Changes In Membrane Surface Properties Research Articles

Performance and deterioration of forward osmosis membrane exposed to various dose of gamma-ray irradiation

The effect of ionizing radiation on membrane performance of forward osmosis (FO) was investigated at doses of 20 and 200 kGy. The performance of CTA membrane and TFC membrane was compared in terms of water flux, nuclide retention and flux, reverse NaCl flux. The changes in membrane surface properties at different doses were also analyzed. For both membranes, the water flux increased with increase of absorbed dose, mainly due to the enhancement of membrane hydrophilicity. The retention of Co ions and Sr ions, reverse NaCl flux, surface chemical information and functional group were not significantly affected by dose. However, the surface morphology and roughness changed with increase of dose. The modification of the commercial FO membrane is necessary for the enhancement of the irradiation resistance, which is very important for practical application FO technology in radioactive wastewater treatment.

Effects of Plasma Proteins on the Transport and Surface Characteristics of Polysulfone/Polyethersulfone and Asymmetric Cellulose Triacetate High Flux Dialyzers.

Blood-membrane interactions can have a large impact on the performance of hemodialysis membranes, particularly for high flux membranes in which the membrane itself provides very low resistance to solute transport. The objective of this study was to examine the effects of exposure to serum on the solute clearance and convective sieving characteristics of high flux polysulfone (Optiflux F250NR), polyethersulfone (ELISIO-25H), and asymmetric cellulose triacetate (SOLACEA-25H) hemodialyzers using both vitamin B12 and a range of polydisperse dextrans. Zeta potential measurements were used to obtain additional insights into the changes in membrane surface properties. Exposure to serum in a simulated dialysis session caused a significant reduction in both solute clearance and sieving coefficients for the polysulfone/polyethersulfone dialyzers, particularly for the larger molecular weight solutes. In contrast, the transport characteristics of the asymmetric cellulose triacetate dialyzers were almost unchanged after exposure to serum. The zeta potential of the cellulose triacetate membrane became slightly more negative after exposure to serum, consistent with an adsorbed protein layer composed largely of albumin. The net result is that the asymmetric cellulose triacetate dialyzer had dramatically higher clearance of the larger dextrans after exposure to serum, with the clearance and sieving coefficient for a 10 kDa molecular weight dextran being more than an order of magnitude greater than that of the polysulfone/polyethersulfone membranes. These results provide important insights into the expected clinical performance of these high flux dialyzers.

Treatment of table olive processing wastewaters using novel photomodified ultrafiltration membranes as first step for recovering phenolic compounds

Table olive processing wastewaters (TOPW) have high salt concentration and total phenolic content (TPC) causing many environmental problems. To reduce them, ultrafiltration (UF) was applied for treating TOPW. However, NaCl, which is the main responsible of salinity in TOPW, and phenols are small molecules that cannot be separated by conventional UF membranes. They have serious problems caused by fouling, which can be overcome using membrane modification techniques. For these reasons, photomodification may be an effective technique to obtain a stream rich in TPC due to the changes in membrane surface properties. UV-modification in the presence of two hydrophilic compounds (polyethylene glycol and aluminium oxide) was performed to achieve membranes with high reductions of organic matter and to keep the TPC as high as possible. Commercial polyethersulfone (PES) membranes of 30kDa were used. Surface modification was evaluated using FTIR-ATR spectroscopy and membrane performance was studied by calculating the rejection ratios of colour, chemical oxygen demand (COD) and TPC. Results demonstrated that UF is a useful pre-treatment to reduce organic matter from TOPW, obtaining a permeate rich in TPC. PES/Al2O3 membranes displayed superior antifouling properties and rejection values, keeping high the TPC (>95%). Therefore, UF using modified membranes is an appropriate and sustainable technique for treating TOPW.

Phase Transition-Controlled Flip-Flop in Asymmetric Lipid Membranes

Lipid membrane asymmetry is of fundamental importance for biological systems and also provides an attractive means for molecular control over biomaterial surface properties (including drug carriers). In particular, temperature-dependent changes of surface properties can be achieved by taking advantage of distinct phase transitions in lipid membrane coatings where lipids exchange (flip-flop) between leaflets. In this study, temperature is used to control flip-flop of lipids in asymmetric lipid membranes on planar solid supports, where the two leaflets of the lipid membrane are in different phase states. More specifically, the lower leaflet is prepared from a supported lipid membrane composed of a high Tm lipid mixture of phosphocholine (PC), phosphatidylserine (PS), and a bioactive lipid on TiO2, followed by selective removal of the top leaflet by detergent. Next, at a lower temperature, where the remaining leaflet is in the gel state, a top leaflet of a different lipid composition and in the fluid phase is formed. Phase transition-induced changes in membrane surface properties following upon temperature-activation of the prepared asymmetric membrane are demonstrated by the detection of biotinylated lipids, which were initially located (thus "hidden") in the lower-gel phase leaflet, at the surface of the top leaflet. These processes were monitored in real-time by the quartz crystal microbalance with dissipation (QCM-D) and the dual polarization interferometry (DPI) techniques, allowing modeling of the mass and the anisotropic property of the lipid structures in different phase states.

Changes in surface properties and separation efficiency of a nanofiltration membrane after repeated fouling and chemical cleaning cycles

The aim of this study was to evaluate the changes in membrane surface properties and solute separation by a nanofiltration membrane during repetitive membrane fouling and chemical cleaning. Secondary treated effluent and model fouling solutions containing humic acids, sodium alginate, or silica colloids were used to simulate membrane fouling. Chemical cleaning was carried out using a commercially available caustic cleaning formulation. Carbamazepine and sulfamethoxazole were selected to examine the filtration behaviour of neutral and negatively charged organic compounds, respectively. Results show that the impact of membrane fouling on solute rejection is governed by pore blocking, modification of the membrane surface charge, and cake enhanced concentration polarisation. Caustic cleaning was effective at controlling membrane fouling and membrane permeability recovery was slightly more than 100%. In good agreement with the literature, the high membrane permeability recovery observed here suggests that caustic cleaning could lead to temporary enlargement of the membrane pores. In addition, microscopic observations based on scanning electron microscopy and energy dispersive spectroscopy revealed some irreversible fouling on the chemical cleaned membrane. Thus caustic cleaning did not completely remove all foulants from the membrane surface and the membrane surface hydrophobicity and zeta potential changed correspondingly. The temporary enlargement of the membrane pores due to caustic cleaning subsequently led to notable changes in the rejection of inorganic salts (measured by conductivity) and carbamazepine. By contrast, the impact of chemical cleaning on the rejection of the negatively charged sulfamethoxazole was negligible. This is because the rejection of sulfamethoxazole is predominantly governed by electrostatic repulsion between the compound and the negatively charged membrane surface and thus is not significantly influenced by any enlargement of the membrane pores.

Effects of membrane degradation on the removal of pharmaceutically active compounds (PhACs) by NF/RO filtration processes

The impacts of membrane degradation due to chlorine attack on the rejection of pharmaceutically active compounds (PhACs) by nanofiltration and reverse osmosis membranes were investigated in this study. Membrane degradation was simulated by soaking the membranes in a sodium hypochlorite solution of various concentrations over 18 h. Changes in membrane surface properties were characterised by contact angle measurement, atomic force microscopy analysis, and streaming potential measurement. The impacts of hypochlorite exposure to the membrane separation processes were ascertained by comparing the rejection of PhACs by virgin and chlorine-exposed membranes. Overall, the reverse osmosis BW30 membrane and the tight nanofiltration NF90 membrane were much more resilient to chlorine exposure than the larger pore size TFC-SR2 and NF270 nanofiltration membranes. In fact, rejection of all three PhACs selected in this study by the BW30 remained largely unchanged after hypochlorite exposure and further characterisation did not reveal any evidence of compromised separation capability. In contrast, the effects of chlorine exposure to the two loose nanofiltration membranes were quite profound. While chlorine exposure generally resulted in reduced rejection of PhACs, a small increase in rejection was observed when a more dilute hypochlorite solution was used. Changes in the membrane surface morphology as well as observed rejection of inorganic salts and PhACs were found to be consistent with mechanisms of chlorine oxidation of polyamide membranes reported in the literature. Chlorine oxidation consistently resulted in a more negative zeta potential of all four membranes investigated in this study. Conformational alterations of the membrane polyamide active skin layer were also evident as reflected by changes in surface roughness before and after chlorine exposure. Such alterations can either loosen or tighten the effective membrane pore size, leading to either a decrease or an increase in rejection. Both of these phenomena were observed in this study, although the decrease in the rejection of PhACs was overwhelming from exposure to highly concentrated hypochlorite solution.

Fouling behavior of aqueous solutions of polyphenolic compounds during ultrafiltration

This paper presents the first part of our study on ultrafiltration (UF) of polyphenolic compounds which is relevant to many industrial food and beverage feed streams. Two commercial polyethersulfone (PES) membranes with different cut-off (10 and 100 kg/mol) and one stabilized cellulose (cellulosic) membrane (10 kg/mol) were used. Membrane–solute interactions (adsorptive fouling) and membrane–solute–solute interactions (UF fouling) as well as the effects of pH, foulant concentration and ionic concentration of the solution on fouling were investigated in order to elucidate the fouling mechanism. Significant water flux reductions and changes in membrane surface properties were observed after static adsorption for all membranes. The possible mechanisms for the attractive interactions between polyphenolic compound and membrane are discussed. Results from UF experiments indicate that both reversible and irreversible fouling have contributed to the overall fouling.

How elevated oxalate can promote kidney stone disease: changes at the surface and in the cytosol of renal cells that promote crystal adherence and growth

The present review assesses the mechanisms by which oxalate-induced alterations in renal cell function may promote stone disease focusing on 1) changes in membrane surface properties that promote the attachment of nascent crystals and 2) changes in the expression/secretion of urinary macromolecules that alter the kinetics of crystal nucleation, agglomeration and growth. The general role of renal cellular injury in promoting these responses and the specific role of urinary oxalate in producing injury is emphasized, and the signaling pathways that lead to the observed changes in cell surface properties and in the viability and growth of renal cells are discussed. Particular attention is paid to evidence linking oxalate-induced activation of cytosolic phospholipase A2 to changes in gene expression and to the activation of a second signaling pathway involving ceramide. The effects of the lipid signals, arachidonic acid, lysophosphatidylcholine and ceramide, on mitochondrial function are considered in some detail since many of the actions of oxalate appear to be secondary to increased production of reactive oxygen molecules within these organelles. Data from these studies and from a variety of other studies in vitro and in vivo were used to construct a model that illustrates possible mechanisms by which an increase in urinary oxalate levels leads to an increase in kidney stone formation. Further studies will be required to assess the validity of various aspects of this proposed model and to determine effective strategies for countering these responses in stone-forming individuals.

Changes in membrane surface properties of hepatic peroxisomes of rats under several conditions as determined by partition in aqueous polymer two-phase systems

Changes in membrane surface properties of hepatic peroxisomes of rats under several conditions were observed by aqueous polymer two-phase systems, which contained 6% (w/w) dextran T 500, 6% (w/w) polyethyleneglycol 4000, 250 mmol sucrose/kg and various concentrations of sodium phosphate buffer. The partition of peroxisomes into the upper phase depended to a large extent on their membrane surface charge. The cross-points of peroxisomes shifted from 5.55 to 5.25 and 5.2 after the administration of clofibrate and aspirin for 2 weeks, respectively, although that of alloxan-diabetic rat peroxisomes was not altered. The hydrophobic properties of peroxisomes, examined by means of a partition containing polyethyleneglycol monostearate, were altered by diabetes and starvation, but no change occurred in rats treated with clofibrate or aspirin. In the liver of rats fed a high-fat diet, the partition of peroxisomes was the same as that of the control. These findings indicate that hypolipidemic drugs such as clofibrate and aspirin induce the proliferation of peroxisomes and lead to the alteration of the surface charge of peroxisomal membranes. Diabetes or fasting lead to an alteration mainly of the hydrophobic properties. Both changes are probably due to alteration of content and/or composition of the proteins and the phospholipids in peroxisomal membrane under the conditions used.

Chapter 3 Partition of Cells in Two-Polymer Aqueous Phases: A Method for Separating Cells and for Obtaining Information on Their Surface Properties

This chapter describes an extremely sensitive method for the separation and sub fractionation of cell populations based on differences in their membrane surface properties (primarily surface charge). In addition, subtle changes in membrane surface properties can be traced that occur as a function of cell differentiation, maturation, age, growth and proliferation, metabolism, in vivo and in vitro treatments. Separation of soluble materials by differential partition between two immiscible phases is one of the classical purification procedures. If one introduces a mixture of substances (for example, A and B) into such a phase system and A is more soluble in the top phase while B is more soluble in the bottom phase, a separation of A and B can be effected. If A is almost exclusively in the top and B in the bottom, the separation is virtually complete in one extraction. If the differences in the relative solubilities of A and B in the top and bottom phases are not so extreme, then separation of the two substances can be achieved only by a multiple extraction procedure (for example, countercurrent distribution).