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Volume 12, January

Membranes, Volume 12, Issue 2 (February 2022) – 148 articles

Cover Story (view full-size image): Antimicrobial resistance is one of the most serious medical threats worldwide. Antimicrobial peptides (AMPs) interact with and damage the cell membranes of antimicrobial-resistant microorganisms. To gain new insights into AMP design strategies, it is necessary to understand the mechanism of AMP–membrane interaction. Here, we used synchrotron-radiation circular dichroism, linear dichroism, and fluorescence spectroscopies to characterize the interaction mechanism between the model AMP, magainin 2 (M2), and dipalmitoyl-phosphatidylglycerol lipid membrane. The results showed that α-helix monomers of M2 assembled and transformed into β-strand oligomers with increasing peptide-to-lipid molar ratio, destabilizing the membrane structure. Our findings suggest that the formation of β-strand oligomers of M2 contributes to the disruption of the cell membrane. View this paper
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Editorial
Electrical Properties of Model Lipid Membranes
Membranes 2022, 12(2), 248; https://doi.org/10.3390/membranes12020248 - 21 Feb 2022
Viewed by 422
Abstract
Biological membranes are essential components of the living systems, and processes occurring with their participation are related mainly to electric phenomena such as signal transduction, existence of membrane potentials, and transport through the membrane [...] Full article
(This article belongs to the Special Issue Electrical Properties of Model Lipid Membranes)
Review
Recent Advancements in Polyphenylsulfone Membrane Modification Methods for Separation Applications
Membranes 2022, 12(2), 247; https://doi.org/10.3390/membranes12020247 - 21 Feb 2022
Viewed by 569
Abstract
Polyphenylsulfone (PPSU) membranes are of fundamental importance for many applications such as water treatment, gas separation, energy, electronics, and biomedicine, due to their low cost, controlled crystallinity, chemical, thermal, and mechanical stability. Numerous research studies have shown that modifying surface properties of PPSU [...] Read more.
Polyphenylsulfone (PPSU) membranes are of fundamental importance for many applications such as water treatment, gas separation, energy, electronics, and biomedicine, due to their low cost, controlled crystallinity, chemical, thermal, and mechanical stability. Numerous research studies have shown that modifying surface properties of PPSU membranes influences their stability and functionality. Therefore, the modification of the PPSU membrane surface is a pressing issue for both research and industrial communities. In this review, various surface modification methods and processes along with their mechanisms and performance are considered starting from 2002. There are three main approaches to the modification of PPSU membranes. The first one is bulk modifications, and it includes functional groups inclusion via sulfonation, amination, and chloromethylation. The second is blending with polymer (for instance, blending nanomaterials and biopolymers). Finally, the third one deals with physical and chemical surface modifications. Obviously, each method has its own limitations and advantages that are outlined below. Generally speaking, modified PPSU membranes demonstrate improved physical and chemical properties and enhanced performance. The advancements in PPSU modification have opened the door for the advance of membrane technology and multiple prospective applications. Full article
(This article belongs to the Special Issue Nanomaterial-Based Membranes for Water Treatment and Desalination)
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Article
Life Cycle Assessment of an Integrated Membrane Treatment System of Anaerobic-Treated Palm Oil Mill Effluent (POME)
Membranes 2022, 12(2), 246; https://doi.org/10.3390/membranes12020246 - 21 Feb 2022
Viewed by 447
Abstract
A life cycle assessment of anaerobic-treated palm oil mill effluent (POME) was conducted to assess the environmental performance on two integrated treatment processes: the typical hollow fiber membrane ultrafiltration module coupled with adsorption and electro-oxidation as pretreatment. The analysis was undertaken using the [...] Read more.
A life cycle assessment of anaerobic-treated palm oil mill effluent (POME) was conducted to assess the environmental performance on two integrated treatment processes: the typical hollow fiber membrane ultrafiltration module coupled with adsorption and electro-oxidation as pretreatment. The analysis was undertaken using the ReCiPe 2016 method and SimaPro v9 software was employed using a ‘cradle-to-gate’ approach. The results showed that hollow fiber membrane from the adsorption integrated membrane impacted significantly at 42% to 99% across all impact categories for both processes. Overall, the electro-oxidation integrated membrane was discovered to have a lesser environmental impact, particularly on the ozone formation (human health) (HOFP) at 0.38 kg NOx-eq in comparison to the adsorption integrated membrane at 0.66 kg NOx-eq. The total characterization factor of the endpoint category for human health is 8.61 × 10−4 DALY (adsorption integrated membrane) and 8.45 × 10−4 DALY (electro-oxidation integrated membrane). As membrane treatment is closely linked to energy consumption, the environmental impact with different sources of energy was evaluated for both processes with the impacts decreasing in the following order: Grid > Biogas > Grid/Solar. Future research should concentrate on determining the overall ‘cradle-to-grave’ environmental impact of treating POME, as well as other scenarios involving membrane treatment energy utilization using LCA. This study can help decision-makers in identifying an environmentally sustainable POME treatment and management, especially in Malaysia. Full article
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Article
Performance of PVDF-TiO2 Membranes during Photo-Filtration in the Presence of Inorganic and Organic Components
Membranes 2022, 12(2), 245; https://doi.org/10.3390/membranes12020245 - 21 Feb 2022
Viewed by 295
Abstract
In this study, the anti-fouling performance of PVDF-TiO2 composite membranes, indicated by their permeate flux, was studied with different types of synthetic feed solutions. Photo-filtration (filtration under continuous UV irradiation) of solutions containing inorganic and organic components, which are ubiquitous in drinking/natural [...] Read more.
In this study, the anti-fouling performance of PVDF-TiO2 composite membranes, indicated by their permeate flux, was studied with different types of synthetic feed solutions. Photo-filtration (filtration under continuous UV irradiation) of solutions containing inorganic and organic components, which are ubiquitous in drinking/natural water, was performed to evaluate their influence on the photo-induced properties and performance of the membranes. The results indicated that inorganic fouling was unlikely to occur on PVDF-TiO2 membranes, and the presence of common inorganic ions in drinking water did not hinder their performance. However, in the particular case where a small amount of Cu2+ coexisted alongside HCO3 in the feed solution, inorganic fouling occurred, causing severe flux decline and prohibiting the photo-induced properties of the membranes. On the other hand, when used to filter organic fouling solutions, the membranes showed strong resistance to sodium alginate fouling, and less so for humic acids. In terms of separation efficiency, the membranes showed no advantages when operated in photo-filtration mode, as the rejection rate of both foulants under photo-filtration was not higher than that under normal filtration. In the case of humic acids, the photodegradation of humic substances into smaller compounds that were able to enter the permeate stream led to a lower rejection rate. Nevertheless, photo-filtration of these organic foulants still offered a higher permeate flux than normal filtration, up to a certain concentration level (5 mg/L for humic acids and 50 mg/L for sodium alginate). Full article
(This article belongs to the Special Issue Advance in Photocatalytic Membrane Reactor)
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Article
Lithium-Sodium Separation by a Lithium Composite Membrane Used in Electrodialysis Process: Concept Validation
Membranes 2022, 12(2), 244; https://doi.org/10.3390/membranes12020244 - 21 Feb 2022
Viewed by 578
Abstract
The recent expansion of global Lithium Ion Battery (LIBs) production has generated a significant stress on the lithium demand. One of the means to produce this element is its extraction from different aqueous sources (salars, geothermal water etc.). However, the presence of other [...] Read more.
The recent expansion of global Lithium Ion Battery (LIBs) production has generated a significant stress on the lithium demand. One of the means to produce this element is its extraction from different aqueous sources (salars, geothermal water etc.). However, the presence of other mono- and divalent cations makes this extraction relatively complex. Herein, we propose lithium-sodium separation by an electrodialysis (ED) process using a Lithium Composite Membrane (LCM), whose effectiveness was previously demonstrated by a Diffusion Dialysis process (previous work). LCM performances in terms of lithium Recovery Ratio (RR(Li+)) and Selectivity (S(Li/Na)) were investigated using different Li+/Na+ reconstituted solutions and two ED cells: a two-compartment cell was chosen for its simplicity, and a four-compartment one was selected for its potential to isolate the redox reactions at the electrodes. We demonstrated that the four-compartment cell use was advantageous since it provided membrane protection from protons and gases generated by the electrodes but that membrane selectivity was negatively affected. The impact of the applied current density and the concentration ratio of Na+ and Li+ in the feed compartment ([Na+]F/[Li+]F) were tested using the four-compartment cell. We showed that increasing the current density led to an improvement of RR(Li+) but to a reduction in the LCM selectivity towards Li+. Increasing the [Na+]F/[Li+]F ratios to 10 had a positive effect on the membrane performance. However, for high values of this ratio, both RR(Li+) and S(Li/Na) decreased. The optimal results were obtained at [Na+]F/[Li+]F near 10, where we succeeded in extracting more than 10% of the initial Li+ concentration with a selectivity value around 112 after 4 h of ED experiment at 0.5 mA·cm−2. Thus, we can objectively estimate that the concept of this selective extraction of Li+ from a mixture even when concentrated in Na+ using an ED process was validated. Full article
(This article belongs to the Special Issue Ion-Exchange Membranes and Processes (Volume III))
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Article
Study of the Electrical Conductivity of Ion-Exchange Resins and Membranes in Equilibrium Solutions of Inorganic Electrolytes
Membranes 2022, 12(2), 243; https://doi.org/10.3390/membranes12020243 - 20 Feb 2022
Viewed by 486
Abstract
The study of the electrical conductivity of ion-exchange membranes in equilibrium electrolyte solutions is of great importance for the theory of membrane processes, in particular for practical electrodialysis. The purpose of the work is to determine the electrical conductivity of industrial ion-exchange membranes [...] Read more.
The study of the electrical conductivity of ion-exchange membranes in equilibrium electrolyte solutions is of great importance for the theory of membrane processes, in particular for practical electrodialysis. The purpose of the work is to determine the electrical conductivity of industrial ion-exchange membranes MK-40 and MA-40, as well as their basis—granules of a bulk layer of industrial ion exchangers KU-2-8 and EDE-10p, by differential and modified contact methods in electrolyte solutions and the development of a new methodology that will give the values that are closest to the true ones; determination of the dependence of electrical membrane conductivity depending on the type of counterion and concentration equilibrium solution and granules of a bulk layer of ion exchangers on the volume fraction of a dry ion exchanger with different degrees of compaction. It is shown that the dependence of the electrical conductivity of diaphragms on the electrolyte concentration, according to theoretical ideas, disappears under compression. It has been experimentally established that the difference method gives lower values of electrical conductivity in the region of low concentrations. The data obtained by the contact method are in good agreement with the results obtained for compressed diaphragms. The membrane conductivity decreases with increasing ion size. 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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Article
Slip Casting and Solid-State Reactive Sintering of BCZY(BaCexZr0.9−xY0.1O3−d)-NiO/BCZY Half-Cells
Membranes 2022, 12(2), 242; https://doi.org/10.3390/membranes12020242 - 19 Feb 2022
Cited by 1 | Viewed by 555
Abstract
Slip casting was used to prepare BaCexZr0.9−xY0.1O3−d(BCZY)-NiO tubes with a diameter of ½ inches (1.25 cm) and ¾ inches (1.875 cm). Two compositions were studied: BCZY18 and BCZY27 for x = 0.1 and 0.2, respectively. [...] Read more.
Slip casting was used to prepare BaCexZr0.9−xY0.1O3−d(BCZY)-NiO tubes with a diameter of ½ inches (1.25 cm) and ¾ inches (1.875 cm). Two compositions were studied: BCZY18 and BCZY27 for x = 0.1 and 0.2, respectively. The unfired tubes were then dip-coated with three layers of the BCZY electrolyte membrane. Solid-state reactive sintering was used, meaning that the support and membrane were prepared with the precursors (oxides and carbonates). After co-sintering at 1550 °C, a 20-micron thick dense BCZY layer was well-adhered to the 1 mm thick BCZY-NiO support, as confirmed by scanning electron microscopy. The sintered BCZY-NiO/BCZY tubes were sealed onto alumina or BCZY substrates using a silver-based braze (with TiO2 and CuO additions). Gas tightness was achieved under 2 bar when covering the silver braze with a ceramic (Resbond) sealing layer. These slip cast tubes are intended for use as hydrogen electrodes in various protonic ceramic devices, and the advantages of short tubes for reactor design are discussed. Full article
(This article belongs to the Special Issue High-Temperature Proton-Conducting Membranes)
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Article
Assessment of Graphical Methods for Determination of the Limiting Current Density in Complex Electrodialysis-Feed Solutions
Membranes 2022, 12(2), 241; https://doi.org/10.3390/membranes12020241 - 18 Feb 2022
Viewed by 531
Abstract
Electrodialysis (ED) is a promising technology suitable for nutrient recovery from a wide variety of liquid waste streams. For optimal operating conditions, the limiting current density (LCD) has to be determined separately for each treated feed and ED equipment. LCD is most frequently [...] Read more.
Electrodialysis (ED) is a promising technology suitable for nutrient recovery from a wide variety of liquid waste streams. For optimal operating conditions, the limiting current density (LCD) has to be determined separately for each treated feed and ED equipment. LCD is most frequently assessed in the NaCl solutions. In this paper, five graphical methods available in literature were reviewed for LCD determination in a series of five feed solutions with different levels of complexity in ion and matrix composition. Wastewater from microbial fermentation was included among the feed solutions, containing charged and uncharged particles. The experiments, running in the batch ED with an online conductivity, temperature, and pH monitoring, were conducted to obtain data for the comparison of various LCD determination methods. The results revealed complements and divergences between the applied LCD methods with increasing feed concentrations and composition complexity. The Cowan and Brown method had the most consistent results for all of the feed solutions. Online conductivity monitoring was linearly correlated with the decreasing ion concentration in the feed solution and corresponding LCD. Therefore, the results obtained in this study can be applied as a base for the automatized dynamic control of the operating current density–voltage in the batch ED. Conductivity alone should not be used for the ED control since LCD depends on the ion exchange membranes, feed flow, temperature and concentration, ionic species, their concentration ratios, and uncharged particles of the feed solution. Full article
(This article belongs to the Special Issue Membranes for Resource Recovery in Bioelectrochemical Systems)
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Article
Experimental Study and Mathematical Modeling of a Nanofiltration Membrane System for the Recovery of Polyphenols from Wine Lees
Membranes 2022, 12(2), 240; https://doi.org/10.3390/membranes12020240 - 18 Feb 2022
Cited by 1 | Viewed by 346
Abstract
The winemaking process in Spain generates a significant amount of wastes such as wine lees. Currently, the nanofiltration process is a viable technique for the revalorization of compounds from wastes. In this aspect, this technique can be used for the recovery of compounds, [...] Read more.
The winemaking process in Spain generates a significant amount of wastes such as wine lees. Currently, the nanofiltration process is a viable technique for the revalorization of compounds from wastes. In this aspect, this technique can be used for the recovery of compounds, such as polyphenols, as well as active principles widely used in industries, such as pharmaceuticals or cosmetics. Polyphenols are found in acceptable amounts in wine lees wastes and it is interesting to study the nanofiltration process viability to recover them. In order to study this possibility, it is necessary to determine the choice of the best membrane to use and the effect of operational parameters such as pressure, temperature, cross-flow rates, and concentration. In addition, it is important to be able to develop a mathematical model that can help in the future design of lees treatment plants. The treatment of red wine lees to concentrate polyphenols has been studied in a laboratory plant using different membranes (RO and NF) at different pressures (4.5, 9.5, and 14.5 bar), different temperatures (293, 303, and 308 K), and two concentrations (2100 and 1100 mg tyrosol eq·L−1). The results have been encouraging to consider nanofiltration as a viable technique for the treatment and revalorization of this waste. The most suitable membrane has been the NF270, in which 96% rejection rates have been obtained, with a flux of 30 L·h−1·m−2. Moreover, in this study, the Spiegler–Kedem model (SKM) was used to calculate mass transfer constants and permeabilities. Suitable adjustments of these parameters were obtained to validate this mathematical model. For this reason, the SKM might be used in future studies to continue in the research work of the treatment of wine lees wastes. Full article
(This article belongs to the Collection New Challenges in Membranes for Water and Wastewater Application)
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Article
Enhanced Antimicrobial Cellulose/Chitosan/ZnO Biodegradable Composite Membrane
Membranes 2022, 12(2), 239; https://doi.org/10.3390/membranes12020239 - 18 Feb 2022
Cited by 1 | Viewed by 439
Abstract
In this study, chitosan and sugarcane cellulose were used as film-forming materials, while the inorganic agent zinc oxide (ZnO) and natural compound phenyllactic acid (PA) were used as the main bacteriostatic components to fabricate biodegradable antimicrobial composite membranes. The water absorption and antimicrobial [...] Read more.
In this study, chitosan and sugarcane cellulose were used as film-forming materials, while the inorganic agent zinc oxide (ZnO) and natural compound phenyllactic acid (PA) were used as the main bacteriostatic components to fabricate biodegradable antimicrobial composite membranes. The water absorption and antimicrobial properties were investigated by adjusting the concentration of PA. The scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results demonstrated that the components of the composite membrane were successfully integrated. The addition of ZnO improved the mechanical and antimicrobial properties of the composite membrane, while the addition of PA with high crystallinity significantly reduced the water absorption and swelling. Moreover, the addition of 0.5% PA greatly improved the water absorption of the composite membrane. The results of antimicrobial experiments showed that PA improved the antimicrobial activity of the composite membrane against Staphylococcus aureus, Escherichia coli, Aspergillus niger and Penicillium rubens. Among them, 0.3% PA had the best antimicrobial effect against S. aureus, E. coli and A. niger, while 0.7% PA had the best antimicrobial effect against P. rubens. Full article
(This article belongs to the Special Issue Development of Green Membranes)
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Article
The Evaluation of DHPMs as Biotoxic Agents on Pathogen Bacterial Membranes
Membranes 2022, 12(2), 238; https://doi.org/10.3390/membranes12020238 - 18 Feb 2022
Viewed by 373
Abstract
Herein, we present biological studies on 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) obtained via Biginelli reaction catalyzed by NH4Cl under solvent-free conditions. Until now, DHPMs have not been tested for biological activity against pathogenic E. coli strains. We tested 16 newly synthesized DHPMs as antimicrobial agents on [...] Read more.
Herein, we present biological studies on 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) obtained via Biginelli reaction catalyzed by NH4Cl under solvent-free conditions. Until now, DHPMs have not been tested for biological activity against pathogenic E. coli strains. We tested 16 newly synthesized DHPMs as antimicrobial agents on model E. coli strains (K12 and R2–R4). Preliminary cellular studies using MIC and MBC tests and digestion of Fpg after modification of bacterial DNA suggest that these compounds may have greater potential as antibacterial agents than typically used antibiotics, such as ciprofloxacin (ci), bleomycin (b) and cloxacillin (cl). The described compounds are highly specific for pathogenic E. coli strains based on the model strains used and may be engaged in the future as new substitutes for commonly used antibiotics in clinical and nosocomial infections in the pandemic era. Full article
(This article belongs to the Special Issue Biocompatible Membranes for Bone Regeneration)
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Review
TRPV4 and PIEZO Channels Mediate the Mechanosensing of Chondrocytes to the Biomechanical Microenvironment
Membranes 2022, 12(2), 237; https://doi.org/10.3390/membranes12020237 - 18 Feb 2022
Cited by 1 | Viewed by 739
Abstract
Articular cartilage and their chondrocytes are physiologically submitted to diverse types of mechanical cues. Chondrocytes produce and maintain the cartilage by sensing and responding to changing mechanical loads. TRPV4 and PIEZOs, activated by mechanical cues, are important mechanosensing molecules of chondrocytes and have [...] Read more.
Articular cartilage and their chondrocytes are physiologically submitted to diverse types of mechanical cues. Chondrocytes produce and maintain the cartilage by sensing and responding to changing mechanical loads. TRPV4 and PIEZOs, activated by mechanical cues, are important mechanosensing molecules of chondrocytes and have pivotal roles in articular cartilage during health and disease. The objective of this review is to introduce the recent progress indicating that the mechanosensitive ion channels, TRPV4 and PIEZOs, are involved in the chondrocyte sensing of mechanical and inflammatory cues. We present a focus on the important role of TRPV4 and PIEZOs in the mechanotransduction regulating diverse chondrocyte functions in the biomechanical microenvironment. The review synthesizes the most recent advances in our understanding of how mechanical stimuli affect various cellular behaviors and functions through differentially activating TRPV4 and PIEZO ion channels in chondrocyte. Advances in understanding the complex roles of TRPV4/PIEZO-mediated mechanosignaling mechanisms have the potential to recapitulate physiological biomechanical microenvironments and design cell-instructive biomaterials for cartilage tissue engineering. Full article
(This article belongs to the Special Issue Membrane Channel of Cells)
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Review
TiO2–Based Nanofibrous Membranes for Environmental Protection
Membranes 2022, 12(2), 236; https://doi.org/10.3390/membranes12020236 - 18 Feb 2022
Cited by 1 | Viewed by 529
Abstract
Electrospinning is a unique technique that can be used to synthesize polymer and metal oxide nanofibers. In materials science, a very active field is represented by research on electrospun nanofibers. Fibrous membranes present fascinating features, such as a large surface area to volume [...] Read more.
Electrospinning is a unique technique that can be used to synthesize polymer and metal oxide nanofibers. In materials science, a very active field is represented by research on electrospun nanofibers. Fibrous membranes present fascinating features, such as a large surface area to volume ratio, excellent mechanical behavior, and a large surface area, which have many applications. Numerous techniques are available for the nanofiber’s synthesis, but electrospinning is presented as a simple process that allows one to obtain porous membranes containing smooth non-woven nanofibers. Titanium dioxide (TiO2) is the most widely used catalyst in photocatalytic degradation processes, it has advantages such as good photocatalytic activity, excellent chemical stability, low cost and non-toxicity. Thus, titanium dioxide (TiO2) is used in the synthesis of nanofibrous membranes that benefit experimental research by easy recyclability, excellent photocatalytic activity, high specific surface areas, and exhibiting stable hierarchical nanostructures. This article presents the synthesis of fiber membranes through the processes of electrospinning, coaxial electrospinning, electrospinning and electrospraying or electrospinning and precipitation. In addition to the synthesis of membranes, the recent progress of researchers emphasizing the efficiency of nanofiber photocatalytic membranes in removing pollutants from wastewater is also presented. Full article
(This article belongs to the Special Issue Electrospun Nanofiber Membranes: From Synthesis to Applications)
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Article
Recovery of Model Pharmaceutical Compounds from Water and Organic Solutions with Alginate-Based Composite Membranes
Membranes 2022, 12(2), 235; https://doi.org/10.3390/membranes12020235 - 18 Feb 2022
Cited by 1 | Viewed by 420
Abstract
In this work, we combined the non-solvent induced phase separation (NIPS) and further cross-linking by cations towards the preparation of nanofiltration membranes based on sodium alginate, a biodegradable, natural polymer. Acetone, ethanol, toluene, and hexane were used as non-solvents, and cations of calcium, [...] Read more.
In this work, we combined the non-solvent induced phase separation (NIPS) and further cross-linking by cations towards the preparation of nanofiltration membranes based on sodium alginate, a biodegradable, natural polymer. Acetone, ethanol, toluene, and hexane were used as non-solvents, and cations of calcium, silver, and aluminum—for polymer cross-linking, respectively. Results showed the precipitation strength of non-solvent played a noticeable role in the membrane’s performance; for instance, the toluene permeability changed by four orders of magnitude with the decrease of precipitation strength of the non-solvent: acetone (Ptoluene = 0.1 kg∙m−2∙h−1∙bar−1) < ethanol (3 kg∙m−2∙h−1∙bar−1) < hexane (41 kg∙m−2∙h−1∙bar−1) < toluene (415 kg∙m−2∙h−1∙bar−1). It was shown that simultaneous precipitation and crosslinking in aqueous solutions AlCl3 or AgNO3 must be used in the preparation of alginate membranes for the highly selective recovery of pharmaceutical compounds from organic media. These membranes show rejection R = 90–93% of substances with MW = 626 g/mol and ethanol permeability PEtOH = 1.5–2.5 kg∙m−2∙h−1∙bar−1. For the highly selective recovery of pharmaceutical compounds from water, the method of obtaining membranes must be changed. Precipitation in toluene and then crosslinking in aqueous solutions of AlCl3 or AgNO3 must be used sequentially instead of simultaneous precipitation and crosslinking in aqueous solutions of the same inorganic salts. The permeability of such membranes varied from 0.44 to 7.8 kg∙m−2∙h−1∙bar−1 depending on the crosslinking cation in the alginate. The rejection of model substances with MW 350 and 626 g/mol were on the level of 99%. Alginate membranes can be used to solve separation problems in the pharmaceutical field, for example, to isolate antibiotics from their extractants and remove the same antibiotics from aqueous pharmaceutical waste to prevent their accumulation in the environment and the emergence of resistant genes and bacteria. Full article
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Article
Forward Osmosis (FO) Membrane Fouling Mitigation during the Concentration of Cows’ Urine
Membranes 2022, 12(2), 234; https://doi.org/10.3390/membranes12020234 - 18 Feb 2022
Viewed by 383
Abstract
FO membrane fouling mitigation during the concentration of cows’ urine was investigated. In particular, the effects on the permeability recovery of cleaning methods such as membrane washing with deionized (DI) water, osmotic backwash, and chemical cleaning were studied. The characterization of foulants that [...] Read more.
FO membrane fouling mitigation during the concentration of cows’ urine was investigated. In particular, the effects on the permeability recovery of cleaning methods such as membrane washing with deionized (DI) water, osmotic backwash, and chemical cleaning were studied. The characterization of foulants that accumulated on the membrane surface was found to be rich in sugars and proteins. The foulants were effectively removed by de-ionized water circulation (washing) and osmotic backwash. While osmotic back was more effective, it did not fully recover the permeability of the membrane. The foulants absorbed in the membrane pores were found to be mainly composed of sugars. Soaking the membrane in a solution of NaClO enabled the removal of foulants absorbed inside the membrane. It was revealed that soaking in 1% NaClO solution for 30 min achieved the best results (83% permeability recovery), while soaking for a longer time (10 h) using 0.2% NaClO resulted in counterproductive results. Full article
(This article belongs to the Special Issue Forward Osmosis - Membrane Developments and Applications)
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Article
Crown-Ether Functionalized Graphene Oxide Membrane for Lithium Recovery from Water
Membranes 2022, 12(2), 233; https://doi.org/10.3390/membranes12020233 - 18 Feb 2022
Viewed by 519
Abstract
The massive worldwide transition of the transport sector to electric vehicles has dramatically increased the demand for lithium. Lithium recovery by means of ion sieves or supramolecular chemistry has been extensively studied in recent years as a viable alternative approach to the most [...] Read more.
The massive worldwide transition of the transport sector to electric vehicles has dramatically increased the demand for lithium. Lithium recovery by means of ion sieves or supramolecular chemistry has been extensively studied in recent years as a viable alternative approach to the most common extraction processes. Graphene oxide (GO) has also already been proven to be an excellent candidate for water treatment and other membrane related applications. Herein, a nanocomposite 12-crown-4-ether functionalized GO membrane for lithium recovery by means of pressure filtration is proposed. GO flakes were via carbodiimide esterification, then a polymeric binder was added to improve the mechanical properties. The membrane was then obtained and tested on a polymeric support in a dead-end pressure setup under nitrogen gas to speed up the lithium recovery. Morphological and physico-chemical characterizations were carried out using pristine GO and functionalized GO membranes for comparison with the nanocomposite. The lithium selectivity was proven by both the conductance and ICP mass measurements on different sets of feed and stripping solutions filtrated (LiCl/HCl and other chloride salts/HCl). The membrane proposed showed promising properties in low concentrated solutions (7 mgLi/L) with an average lithium uptake of 5 mgLi/g in under half an hour of filtration time. Full article
(This article belongs to the Special Issue Selected Papers from Euromembrane 2021)
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Article
Effect of Temperature on Oil–Water Separations Using Membranes in Horizontal Separators
Membranes 2022, 12(2), 232; https://doi.org/10.3390/membranes12020232 - 17 Feb 2022
Viewed by 463
Abstract
The effect of temperature on oil–water separations is studied in this paper, focusing on the changed penetration velocities of water droplets on the separation membrane in a horizontal separator. A compact numerical scheme is developed based on the phase-field model, and the temperature [...] Read more.
The effect of temperature on oil–water separations is studied in this paper, focusing on the changed penetration velocities of water droplets on the separation membrane in a horizontal separator. A compact numerical scheme is developed based on the phase-field model, and the temperature effect is first theoretically analyzed regarding the key thermodynamic properties that may affect the separation performance. The computational scenario is designed based on practical horizontal separators in the oil field, and the droplet motions in the oil–water two-phase flow are simulated using our scheme under various operation conditions. It was found that a higher temperature may result in a faster penetration of the water droplets, and a larger density difference in the oil–water system is also preferred to accelerate the separation using membranes. Furthermore, increasing the operation temperature is proved to benefit the separation of water and heavy oil. Full article
(This article belongs to the Special Issue Water and Wastewater Treatment Technologies with Membrane Filtration)
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Review
Structures and Dynamics of Dengue Virus Nonstructural Membrane Proteins
Membranes 2022, 12(2), 231; https://doi.org/10.3390/membranes12020231 - 17 Feb 2022
Viewed by 476
Abstract
Dengue virus is an important human pathogen threating people, especially in tropical and sub-tropical regions. The viral genome has one open reading frame and encodes one polyprotein which can be processed into structural and nonstructural (NS) proteins. Four of the seven nonstructural proteins, [...] Read more.
Dengue virus is an important human pathogen threating people, especially in tropical and sub-tropical regions. The viral genome has one open reading frame and encodes one polyprotein which can be processed into structural and nonstructural (NS) proteins. Four of the seven nonstructural proteins, NS2A, NS2B, NS4A and NS4B, are membrane proteins. Unlike NS3 or NS5, these proteins do not harbor any enzymatic activities, but they play important roles in viral replication through interactions with viral or host proteins to regulate important pathways and enzymatic activities. The location of these proteins on the cell membrane and the functional roles in viral replication make them important targets for antiviral development. Indeed, NS4B inhibitors exhibit antiviral activities in different assays. Structural studies of these proteins are hindered due to challenges in crystallization and the dynamic nature of these proteins. In this review, the function and membrane topologies of dengue nonstructural membrane proteins are presented. The roles of solution NMR spectroscopy in elucidating the structure and dynamics of these proteins are introduced. The success in the development of NS4B inhibitors proves that this class of proteins is an attractive target for antiviral development. Full article
(This article belongs to the Special Issue The Structure, Dynamics and Function of Membrane Proteins)
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Communication
Volumetric Scale-Up of a Packed-Bed Ion-Exchange System to Extract Phytate from Thin Stillage
Membranes 2022, 12(2), 230; https://doi.org/10.3390/membranes12020230 - 17 Feb 2022
Viewed by 361
Abstract
Phytate is the main form of phosphorus in corn ethanol coproducts and poses digestion issues in monogastric-animal feed. Extracting phytate as a commodity chemical will bring extra revenue to the corn ethanol industry and reduces potential phosphorus pollution from livestock waste management. We [...] Read more.
Phytate is the main form of phosphorus in corn ethanol coproducts and poses digestion issues in monogastric-animal feed. Extracting phytate as a commodity chemical will bring extra revenue to the corn ethanol industry and reduces potential phosphorus pollution from livestock waste management. We assessed a simplified scale-up approach of an ion-exchange separation system applied to extract phytate from thin stillage using volumetric parameters and simplifications of the van Deemter model. Thin stillage is one of the main byproducts generated on dry-grind corn-to-ethanol plants and accounts for the liquid portion of the bottom product generated in the ethanol distillation process. Thin stillage is rich in dissolved phytate, which served as the basis for an ion-exchange extraction system developed with a scalability factor of 50. Under the evaluated conditions, similar breakthrough profiles were obtained when similar Péclet and Stanton numbers were maintained for the scales studied, demonstrating that a simple and straightforward scale-up can be attained if special attention is given to maintaining both parameters as the basis of calculations of the plate numbers of ion-exchange columns. Full article
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Review
P-Loop Channels: Experimental Structures, and Physics-Based and Neural Networks-Based Models
Membranes 2022, 12(2), 229; https://doi.org/10.3390/membranes12020229 - 16 Feb 2022
Viewed by 597
Abstract
The superfamily of P-loop channels includes potassium, sodium, and calcium channels, as well as TRP channels and ionotropic glutamate receptors. A rapidly increasing number of crystal and cryo-EM structures have revealed conserved and variable elements of the channel structures. Intriguing differences are seen [...] Read more.
The superfamily of P-loop channels includes potassium, sodium, and calcium channels, as well as TRP channels and ionotropic glutamate receptors. A rapidly increasing number of crystal and cryo-EM structures have revealed conserved and variable elements of the channel structures. Intriguing differences are seen in transmembrane helices of channels, which may include π-helical bulges. The bulges reorient residues in the helices and thus strongly affect their intersegment contacts and patterns of ligand-sensing residues. Comparison of the experimental structures suggests that some π-bulges are dynamic: they may appear and disappear upon channel gating and ligand binding. The AlphaFold2 models represent a recent breakthrough in the computational prediction of protein structures. We compared some crystal and cryo-EM structures of P-loop channels with respective AlphaFold2 models. Folding of the regions, which are resolved experimentally, is generally similar to that predicted in the AlphaFold2 models. The models also reproduce some subtle but significant differences between various P-loop channels. However, patterns of π-bulges do not necessarily coincide in the experimental and AlphaFold2 structures. Given the importance of dynamic π-bulges, further studies involving experimental and theoretical approaches are necessary to understand the cause of the discrepancy. Full article
(This article belongs to the Special Issue Membrane Channel of Cells)
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Article
Carbon Nanodots-Embedded Pullulan Nanofibers for Sulfathiazole Removal from Wastewater Streams
Membranes 2022, 12(2), 228; https://doi.org/10.3390/membranes12020228 - 16 Feb 2022
Cited by 1 | Viewed by 606
Abstract
Carbon nanodots (CNDs)-embedded pullulan (PUL) nanofibers were developed and successfully applied for sulfathiazole (STZ) removal from wastewater streams for the first time. The CNDs were incorporated into PUL at 0.0%, 1.0%, 2.0%, and 3.0% (w/w) to produce M1, M2, [...] Read more.
Carbon nanodots (CNDs)-embedded pullulan (PUL) nanofibers were developed and successfully applied for sulfathiazole (STZ) removal from wastewater streams for the first time. The CNDs were incorporated into PUL at 0.0%, 1.0%, 2.0%, and 3.0% (w/w) to produce M1, M2, M3, and M4 nanofibers (PUL-NFs), respectively. The produced PUL-NFs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), thermal gravimetric analysis (TGA) and Differential scanning calorimetry (DSC) and applied for STZ removal from aqueous solutions through pH, kinetics, and equilibrium batch sorption trials. A pH range of 4.0–6.0 was observed to be optimal for maximum STZ removal. Pseudo-second order, intraparticle diffusion, and Elovich models were suitably fitted to kinetics adsorption data (R2 = 0.82–0.99), whereas Dubinin–Radushkevich, Freundlich, and Langmuir isotherms were fitted to equilibrium adsorption data (R2= 0.88–0.99). STZ adsorption capacity of PUL-NFs improved as the amount of embedded CNDs increased. Maximum STZ adsorption capacities of the synthesized PUL-NFs were in the order of: M4 > M3 > M2 > M1 (133.68, 124.27, 93.09, and 35.04 mg g−1, respectively). Lewis acid–base reaction and π-π electron donor–acceptor interactions were the key STZ removal mechanisms under an acidic environment, whereas H-bonding and diffusion were key under a basic environment. Therefore, CNDs-embedded PUL-NFs could be employed as an environmentally friendly, efficient, and non-toxic adsorbent to remove STZ from wastewater streams. Full article
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Review
New Horizons in Structural Biology of Membrane Proteins: Experimental Evaluation of the Role of Conformational Dynamics and Intrinsic Flexibility
Membranes 2022, 12(2), 227; https://doi.org/10.3390/membranes12020227 - 16 Feb 2022
Viewed by 1042
Abstract
A plethora of membrane proteins are found along the cell surface and on the convoluted labyrinth of membranes surrounding organelles. Since the advent of various structural biology techniques, a sub-population of these proteins has become accessible to investigation at near-atomic resolutions. The predominant [...] Read more.
A plethora of membrane proteins are found along the cell surface and on the convoluted labyrinth of membranes surrounding organelles. Since the advent of various structural biology techniques, a sub-population of these proteins has become accessible to investigation at near-atomic resolutions. The predominant bona fide methods for structure solution, X-ray crystallography and cryo-EM, provide high resolution in three-dimensional space at the cost of neglecting protein motions through time. Though structures provide various rigid snapshots, only an amorphous mechanistic understanding can be inferred from interpolations between these different static states. In this review, we discuss various techniques that have been utilized in observing dynamic conformational intermediaries that remain elusive from rigid structures. More specifically we discuss the application of structural techniques such as NMR, cryo-EM and X-ray crystallography in studying protein dynamics along with complementation by conformational trapping by specific binders such as antibodies. We finally showcase the strength of various biophysical techniques including FRET, EPR and computational approaches using a multitude of succinct examples from GPCRs, transporters and ion channels. Full article
(This article belongs to the Special Issue The Structure, Dynamics and Function of Membrane Proteins)
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Editorial
Polymer Inclusion Membranes
Membranes 2022, 12(2), 226; https://doi.org/10.3390/membranes12020226 - 16 Feb 2022
Viewed by 553
Abstract
Polymer inclusion membranes (PIMs) are a kind of membrane in which a carrier is physically trapped within a polymer network usually in, but not restricted to, the presence of a plasticizer [...] Full article
(This article belongs to the Special Issue Polymer Inclusion Membranes)
Article
Hypoxia-Preconditioned Extracellular Vesicles from Mesenchymal Stem Cells Improve Cartilage Repair in Osteoarthritis
Membranes 2022, 12(2), 225; https://doi.org/10.3390/membranes12020225 - 16 Feb 2022
Viewed by 772
Abstract
In the past decade, mesenchymal stem cells (MSCs) have been widely used for the treatment of osteoarthritis (OA), and extracellular vesicles (EVs) may play a major role in the efficacy of this treatment. Hypoxia can change the cargo and biological functions of MSC-derived [...] Read more.
In the past decade, mesenchymal stem cells (MSCs) have been widely used for the treatment of osteoarthritis (OA), and extracellular vesicles (EVs) may play a major role in the efficacy of this treatment. Hypoxia can change the cargo and biological functions of MSC-derived EVs (MSC-EVs). The aim of the present study was to determine whether the effects of hypoxia-preconditioned MSC-EVs on OA cartilage repair are superior to normoxia-preconditioned MSC-EVs. By using in vitro and in vivo OA models, we verified that hypoxia-preconditioned MSC-EVs improved chondrocyte proliferation and migration and suppressed chondrocyte apoptosis to a greater extent than normoxia-preconditioned MSC-EVs. Furthermore, we found that hypoxia altered the microRNA expression in MSC-EVs and identified four differentially expressed microRNAs: hsa-miR-181c-5p, hsa-miR-18a-3p, hsa-miR-376a-5p, and hsa-miR-337-5p. Bioinformatics analysis revealed that hypoxic pretreatment may promote cartilage repair by stimulating chondrocyte proliferation and migration and suppressing chondrocyte apoptosis through the miRNA-18-3P/JAK/STAT or miRNA-181c-5p/MAPK signaling pathway. Therefore, hypoxia-preconditioned EVs may be a novel treatment for OA. Full article
(This article belongs to the Special Issue Cell Membrane Vesicles)
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Article
Preparation of Polyvinylidene Fluoride Nano-Filtration Membranes Modified with Functionalized Graphene Oxide for Textile Dye Removal
Membranes 2022, 12(2), 224; https://doi.org/10.3390/membranes12020224 - 15 Feb 2022
Cited by 3 | Viewed by 616
Abstract
Water scarcity has become one of the most significant problems globally. Membrane technology has gained considerable attention in water treatment technologies. Polymeric nanocomposite membranes are based on several properties, with enhanced water flux, high hydrophilicity and anti-biofouling behavior, improving the membrane performance, flexibility, [...] Read more.
Water scarcity has become one of the most significant problems globally. Membrane technology has gained considerable attention in water treatment technologies. Polymeric nanocomposite membranes are based on several properties, with enhanced water flux, high hydrophilicity and anti-biofouling behavior, improving the membrane performance, flexibility, cost-effectiveness and excellent separation properties. In this study, aminated graphene oxide (NH2-GO)-based PVDF membranes were fabricated using a phase-inversion method for textile dye removal. These fabricated membranes showed the highest water flux at about 170.2 (J/L.h−1.m−2) and 98.2% BSA rejection. Moreover, these membranes removed about 96.6% and 88.5% of methylene blue and methyl orange, respectively. Aminated graphene oxide-based polyvinylidene fluoride (PVDF) membranes emerge as a good membrane material that enhances the membrane performance. Full article
(This article belongs to the Special Issue Mixed-Matrix Membranes and Polymeric Membranes)
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Article
Reuse of Water in Laundry Applications with Micro- and Ultrafiltration Ceramic Membrane
Membranes 2022, 12(2), 223; https://doi.org/10.3390/membranes12020223 - 15 Feb 2022
Cited by 1 | Viewed by 641
Abstract
This study compares the performance of a microfiltration membrane, made by silicon carbide (SiC) and an ultrafiltration membrane, made by zirconia (ZrO2), in the treatment of wastewater from a washing machine designed to clean industrial tents. The filtration of deionized water, [...] Read more.
This study compares the performance of a microfiltration membrane, made by silicon carbide (SiC) and an ultrafiltration membrane, made by zirconia (ZrO2), in the treatment of wastewater from a washing machine designed to clean industrial tents. The filtration of deionized water, containing model microplastics (i.e., nylon fiber), was performed. This was followed by the filtration of real wastewater from a single washing cycle of industrial tents, made from polyvinyl chloride (PVC) textile. The filtration parameters of the membranes and physical-chemical parameters of the wastewater, including the concentration of microplastics in the shape of tent fibers (PVC), were calculated before and after filtration. The microfiltration membrane manifested a greater decrease in permeability (95%) compared to the ultrafiltration membrane (37%). The resulting water quality in terms of Total Solids, turbidity, and microplastics concentration was better for the ultrafiltration. This is evident from 99.2% versus 98.55% removal efficiency of microplastics from the laundering wastewater, respectively. Full article
(This article belongs to the Special Issue Troubleshooting of Membrane Processes in Real Operation)
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Article
Collective Enhancements on Thermal-Electrical and Mechanical Properties of Graphite-Based Composite Bipolar Plates through the Coupled Manipulations of Molding and Impregnation Pressures
Membranes 2022, 12(2), 222; https://doi.org/10.3390/membranes12020222 - 15 Feb 2022
Viewed by 548
Abstract
The performance and durability of proton exchange fuel cells (PEMFCs) are greatly affected by the bipolar plate (BP). In this paper, the thermal and electrical conductivities and mechanical property of graphite filled with resin composite BPs were collectively enhanced through the effectively coupled [...] Read more.
The performance and durability of proton exchange fuel cells (PEMFCs) are greatly affected by the bipolar plate (BP). In this paper, the thermal and electrical conductivities and mechanical property of graphite filled with resin composite BPs were collectively enhanced through the effectively coupled manipulations of molding pressure and impregnation pressure. The microstructures show that the resin tends to distribute at the top region of the rib under high impregnation pressure. The thermal and electrical conductivities of the pure expanded graphite BP is well reserved in the composite BPs under high molding pressure, which can facilitate the heat transfer and electron conduction in the PEMFCs. The relative density and compressive strength of composite BPs were greatly enhanced by the impregnation of resin compared to the expanded graphite under high molding pressure without the impregnation of resin (HU-BP). The maximum thermal conductivity, compressive strength, and minimum interfacial contact resistance (ICR) are collectively achieved in the HL-BP. The enhanced thermal-electrical and mechanical properties could be mainly attributed to the well-reserved continuous networks of graphite in the composite BPs. The findings in this paper are expected to synergetically improve the thermal, electrical, and mechanical properties of composite BPs through coupled manipulations of the molding and impregnation pressures, which in turn enhances the power density and durability of PEMFCs. Full article
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Editorial
Special Issue “Biomembranes and Biomimetic Membranes—From Model Analysis to ‘In Vivo’ Study”
Membranes 2022, 12(2), 221; https://doi.org/10.3390/membranes12020221 - 14 Feb 2022
Viewed by 483
Abstract
Membrane processes are one of the key factors influencing the function of living cells [...] Full article
Article
Dielectric Properties of Aqueous Electrolyte Solutions Confined in Silica Nanopore: Molecular Simulation vs. Continuum-Based Models
Membranes 2022, 12(2), 220; https://doi.org/10.3390/membranes12020220 - 14 Feb 2022
Viewed by 489
Abstract
Dielectric behavior of electrolyte aqueous solutions with various concentrations in a cylindrical nanopore of MCM 41 silica has been investigated. The effect of confinement is investigated by using isothermal-isosurface-isobaric statistical ensemble, which has proved to be an effective alternative to the Grand Canonical [...] Read more.
Dielectric behavior of electrolyte aqueous solutions with various concentrations in a cylindrical nanopore of MCM 41 silica has been investigated. The effect of confinement is investigated by using isothermal-isosurface-isobaric statistical ensemble, which has proved to be an effective alternative to the Grand Canonical Monte Carlo (GCMC) simulation method. Several single-salt solutions have been considered (e.g., NaCl, NaI, BaCl2, MgCl2) in order to investigate the effect of ion polarizability, ion size, and ion charge. The effect of salt concentration has also been addressed by considering NaCl solutions at different concentrations (i.e., 0.1 mol/L, 0.5 mol/L, and 1 mol/L). The motivation in performing this integrated set of simulations is to provide deep insight into the dielectric exclusion in NF theory that plays a significant role in separation processes. It was shown that the dielectric constant increased when ions were added to water inside the nanopore (with respect to the dielectric constant of confined pure water) unlike what was obtained in the bulk phase and this phenomenon was even more pronounced for electrolytes with divalent ions (MgCl2 and BaCl2). Therefore, our simulations indicate opposite effects of ions on the dielectric constant of free (bulk) and nanoconfined aqueous solutions. Full article
(This article belongs to the Special Issue Liquid Transport and Membrane Behavior at High Pressures)
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Article
Radiographic Evaluation of Regeneration Strategies for the Treatment of Advanced Mandibular Furcation Defects: A Retrospective Study
Membranes 2022, 12(2), 219; https://doi.org/10.3390/membranes12020219 - 14 Feb 2022
Cited by 1 | Viewed by 602
Abstract
Teeth with furcation involvement (FI) present a higher risk of loss and are difficult to maintain. This study evaluated the efficacy of furcation defect regeneration (FDR) as a regeneration strategy. Pre-operative and 6-month postoperative radiographs were collected from patients receiving regeneration therapy for [...] Read more.
Teeth with furcation involvement (FI) present a higher risk of loss and are difficult to maintain. This study evaluated the efficacy of furcation defect regeneration (FDR) as a regeneration strategy. Pre-operative and 6-month postoperative radiographs were collected from patients receiving regeneration therapy for mandibular teeth with degree II and early degree III FI. The linear furcation involvement (LFI), ratio of LFI (RLI), LFI and RLI adjusted bythe alveolar bone crest (ABC), and radiographic intensity were assessed. The effects of demographic characteristics, regeneration treatment strategies, the relationship between furcation and ABC, and adjacent intrabony defect regeneration (AIDR) were evaluated using a generalized linear model and logistic regression. The results demonstrated that 1.5 mm adjusted LFI and 40% adjusted RLI were achieved in both pure furcation defects and combined furcation–angular defects by the combination of bone replacement grafts (BRG) and enamel matrix derivatives (EMD) or collagen membrane (CM); deproteinized bovine bone matrix (DBBM) showed a superior outcome among BRG. In combined furcation–angular defects, EMD appeared more beneficial than CM, and AIDR significantly promoted adjusted LFI and RLI. In conclusion, DBBM with EMD or CM was effective for FDR, and AIDR had a positive effect on FDR in the combined furcation–angular defect. Full article
(This article belongs to the Special Issue Membranes for Tissue Engineering and Clinical Applications)
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