Membranes

19 pages, 4609 KiB

Open AccessArticle

Poly(ethylene glycol) Diacrylate Iongel Membranes Reinforced with Nanoclays for CO₂ Separation

by Ana R. Nabais, Rute O. Francisco, Vítor D. Alves, Luísa A. Neves and Liliana C. Tomé

Membranes 2021, 11(12), 998; https://doi.org/10.3390/membranes11120998 - 20 Dec 2021

Cited by 3 | Viewed by 3177

Despite the fact that iongels are very attractive materials for gas separation membranes, they often show mechanical stability issues mainly due to the high ionic liquid (IL) content (≥60 wt%) needed to achieve high gas separation performances. This work investigates a strategy to [...] Read more.

Despite the fact that iongels are very attractive materials for gas separation membranes, they often show mechanical stability issues mainly due to the high ionic liquid (IL) content (≥60 wt%) needed to achieve high gas separation performances. This work investigates a strategy to improve the mechanical properties of iongel membranes, which consists in the incorporation of montmorillonite (MMT) nanoclay, from 0.2 to 7.5 wt%, into a cross-linked poly(ethylene glycol) diacrylate (PEGDA) network containing 60 wt% of the IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₂mim][TFSI]). The iongels were prepared by a simple one-pot method using ultraviolet (UV) initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) and characterized by several techniques to assess their physico-chemical properties. The thermal stability of the iongels was influenced by the addition of higher MMT contents (>5 wt%). It was possible to improve both puncture strength and elongation at break with MMT contents up to 1 wt%. Furthermore, the highest ideal gas selectivities were achieved for iongels containing 0.5 wt% MMT, while the highest CO₂ permeability was observed at 7.5 wt% MMT content, due to an increase in diffusivity. Remarkably, this strategy allowed for the preparation and gas permeation of self-standing iongel containing 80 wt% IL, which had not been possible up until now. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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13 pages, 5077 KiB

Open AccessEditor’s ChoiceArticle

Nanofibrous Membrane with Encapsulated Glucose Oxidase for Self-Sustained Antimicrobial Applications

by Fernaldy Leonarta and Cheng-Kang Lee

Membranes 2021, 11(12), 997; https://doi.org/10.3390/membranes11120997 - 20 Dec 2021

Cited by 8 | Viewed by 3341

Abstract

Polyvinyl alcohol (PVA) nanofibrous membrane, consisting of separately encapsulated glucose oxidase (GOx) and glucose (Glu) nanofibers, was prepared via simultaneously electrospinning PVA/GOx and PVA/Glu dopes. The as-prepared pristine membrane could self-sustainably generate hydrogen peroxide (H₂O₂) only in contact with [...] Read more.

Polyvinyl alcohol (PVA) nanofibrous membrane, consisting of separately encapsulated glucose oxidase (GOx) and glucose (Glu) nanofibers, was prepared via simultaneously electrospinning PVA/GOx and PVA/Glu dopes. The as-prepared pristine membrane could self-sustainably generate hydrogen peroxide (H₂O₂) only in contact with an aqueous solution. The H₂O₂ production level was well maintained even after storing the dry membrane at room temperature for 7 days. Cross-linking the membrane via reaction with glutaraldehyde (GA) vapor could not only prevent the nanofibrous membrane from dissolving in water but also prolonged the release of H₂O₂. The sustained release of H₂O₂ from the membrane achieved antimicrobial capability equivalent to that of 1% H₂O₂ against both Escherichia coli and Staphylococcus aureus. Gram(+) S. aureus cells were more susceptible to H₂O₂ than Gram(−) E. coli and >99% of S. aureus were killed after 1 h incubation with the membrane. Pristine and GA-crosslinked nanofibrous membrane with in situ production of H₂O₂ were self-sterilized in which no microorganism contamination on the membrane could be detected after 2 weeks incubation on an agar plate. The GOx/Glu membrane may find potential application as versatile antimicrobial materials in the field of biomedicine, in the food and health industries, and especially challenges related to wound healing in diabetic patients. Full article

(This article belongs to the Collection Polymeric Membranes: Science, Materials and Applications)

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12 pages, 2955 KiB

Open AccessArticle

Fabrication of Suspended PMMA-Graphene Membrane for High Sensitivity LC-MEMS Pressure Sensor

by Norliana Yusof, Badariah Bais, Jumril Yunas, Norhayati Soin and Burhanuddin Yeop Majlis

Membranes 2021, 11(12), 996; https://doi.org/10.3390/membranes11120996 - 20 Dec 2021

Cited by 7 | Viewed by 3788

Abstract

The LC-MEMS pressure sensor is an attractive option for an implantable sensor. It senses pressure wirelessly through an LC resonator, eliminating the requirement for electrical wiring or a battery system. However, the sensitivity of LC-MEMS pressure sensors is still comparatively low, especially in [...] Read more.

The LC-MEMS pressure sensor is an attractive option for an implantable sensor. It senses pressure wirelessly through an LC resonator, eliminating the requirement for electrical wiring or a battery system. However, the sensitivity of LC-MEMS pressure sensors is still comparatively low, especially in biomedical applications, which require a highly-sensitive sensor to measure low-pressure variations. This study presents the microfabrication of an LC wireless MEMS pressure sensor that utilizes a PMMA-Graphene (PMMA/Gr) membrane supported on a silicon trench as the deformable structure. The (PMMA/Gr) membrane was employed to increase the sensor’s sensitivity due to its very low elastic modulus making it easy to deform under extremely low pressure. The overall size of the fabricated sensor was limited to 8 mm × 8 mm. The experimental results showed that the capacitance value changed from 1.64 pF to 12.32 pF when the applied pressure varied from 0 to 5 psi. This capacitance variation caused the frequency response to change from 28.74 MHz to 78.76 MHz. The sensor sensitivity was recorded with a value of 193.45 kHz/mmHg and a quality factor of 21. This study concludes that the (PMMA/Gr) membrane-based LC-MEMS pressure sensor has been successfully designed and fabricated and shows good potential in biomedical sensor applications. Full article

(This article belongs to the Special Issue Electrically Conductive Membranes)

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36 pages, 4913 KiB

Open AccessReview

Recent Progress on Nanomaterial-Based Membranes for Water Treatment

by Majeda Khraisheh, Salma Elhenawy, Fares AlMomani, Mohammad Al-Ghouti, Mohammad K. Hassan and Bassim H. Hameed

Membranes 2021, 11(12), 995; https://doi.org/10.3390/membranes11120995 - 20 Dec 2021

Cited by 50 | Viewed by 7744

Abstract

Nanomaterials have emerged as the new future generation materials for high-performance water treatment membranes with potential for solving the worldwide water pollution issue. The incorporation of nanomaterials in membranes increases water permeability, mechanical strength, separation efficiency, and reduces fouling of the membrane. Thus, [...] Read more.

Nanomaterials have emerged as the new future generation materials for high-performance water treatment membranes with potential for solving the worldwide water pollution issue. The incorporation of nanomaterials in membranes increases water permeability, mechanical strength, separation efficiency, and reduces fouling of the membrane. Thus, the nanomaterials pave a new pathway for ultra-fast and extremely selective water purification membranes. Membrane enhancements after the inclusion of many nanomaterials, including nanoparticles (NPs), two-dimensional (2-D) layer materials, nanofibers, nanosheets, and other nanocomposite structural materials, are discussed in this review. Furthermore, the applications of these membranes with nanomaterials in water treatment applications, that are vast in number, are highlighted. The goal is to demonstrate the significance of nanomaterials in the membrane industry for water treatment applications. It was found that nanomaterials and nanotechnology offer great potential for the advancement of sustainable water and wastewater treatment. Full article

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16 pages, 5355 KiB

Open AccessArticle

Effects of NH₃ Plasma and Mg Doping on InGaZnO pH Sensing Membrane

by Chyuan-Haur Kao, Chia-Shao Liu, Shih-Ming Chan, Chih-Chen Kuo, Shang-Che Tsai, Ming-Ling Lee and Hsiang Chen

Membranes 2021, 11(12), 994; https://doi.org/10.3390/membranes11120994 - 20 Dec 2021

Cited by 2 | Viewed by 2733

Abstract

In this study, the effects of magnesium (Mg) doping and Ammonia (NH₃) plasma on the pH sensing capabilities of InGaZnO membranes were investigated. Undoped InGaZnO and Mg-doped pH sensing membranes with NH₃ plasma were examined with multiple material analyses including [...] Read more.

In this study, the effects of magnesium (Mg) doping and Ammonia (NH₃) plasma on the pH sensing capabilities of InGaZnO membranes were investigated. Undoped InGaZnO and Mg-doped pH sensing membranes with NH₃ plasma were examined with multiple material analyses including X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectroscopy and transmission electron microscope, and pH sensing behaviors of the membrane in electrolyte-insulator-semiconductors. Results indicate that Mg doping and NH₃ plasma treatment could superpositionally enhance crystallization in fine nanostructures, and strengthen chemical bindings. Results indicate these material improvements increased pH sensing capability significantly. Plasma-treated Mg-doped InGaZnO pH sensing membranes show promise for future pH sensing biosensors. Full article

(This article belongs to the Section Membrane Applications)

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15 pages, 3509 KiB

Open AccessArticle

Role of Ligand Distribution in the Cytoskeleton-Associated Endocytosis of Ellipsoidal Nanoparticles

by Yudie Zhang, Long Li and Jizeng Wang

Membranes 2021, 11(12), 993; https://doi.org/10.3390/membranes11120993 - 19 Dec 2021

Cited by 3 | Viewed by 2616

Abstract

Nanoparticle (NP)–cell interaction mediated by receptor–ligand bonds is a crucial phenomenon in pathology, cellular immunity, and drug delivery systems, and relies strongly on the shape of NPs and the stiffness of the cell. Given this significance, a fundamental question is raised on how [...] Read more.

Nanoparticle (NP)–cell interaction mediated by receptor–ligand bonds is a crucial phenomenon in pathology, cellular immunity, and drug delivery systems, and relies strongly on the shape of NPs and the stiffness of the cell. Given this significance, a fundamental question is raised on how the ligand distribution may affect the membrane wrapping of non-spherical NPs under the influence of cytoskeleton deformation. To address this issue, in this work we use a coupled elasticity–diffusion model to systematically investigate the role of ligand distribution in the cytoskeleton-associated endocytosis of ellipsoidal NPs for different NP shapes, sizes, cytoskeleton stiffness, and the initial receptor densities. In this model, we have taken into account the effects of receptor diffusion, receptor–ligand binding, cytoskeleton and membrane deformations, and changes in the configuration entropy of receptors. By solving this model, we find that the uptake process can be significantly influenced by the ligand distribution. Additionally, there exists an optimal state of such a distribution, which corresponds to the fastest uptake efficiency and depends on the NP aspect ratio and cytoskeleton stiffness. We also find that the optimal distribution usually needs local ligand density to be sufficiently high at the large curvature region. Furthermore, the optimal state of NP entry into cells can tolerate slight changes to the corresponding optimal distribution of the ligands. The tolerance to such a change is enhanced as the average receptor density and NP size increase. These results may provide guidelines to control NP–cell interactions and improve the efficiency of target drug delivery systems. Full article

(This article belongs to the Section Biological Membrane Dynamics and Computation)

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11 pages, 736 KiB

Open AccessArticle

Cytochrome P450 and P-gp Mediated Herb-Drug Interactions and Molecular Docking Studies of Garcinol

by Lavanya Bolla, Pratima Srivastava, Velayutham Ravichandiran and Satheesh Kumar Nanjappan

Membranes 2021, 11(12), 992; https://doi.org/10.3390/membranes11120992 - 19 Dec 2021

Cited by 9 | Viewed by 3426

Abstract

Garcinol is an active constituent of Garcinia indica and Garcinia cambogia. Recent studies have proven that garcinol has anti-inflammatory, anti-cancer, and anti-oxidant activities. The objective of this study was to evaluate the inhibitory effects of garcinol on the activities of the drug [...] Read more.

Garcinol is an active constituent of Garcinia indica and Garcinia cambogia. Recent studies have proven that garcinol has anti-inflammatory, anti-cancer, and anti-oxidant activities. The objective of this study was to evaluate the inhibitory effects of garcinol on the activities of the drug metabolizing cytochrome P450 (CYP) isozymes to predict potential herb-drug interactions with co-administered drugs. Garcinol was incubated with a mixture of rat liver microsomes and eight CYP probe substrate cocktail under optimized incubation conditions and the samples were analyzed using a validated method on LC-MS/MS. Garcinol showed strong inhibition with IC₅₀ values of CYP1A2 (7.6 µM), CYP2C9 (8.0 µM), CYP2B6 (2.1 µM), CYP2D6 (9.5 µM), and CYP3A4 (5.1 µM), respectively, and moderate inhibition towards CYP2C19 (16.4 µM) and CYP2E1 (19.0 µM). Molecular docking studies were performed on garcinol against the active sites of CYP2B6 and CYP3A4 proteins. These results further confirmed that the inhibitory activity of garcinol occurred by occupying the active sites of these human CYPs and by making favorable interactions with its key residues. In-vivo CYP inhibition studies were carried out in Sprague-Dawley rats. These results suggest garcinol may cause herb-drug interactions, mediated by inhibition of CYPs involved in drug metabolism in-vivo by altering the pharmacokinetic parameters like AUC and C_max in a clinically significant manner. Garcinol was found to upregulate the expression and activity of P-gp in western blotting study and P-gp inhibition study in-vivo. These findings give a clear understanding to predict potential herb-drug/drug-drug interactions of garcinol for safe clinical use in future. Full article

(This article belongs to the Special Issue Study on Drug-Membrane Interactions, Volume II)

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9 pages, 438 KiB

Open AccessArticle

Separation Iron(III)-Manganese(II) via Supported Liquid Membrane Technology in the Treatment of Spent Alkaline Batteries

by Francisco J. Alguacil and Félix A. Lopez

Membranes 2021, 11(12), 991; https://doi.org/10.3390/membranes11120991 - 19 Dec 2021

Cited by 6 | Viewed by 2704

Abstract

In this paper, the transport of iron(III) from iron(III)-manganese(II)-hydrochloric acid mixed solutions, coming from the treatment of spent alkaline batteries through a flat-sheet supported liquid membrane, is investigated (the carrier phase being of Cyanex 923 (commercially available phosphine oxide extractant) dissolved in Solvesso [...] Read more.

In this paper, the transport of iron(III) from iron(III)-manganese(II)-hydrochloric acid mixed solutions, coming from the treatment of spent alkaline batteries through a flat-sheet supported liquid membrane, is investigated (the carrier phase being of Cyanex 923 (commercially available phosphine oxide extractant) dissolved in Solvesso 100 (commercially available diluent)). Iron(III) transport is studied as a function of hydrodynamic conditions, the concentration of manganese and HCl in the feed phase, and the carrier concentration in the membrane phase. A transport model is derived that describes the transport mechanism, consisting of diffusion through a feed aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of the iron(III) species-Cyanex 923 complex across the membrane phase. The membrane diffusional resistance (Δ_m) and feed diffusional resistance (Δ_f) are calculated from the model, and their values are 145 s/cm and 361 s/cm, respectively. It is apparent that the transport of iron(III) is mainly controlled by diffusion through the aqueous feed boundary layer, this being the thickness of this layer calculated as 2.9 × 10⁻³ cm. Since manganese(II) is not transported through the membrane phase, the present system allows the purification of these manganese-bearing solutions. Full article

(This article belongs to the Special Issue State-of-the-Art Membrane Science and Technology in the Iberian Peninsula 2021-2022)

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Graphical abstract

12 pages, 2879 KiB

Open AccessArticle

Novel Surrogates for Membrane Fouling and the Application of Support Vector Machine in Analyzing Fouling Mechanism

by Xianghao Meng, Fukuan Wang, Shujuan Meng, Rui Wang, Zhongyuan Mao, Yue Li, Meifeng Yu, Xuye Wang, Qian Zhao and Linyan Yang

Membranes 2021, 11(12), 990; https://doi.org/10.3390/membranes11120990 - 18 Dec 2021

Cited by 7 | Viewed by 2436

Abstract

It is difficult to recognize specific fouling mechanisms due to the complexity of practical feed water, thus the current studies usually employ foulant surrogates to carry out research, such as alginate and xanthan gum. However, the representativeness of these surrogates is questionable. In [...] Read more.

It is difficult to recognize specific fouling mechanisms due to the complexity of practical feed water, thus the current studies usually employ foulant surrogates to carry out research, such as alginate and xanthan gum. However, the representativeness of these surrogates is questionable. In this work, the classical surrogates (i.e., alginate and xanthan gum) were systematically studied, and results showed that they behaved differently during filtration. For the mixture of alginate and xanthan gum, both filtration behaviors and adsorption tests performed by quartz-crystal microbalance with dissipation monitoring (QCM-D) indicated that alginate plays a leading role in fouling development. Furthermore, by examining the filtration behaviors of extracellular polymeric substances (EPS) extracted from practical source water, it turns out that the gel layer formation is responsible for EPS fouling, and the properties of gel layer formed by EPS share more similarities with that formed from pectin instead of alginate. In addition, with the use of experimental data sets extracted from this study and our previous studies, a modeling method was established and tested by the support vector machine (SVM) to predict complex filtration behaviors. Results showed that the small differences of fouling mechanisms lying between alginate and pectin cannot be recognized by Hermia’s models, and SVM can show a discrimination as high as 76.92%. As such, SVM may be a powerful tool to predict complex filtration behaviors. Full article

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29 pages, 5031 KiB

Open AccessArticle

A Stochastic Spatiotemporal Model of Rat Ventricular Myocyte Calcium Dynamics Demonstrated Necessary Features for Calcium Wave Propagation

by Tuan Minh Hoang-Trong, Aman Ullah, William Jonathan Lederer and Mohsin Saleet Jafri

Membranes 2021, 11(12), 989; https://doi.org/10.3390/membranes11120989 - 18 Dec 2021

Cited by 9 | Viewed by 3001

Abstract

Calcium (Ca²⁺) plays a central role in the excitation and contraction of cardiac myocytes. Experiments have indicated that calcium release is stochastic and regulated locally suggesting the possibility of spatially heterogeneous calcium levels in the cells. This spatial heterogeneity might be [...] Read more.

Calcium (Ca²⁺) plays a central role in the excitation and contraction of cardiac myocytes. Experiments have indicated that calcium release is stochastic and regulated locally suggesting the possibility of spatially heterogeneous calcium levels in the cells. This spatial heterogeneity might be important in mediating different signaling pathways. During more than 50 years of computational cell biology, the computational models have been advanced to incorporate more ionic currents, going from deterministic models to stochastic models. While periodic increases in cytoplasmic Ca²⁺ concentration drive cardiac contraction, aberrant Ca²⁺ release can underly cardiac arrhythmia. However, the study of the spatial role of calcium ions has been limited due to the computational expense of using a three-dimensional stochastic computational model. In this paper, we introduce a three-dimensional stochastic computational model for rat ventricular myocytes at the whole-cell level that incorporate detailed calcium dynamics, with (1) non-uniform release site placement, (2) non-uniform membrane ionic currents and membrane buffers, (3) stochastic calcium-leak dynamics and (4) non-junctional or rogue ryanodine receptors. The model simulates spark-induced spark activation and spark-induced Ca²⁺ wave initiation and propagation that occur under conditions of calcium overload at the closed-cell condition, but not when Ca²⁺ levels are normal. This is considered important since the presence of Ca²⁺ waves contribute to the activation of arrhythmogenic currents. Full article

(This article belongs to the Special Issue Membrane Channel of Cells)

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25 pages, 11384 KiB

Open AccessArticle

Membrane Distillation of Saline Water Contaminated with Oil and Surfactants

by Wirginia Tomczak and Marek Gryta

Membranes 2021, 11(12), 988; https://doi.org/10.3390/membranes11120988 - 17 Dec 2021

Cited by 11 | Viewed by 3243

Abstract

Application of the membrane distillation (MD) process for the treatment of high-salinity solutions contaminated with oil and surfactants represents an interesting area of research. Therefore, the aim of this study is to investigate the effect of low-concentration surfactants in oil-contaminated high-salinity solutions on [...] Read more.

Application of the membrane distillation (MD) process for the treatment of high-salinity solutions contaminated with oil and surfactants represents an interesting area of research. Therefore, the aim of this study is to investigate the effect of low-concentration surfactants in oil-contaminated high-salinity solutions on the MD process efficiency. For this purpose, hydrophobic capillary polypropylene (PP) membranes were tested during the long-term MD studies. Baltic Sea water and concentrated NaCl solutions were used as a feed. The feed water was contaminated with oil collected from bilge water and sodium dodecyl sulphate (SDS). It has been demonstrated that PP membranes were non-wetted during the separation of pure NaCl solutions over 960 h of the module exploitation. The presence of oil (100–150 mg/L) in concentrated NaCl solutions caused the adsorption of oil on the membranes surface and a decrease in the permeate flux of 30%. In turn, the presence of SDS (1.5–2.5 mg/L) in the oil-contaminated high-salinity solutions slightly accelerated the phenomenon of membrane wetting. The partial pores’ wetting accelerated the internal scaling and affected degradation of the membrane’s structure. Undoubtedly, the results obtained in the present study may have important implications for understanding the effect of low-concentration SDS on MD process efficiency. Full article

(This article belongs to the Special Issue State-of-the-Art Membrane Science and Technology in Poland 2021-2022)

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20 pages, 2538 KiB

Open AccessArticle

Surface Properties of Synaptosomes in the Presence of L-Glutamic and Kainic Acids: In Vitro Alteration of the ATPase and Acetylcholinesterase Activities

by Virjinia Doltchinkova, Nevena Mouleshkova and Victoria Vitkova

Membranes 2021, 11(12), 987; https://doi.org/10.3390/membranes11120987 - 17 Dec 2021

Cited by 3 | Viewed by 2832

Abstract

Morphologically and functionally identical to brain synapses, the nerve ending particles synaptosomes are biochemically derived membrane structures responsible for the transmission of neural information. Their surface and mechanical properties, measured in vitro, provide useful information about the functional activity of synapses in the [...] Read more.

Morphologically and functionally identical to brain synapses, the nerve ending particles synaptosomes are biochemically derived membrane structures responsible for the transmission of neural information. Their surface and mechanical properties, measured in vitro, provide useful information about the functional activity of synapses in the brain in vivo. Glutamate and kainic acid are of particular interest because of their role in brain pathology (including causing seizure, migraine, ischemic stroke, aneurysmal subarachnoid hemorrhage, intracerebral hematoma, traumatic brain injury and stroke). The effects of the excitatory neurotransmitter L-glutamic acid and its agonist kainic acid are tested on Na⁺, K⁺-ATPase and Mg²⁺-ATPase activities in synaptic membranes prepared from the cerebral cortex of rat brain tissue. The surface parameters of synaptosome preparations from the cerebral cortex in the presence of L-glutamic and kainic acids are studied by microelectrophoresis for the first time. The studied neurotransmitters promote a significant increase in the electrophoretic mobility and surface electrical charge of synaptosomes at 1–4 h after isolation. The measured decrease in the bending modulus of model bimolecular membranes composed of monounsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine provides evidence for softer membranes in the presence of L-glutamate. Kainic acid does not affect membrane mechanical stability even at ten-fold higher concentrations. Both the L-glutamic and kainic acids reduce acetylcholinesterase activity and deviation from the normal functions of neurotransmission in synapses is presumed. The presented results regarding the modulation of the enzyme activity of synaptic membranes and surface properties of synaptosomes are expected by biochemical and biophysical studies to contribute to the elucidation of the molecular mechanisms of neurotransmitters/agonists’ action on membranes. Full article

(This article belongs to the Special Issue Biological Membranes as Targets for Natural and Synthetic Compounds)

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14 pages, 1910 KiB

Open AccessArticle

Antibacterial Ferroelectric Hybrid Membranes Fabricated via Electrospinning for Wound Healing

by Ivan V. Lukiev, Ludmila S. Antipina, Semen I. Goreninskii, Tamara S. Tverdokhlebova, Dmitry V. Vasilchenko, Anna L. Nemoykina, Daria A. Goncharova, Valery A. Svetlichnyi, Georgiy T. Dambaev, Vyacheslav M. Bouznik and Evgeny N. Bolbasov

Membranes 2021, 11(12), 986; https://doi.org/10.3390/membranes11120986 - 17 Dec 2021

Cited by 7 | Viewed by 2946

Abstract

In the present study, wound healing ferroelectric membranes doped with zinc oxide nanoparticles were fabricated from vinylidene fluoride-tetrafluoroethylene copolymer and polyvinylpyrrolidone using the electrospinning technique. Five different ratios of vinylidene fluoride-tetrafluoroethylene to polyvinylpyrrolidone were used to control the properties of the membranes at [...] Read more.

In the present study, wound healing ferroelectric membranes doped with zinc oxide nanoparticles were fabricated from vinylidene fluoride-tetrafluoroethylene copolymer and polyvinylpyrrolidone using the electrospinning technique. Five different ratios of vinylidene fluoride-tetrafluoroethylene to polyvinylpyrrolidone were used to control the properties of the membranes at a constant zinc oxide nanoparticle content. It was found that an increase of polyvinylpyrrolidone content leads to a decrease of the spinning solution conductivity and viscosity, causing a decrease of the average fiber diameter and reducing their strength and elongation. By means of X-ray diffraction and infrared spectroscopy, it was revealed that increased polyvinylpyrrolidone content leads to difficulty in crystallization of the vinylidene fluoride-tetrafluoroethylene copolymer in the ferroelectric β-phase in membranes. Changing the ratio of vinylidene fluoride-tetrafluoroethylene copolymer and polyvinylpyrrolidone with a constant content of zinc oxide nanoparticles is an effective approach to control the antibacterial properties of membranes towards Staphylococcus aureus. After carrying out in vivo experiments, we found that ferroelectric hybrid membranes, containing from five to ten mass percent of PVP, have the greatest wound-healing effect for the healing of purulent wounds. Full article

(This article belongs to the Special Issue Application of Ferroelectric-Polymer Composites)

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12 pages, 2084 KiB

Open AccessArticle

Impedance Spectroscopy Measurements of Ionomer Film Oxygen Transport Resistivity in Operating Low-Pt PEM Fuel Cell

by Tatyana V. Reshetenko and Andrei Kulikovsky

Membranes 2021, 11(12), 985; https://doi.org/10.3390/membranes11120985 - 16 Dec 2021

Cited by 2 | Viewed by 3427

Abstract

The work presents a model for local impedance of low-Pt proton exchange membrane fuel cells (PEMFCs), including cathode pore size distribution and O₂ transport along pores and through a thin ionomer film covering Pt/C agglomerates. The model was applied to fit the [...] Read more.

The work presents a model for local impedance of low-Pt proton exchange membrane fuel cells (PEMFCs), including cathode pore size distribution and O₂ transport along pores and through a thin ionomer film covering Pt/C agglomerates. The model was applied to fit the local impedance spectra of low-Pt fuel cells operated at current densities from 100 to 800 mA cm⁻² and recorded by a segmented cell system. Assuming an ionomer film thickness of 10 nm, the fitting returned the product of the dimensionless Henry’s constant of oxygen dissolution in ionomer K_H by the oxygen diffusivity D_N in the ionomer (K_HD_N). This parameter allowed us to determine the fundamental O₂ transport resistivity

R_{N}

through the ionomer film in the working electrode under conditions relevant to the realistic operation of PEMFCs. The results show that variation of the operating current density does not affect

R_{N}

, which remains nearly constant at ≃0.4 s cm⁻¹. Full article

(This article belongs to the Special Issue Advanced Membrane Electrode Assembly (MEA) for Applications in Fuel Cell and Electrolyzer Based Systems)

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28 pages, 6006 KiB

Open AccessReview

The Mechanism of Metal Homeostasis in Plants: A New View on the Synergistic Regulation Pathway of Membrane Proteins, Lipids and Metal Ions

by Danxia Wu, Muhammad Saleem, Tengbing He and Guandi He

Membranes 2021, 11(12), 984; https://doi.org/10.3390/membranes11120984 - 15 Dec 2021

Cited by 15 | Viewed by 4992

Abstract

Heavy metal stress (HMS) is one of the most destructive abiotic stresses which seriously affects the growth and development of plants. Recent studies have shown significant progress in understanding the molecular mechanisms underlying plant tolerance to HMS. In general, three core signals are [...] Read more.

Heavy metal stress (HMS) is one of the most destructive abiotic stresses which seriously affects the growth and development of plants. Recent studies have shown significant progress in understanding the molecular mechanisms underlying plant tolerance to HMS. In general, three core signals are involved in plants’ responses to HMS; these are mitogen-activated protein kinase (MAPK), calcium, and hormonal (abscisic acid) signals. In addition to these signal components, other regulatory factors, such as microRNAs and membrane proteins, also play an important role in regulating HMS responses in plants. Membrane proteins interact with the highly complex and heterogeneous lipids in the plant cell environment. The function of membrane proteins is affected by the interactions between lipids and lipid-membrane proteins. Our review findings also indicate the possibility of membrane protein-lipid-metal ion interactions in regulating metal homeostasis in plant cells. In this review, we investigated the role of membrane proteins with specific substrate recognition in regulating cell metal homeostasis. The understanding of the possible interaction networks and upstream and downstream pathways is developed. In addition, possible interactions between membrane proteins, metal ions, and lipids are discussed to provide new ideas for studying metal homeostasis in plant cells. Full article

(This article belongs to the Special Issue Lipid Regulation of Ion Channels and Transporters)

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9 pages, 619 KiB

Open AccessReview

Secretases Related to Amyloid Precursor Protein Processing

by Xiaoling Liu, Yan Liu and Shangrong Ji

Membranes 2021, 11(12), 983; https://doi.org/10.3390/membranes11120983 - 15 Dec 2021

Cited by 16 | Viewed by 3193

Abstract

Alzheimer’s disease (AD) is a common neurodegenerative disease whose prevalence increases with age. An increasing number of findings suggest that abnormalities in the metabolism of amyloid precursor protein (APP), a single transmembrane aspartic protein that is cleaved by β- and γ-secretases to produce [...] Read more.

Alzheimer’s disease (AD) is a common neurodegenerative disease whose prevalence increases with age. An increasing number of findings suggest that abnormalities in the metabolism of amyloid precursor protein (APP), a single transmembrane aspartic protein that is cleaved by β- and γ-secretases to produce β-amyloid protein (Aβ), are a major pathological feature of AD. In recent years, a large number of studies have been conducted on the APP processing pathways and the role of secretion. This paper provides a summary of the involvement of secretases in the processing of APP and the potential drug targets that could provide new directions for AD therapy. Full article

(This article belongs to the Special Issue Ectodomain Shedding: Current Trends and Challenges to Investigate Functions of Sheddases)

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19 pages, 4695 KiB

Open AccessArticle

Mixed Matrix Membranes Based on Torlon^® and ZIF-8 for High-Temperature, Size-Selective Gas Separations

by Matilde De Pascale, Francesco Maria Benedetti, Elsa Lasseuguette, Maria-Chiara Ferrari, Kseniya Papchenko, Micaela Degli Esposti, Paola Fabbri and Maria Grazia De Angelis

Membranes 2021, 11(12), 982; https://doi.org/10.3390/membranes11120982 - 15 Dec 2021

Cited by 4 | Viewed by 3038

Abstract

Torlon^® is a thermally and plasticization-resistant polyamide imide characterized by low gas permeability at room temperature. In this work, we aimed at improving the polymer performance in the thermally-enhanced He/CO₂ and H₂/CO₂ separations, by compounding Torlon^® with [...] Read more.

Torlon^® is a thermally and plasticization-resistant polyamide imide characterized by low gas permeability at room temperature. In this work, we aimed at improving the polymer performance in the thermally-enhanced He/CO₂ and H₂/CO₂ separations, by compounding Torlon^® with a highly permeable filler, ZIF-8, to fabricate Mixed Matrix Membranes (MMMs). The effect of filler loading, gas size, and temperature on the MMMs permeability, diffusivity, and selectivity was investigated. The He permeability increased by a factor of 3, while the He/CO₂ selectivity decreased by a factor of 2, when adding 25 wt % of ZIF-8 at 65 °C to Torlon^®; similar trends were observed for the case of H₂. The MMMs permeability and size-selectivity were both enhanced by temperature. The behavior of MMMs is intermediate between the pure polymer and pure filler ones, and can be described with models for composites, indicating that such materials have a good polymer/filler adhesion and their performance could be tailored by acting on the formulation. The behavior observed is in line with previous investigations on MMMs based on glassy polymers and ZIF-8, in similar conditions, and indicates that ZIF-8 can be used as a polymer additive when the permeability is a controlling aspect, with a proper choice of loading and operative temperature. Full article

(This article belongs to the Special Issue Polymer Membranes for Gas Separation, Volume II)

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16 pages, 6362 KiB

Open AccessEditor’s ChoiceArticle

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

by Takashi Ohkame, Kazushi Minegishi, Hideki Sugihara, Keizo Nakagawa, Takuji Shintani, Hideto Matsuyama and Tomohisa Yoshioka

Membranes 2021, 11(12), 981; https://doi.org/10.3390/membranes11120981 - 15 Dec 2021

Cited by 3 | Viewed by 3074

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue State-of-the-Art Membrane Science and Technology in Japan 2021, 2022)

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13 pages, 1502 KiB

Open AccessArticle

Removal of Excess Alkali from Sodium Naphthenate Solution by Electrodialysis Using Bilayer Membranes for Subsequent Conversion to Naphthenic Acids

by Aslan Achoh, Ilya Petriev and Stanislav Melnikov

Membranes 2021, 11(12), 980; https://doi.org/10.3390/membranes11120980 - 14 Dec 2021

Cited by 4 | Viewed by 2563

Abstract

The processing of solutions containing sodium salts of naphthenic acids (sodium naphthenate) is in high demand due to the high value of the latter. Such solutions usually include an excessive amount of alkali and a pH of around 13. Bipolar electrodialysis can convert [...] Read more.

The processing of solutions containing sodium salts of naphthenic acids (sodium naphthenate) is in high demand due to the high value of the latter. Such solutions usually include an excessive amount of alkali and a pH of around 13. Bipolar electrodialysis can convert sodium naphthenates into naphthenic acids; however, until pH 6.5, the naphthenic acids are not released from the solution. The primary process leading to a decrease in pH is the removal of excess alkali that implies that some part of electricity is wasted. In this work, we propose a technique for the surface modification of anion-exchange membranes with sulfonated polyetheretherketone, with the formation of bilayer membranes that are resistant to poisoning by the naphthenate anions. We investigated the electrochemical properties of the obtained membranes and their efficiency in a laboratory electrodialyzer. Modified membranes have better electrical conductivity, a high current efficiency for hydroxyl ions, and a low tendency to poisoning than the commercial membrane MA-41. We propose that the primary current carrier is the hydroxyl ion in both electromembrane systems with the MA-41 and MA-41M membranes. At the same time, for the modified MA-41M membrane, the concentration of hydroxyl ions in the anion-exchanger phase is higher than in the MA-41 membrane, which leads to almost five-fold higher values of the specific permeability coefficient. The MA-41M membranes are resistant to poisoning by naphthenic acids anions during at least six cycles of processing of the sodium naphthenate solution. Full article

(This article belongs to the Special Issue Ion-Exchange Membranes and Processes (Volume III))

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9 pages, 10717 KiB

Open AccessArticle

The Application of Principal Component Analysis (PCA) for the Optimization of the Conditions of Fabrication of Electrospun Nanofibrous Membrane for Desalination and Ion Removal

by Khaled Younes, Omar Mouhtady, Hamdi Chaouk, Emil Obeid, Rabih Roufayel, Ahmad Moghrabi and Nimer Murshid

Membranes 2021, 11(12), 979; https://doi.org/10.3390/membranes11120979 - 13 Dec 2021

Cited by 14 | Viewed by 2862

Abstract

Nowadays, acquiring a water supply for urban and industrial uses is one of the greatest challenges facing humanity for ensuring sustainability. Membrane technology has been considered cost-effective, encompasses lower energy requirements, and at the same time, offers acceptable performance. Electrospun nanofibrous membranes (ENMs) [...] Read more.

Nowadays, acquiring a water supply for urban and industrial uses is one of the greatest challenges facing humanity for ensuring sustainability. Membrane technology has been considered cost-effective, encompasses lower energy requirements, and at the same time, offers acceptable performance. Electrospun nanofibrous membranes (ENMs) are considered a novel and promising strategy for the production of membranes that could be applied in several treatment processes, especially desalination and ion removal. In this study, we apply an unsupervised machine-learning strategy, the so-called principal component analysis (PCA), for the purpose of seeking discrepancies and similarities between different ENMs. The main purpose was to investigate the influence of membrane fabrication conditions, characteristics, and process conditions in order to seek the relevance of the application of different electrospun nanofibrous membranes (ENMs). Membranes were majorly classified into single polymers/layers, from one side, and dual multiple layer ENMs, from another side. For both classes, variables related to membrane fabrication conditions were not separated from membrane characterization variables. This reveals that membranes’ characteristics not only depend on the chemical composition, but also on the fabrication conditions. On the other hand, the process conditions of ENM fabrication showed an extensive effect on membranes’ performance. Full article

(This article belongs to the Special Issue Water Treatment Process)

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31 pages, 5256 KiB

Open AccessEditor’s ChoiceArticle

Membrane Domain Localization and Interaction of the Prion-Family Proteins, Prion and Shadoo with Calnexin

by Divya Teja Dondapati, Pradeep Reddy Cingaram, Ferhan Ayaydin, Antal Nyeste, Andor Kanyó, Ervin Welker and Elfrieda Fodor

Membranes 2021, 11(12), 978; https://doi.org/10.3390/membranes11120978 - 13 Dec 2021

Cited by 1 | Viewed by 3910

Abstract

The cellular prion protein (PrP^C) is renowned for its infectious conformational isoform PrP^Sc, capable of templating subsequent conversions of healthy PrP^Cs and thus triggering the group of incurable diseases known as transmissible spongiform encephalopathies. Besides this mechanism [...] Read more.

The cellular prion protein (PrP^C) is renowned for its infectious conformational isoform PrP^Sc, capable of templating subsequent conversions of healthy PrP^Cs and thus triggering the group of incurable diseases known as transmissible spongiform encephalopathies. Besides this mechanism not being fully uncovered, the protein’s physiological role is also elusive. PrP^C and its newest, less understood paralog Shadoo are glycosylphosphatidylinositol-anchored proteins highly expressed in the central nervous system. While they share some attributes and neuroprotective actions, opposing roles have also been reported for the two; however, the amount of data about their exact functions is lacking. Protein–protein interactions and membrane microdomain localizations are key determinants of protein function. Accurate identification of these functions for a membrane protein, however, can become biased due to interactions occurring during sample processing. To avoid such artifacts, we apply a non-detergent-based membrane-fractionation approach to study the prion protein and Shadoo. We show that the two proteins occupy similarly raft and non-raft membrane fractions when expressed in N2a cells and that both proteins pull down the chaperone calnexin in both rafts and non-rafts. These indicate their possible binding to calnexin in both types of membrane domains, which might be a necessary requisite to aid the inherently unstable native conformation during their lifetime. Full article

(This article belongs to the Special Issue Membrane Domains Organization and Interactions)

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15 pages, 2259 KiB

Open AccessArticle

How to Produce an Alternative Carbon Source for Denitrification by Treating and Drastically Reducing Biological Sewage Sludge

by Maria Cristina Collivignarelli, Alessandro Abbà, Francesca Maria Caccamo, Marco Carnevale Miino, Angela Durante, Stefano Bellazzi, Marco Baldi and Giorgio Bertanza

Membranes 2021, 11(12), 977; https://doi.org/10.3390/membranes11120977 - 12 Dec 2021

Cited by 12 | Viewed by 2953

Abstract

Minimizing the biological sewage sludge (BSS) produced by wastewater treatment plants (WWTPs) represents an increasingly difficult challenge. With this goal, tests on a semi-full scale Thermophilic Alternate Membrane Biological Reactor (ThAlMBR) were carried out for 12 months. ThAlMBR was applied both on thickened [...] Read more.

Minimizing the biological sewage sludge (BSS) produced by wastewater treatment plants (WWTPs) represents an increasingly difficult challenge. With this goal, tests on a semi-full scale Thermophilic Alternate Membrane Biological Reactor (ThAlMBR) were carried out for 12 months. ThAlMBR was applied both on thickened (TBSS) and digested biological sewage sludge (DBSS) with alternating aeration conditions, and emerged: (i) high COD removal yields (up to 90%), (ii) a low specific sludge production (0.02–0.05 kg_{VS produced}/kg_CODremoved), (iii) the possibility of recovery the aqueous carbon residue (permeate) in denitrification processes, replacing purchased external carbon sources. Based on the respirometric tests, an excellent biological treatability of the permeate by the mesophilic biomass was observed and the denitrification kinetics reached with the diluted permeate ((4.0 mgN-NO₃⁻/(g_VSS h)) were found comparable to those of methanol (4.4 mgN-NO₃⁻/(g_VSS h)). Moreover, thanks to the similar results obtained on TBSS and DBSS, ThAlMBR proved to be compatible with diverse sludge line points, ensuring in both cases an important sludge minimization. Full article

(This article belongs to the Special Issue Application of Membrane Technologies for Water, Energy, and Nutrient Recovery from Wastewater)

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12 pages, 1331 KiB

Open AccessArticle

Reverse Osmosis Treatment of Wastewater for Reuse as Process Water—A Case Study

by Marjana Simonič

Membranes 2021, 11(12), 976; https://doi.org/10.3390/membranes11120976 - 10 Dec 2021

Cited by 18 | Viewed by 6519

Abstract

The aim of this work was to purify mixed wastewater from three different production processes in such a manner that they could be reused as process water. The maximum allowed concentrations (MAC) from the Environmental Standards for emissions of substances released into surface [...] Read more.

The aim of this work was to purify mixed wastewater from three different production processes in such a manner that they could be reused as process water. The maximum allowed concentrations (MAC) from the Environmental Standards for emissions of substances released into surface water were set as target concentrations. Wastewaters contained solid particles, sodium, aluminium, chloride, and nitrogen in high amounts. Quantitatively, most wastewaters were generated in the production line of alumina washing. The second type of wastewater was generated from the production line of boehmite. The third type of wastewater was from regeneration of ion exchangers, which are applied for feed boiler water treatment. The initial treatment step of wastewater mixture was neutralisation, using 35% HCl. The precoat filtration followed, and the level of suspended solids was reduced from 320 mg/L to only 9 mg/L. The concentrations of ions, such as aluminium, sodium and chlorides remained above the MAC. Therefore, laboratory reverse osmosis was applied to remove the listed pollutants from the water. We succeeded in removal of all the pollutants. The concentration of aluminium decreased below 3 mg/L, the sodium to 145 mg/L and chlorides to 193 mg/L. The concentration of nitrate nitrogen decreased below 20 mg/L. Full article

(This article belongs to the Collection New Challenges in Membranes for Water and Wastewater Application)

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22 pages, 4802 KiB

Open AccessArticle

Wastewater Purification with Nutrient and Carbon Recovery in a Mobile Resource Container

by Hanna Kyllönen, Juha Heikkinen, Eliisa Järvelä, Lotta Sorsamäki, Virpi Siipola and Antti Grönroos

Membranes 2021, 11(12), 975; https://doi.org/10.3390/membranes11120975 - 9 Dec 2021

Cited by 2 | Viewed by 3236

Abstract

Water reuse from wastewater treatment plants can significantly reduce freshwater demand. Additionally municipal sewage and some industrial wastewaters could be used as sources of nutrients and carbon more effectively than they are used today. Biological treatments have attracted the most attention in wastewater [...] Read more.

Water reuse from wastewater treatment plants can significantly reduce freshwater demand. Additionally municipal sewage and some industrial wastewaters could be used as sources of nutrients and carbon more effectively than they are used today. Biological treatments have attracted the most attention in wastewater purification, whereas, so far, only a little attention has been paid to the physico-chemical technologies. These technologies could, however, have great potential to recover nutrients when purifying wastewater. In this study, the main emphasis was to study the possibilities to utilize existing physico-chemical unit operations for wastewater purification and nutrients as well as carbon recovery. Unit operations were selected so that they could produce exploitable circular economy products from wastewaters and be assembled in a mobile container for carrying out recovery anywhere that is suitable. The results showed that in a mobile container, solids could be successfully separated from the studied wastewaters by flocculation-assisted solid/liquid separation and then processed into hydrochar by hydrothermal carbonization. Phosphate was precipitated using lime milk as calcium phosphate, and ammonium nitrogen was captured from the wastewater using membrane contactor technology resulting in ammonium sulphate for fertilizer use. Additionally, reverse osmosis retained residual impurities well, producing good quality water for reuse. The techno-economic feasibility seems promising. Full article

(This article belongs to the Topic Water Reclamation and Reuse)

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11 pages, 1986 KiB

Open AccessArticle

Free Energy Analyses of Cell-Penetrating Peptides Using the Weighted Ensemble Method

by Seungho Choe

Membranes 2021, 11(12), 974; https://doi.org/10.3390/membranes11120974 - 9 Dec 2021

Cited by 4 | Viewed by 2687

Abstract

Cell-penetrating peptides (CPPs) have been widely used for drug-delivery agents; however, it has not been fully understood how they translocate across cell membranes. The Weighted Ensemble (WE) method, one of the most powerful and flexible path sampling techniques, can be helpful to reveal [...] Read more.

Cell-penetrating peptides (CPPs) have been widely used for drug-delivery agents; however, it has not been fully understood how they translocate across cell membranes. The Weighted Ensemble (WE) method, one of the most powerful and flexible path sampling techniques, can be helpful to reveal translocation paths and free energy barriers along those paths. Within the WE approach we show how Arg

_{9}

(nona-arginine) and Tat interact with a DOPC/DOPG(4:1) model membrane, and we present free energy (or potential mean of forces, PMFs) profiles of penetration, although a translocation across the membrane has not been observed in the current simulations. Two different compositions of lipid molecules were also tried and compared. Our approach can be applied to any CPPs interacting with various model membranes, and it will provide useful information regarding the transport mechanisms of CPPs. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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21 pages, 6568 KiB

Open AccessEditor’s ChoiceArticle

Distillate Flux Enhancement of Direct Contact Membrane Distillation Modules with Inserting Cross-Diagonal Carbon-Fiber Spacers

by Chii-Dong Ho, Luke Chen, Jun-Wei Lim, Po-Hung Lin and Pin-Tsen Lu

Membranes 2021, 11(12), 973; https://doi.org/10.3390/membranes11120973 - 9 Dec 2021

Cited by 5 | Viewed by 2663

Abstract

A new design of direct-contact membrane distillation (DCMD) modules with cross-diagonal carbon-fiber spacers of various hydrodynamic angles in flow channels to promote turbulence intensity was proposed to enhance pure water productivity. Attempts to reduce the temperature polarization coefficient were achieved by inserting cross-diagonal [...] Read more.

A new design of direct-contact membrane distillation (DCMD) modules with cross-diagonal carbon-fiber spacers of various hydrodynamic angles in flow channels to promote turbulence intensity was proposed to enhance pure water productivity. Attempts to reduce the temperature polarization coefficient were achieved by inserting cross-diagonal carbon-fiber spacers in channels, which create wakes and eddies in both heat and mass transfer behaviors to enhance the permeate flux enhancement. A simplified equation was formulated to obtain the theoretical predictions of heat transfer coefficients in the current DCMD device. The permeate fluxes and temperature distributions of both hot and cold feed streams are represented graphically with the inlet volumetric flow rate and inlet temperature of the hot saline feed stream as parameters. The higher distillate flux of countercurrent-flow operations for saline water desalination was accomplished as compared to the concurrent-flow operations of various hydrodynamic angles. The results show that the agreement between the theoretical predictions and experimental results is reasonably good. The effects of countercurrent-flow operations and inserting carbon fiber spacers have confirmed technical feasibility and device performance enhancement of up to 45%. The influences of operating and design parameters on the pure water productivity with the expense of energy consumption are also discussed. Full article

(This article belongs to the Special Issue Special Issue in Honor of Professor Ahmad Fauzi Ismail)

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23 pages, 3892 KiB

Open AccessArticle

Electrospun Magnetic Nanocellulose–Polyethersulfone-Conjugated Aspergillus oryzae Lipase for Synthesis of Ethyl Valerate

by Nurul Hidayah Hussin, Roswanira Abdul Wahab, Nursyafiqah Elias, Adikwu Gowon Jacob, Mohamad Hamdi Zainal-Abidin, Faizuan Abdullah, Nurul Jannah Sulaiman and Mailin Misson

Membranes 2021, 11(12), 972; https://doi.org/10.3390/membranes11120972 - 9 Dec 2021

Cited by 2 | Viewed by 3129

Abstract

A novel greener MNC/PES membrane was developed through an electrospinning technique for lipase immobilization to catalyze the synthesis of ethyl valerate (EV). In this study, the covalent immobilization of Aspergillus oryzae lipase (AOL) onto an electrospun nanofibrous membrane consisting of magnetic nanocellulose (MNC) [...] Read more.

A novel greener MNC/PES membrane was developed through an electrospinning technique for lipase immobilization to catalyze the synthesis of ethyl valerate (EV). In this study, the covalent immobilization of Aspergillus oryzae lipase (AOL) onto an electrospun nanofibrous membrane consisting of magnetic nanocellulose (MNC) and polyethersulfone (PES) to produce EV was statistically optimized. Raman spectroscopy, Fourier-transform infrared spectroscopy: attenuated total reflection, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, thermal gravimetric analysis (TGA), and differential thermal gravimetric (DTG) of MNC/PES-AOL demonstrated that AOL was successfully immobilized onto the fibers. The Taguchi design-assisted immobilization of AOL onto MNC/PES fibers identified that 1.10 mg/mL protein loading, 4 mL reaction volume, 250 rpm stirring rate, and 50 °C were optimal to yield 72.09% of EV in 24 h. The thermal stability of MNC/PES-AOL was improved by ≈20% over the free AOL, with reusability for up to five consecutive esterification cycles while demonstrating an exceptional half-life of 120 h. Briefly, the electrospun MNC/PES fibers that immobilized AOL showed promising applicability in yielding relatively good EV levels. This study suggests that using MNC as fillers in a PES to improve AOL activity and durability for a longer catalytic process could be a viable option. Full article

(This article belongs to the Special Issue Cellulose and Nano-Cellulose Based Flexible Membranes)

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19 pages, 1992 KiB

Open AccessReview

Membrane Contact Sites in Yeast: Control Hubs of Sphingolipid Homeostasis

by Philipp Schlarmann, Atsuko Ikeda and Kouichi Funato

Membranes 2021, 11(12), 971; https://doi.org/10.3390/membranes11120971 - 9 Dec 2021

Cited by 7 | Viewed by 5160

Abstract

Sphingolipids are the most diverse class of membrane lipids, in terms of their structure and function. Structurally simple sphingolipid precursors, such as ceramides, act as intracellular signaling molecules in various processes, including apoptosis, whereas mature and complex forms of sphingolipids are important structural [...] Read more.

Sphingolipids are the most diverse class of membrane lipids, in terms of their structure and function. Structurally simple sphingolipid precursors, such as ceramides, act as intracellular signaling molecules in various processes, including apoptosis, whereas mature and complex forms of sphingolipids are important structural components of the plasma membrane. Supplying complex sphingolipids to the plasma membrane, according to need, while keeping pro-apoptotic ceramides in check is an intricate task for the cell and requires mechanisms that tightly control sphingolipid synthesis, breakdown, and storage. As each of these processes takes place in different organelles, recent studies, using the budding yeast Saccharomyces cerevisiae, have investigated the role of membrane contact sites as hubs that integrate inter-organellar sphingolipid transport and regulation. In this review, we provide a detailed overview of the findings of these studies and put them into the context of established regulatory mechanisms of sphingolipid homeostasis. We have focused on the role of membrane contact sites in sphingolipid metabolism and ceramide transport, as well as the mechanisms that prevent toxic ceramide accumulation. Full article

(This article belongs to the Special Issue Novel Research on Membrane Trafficking and Membrane Contact Sites)

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15 pages, 1984 KiB

Open AccessArticle

Biodegradable Polymeric Membranes for Organic Solvent/Water Pervaporation Applications

by Pao-Yueh Chang, Jane Wang, Si-Yu Li and Shing-Yi Suen

Membranes 2021, 11(12), 970; https://doi.org/10.3390/membranes11120970 - 9 Dec 2021

Cited by 4 | Viewed by 3776

Abstract

Biodegradable polymers are a green alternative to apply as the base membrane materials in versatile processes. In this study, two dense membranes were made from biodegradable PGS (poly(glycerol sebacate)) and APS (poly(1,3-diamino-2-hydroxypropane-co-polyol sebacate)), respectively. The prepared membranes were characterized by FE-SEM, AFM, ATR-FTIR, [...] Read more.

Biodegradable polymers are a green alternative to apply as the base membrane materials in versatile processes. In this study, two dense membranes were made from biodegradable PGS (poly(glycerol sebacate)) and APS (poly(1,3-diamino-2-hydroxypropane-co-polyol sebacate)), respectively. The prepared membranes were characterized by FE-SEM, AFM, ATR-FTIR, TGA, DSC, water contact angle, and degree of swelling, in comparison with the PDMS (polydimethylpolysiloxane) membrane. In the pervaporation process for five organic solvent/water systems at 37 °C, both biodegradable membranes exhibited higher separation factors for ethanol/water and acetic acid/water separations, while the PDMS membrane attained better effectiveness in the other three systems. In particular, a positive relationship between the separation factor and the swelling ratio of organic solvent to water (DS_o/DS_w) was noticed. In spite of their biodegradability, the stability of both PGS and APS membranes was not deteriorated on ethanol/water pervaporation for one month. Furthermore, these two biodegradable membranes were applied in the pervaporation of simulated ABE (acetone-butanol-ethanol) fermentation solution, and the results were comparable with those reported in the literature. Full article

(This article belongs to the Special Issue Membrane Processes for Liquid and Gas Separations: Opportunities and Challenges)

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14 pages, 5073 KiB

Open AccessArticle

Enhancement of Physical Characteristics of Styrene–Acrylonitrile Nanofiber Membranes Using Various Post-Treatments for Membrane Distillation

by Reza Sallakhniknezhad, Manijeh Khorsi, Ali Sallakh Niknejad, Saeed Bazgir, Ali Kargari, Mohsen Sazegar, Mohsen Rasouli and Soryong Chae

Membranes 2021, 11(12), 969; https://doi.org/10.3390/membranes11120969 - 9 Dec 2021

Cited by 13 | Viewed by 3239

Abstract

Insufficient mechanical strength and wide pore size distribution of nanofibrous membranes are the key hindrances for their concrete applications in membrane distillation. In this work, various post-treatment methods such as dilute solvent welding, vapor welding, and cold-/hot-pressing processes were used to enhance the [...] Read more.

Insufficient mechanical strength and wide pore size distribution of nanofibrous membranes are the key hindrances for their concrete applications in membrane distillation. In this work, various post-treatment methods such as dilute solvent welding, vapor welding, and cold-/hot-pressing processes were used to enhance the physical properties of styrene–acrylonitrile (SAN) nanofiber membranes fabricated by the modified electrospinning process. The effects of injection rate of welding solution and a working distance during the welding process with air-assisted spraying on characteristics of SAN nanofiber membranes were investigated. The welding process was made less time-consuming by optimizing system parameters of the electroblowing process to simultaneously exploit residual solvents of fibers and hot solvent vapor to reduce exposure time. As a result, the welded SAN membranes showed considerable enhancement in mechanical robustness and membrane integrity with a negligible reduction in surface hydrophobicity. The hot-pressed SAN membranes obtained the highest mechanical strength and smallest mean pore size. The modified SAN membranes were used for the desalination of synthetic seawater in a direct contact membrane distillation (DCMD). As a result, it was found that the modified SAN membranes performed well (>99.9% removal of salts) for desalination of synthetic seawater (35 g/L NaCl) during 30 h operation without membrane wetting. The cold-/hot-pressing processes were able to improve mechanical strength and boost liquid entry pressure (LEP) of water. In contrast, the welding processes were preferred to increase membrane flexibility and permeation. Full article

(This article belongs to the Special Issue State-of-the-Art Membrane Science and Technology in North America)

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