Wavy Membrane Research Articles

Performance characteristics on up-scaling vacuum membrane distillation modules

Large-scale CFD studies are currently lacking in membrane distillation due to high computational overhead. This study utilizes a validated CFD model for vacuum membrane distillation and reduces the order of the model to enable prototype scale simulations. Different module designs were considered: a baseline flat sheet membrane module, a spacer-filled channel, a wavy channel, and a wavy channel with embedded stiffeners. Different lengths (330 mm, 660 mm, and 990 mm) were studied to simulate lab to prototype upscaling. Large Eddy Simulations were run in the laminar (Re 900) and turbulent (Re 3600) flow regimes. For Re 900, cases with geometric alterations (wavy membrane, spacer-filled channel) locally outperformed the baseline case within the first 330 mm before axial temperature polarization equilibrated the performance between the baseline and altered channels. The improvement in local performance was seen over the whole 990 mm length at Re 3600, culminating in a 35–40 % flux improvement versus the baseline at Re 3600 versus a 0–35 % difference at Re 900. Axial temperature polarization was mitigated using heat injection, showing a 5 % flux drop as length tripled compared to a 20–27 % decline. Higher operational Reynolds numbers should be considered cautiously for increasing pressure drop and violating the liquid entry pressure limit for wetting.

Quantification of Curvature Sensing Behavior of Curvature-Inducing Proteins on Model Wavy Substrates.

Curvature-inducing proteins are involved in a variety of membrane remodeling processes in the cell. Several in vitro experiments have quantified the curvature sensing behavior of these proteins in model lipid systems. One such system consists of a membrane bilayer laid atop a wavy substrate (Hsieh in Langmuir 28:12838-12843, 2012). In these experiments, the bilayer conforms to the wavy substrate, and curvature-inducing proteins show preferential segregation on the wavy membrane. Using a mesoscale computational membrane model based on the Helfrich Hamiltonian, here we present a study which analyzes the curvature sensing characteristics of this membrane-protein system, and elucidates key physical principles governing protein segregation on thewavy substrate and other in vitro systems. In this article we compute the local protein densities from the free energy landscape associated with membrane remodeling by curvature-inducing proteins. In specific, we use the Widom insertion technique to compute the free energy landscape for an inhomogeneous system with spatially varying density and the results obtained with this minimal model show excellent agreement with experimental studies that demonstrate the association between membrane curvature and local protein density. The free energy-based framework employed in this study can be used for different membrane morphologies and varied protein characteristics to gain mechanistic insights into protein sorting on membranes.

A wavy flow channel system for membrane fouling control in oil/water emulsion filtration

The membrane-based process is attractive for the treatment of oil/water emulsion because of its effectiveness in handling micron size oil droplets. However, membrane fouling due to the strong oil droplets/membrane surface interplay remains its major challenge that limits its widespread application. This study reports a new approach for membrane fouling control via a wavy flow channel to enhance the effective area and improve the local mixing. The hydraulic performance of a membrane was used to assess the effectiveness of the system against the traditional straight flow for oil/water emulsion treatment. Results show that the wavy flow channel offers two main advantages: increasing the membrane effective surface area and facilitate swirling flows that effectively promote fouling control. The wavy flow channel showed up to ~58% higher permeability (of 219.1 ± 5.8 L.m−2.hr−1.bar−1) than the reference, in which 18% was due to the enhanced flow property. The energy loss due to additional shear stress and longer flow path only contributed to a 7% additional pressure drop. The energy to overcome the pressure drop was insignificant to the specific energy consumption, which showed that the wavy membrane offered 21% energy saving (0.015 vs 0.019 kWh/m3). This study opens an option in improving membrane filtration performances via a simple module-scale modification suitable for fouling prone pressure-driven membrane systems.

Detailed morphological analysis of axolotl sperm

The axolotl has extraordinary regeneration capacity compared to other vertebrates. This remarkable potential has been attributed to its life-long neoteny, characterized by the exhibition of embryonic characteristics at the adult stage. A recent study provided a detailed morphological analysis of the sperm morphology of the Ambystoma mexicanum using routine and detailed histological techniques. The primary purpose of the present study is to describe a simple and inexpensive method for evaluating the morphology of axolotl sperm. In this study, spermatophore structures were collected and spread on slides and air-dried. The slides were stained with periodic acid Schiff, toluidine blue, Masson’s trichrome, Giemsa, Spermac, and Diff-Quik dye for a morphological examination. The slides were coated with gold/palladium for a scanning electron microscopy examination. The sperm of the axolotl consisted of an elongated head, a neck, and a flagellum covered with an undulating membrane. The lengths of the midpiece, tail, and head were 8.575 µm, 356.544 µm, and 103.661 µm, respectively. In the flagellum part, the wavy membrane structure, whose function has not been explained, surrounds the tail. The data obtained from this study will constitute an important step in designing future research on the reproductive and regeneration capacity of the axolotl.

Investigation of dehumidification performance and flow characteristics of wavy vacuum membrane-based dehumidification modules

This work investigates the dehumidification performance of vacuum membrane-based dehumidification with difference wavy membranes. Firstly, this paper constructs four different models of wavy membrane support layers, and proposes their explicit functions. In addition, the accuracy of different turbulence models under wavy boundary condition are compared. Using the verified turbulence model, this paper studies the dehumidification performance of four wavy membrane-based dehumidification modules. Finally, according to the details of flow field, the mechanism behind these dehumidification phenomena are discussed. Results indicate that low-Reynolds number k–ε turbulence model has a higher accuracy than other models in wavy boundary. Wavy membrane does not always increase the dehumidification efficiency, even if it can always increase dehumidification area. When waviness is in the range of 0∼0.06, the dehumidification effect of four wavy membranes are weaker than that of flat membrane, and the flow resistance of four wavy membranes are higher than that of flat membrane. Vertical velocity induced by wavy membrane is the key factor to enhancing dehumidification performance, and a steeper wavy membrane shape at the tail of backflow is beneficial to dehumidification. This work demonstrates the basic dehumidification mechanism of wavy membrane and can provide suggestions for diversified development of vacuum membrane-based dehumidification module.

3D Printed Fouling-Resistant Composite Membranes.

Fouling remains a long-standing unsolved problem that hinders the widespread use of membrane applications in industry. This article reports the use of numerical simulations coupled with extensive material synthesis and characterization to fabricate fouling-resistant 3D printed composite membranes. The membranes consist of a thin polyethersulfone selective layer deposited onto a 3D printed flat and double sinusoidal (wavy) support. Fouling and cleaning of the composite membranes were tested by using bovine serum albumin solution in a cross-flow ultrafiltration setup. The transmembrane pressure was regulated at 1 bar and the cross-flow Reynolds number (Re) varied between 400 and 1000. In comparison to the flat membrane, the wavy membrane showed superior performance in terms of pure water permeance (PWP) (10% higher) and permeance recovery ratio (87% vs 53%) after the first filtration cycle at Re = 1000. Prolong testing showed that the wavy membrane could retain approximately 87% of its initial PWP after 10 complete filtration cycles. This impressive fouling-resistant behavior is attributed to the localized fluid turbulence induced by the 3D printed wavy structure. These results show that not only the lifetime of membrane operations could be favorably extended but also the operational costs and environmental damage of membrane-based processes could also be significantly reduced.

3D printed composite membranes with enhanced anti-fouling behaviour

The fabrication of three dimensional (3D) printed composite membranes by depositing a thin polyethersulfone (PES) selective layer onto ABS-like 3D printed flat and wavy structured supports is presented here for the first time. The 50 mm disk supports were printed using an industrial 3D printer with both flat and double sinusoidal, i.e. wavy, surface structures. The thin selective layers were deposited onto the 3D supports via vacuum filtration. The resulting flat and wavy composite membranes were characterised and tested in terms of permeance, rejection, and cleanability by filtering oil-in-water emulsions of 0.3−0.5 vol% through a cross-flow (Reynolds number, Re = 100, 500 and 1000) ultrafiltration set-up under a constant transmembrane pressure of 1 bar. Results showed that pure water permeance through the wavy membrane was 30% higher than the flat membrane for Re = 1000. The wavy 3D printed membrane had a 52% higher permeance recovery ratio compared to the flat one after the first filtration cycle, with both membranes having an oil rejection of 96% ± 3%. The wavy 3D composite membrane maintained some level of permeation after 5 complete filtration cycles using only water as the cleaning/rinsing agent, whereas the flat one was completely fouled after the first cycle. Cleaning with NaOCl after the sixth cycle restored ~70% of the initial permeance for the wavy membrane. These results demonstrate that 3D printed wavy composite membranes can be used to significantly improve permeation and cleanability performance, particularly in terms of reducing fouling build-up, i.e. the main obstacle limiting more widespread adoption of membranes in industrial applications.

Curvature Sorting of Peripheral Proteins on Solid-Supported Wavy Membranes

Cellular membrane deformation and the associated redistribution of membrane-bound proteins are important aspects of membrane function. Current model membrane approaches for studying curvature sensing are limited to positive curvatures and often require complex and delicate experimental setups. To overcome these challenges, we fabricated a wavy substrate by imposing a range of curvatures onto an adhering lipid bilayer membrane. We examined the curvature sorting of several peripheral proteins binding to the wavy membrane and observed them to partition into distinct regions of curvature. Furthermore, single-molecule imaging experiments suggested that the curvature sensing of proteins on low-curvature substrates requires cooperative interactions.

Self-Assembly of Amphiphilic Liquid Crystal Polymers Obtained from a Cyclopropane-1,1-Dicarboxylate Bearing a Cholesteryl Mesogen

We study the self-assembly of a new family of amphiphilic liquid crystal (LC) copolymers synthesized by the anionic ring-opening polymerization of a new cholesterol-based LC monomer, 4-(cholesteryl)butyl ethyl cyclopropane-1,1-dicarboxylate. Using the t-BuP(4) phosphazene base and thiophenol or a poly(ethylene glycol) (PEG) functionalized with thiol group to generate in situ the initiator during the polymerization, LC homopolymer and amphiphilic copolymers with narrow molecular weight distributions were obtained. The self-assemblies of the LC monomer, homopolymer, and block copolymers in bulk and in solution were studied by small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and transmission electron microscopy (TEM). All polymers exhibit in bulk an interdigitated smectic A (SmA(d)) phase with a lamellar period of 4.6 nm. The amphiphilic copolymers self-organize in solution into vesicles with wavy membrane and nanoribbons with twisted and folded structures, depending on concentration and size of LC hydrophobic block. These new morphologies will help the comprehension of the fascinating organization of thermotropic mesophase in lyotropic structures.

Preparation of the Hydroxyapatite/Collagen Three-Dimensional Scaffold from its Membrane

Effect of osteogenic activities of MG63 on the HAp/Col membrane was examined at day 10 and 14 by reverse-transcript and real-time polymerase chain reactions. Osteogenic activities of MG63 were upregulated by culture them on the HAp/Col membrane in comparison to those on tissue culture polystyrene. The novel three-dimensional HAp/Col scaffold was prepared from the HAp/Col wavy membrane. The cylindrical HAp/Col scaffold was successfully prepared and indicated at least 2.5-times higher compressive strength and Young's modulus compared to the previous HAp/Col composites. The novel scaffold could be useful for regenerative medicine.

Electro-osmotically induced convection at a permselective membrane

The paper is concerned with convection at an ion exchange electrodialysis membrane induced by nonequilibrium electro-osmosis in the course of concentration polarization under the passage of electric current through the membrane. Derivation of nonequilibrium electro-osmotic slip condition is recapitulated along with the linear stability analysis of quiescent electrodiffusion through a flat ion exchange membrane. Results of numerical calculation for nonlinear steady state convection, developing from the respective instability, are reported along with those for a slightly wavy membrane. Besides these results, we report those of time dependent calculations for periodic and chaotic oscillations, resulting from instability of the respective steady state flows, and also the results of recent experiments with modified membranes. These latter rule in favor of electro-osmotic versus bulk electroconvective origin of overlimiting conductance through ion exchange membranes.

Spatially periodic membrane-membrane contact through surface wave growth

Membrane-membrane contact is a requirement for membrane fusion. We present evidence here that interfacial instability occurs during the agglutination of erythrocytes by polylysine and suggest that interfacial instability may be involved in achieving membrane contact in some cases of fusion. An interface is stable if after a small disturbance it returns to its initial form. The disturbance may originate from vibration outside the system, or from thermal motion. Any perturbation of an interface may be described by a sum of simple periodic sine disturbances. If all the simple disturbances die out so will the general one and the system will be stable. If any sine disturbances grow the system is unstable. The wavelength with the fastest growth rate dominates the instability growth. This growth will lead to either (i) a new steady state with a deformed but intact interface or (ii) the break up of the interface to form membrane vesicles (Coakley & Deeley, 1980). When two cells come close to each other intermembrane forces become important. Such forces include attractive van der Waal forces and repulsive electrostatic, hydration and steric forces. All of these forces increase in magnitude with decreasing membrane seperation (Gallez et al., 1984). A small disturbance of the thin aqueous layer between the cells will grow only if the net attractive force on the membranes is sufficient to drive the surface wave against bending and capillarity forces. Evidence for the growth of such a surface wave on erythrocytes agglutinated by polylysine is now presented. Human erythrocytes were incubated with polylysine of molecular mass range 4-220 kDa and concentration range 0.5-2000 pg/ml at 37°C. Light micrographs (Fig. la and lb) of erythrocytes exposed to polylysine show a mosaic pattern within a small aggregate of cells. The pattern only occurs in the region of overlap of cells (Fig. 1 b). Transmission electron microscopy (Fig. Ic) clearly shows a wavy membrane with regular arrays of contact regions in cell aggregates. The regularly pitted regions in the selected scanning electron micrograph of Fig. l ( d ) (where the pitted pattern contrasts with the surrounding smooth membrane which is typical of scanning electron micrographs of agglutinates) arose from the break up of an agglutinate on handling during, or after, fixation. The average wavelength of the surface waves was 0.83pm (Coakley et al., 1985). In other work (Fricke 8z Sackmann, 1984) the spontaneous fluctuation of the thickness of erythrocytes in suspension (cell flickering) has been attributed to the development of overdamped surface waves on the cell. The calculated value of the fundamental frequency of cell flicker is 0.59 pm (Brochard & Lennon, 1975). Agglutination occurs only in cell samples whose electrophoretic mobility is significantly altered by the polycation (Katchalsky et al., 1959; Coakley et al., 1985). Modern interpretations of electrophoretic mobility data imply that polycation protrusion from the glycocalyx is a requirement for aggregation. In the absence of polylysine surface wave growth is suppressed by steric and electrostatic repulsive forces of the two glycocalyxs. When polylysine is present cross-linking of the two glycocalyxs by protruding polycation introduces a new destabilizing attractive force and allows surface wave growth. During Fig. 1 . Micrographs of erythrocytes exposed to 20pgcglml polylysine of molecular mass 14 kDa, at 37°C

Fine structure of the spermatozoon of Proteocephalus longicollis (Cestoda proteocephalidea)

The spermatozoon of the proteocephalid cestode Proteocephalus longicollis (Zeder, 1800) is a very elongate, thread-shaped cell, about 300 μ m long and 0, 1 - 0, 9 pm in diameter, with no differentiation into head, midpiece and tail.The spermatozoon body (Figs. A-K) consists of: (a) two axonemes of the unique “9+1“ pattern, (b) an elongate nucleus, (c) numerous electron-dense, glycogen-like granules of different sizes and shapes and (d) cortical, cytoplasmic microtubules associated with the limiting plasma membrane. The total lack of acrosome and mitochondria is a remarkable and unusual finding which seems to be characteristic for all cestode spermatozoa examined so far.The nucleus of the spermatozoon, narrow and rod-shaped in its anterior part, becomes progressively enlarged and flattened toward the posterior end. The nuclear envelope is relatively thick and composed of two wavy membranes (Figs. G and H). The nucleoplasm is very loose and consists of fine filaments and granules of chromatin.

A pox virus of the army cutworm

A pox virus was isolated from a field-collected larva of the army cutworm, Euxoa auxiliaris. Death of diseased larvae usually occurred 16–18 days after infection when from 1 to 1.5 million polyhedral inclusion bodies per milligram of larval tissue were recovered. The primary site of viral replication appeared to be the cytoplasm of fat body cells; limited infection occurred in the tracheal matrix and gut musculature. Within the fat body, oval immature virions bounded by double membranes were observed budding from viroplasms. After further maturation but before they were occluded in a protein matrix, these virions contained brick-shaped cores. Mature virions, which measured 165 × 260 nm and were loosely bounded by a wavy membrane, were occluded in polyhedra that averaged 3.7 × 4.7 μ.

The ultrastructure of wheat leaves I. Changes due to natural senescence and the effects of kinetin and ABA on detached leaves incubated in the dark

Detached wheat leaves incubated in water in darkness rapidly lose starch and are ultrastructurally degenerate by 5 days. Chloroplast ribosomes disappear before cytoplasmic ribosomes and groups of wavy membranes can be detected in both mature and degenerating chloroplasts. Large lipid bodies appear in the cytoplasm and vacuole during senescence, and osmiophilic fibrils and deposits develop in the microbodies. Treatment with kinetin via the transpiration stream markedly delays the loss of starch and maintains, but does not increase, chloroplast and cytoplasmic ribosome populations. ABA accelerates degenerative changes as compared with the water treated control leaves but does not induce any specific ultrastructural effects.

Fine structure of neuroblastoma--a case report.

Ultrastructural observation was carried out on neuroblastoma cells in a 4‐year‐old girl. The nuclei of these neoplastic cells were irregular with occasional cytoplasmic invaginations, and proportionally large with diffusely dispersed chromatin substance. Rare mitotic figures were also present. The cell‐to‐cell interfaces were relatively simple with only finely wavy membranes but without interdigitations. A few desmosomes were, however, apparent. The cytoplasmic pseudopodes were frequently observed in a limited area of the cell surface and nearly free of organelles. The main findings of the intracytoplasmic organelles consisted of some mitochondrial changes, poor development of Golgi bodies, occasional formation of focal cytoplasmic degradation, and intracytoplasmic Abrillar aggregates. Numerous large round to oval dense bodies encircled by a double membrane were highly suggestive of lipid bodies. The central area of rosette‐like cell aggregates was noted to be composed of cytoplasmic processes of neoplastic cells.

Phagotrophy and two new structures in the malaria parasite Plasmodium berghei.

Blood collected from rats infected with Plasmodium berghei was centrifuged and the pellet was fixed for 1 hour in 1 per cent buffered OsO(4) with 4.9 per cent sucrose. The material was embedded in n-butyl methacrylate and the resulting blocks sectioned for electron microscopy. The parasites were found to contain, in almost all sections, oval bodies of the same density and structure as the host cytoplasm. Continuity between these bodies and the host cytoplasm was found in a number of electron micrographs, showing that the bodies are formed by invagination of the double plasma membrane of the parasite. In this way the host cell is incorporated by phagotrophy into food vacuoles within the parasite. Hematin, the residue of hemoglobin digestion, was never observed inside the food vacuole but in small vesicles lying around it and sometimes connected with it. The vesicles are pinched off from the food vacuole proper and are the site of hemoglobin digestion. The active double limiting membrane is responsible not only for the formation of food vacuoles but also for the presence of two new structures. One is composed of two to six concentric double wavy membranes originating from the plasma membrane. Since no typical mitochondria were found in P. berghei, it is assumed that the concentric structure performs mitochondrial functions. The other structure appears as a sausage-shaped vacuole surrounded by two membranes of the same thickness, density, and spacing as the limiting membrane of the body. The cytoplasm of the parasite is rich in vesicles of endoplasmic reticulum and Palade's small particles. Its nucleus is of low density and encased in a double membrane. The host cells (reticulocytes) have mitochondria with numerous cristae mitochondriales. In many infected and intact reticulocytes ferritin was found in vacuoles, mitochondria, canaliculi, or scattered in the cytoplasm.