Factors in the Membrane Filtration of Enteroviruses

The filtration of two species of enteroviruses through membranes of porosity ranging from 50 to 220 mμ was studied. It was shown that extensive or total losses of virus may attend filtration at these porosities, apparently owing to adsorption of the virus to the membrane matrix. This could be minimized by the incorporation of serum into the virus suspension at the time of filtration, or by pretreating the membrane with serum or with a gelatin solution. It was also found that the first few drops of filtrate, even under optimal conditions, were likely to be virus-free, so that the filtration of too small a volume of virus suspension would result in a relatively great loss of titer. The degree to which these factors were critical was found to decrease with increasing pore diameter.     

Recovery of alkaline proteases by membrane filtration

This work describes the recovery of an extracellular alkaline protease from fermentation broths of a Bacillus sp ATCC 21536, at pH=10.0 using ultrafiltration (MWCO 100,000) and microfiltration (0.1 m) membranes in hollow fiber devices. The influence of membrane pore size and polymeric material and membrane filtration performance was studied. High protein recoveries and high average flux rates were obtained with polysulfone membranes. A decrease of concentration polarization was obtained, simultaneously with enhancement of filtration flux rate and enzyme recovery by using submicron sized charged particles. These polymers lead to flocculation and adsorption of whole cells and soluble factors from the fermentation broth. The best results were obtaiend by combination of cationic (0.1%) and anionic (0.04%) polymers.     

Effects of biofilm formation on membrane performance in submerged membrane bioreactors

The effects of biofilm formation on membrane performance were evaluated for a submerged membrane bioreactor (sMBR) system with six different types of micro- and ultrafiltration membranes (working volume=19 l). After operation for 24 h the permeability of the membranes with a larger pore size (microfiltration) decreased to that of the membranes with a much smaller pore size (ultrafiltration). Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) confirmed that biofilms could reduce the influence of the membrane surface properties. The chemical oxygen demand (COD) removal efficiency was 95% for the oily wastewater treatment in the sMBR where the filtration process made an important contribution (47% based on feed COD). Significant enhancement in COD removal occurred at the initial filtration stage because of biofilm formation and the dynamic member role of the biofilm layer. Membranes with various pore sizes had approximately the same permeate quality that was attributed to the biofilm on the membrane surfaces. Nevertheless, the ultrafiltration membranes had 43% more COD removal efficiency than the other applied membranes at the beginning of filtration (before biofilm formation) because of the smaller pore sizes and better sieving.     

Effects of biofilm formation on membrane performance in submerged membrane bioreactors

The effects of biofilm formation on membrane performance were evaluated for a submerged membrane bioreactor (sMBR) system with six different types of micro- and ultrafiltration membranes (working volume = 19 l). After operation for 24 h the permeability of the membranes with a larger pore size (microfiltration) decreased to that of the membranes with a much smaller pore size (ultrafiltration). Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) confirmed that biofilms could reduce the influence of the membrane surface properties. The chemical oxygen demand (COD) removal efficiency was 95% for the oily wastewater treatment in the sMBR where the filtration process made an important contribution (47% based on feed COD). Significant enhancement in COD removal occurred at the initial filtration stage because of biofilm formation and the dynamic member role of the biofilm layer. Membranes with various pore sizes had approximately the same permeate quality that was attributed to the biofilm on the membrane surfaces. Nevertheless, the ultrafiltration membranes had 43% more COD removal efficiency than the other applied membranes at the beginning of filtration (before biofilm formation) because of the smaller pore sizes and better sieving.     

Filtration-based perfusion of hybridoma cultures in protein-free medium: Reduction of membrane fouling by medium supplementation with DNase I

In this study, a filtration-based perfusion process was developed for the production of monoclonal antibodies (IgM) by suspended hybridoma cells grown in protein-free medium. It was found that the use of protein-free medium for perfusion culture generated the formation of numerous visible suspended particles consisting of dead cells and cellular debris aggregated into fibrous material. Surprisingly high apparent viabilities were observed in such protein-free cultures. In addition, membrane fouling occurred more rapidly in protein-free medium than in conventional serum-supplemented medium. By the addition of deoxyribonuclease I (DNase I) to the protein-free medium, it was possible to prevent the formation of aggregates and to follow the evolution of the total cell population more accurately. Moreover, DNase I significantly reduced the fouling of filtration membranes, and that, for two different types of separation systems (cross-flow and vortex-flow filtration) and two different types of membranes (polycarbonate and hydrophilized polysultone). From these results, it is clear that the presence of DNA fragments liberated following cellular death is playing an important role in membrane fouling. Longevity of filtration membranes was found to be considerably greater using a vortex-flow filtration module than with a static plate-and-frame cross-flow filtration module. The use of vortex-flow filtration of conjuction with DNase I allowed maintenance of perfusion cultures for more than 1 month without membrane fouling or antibody retention and with a constant permeate IgM concentration of 250 mg/L. Hybridomacells appeared to gradually adapt to increasing rotational speed in the vortex-flow filtration module.     

Evaluation of membranes for use in on-line cell separation during mammalian cell perfusion processes

In this study two microporous hollow fibre membranes were evaluated for their use as cell retention device in continuous perfusion systems. A chemically modified permanent hydrophillic PTFE membrane and a hydrophilized PP membrane were tested. To investigate the filtration characteristics under process conditions each membrane was tested during a long term perfusion cultivation of a hybridoma cell line. In both cultivations the conditions influencing membrane filtration (e.g. transmembrane flux) were kept constant. Filtration behaviour was investigated by monitoring transmembrane pressure and protein permeability. Transmembrane pressure was measured on-line with an autoclavable piezo-resistive pressure sensor. Protein permeability was determined by quantitative evaluation of unreduced, Coomassie stained SDS-PAGE. The membrane fouling process influences the filtration characteristics of both membranes in a different way. After fermentation the PP membrane was blocked by a thick gel layer located in the big outer pores of the asymmetric membrane structure. The hydraulic resistance was higher but the protein permeability was slightly better than of the PTFE membrane. For this reason the PP membrane should be preferred. On the other hand, transmembrane pressure decreases slower when the PTFE membrane is used, which favours this membrane for long term cultivations, especially when low molecular weight proteins (<30 KD) are produced.Abbreviations PP Polypropylene - PTFE Polytetrafluoroethylene     

Effect of solution pH on protein transmission and membrane capacity during virus filtration

Although virus filtration is now an integral part of the overall viral clearance strategy for the purification of many commercial therapeutic proteins, there is currently little understanding of the factors controlling the performance of the virus filters. The objective of this study was to examine the effects of solution pH on protein transmission and capacity during virus filtration. Data were obtained using bovine serum albumin as a model protein with Viresolve 180 membranes oriented with both the skin-side up and skin-side down. Membranes were also characterized using dextran sieving measurements both before and after protein filtration. Membrane capacity and protein yield were minimal at the protein isoelectric point, which was due to the greater degree of concentration polarization associated with the smaller protein diffusion coefficient at this pH. In contrast, the actual protein sieving coefficient was maximum at the protein isoelectric point due to the absence of any strong electrostatic exclusion under these conditions. The yield and capacity were both significantly greater when the membrane was oriented with the skin-side down. These results provide important insights into the effects of solution conditions on the performance of virus filtration membranes for protein purification.     

ELECTRICAL FACTORS INFLUENCING THE RATE OF FILTRATION OF AQUEOUS ELECTROLYTE SOLUTIONS THROUGH CELLOPHANE MEMBRANES

The mechanisms by which electrokinetic factors might influence the filtration rate of aqueous electrolyte solutions through membranes are discussed. The filtration rate of a thorium chloride solution in which the membrane is isoelectric is compared with those of other solutions. The maximum filtration rate is found at the isoelectric concentration, the rate falling as the electrokinetic potential increases. The results demonstrate an inverse relation between the electrokinetic potential and the filtration rate but do not permit the evaluation with any great exactitude of the respective rôles played by the two proposed mechanisms, namely, a stream potential-electroosmotic back-transport and a variation in effective pore diameter due to an orientation of water dipoles determined by electrical factors. Evidence is presented that Lepeschkin''s membrane resistance is an artifact.     

基于 AOPAN 纳米纤维膜的粘杆菌素发酵液后处理研究

使用静电纺丝再经胺肟化改性制备AOPAN纳米纤维膜,并基于AOPAN纳米纤维膜构建膜分离装置,用于粘杆菌素发酵液的后处理。研究中,对不同厚度的纳米纤维膜的渗透通量及分离性能进行比较,最终确定双层叠合的纳米纤维膜为分离膜,最适操作压力为0.14 MPa。在此条件下,分离膜的渗透通量为2.61 L/m2．min,蛋白质的截留率达到90％,色素等其他杂质也得到有效去除。     

Na, k, and nonspecific solute requirements for induction and function of galactose active transport in an antarctic psychrophilic marine bacterium

Strong adherence of bacteria, yeast, erythrocytes, leukocytes, platelets, spores, and polystyrene spheres to membrane filter materials was noted during filtration through membranes with pore size diameters much larger than the particles themselves. Quantitative recovery on the membrane filters of these particles from low-concentration suspensions was achieved during gravity- or vacuum-assisted filtration through membranes with pore diameters as much as 30 times that of the filtered particles. Mechanical sieving was not responsible. The phenomenon was judged to be electrostatic. It could be partially blocked by pretreating the filter with a nonionic surfactant (Tween 20), and elution of adherent particles was achieved with 0.05% Tween 20. Gram-positive cocci were removed from suspension more efficiently than gram-negative rods. The commonly used cellulose membranes adsorbed more bacteria, blood cells, and other particles than did polycarbonate filters. Of lesser adsorptive capacity were vinyl acetate, nylon, acrylic, and Teflon membranes. Backwashing with saline, serum, 6% NaCl, dextran solutions, or phosphate buffers of varying molality and pH removed only a fraction of adherent particles. Tween 20 (0.05%) eluted up to 45% of adherent particles in a single back-filtration. Selected filters quantitatively removed the particles tested, which then could be washed and subjected to reagents for a variety of purposes. It is important to anticipate the removal of particles during membrane filtration, since it is not a simple mechanical event.     

In situ synthesis of molecularly imprinted nanoparticles in porous support membranes using high-viscosity polymerization solvents

There is a growing need in membrane separations for novel membrane materials providing selective retention. Molecularly imprinted polymers (MIPs) are promising candidates for membrane functionalization. In this work, a novel approach is described to prepare composite membrane adsorbers incorporating molecularly imprinted microparticles or nanoparticles into commercially available macroporous filtration membranes. The polymerization is carried out in highly viscous polymerization solvents, and the particles are formed in situ in the pores of the support membrane. MIP particle composite membranes selective for terbutylazine were prepared and characterized by scanning electron microscopy and N? porosimetry. By varying the polymerization solvent microparticles or nanoparticles with diameters ranging from several hundred nanometers to 1 μm could be embedded into the support. The permeability of the membranes was in the range of 1000 to 20,000 Lm?2 hr?1 bar?1. The imprinted composite membranes showed high MIP/NIP (nonimprinted polymer) selectivity for the template in organic media both in equilibrium-rebinding measurements and in filtration experiments. The solid phase extraction of a mixture of the template, its analogs, and a nonrelated compound demonstrated MIP/NIP selectivity and substance selectivity of the new molecularly imprinted membrane. The synthesis technique offers a potential for the cost-effective production of selective membrane adsorbers with high capacity and high throughput.     

Adherence of bacteria, yeast, blood cells, and latex spheres to large-porosity membrane filters.

Strong adherence of bacteria, yeast, erythrocytes, leukocytes, platelets, spores, and polystyrene spheres to membrane filter materials was noted during filtration through membranes with pore size diameters much larger than the particles themselves. Quantitative recovery on the membrane filters of these particles from low-concentration suspensions was achieved during gravity- or vacuum-assisted filtration through membranes with pore diameters as much as 30 times that of the filtered particles. Mechanical sieving was not responsible. The phenomenon was judged to be electrostatic. It could be partially blocked by pretreating the filter with a nonionic surfactant (Tween 20), and elution of adherent particles was achieved with 0.05% Tween 20. Gram-positive cocci were removed from suspension more efficiently than gram-negative rods. The commonly used cellulose membranes adsorbed more bacteria, blood cells, and other particles than did polycarbonate filters. Of lesser adsorptive capacity were vinyl acetate, nylon, acrylic, and Teflon membranes. Backwashing with saline, serum, 6% NaCl, dextran solutions, or phosphate buffers of varying molality and pH removed only a fraction of adherent particles. Tween 20 (0.05%) eluted up to 45% of adherent particles in a single back-filtration. Selected filters quantitatively removed the particles tested, which then could be washed and subjected to reagents for a variety of purposes. It is important to anticipate the removal of particles during membrane filtration, since it is not a simple mechanical event.     

Investigation of virus retention by size exclusion membranes under different flow regimes

Virus removal by filter membranes is regarded as a robust and efficient unit operation, which is frequently applied in the downstream processing of biopharmaceuticals. The retention of viruses by virus filtration membranes is predominantly based on size exclusion. However, recent results using model membranes and bacteriophage PP7 point to the fact that virus retention can also significantly be influenced by adsorptive interactions between virus, product molecules, and membranes. Furthermore, the impact of flow rate and flow interruptions on virus retention have been studied and responsible mechanisms discussed. The aim of this investigation was to gain a holistic understanding of the underlying mechanisms for virus retention in size exclusion membranes as a function of membrane structure and membrane surface properties, as well as flow and solution conditions. The results of this study contribute to the differentiation between size exclusion and adsorptive effects during virus filtration and broaden the current understanding of mechanisms related to virus breakthroughs after temporary flow interruptions. Within the frame of a Design of Experiments approach it was found that the level of retention of virus filtration membranes was mostly influenced by the membrane structure during typical process-related flow conditions. The retention performance after a flow interruption was also significantly influenced by membrane surface properties and solution conditions. While size exclusion was confirmed as main retention mechanism, the analysis of all results suggests that especially after a flow interruption virus retention can be influenced by adsorptive effects between the virus and the membrane surface. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2747, 2019.     

Membrane fouling in sterile filtration of recombinant human growth hormone

The most troublesome problem encountered during the sterile filtration of protein solutions is membrane fouling. This article presents our study on sterile filtration of a model protein, recombinant human growth hormone (rhGH). Scanning electron microscopy (SEM) analysis shows that 0.22-mum membranes, when used to filter the mannitol-formulated protein solution under a 0.35-bar transmembrane pressure, were plugged to a great extent. When zinc ions were added to induce aggregates, the fouling tendency of rhGH solutions increased with increasing amount and size of the aggregates, indicating that the aggregates present before filtration might be responsible for membrane fouling. However, repeated filtration of the same solution using a fresh filter each time cannot reduce membrane fouling, and all filtrates contain the same trace amount of hGH particulates as the prefiltered solution. Particulate size was determined to be between 0.03 and 0.15 mum by dynamic light scattering. Also, in view of the fact that protein formulations significantly affected the tendency of fouling with the same preexisting aggregates, it is likely that fouling was more attributed to the aggregation taking place in the filter pores during filtration (secondary aggregation) than to the aggregates present before filtration. Adding a surfactant to or increasing the pH of the protein solution improves the filtration, whereas increasing ionic strength slows down the filtration. This result suggests that the balance of the protein's interaction and electrostatic repulsion plays an important role in the protein's fouling tendency. Many factors might change the microenvironment in the pores and disturb this balance. Those considerations and the aggregation tendency of rhGH in the filter pores will be discussed in detail separately. (c) 1996 John Wiley & Sons, Inc.     

Altered renal morphology in transgenic mice with cholecystokinin overexpression

Although cholecystokinin is a regulatory peptide with a predominant role in the brain and the gastrointestinal tract, there is an increasing evidence for its role in the kidney. The aim of this study was to reveal morphological changes in the structure of kidney of mice with cholecystokinin overexpression by means of light, transmission and scanning electron microscope, and atomic force microscopy. Using immunohistochemistry the expression of important basement membrane proteins collagen IV, laminin and fibronectin, as well the distribution of cholecystokinin-8 in the renal structures was evaluated. The altered morphology of kidneys of mice with cholecystokinin overexpression was seen by all microscopic techniques used. The renal corpuscles were relatively small with narrow capsular lumen. The basement membranes of renal tubules were thickened and the epithelial cells were damaged, which was more pronounced for distal tubules. Characteristic feature was the increased number of vesicles seen throughout the epithelial cells of proximal and especially in distal tubules reflecting to the enhanced cellular degeneration. The relative expression of laminin but not collagen IV in the glomerular basement membrane was higher than in the tubular basement membranes. The content of fibronectin, in opposite, was higher in tubular membranes. Cholecystokinin-8 was clearly expressed in the glomeruli, in Bowman’s capsule, in proximal and distal tubules, and in collecting ducts. Ultrastructural studies showed irregularly thickened glomerular basement membranes to which elongated cytopodia of differently shaped podocytes were attached. As foot processes were often fused the number of filtration pores was decreased. In conclusion, cholecystokinin plays important role in renal structural formation and in functioning as different aspects of urine production in mice with cholecystokinin overexpression are affected-the uneven glomerular basement membrane thickening, structural changes in podocytes and in filtration slits affect glomerular filtration, while damaged tubular epithelial cells and changed composition of thickened tubular basement membranes affect reabsorption.     

Factors affecting membrane fouling in filtration of Saccharomyces cerevisiae in an internal ceramic filter bioreactor

Filtration of ethanol fermentation medium and broth by using symmetric and asymmetric ceramic membranes has been studied in an internal filter bioreactor. Factors studied included membrane structure and pore size, medium sterilization, and concentrations of glucose, yeast extract in the medium, yeast cell and protein in broth. The aim was to determine the main factors responsible for the decline in filtration performance during ethanol fermentation by Saccharomyces cerevisiae. Flux index (Fi) of a new concept has been developed to evaluate the degree of flux decline during the membrane fouling process. Fi was defined as the ratio of the membrane flux at certain filtration time (t?=?t) to the initial (t?=??0) flux of pure water, not the initial (t?=?+0) flux of the test fluid. Flux with sterilized medium was approximately two-fold higher than that with unsterilized medium although the reason could not be explained clearly. Glucose, interaction between glucose and yeast extract, yeast cells, and proteins in fermentation broth were found to play an important part in membrane fouling. Fi of the symmetric membrane decreased to a less extent than that of the asymmetric membrane with increasing glucose concentration. But, the result with various yeast cell concentrations turned out to be contrary. Fouling was more serious for asymmetric membrane during the filtration of fermentation supernatant. This was thought to be due to different fouling mechanisms for the two types of membrane.     

Protein fouling of virus filtration membranes: effects of membrane orientation and operating conditions

The capacity of virus filters used in the purification of therapeutic proteins is determined by the rate and extent of membrane fouling. Current virus filtration membranes have a complex multilayer structure that can be used with either the skin-side up or with the skin-side facing away from the feed, but there is currently no quantitative understanding of the effects of membrane orientation or operating conditions on the filtration performance. Experiments were performed using Millipore's Viresolve 180 membrane under both constant pressure and constant flux operation with sulfhydryl-modified BSA used as a model protein. The capacity with the skin-side up was greater during operation with constant flux and at low transmembrane pressures, with the flux decline or pressure rise due primarily to osmotic pressure effects. In contrast, data obtained with the skin-side down showed a slower, steady increase in total resistance with the cumulative filtrate volume, with minimal contribution from osmotic pressure. The capacity with the skin-side down was significantly greater than that with the skin-side up, reflecting the different fouling mechanisms in the different membrane orientations. These results provide important insights for the design and operation of virus filtration membranes.     

Characterization and fouling properties of exopolysaccharide produced by Klebsiella oxytoca

Klebsiella oxytoca produced a type of exopolysaccharide (EPS) with the average molecular weight (Mw) of 116,018 Da and the average size of 260 nm. The EPS monosaccharide components contained rhamnose, fucose, arabinose, xylose, mannose, galactose and glucose and the molar ratio among them was 0.033:0.0411:0.0147:0.0051:0.2393:0.0986:0.1304. Typical EPS absorption peaks in FT-IR spectrum and pseudoplastic properties were also revealed. The polyvinylidenefluoride (PVDF) membrane showed a relatively larger flux decline resulted from the EPS fouling. The EPS filtration was dominated by more than one mechanism at the beginning phase and mainly by the cake formation at the later phase for both membranes. The pore blocking resistance had a predominant contribution to the filtration resistance and the cake resistance played a secondary role for both the membranes. The EPS adsorption resulted in a weak membrane fouling. The PVDF membrane exhibited a larger adsorption resistance than the polypropylene (PP) membrane.     

Catecholamine binding to plasma membrane enriched fractions of heart and skeletal muscle.

Binding of [3H]epinephrine to plasma membrane enriched fractions from guinea pig heart and rabbit skeletal muscle was investigated using the micropore filtration technique. [3H]Epinephrine and [3H]norepinephrine were found to be degraded rapidly in aqueous buffer at pH 7.6 and 37 degrees C. Deterioration of the compounds could be prevented by low concentrations of dithiothreitol. Binding of [3H]epinephrine to both membrane preparations was a slow process requiring 60 min to approach equilibrium in the case of cardiac membranes at 37 degrees C, and 20 min for skeletal muscle membranes at O degrees C. Binding was antagonized by the unlabeled beta-agonists, isopropylnorepinephrine, epinephrine, and norepinephrine but all were equipotent. A variety of catechol compounds were as effective antagonists of binding as the catecholamines. The beta-adrenergic antagonists propranolol, pronethalol, and dichloroisoproterenol were not effective in inhibiting binding to either membrane preparation. D-Norepinephrine and L-norepinephrine were equi-effective in antagonizing binding of [3H]norephinephrine to skeletal muscle membranes. It was concluded that binding of labeled catecholamine to isolated tissue membranes using the micropore filtration technique does not represent interaction with the specific beta-adrenergic receptor, but more likely reflects a less specific binding of compounds having one or more hydroxyl groups on a ring.     

Application of electrospun poly(ethylene terephthalate) nanofiber mat to apple juice clarification

Electrospinning was used to produce self-supporting nanofibrous poly(ethylene terephthalate) membranes with good mechanical properties and straightforward handling. The application of this type of membranes in apple juice clarification process was investigated. Processing characteristics and quality parameters of apple juice were analyzed in order to compare the proposed method to traditional clarification techniques. In general, the apple juice obtained from electrospun nanofiber membrane filtration revealed physico-chemical characteristics comparable to those from juice clarified by ultrafiltration or by conventional clarification using filtering aids. Nevertheless, the new process showed a high flux performance and revealed to be much faster, simple and more economical than the traditional processes. This work demonstrated the filtration potential of an electrospun PET membrane thus introducing a new concept of clarification and opening new approaches for the juice processing industry or even for other food industry fields.