Molecular dynamics study on the elucidation of polyamide membrane fouling by nonionic surfactants and disaccharides.

Reverse osmosis (RO) is a widely used energy-efficient separation technology for water treatment. Polyamide (PA) membranes are the conventional choice for this process. Fouling is a serious problem for RO separation. This issue leads to significant decreases in the water permeability of PA membranes, and it has yet to be fully elucidated. In particular, the fouling behavior of a nonionic substance on the negatively charged surface of a PA membrane in an aqueous environment has not been previously studied. In this work, the mechanisms of nonionic substances such as polyoxyethylene octyl ether (PE5) and maltose (Mal) were investigated using molecular dynamics (MD) simulations. In a PA membrane in which the carboxyl group was not dissociated, the hydrophobic portion of the membrane was exposed due to the localization of water molecules around the carboxyl groups in the PA membrane. This caused hydrophobic interaction with the hydrophobic groups of PE5. In the case of an amine-modified PA membrane containing no carboxyl groups, water was not localized around the functional group, and the water orientation of the polyamide surface was also low. Due to this membrane property, the presence of stabilized water around PE5 reduced the number of hydrophobic interactions. In similar manner, a PA membrane with a slightly dissociated carboxyl group was hydrophilic, which reduced the PE5 adsorption. The presence of many dissociated carboxyl groups, however, enhanced the adsorption of PE5 due to the increase in interactions between the dissociated carboxyl groups and the hydrophilic groups of PE5. Therefore, PE5 exhibited an amphipathic adsorption wherein both hydrophilic and hydrophobic groups contributed to adsorption onto the PA membrane. Mal, on the other hand, was highly stable in every aqueous environment independent of the state of the functional groups of the PA membrane, and was not easily affected by the properties of the PA membrane.

Preparation of poly(phthalazinone-ether-sulfone) sponge-like ultrafiltration membrane.

Poly(phthalazinone-ether-sulfone) (PPES) polymer is a relatively newly developed material with a bis(4-fluorodiphenyl) sulfone group. The formation of the PPES membrane by wet-phase inversion can proceed according to a slow or fast gelation method. These formation mechanisms were studied experimentally. The resulting membrane morphology was investigated using both optical and scanning electron micrography. The effects of PPES concentration and two additives, polyvinylpyrrolidone (PVP) and oxalic acid (OA), on the apparent viscosity and gelation rate of PPESK/NMP solutions and membrane performance have also been investigated. It was found that the gelation rate is important to obtain a sponge-like membrane structure, however favored by a fast gelation rate. The membrane obtained by a fast gelation rate showed a high pure water flux and rejection of bovine serum albumin (BSA), contrary to previous findings. On the basis of the experimental results, the actual membrane structure and pure water flux were related, and in agreement with the optical micrograph and gelation rate, respectively. The current results provide a fundamental insight in this novel copolymer, useful in future applications, especially in the membrane formation process.

[Dilated cardiomyopathy with improved exercise tolerance after cardiac resynchronization therapy and mitral valve replacement with bileaflet preservation].

It has been reported that cardiac resynchronization therapy( CRT) improves cardiac systolic function and reverses cardiac remodeling by correcting intra- and interventricular asynchrony, and that mitral valve replacement (MVR) with bileaflet preservation dose not impair left ventricular systolic function through preserving the continuity of the mitral complex.The present report describes a case of a 68-year-old female with severe chronic heart failure and mitral valve regurgitation due to end-stage dilated cardiomyopathy who showed improved exercise tolerance following CRT and MVR with bileaflet preservation. Based on this case, we considered that the combination therapy of CRT and MVR with bileaflet preservation might be one of the effective strategies for severe chronic heart failure and mitral valve regurgitation due to end-stage dilated cardiomyopathy.

Preparation of Microfiltration Hollow Fiber Membranes from Cellulose Triacetate by Thermally Induced Phase Separation.

For the first time, self-standing microfiltration (MF) hollow fiber membranes were prepared from cellulose triacetate (CTA) via the thermally induced phase separation (TIPS) method. The resultant membranes were compared with counterparts prepared from cellulose diacetate (CDA) and cellulose acetate propionate (CAP). Extensive solvent screening by considering the Hansen solubility parameters of the polymer and solvent, the polymer's solubility at high temperature, solidification of the polymer solution at low temperature, viscosity, and processability of the polymeric solution, is the most challenging issue for cellulose membrane preparation. Different phase separation mechanisms were identified for CTA, CDA, and CAP polymer solutions prepared using the screened solvents for membrane preparation. CTA solutions in binary organic solvents possessed the appropriate properties for membrane preparation via liquid-liquid phase separation, followed by a solid-liquid phase separation (polymer crystallization) mechanism. For the prepared CTA hollow fiber membranes, the maximum stress was 3-5 times higher than those of the CDA and CAP membranes. The temperature gap between the cloud point and crystallization onset in the polymer solution plays a crucial role in membrane formation. All of the CTA, CDA, and CAP membranes had a very porous bulk structure with a pore size of ∼100 nm or larger, as well as pores several hundred nanometers in size at the inner surface. Using an air gap distance of 0 mm, the appropriate organic solvents mixed in an optimized ratio, and a solvent for cellulose derivatives as the quench bath media, it was possible to obtain a CTA MF hollow fiber membrane with high pure water permeance and notably high rejection of 100 nm silica nanoparticles. It is expected that these membranes can play a great role in pharmaceutical separation.

Water Transport and Ion Diffusion Investigation of an Amphotericin B-Based Channel Applied to Forward Osmosis: A Simulation Study.

The use of an Amphotericin B_Ergosterol (AmBEr) channel as an artificial water channel in forward osmosis filtration (FO) was studied via molecular dynamics (MD) simulation. Three channel models were constructed: a common AmBEr channel and two modified C3deOAmB_Ergosterol (C3deOAmBEr) channels with different diameters (12 Å and 18 Å). During FO filtration simulation, the osmotic pressure of salt-water was a driving force for water permeation. We examined the effect of the modified C3deOAmBEr channel on the water transport performance. By tracing the change of the number of water molecules along with simulation time in the saltwater region, the water permeability of the channel models could be calculated. A higher water permeability was observed for a modified C3deOAmBEr channel, and there was no ion permeation during the entire simulation period. The hydrated ions and water molecules were placed into the channel to explore the ion leakage behavior of the channels. The mean squared displacement (MSD) of ions and water molecules was obtained to study the ion leakage performance. The Amphotericin B-based channels showed excellent selectivity of water molecules against ions. The results obtained on an atomistic scale could assist in determining the properties and the optimal filtration applications for Amphotericin B-based channels.

Hollow-Fiber RO Membranes Fabricated via Adsorption of Low-Charge Poly(vinyl alcohol) Copolymers.

We report a new type of alkaline-stable hollow-fiber reverse osmosis (RO) membrane with an outside-in configuration that was established via adsorption of positively charged poly(vinyl alcohol) copolymers containing a small amount of quaternary ammonium moieties. Anionic sulfonated poly(arylene ether sulfone nitrile) hollow-fiber membranes were utilized as a substrate upon which the cationic copolymer layer was self-organized via electrostatic interaction. While the adsorption of the low-charge copolymer on the membrane support proceeded in a Layer-by-Layer (LbL) fashion, it was found that the adsorbed amount by one immersion step was enough to form a defect-free separation layer with a thickness of around 20 nm after cross-linking of vinyl alcohol units with glutaraldehyde. The resultant hollow-fiber membrane showed excellent desalination performances (NaCl rejection of 98.3% at 5 bar and 1500 mg/L), which is comparable with commercial low-pressure polyamide RO membranes, as well as good alkaline resistance. The separation performance could be restored by repeating the LbL treatment after alkaline degradation. Such features of LbL membranes may contribute to extending RO membrane lifetimes.

Gas Permeation Characteristics of TiO2-ZrO2-Aromatic Organic Chelating Ligand (aOCL) Composite Membranes.

Methyl gallate (MG) and ethyl ferulate (EF) with a benzene ring were separately used as aromatic organic chelating ligands (aOCLs) to prepare two versions of TiO2-ZrO2-aOCL composite sols via hydrolysis and polycondensation reactions with titanium(IV) isopropoxide (Ti(OC3H7)4) and zirconium(IV) butoxide (Zr(OC4H9)4). Thermogravimetric and FT-IR analysis of dry gels revealed that aromatic rings were present in the residual organic matter when the gel was fired under nitrogen at 300 °C. In X-ray diffraction (XRD) measurements, the TiO2-ZrO2 composite material prepared using these two aOCLs showed an amorphous structure with no crystalline peaks for TiO2 and ZrO2. In N2 adsorption/desorption measurements at 77 K, the TiO2-ZrO2 samples using the aOCLs as a template appeared porous with a larger specific surface area than TiO2-ZrO2 without aOCL. TiO2-ZrO2-aOCL composite membranes were prepared by coating and firing TiO2-ZrO2-aOCL sol onto a SiO2 intermediate layer using an α-alumina porous tube as a substrate. Compared with the TiO2-ZrO2 membrane, the TiO2-ZrO2-aOCL membranes had higher gas permselectivity. The TiO2-ZrO2-EF membrane showed a He permeance of 2.69 × 10-6 mol m-2 s-1 Pa-1 with permeance ratios of He/N2 = 10.6 and He/CF4 = 163, while the TiO2-ZrO2-MG membrane revealed a bit less He permeance at 8.56 × 10-7 mol m-2 s-1 Pa-1 with greater permeance ratios of He/N2 = 61.7 and He/CF4 = 209 at 200 °C. A microporous TiO2-ZrO2 amorphous structure was obtained by introducing aOCL. The differences in the side chains of each aOCL could possibly account for the differences in the microporous structures of the resultant TiO2-ZrO2-aOCL membranes.

Organic Liquid Mixture Separation Using an Aliphatic Polyketone-Supported Polyamide Organic Solvent Reverse Osmosis (OSRO) Membrane.

Energy-efficient membrane technology has received tremendous attention for the separation of organic molecules; however, the separation of molecules of less than 100 Da has remained challenging. Herein, a membrane fabricated from interfacial polymerization on a polyketone support was used as an organic solvent reverse osmosis (OSRO) membrane for the separation of organic liquid mixtures. The chemically stable and highly cross-linked selective layer exhibited outstanding separation factors toward large nonpolar molecules from small polar ones with high fluxes. For example, separation factors of 8.4, 11.1, 14.9, and 38.0 were achieved toward toluene, pentane, hexane, and heptane (10 wt % in mixtures), respectively, from methanol solution at 3 MPa, with fluxes around 5 LMH. This membrane outperformed the currently available reverse osmosis membrane and organic solvent nanofiltration membranes in terms of stability and separation factor. This work promotes the development of OSRO separation of organic liquid mixtures without phase change.

High rejection reverse osmosis membrane for removal of N-nitrosamines and their precursors.

Direct potable reuse is becoming a feasible option to cope with water shortages. It requires more stringent water quality assurance than indirect potable reuse. Thus, the development of a high-rejection reverse osmosis (RO) membrane for the removal of one of the most challenging chemicals in potable reuse - N-nitrosodimethylamine (NDMA) - ensures further system confidence in reclaimed water quality. This study aimed to achieve over 90% removal of NDMA by modifying three commercial and one prototype RO membrane using heat treatment. Application of heat treatment to a prototype membrane resulted in a record high removal of 92% (1.1-log) of NDMA. Heat treatment reduced conductivity rejection and permeability, while secondary amines, selected as N-nitrosamine precursors, were still well rejected (>98%) regardless of RO membrane type. This study also demonstrated the highly stable separation performance of the heat-treated prototype membrane under conditions of varying feed temperature and permeate flux. Fouling propensity of the prototype membrane was lower than a commercial RO membrane. This study identified a need to develop highly selective RO membranes with high permeability to ensure the feasibility of using these membranes at full scale.

One-step fabrication of polyamide 6 hollow fibre membrane using non-toxic diluents for organic solvent nanofiltration.

We developed new polyamide 6 hollow fibre membranes using a green process to fabricate cutting-edge "organic solvent nanofiltration" membranes by one-step spinning process for organic solvent separation. This economic and sustainable membrane showed good rejection and durability performance in various organic solvents.

Molecular Dynamics Simulation Study of Polyamide Membrane Structures and RO/FO Water Permeation Properties.

Polyamide (PA) membranes possess properties that allow for selective water permeation and salt rejection, and these are widely used for reverse osmotic (RO) desalination of sea water to produce drinking water. In order to design high-performance RO membranes with high levels of water permeability and salt rejection, an understanding of microscopic PA membrane structures is indispensable, and this includes water transport and ion rejection mechanisms on a molecular scale. In this study, two types of virtual PA membranes with different structures and densities were constructed on a computer, and water molecular transport properties through PA membranes were examined on a molecular level via direct reverse/forward osmosis (RO/FO) filtration molecular dynamics (MD) simulations. A quasi-non-equilibrium MD simulation technique that uses applied (RO mode) or osmotic (FO mode) pressure differences of several MPa was conducted to estimate water permeability through PA membranes. A simple NVT (Number, Volume, and Temperature constant ensemble)-RO MD simulation method was presented and verified. The simulations of RO and FO water permeability for a dense PA membrane model without a support layer agreed with the experimental value in the RO mode. This PA membrane completely rejected Na⁺ and Cl- ions during a simulation time of several nano-seconds. The naturally dense PA structure showed excellent ion rejection. The effect that the void size of PA structure exerted on water permeability was also examined.

Fabrication of Stacked Graphene Oxide Nanosheet Membranes Using Triethanolamine as a Crosslinker and Mild Reducing Agent for Water Treatment.

Two-dimensional (2D) nanosheets show promise for the development of water treatment membranes with extraordinary separation properties and the advantages of atomic thickness with micrometer-sized lateral dimensions. Stacked graphene oxide (GO)-based membranes can demonstrate unique molecular sieving properties with fast water permeation. However, improvements to the structural stability of the membranes in water to avoid problems such as swelling, disruption of the ordered GO layer and decreased rejection are crucial issues. This study reports the fabrication of stacked GO nanosheet membranes by simple vacuum filtration using triethanolamine (TEOA) as a crosslinker and mild reducing agent for improved structural stability and membrane performance. Results show that GO membranes modified with TEOA (GO-TEOA membranes) have a higher structural stability in water than unmodified GO membranes, resulting in improved salt rejection performance. Furthermore, GO-TEOA membranes show stable water permeance at applied pressures up to 9 bar with Na2SO4 rejection of 85%, suggesting the potential benefits for water treatment applications.

Intraoperative transfection of vein grafts with the NFkappaB decoy in a canine aortocoronary bypass model: a strategy to attenuate intimal hyperplasia.

BACKGROUND: The nuclear transcriptional factor NFkappaB is reported to play an important role in the expression of genes for neutrophil and macrophage chemotactic factors, adhesion molecules, and cell cycle-regulating proteins. In aortocoronary bypass surgery, the saphenous vein often develops vein graft disease. Here, we investigated whether transfection of a cis element decoy oligodeoxynucleotide of NFkappaB (NFkappaB decoy) into the vein graft wall suppresses neointimal hyperplasia and the differentiation of medial smooth muscle cells. METHODS: We established a canine aortocoronary bypass grafting model that has a saphenous vein graft between the left anterior descending coronary artery and the descending aorta. Pressure-mediated transfection of a scrambled (SD group; n = 5) or NFkappaB decoy (ND group; n = 5) into the graft wall was performed intraoperatively. The grafts were gently harvested at 4 weeks postoperative, and the middle portion of the graft was examined histopathologically. RESULTS: The average neointimal area of the ND group was significantly suppressed (SD group, 2.63 +/- 1.00 mm2 vs ND group, 0.88 +/- 0.66, p < 0.05), and the differentiation and proliferation of the medial smooth muscle cells in the ND group were also suppressed (proliferating cell nuclear antigen index: SD group, 56 +/- 24 vs ND, 13 +/- 4, p < 0.05). CONCLUSIONS: These results demonstrated the efficacy of intraoperative transfection of the NFkappaB decoy into the vein graft wall for attenuation of neointima formation.