled in this work. The feasibility of HSA regeneration after D,L -tryptophan separation has also been demonstrated through a series of pH adjustment experiments. This study reveals the applicability of HSA in affinity UF systems for chiral separation due to economization of material costs. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Nanoporous aluminum oxide affects neutrophil behaviourMICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2004M. Karlsson Abstract This study evaluates neutrophil responses on aluminum oxide membranes. Using an in vitro cell culture system, we have found that the pore size (20 and 200 nm in diameter) of alumina membranes have a significant effect on leukocyte morphology and activation. Specifically, our results show that 20-nm pore-size membranes were more potent in triggering PMN spreading and extending of pseudopodia than 200-nm pore-size membranes. The morphological changes are also associated with cell activation. In fact, adherent neutrophils on 20-nm pore-size membranes elicit much stronger initial oxygen free radical production. Overall, our results point out that membrane pore size significantly affects the extent of cellular responses of adherent neutrophils. Microsc. Res. Tech. 63:259,265, 2004. © 2004 Wiley-Liss, Inc. [source] Scaleable purification process for gene therapy retroviral vectorsTHE JOURNAL OF GENE MEDICINE, Issue 4 2007Teresa Rodrigues Abstract Background Retroviral vectors (RVs) constitute one of the preferred gene therapy tools against inherited and acquired diseases. Development of scaleable downstream processes allowing purification under mild conditions and yielding viral preparations with high titer, potency and purity is critical for the success of clinical trials and subsequent clinical use of this technology. Methods A purification process for murine leukaemia virus (MLV)-derived vector supernatants was developed based on membrane separation and anion-exchange chromatography (AEXc). Initial clarification of the vector stocks was performed using 0.45 µm membranes followed by concentration with 500 kDa molecular weight cut-off (MWCO) membranes; further purification was performed by AEXc using a tentacle matrix bearing DEAE functional ligands. Finally, concentration/diafiltration was performed by 500 kDa MWCO membranes. To validate final product quality the process was scaled up 16-fold. Results Optimization of microfiltration membrane pore size and ultrafiltration transmembrane pressure allowed the recovery of nearly 100% infectious particles. Further purification of the RVs by AEXc resulted in high removal of protein contaminants while maintaining high recoveries of infectious vectors (77 ± 11%). Up-scaling of the process resulted in high titer vector preparations, 3.2 × 108 infectious particles (IP)/ml (85-fold concentration), with an overall recovery reaching 26%. The process yielded vectors with transduction efficiencies higher than the starting material and more than 99% pure, relative to protein contamination. Conclusions The combination of membrane separation and AEXc processes results in a feasible and scaleable purification strategy for MLV-derived vectors, allowing the removal of inhibitory contaminants thus yielding pure vectors with increased transduction efficiencies. Copyright © 2007 John Wiley & Sons, Ltd. [source] Optimization of mass transfer for toxin removal and immunoprotection of hepatocytes in a bioartificial liverBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009Geir I. Nedredal Abstract This study was designed to determine optimal operating conditions of a bioartificial liver (BAL) based on mass transfer of representative hepatotoxins and mediators of immune damage. A microprocessor-controlled BAL was used to study mass transfer between patient and cell compartments separated by a hollow fiber membrane. Membrane permeability (70, 150, or 400,kDa molecular weight cut-off,MWCO), membrane convection (high: 50,mL/min; medium: 25,mL/min; low: 10,mL/min; diffusion: 0,mL/min), and albumin concentration in the cell compartment (0.5 or 5,g%) were considered for a total of 24 test conditions. Initially, the patient compartment contained pig plasma supplemented with ammonia (0.017,kDa), unconjugated bilirubin (0.585,kDa), conjugated bilirubin (0.760,kDa), TNF-, (17,kDa), pig albumin (67,kDa), pig IgG (147,kDa), and pig IgM (900,kDa). Mass transfer of each substance was determined by its rate of appearance in the cell compartment. Membrane fouling was assessed by dextran polymer technique. Of the three tested variables (membrane pore size, convection, and albumin concentration), membrane permeability had the greatest impact on mass transfer (P,<,0.001). Mass transfer of all toxins was greatest under high convection with a 400,kDa membrane. Transfer of IgG and IgM was insignificant under all conditions. Bilirubin transfer was increased under high albumin conditions (P,=,0.055). Fouling of membranes ranged from 7% (400,kDa), 24% (150,kDa) to 62% (70,kDa) during a 2-h test interval. In conclusion, optimal toxin removal was achieved under high convection with a 400-kDa membrane, a condition which should provide adequate immunoprotection of hepatocytes in the BAL. Biotechnol. Bioeng. 2009; 104: 995,1003. © 2009 Wiley Periodicals, Inc. [source] Selective precipitation-assisted recovery of immunoglobulins from bovine serum using controlled-fouling crossflow membrane microfiltrationBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2008Adith Venkiteshwaran Abstract Efficient and economic recovery of immunoglobulins (Igs) from complex biological fluids such as serum, cell culture supernatant or fermentation cell lysate or supernatant, represents a substantial challenge in biotechnology. Methods such as protein A affinity chromatography and anion exchange chromatography are limited by cost and selectivity, respectively, while membrane chromatography is limited by low adsorptive area, flow distribution problems and scale-up difficulties. By combining the traditional salt-assisted precipitation process for selective removal of Igs from serum followed by constant-permeate flux membrane microfiltration for low fouling, we demonstrate an exciting new, efficient and economic hybrid method. The high selectivity of an ammonium sulfate-induced precipitation step was used to precipitate the Igs leaving the major undesirable impurity, the bovine serum albumin (BSA), in solution. Crossflow membrane microfiltration in diafiltration mode was then employed to retain the precipitate, while using axial flow rates to optimize removal of residual soluble BSA to the permeate. The selectivity between immunoglobulin G (IgG) and BSA obtained from the precipitation step was ,36, with 97% removal of the BSA with diafiltration in 5 diavolumes with resulting purity of the IgG of ,93% after the membrane microfiltration step. Complete resolubilization of the IgG was obtained without any aggregation at the concentrations of ammonium sulfate employed in this work. Further, membrane pore size and axial Reynolds number (recirculation rate) were shown to be important for minimizing fouling and loss of protein precipitate. Biotechnol. Bioeng. © 2008 Wiley Periodicals, Inc. [source] Interfacial formation of porous membranes with poly(ethylene glycol) in a microfluidic environmentJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Dongshin Kim Abstract In a microfluidic environment, the liquid,liquid interface, formed by laminar flows of immiscible solutions, can be used to generate thin membranes via interfacial polymerization. Because these thin nylon membranes have a very small pore size or lack porosity entirely, their utilization in some biological applications is greatly limited. We introduce an in situ fabrication method using the interfacial reaction of a two-phase system to generate a porous nylon membrane. The membranes were characterized with scanning electron microscopy and fluorescent beads. Scanning electron microscopy micrographs verified the asymmetrical structure of the porous membrane, and the membrane pore sizes ranged from 0.1 to 1 ,m. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008. [source] CLARIFICATION AND PURIFICATION OF AQUEOUS STEVIA EXTRACT USING MEMBRANE SEPARATION PROCESSJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2009M.H.M. REIS ABSTRACT Stevia rebaudiana Bertoni is a native plant from South America and its active constituents have been considered the "sweeteners of the future."Stevia is a natural diet-sweetening source, safe to health and without calories. However, the obtained raw extract is foul smelling, bitter tasting, dark brown colored, and presents suspension matter due to organic and inorganic compounds. Therefore, further purification/clarification is essential in order to get a product of commercial quality. In this work ceramic membranes were applied in the stevia extract clarification process. The process was carried out under different membrane pore sizes and at different pressure values. The best clarification result was obtained with the membrane of 0.1 µm at 4 bar. On the other hand, the best condition for the flux was obtained with the membrane of 0.2 µm at 6 bar. The process with all the tested membranes and conditions achieved recovery of sweeteners higher than 90%. Finally, a filtration mathematical model was applied to describe the flux behavior, showing that the main fouling phenomenon during the process occurred because of the complete blocking of pores. PRACTICAL APPLICATION Stevia is the world's only all-natural sweetener with zero calories, zero carbohydrates and a zero glycemic index. However, the obtained stevia extract has a dark brown appearance, mainly because of the presence of impurities. In this work the membrane separation process was studied for stevia extract clarification and purification in order to get a product with higher commercial acceptability. The obtained results showed that total clarification and recuperation of sweeteners was almost achieved. Nonetheless, membrane fouling is an inevitable problem during membrane filtration. The mathematical analysis of the fouling occurrences showed that the complete blocking of pores is the main cause for the membrane permeability decrease. [source] | |||||||||||||