Single-layer Membrane Research Articles

Optimal Design of Sound Insulation Frequency Band of Local Resonance Membrane Material

In order to broaden the sound insulation frequency band of local resonance membrane materials, established an acoustic-vibration coupling model of multilayer membrane materials, based on the derived analytical solutions of the coupling equations. Simulate the sound insulation performance of the designed single-layer membrane materials with four different mass structures. Then combine different membrane materials to analyse the changes in the sound insulation frequency band. Calculations proves that: (1) The four single-layer membrane structures have a maximum TL peak of 40.08dB and the frequency of the smallest TL peak is at 204.56Hz in the frequency range of 100-1000Hz.(2) Combination of two same structures will significantly increase the sound insulation at the sound insulation peak;(3) The combination of single-layer membrane with different structures can broaden the sound insulation frequency band and enhance the sound insulation performance.

Thermal ripples in bilayer graphene

We study thermal fluctuations of freestanding bilayer graphene subject to vanishing external tension. Within a phenomenological theory, the system is described as a stack of two continuum crystalline membranes, characterized by finite elastic moduli and a nonzero bending rigidity. A nonlinear rotationally invariant model guided by elasticity theory is developed to describe interlayer interactions. After neglection of in-plane phonon nonlinearities and anharmonic interactions involving interlayer shear and compression modes, an effective theory for soft flexural fluctuations of the bilayer is constructed. The resulting model, neglecting anisotropic interactions, has the same form of a well-known effective theory for out-of-plane fluctuations in a single-layer membrane, but with a strongly wave-vector-dependent bare bending rigidity. Focusing on AB-stacked bilayer graphene, parameters governing interlayer interactions in the theory are derived by first-principles calculations. Statistical-mechanical properties of interacting flexural fluctuations are then calculated by a numerical iterative solution of field-theory integral equations within the self-consistent screening approximation. The bare bending rigidity in the considered model exhibits a crossover between a long-wavelength regime governed by in-plane elastic stress and a short wavelength region controlled by monolayer curvature stiffness. Interactions between flexural fluctuations drive a further crossover between a harmonic and a strong-coupling regime, characterized by anomalous scale invariance. The overlap and interplay between these two crossover behaviors is analyzed at varying temperatures.

Centimeter-scale gas-sieving nanoporous single-layer graphene membrane

High-permeance, molecular-sieving, nanoporous single-layer graphene (NSLG) membranes are highly promising for gas separation. However, the formation of cracks during the transfer of NSLG to a low-cost porous support is difficult to avoid. These cracks are detrimental to gas selectivity, and therefore, make the scale-up of the gas-sieving NSLG membranes challenging. To mitigate the crack formation on low-cost macroporous supports, herein, we demonstrate mechanical reinforcement of the graphene film with a two-layer composite carbon film. The bottom layer of the composite film is a 100-nm-thick block-copolymer film derived nanoporous carbon (NPC) film with a pore size of 20–30 nm. This layer makes an intimate contact with NSLG and prevents generation of crack. However, the NPC film by itself is not robust enough to cover the rough surface of low-cost macroporous supports and tends to generate occasional cracks. This is prevented by spin-coating a 500-nm-thick multi-walled carbon nanotube (MWNT) film, hosting pore size of 200–300 nm, on top of the NPC film. This imparts enough mechanical strength to NSLG/NPC film to be successfully suspended on a low-cost, macroporous, nonwoven metal wire mesh on a centimeter-scale while completely avoiding cracks. As a result, H2/CH4 and H2/CO2 selectivities of 11–23 and 5–8, respectively, higher than the corresponding Knudsen selectivities of 2.8 and 4.7, respectively, are obtained from the centimeter-scale NSLG membranes. The reinforced membranes are mechanically robust and can successfully withstand transmembrane pressure difference of 4 bar. When the MWNT film is directly coated on NSLG without using the intermediate NPC layer, the gas sieving behavior is not observed, likely due to the development of nanoscale cracks. This underlines the crucial role of the hierarchical pore structure in the composite carbon film in realizing the gas-sieving graphene membranes.

A reusable, isoporous through-hole membrane filter for airborne particulate matter removal

This work introduces a new cleanable (and thus reusable) membrane air filter. The membrane filters were fabricated using a soft-lithographic technique, and they are isoporous having through-hole pores. The soft-lithographic technique can be applied to the fabrication of the membranes on various supporting structures such as meshes, or even on freestanding isoporous membranes in an additive fashion leading to bi- or tri-layered membranes. When freestanding single layer membrane filters are used for the removal of PM2.5 contained in the air stream, isoporous through-hole membranes show 60–80% (depending on pore size) filtration efficiency with low pressure drop (less than 40 Pa), which is quite contrary to the common belief that the filtration mechanism would be size sieving. Using a bi-layer configurations of 800 nm isopore membrane layers on top of 5, 10, or 25 μm membranes, these filters’ removal efficiency is >96%, but with a bit high (200–300 Pa) pressure drop. To mitigate the trade-off between efficiency and pressure drop in single and bi-layer isoporous membrane filters, multiple 5 μm-pore membranes with a varying separation gap of 3–15 mm have shown an efficiency of up to 98% with pressure a drop of less than 100 Pa. The main filtration mechanisms, inertial impaction and interception, were identified based on experimental data and finite element analysis. Importantly, the membrane filters can easily be cleaned by wiping with wet tissue or by spraying them with water/ethanol (9:1) mixture, which enables many subsequent re-uses. In addition, the thermoset nature of the membrane material shows high temperature stability, exhibiting ~5% shrinkage at 350 °C and ~15% shrinkage at 400 °C. The membrane can also endure very low temperatures (−80 °C via dry ice), which makes the operating temperature range of the membranes very wide. Due to their simple soft-lithographic fabrication process and their good efficiency and reasonable pressure drop, the isoporous through-hole membrane filters described here present compelling alternative to more conventional filters used for the removal of airborne particulate contaminants.

Beneficial utilization of Al/Si/O-rich solid wastes for environment-oriented ceramic membranes

Wide application of traditional multilayer ceramic membrane has been severely restricted by high costs associated with rare membrane materials and high sintering temperature. In this study, typical solid wastes (coal fly ash, river sediment and sewage sludge) were adopted as raw materials to provide an Al-Si-O matrix for single-layer ceramic membranes. Phase identification shows anorthite as major crystalline phase, while bulk density and pore characteristics of the membranes varied with different raw material compositions, with flexural strengths of 40.82–71.46 MPa, and average pore size of 0.23 μm, 0.28 μm, 0.32 μm and 0.84 μm. When the membranes were applied in an oily water treatment, the oil rejection reached >98 % when using any of the four membranes with oil/water emulsion permeate flux remaining at ∼1200 L/m2·h. Furthermore, the stability of ceramic membranes in harsh environmental conditions was confirmed, with negligible weight loss ratios after being corroded in acidic/alkalic media. In addition, more than 95 % of original flux can be achieved even after six cycles, which confirmed the excellent recyclability of the membranes. The successful fabrication and application of the environment-oriented single layer ceramic membranes from the Al-Si-O solid waste matrix provided a promising “waste-to-resource” strategy for beneficial utilization of typical solid wastes as ceramic raw materials.

Label-free chlorine and nitrogen-doped fluorescent carbon dots for target imaging of lysosomes in living cells.

Lysosomes with a single-layered membrane structure are mainly involved in the scavenging of foreign substances and play an important role in maintaining normal physiological functions of living cells. In this work, near-neutrally charged fluorescent carbon dots (CDs) were preparedwith lipophilicity through a facile one-pot hydrothermal carbonization of chloranil and triethylenetetramine at 160°C for 3h. The as-obtained CDs are proved to have good photostability, low cost, and excellent biocompatibility. Importantly, the as-prepared CDs with high quantum yield of 30.8% show excitation-dependent emission with great stability, and thus, they can be well used for the long-term target imaging of lysosomes in living cells without further modification. Meanwhile, the CDs can quickly enter into the lysosomes within 30min, and the green fluorescence (FL) of CDs reaches the plateau when incubated for 60min. By comparing the fluorescent intensity, the information aboutdistribution and amount of lysosomes in different cells can be obtained. Theproposed CD-based strategy demonstrates great promise for label-free target imaging of lysosomes in living cells. Graphical abstract The near-neutral carbon dots (CDs) with lipophilicity are used as label-free fluorescent nanoprobes for the long-term imaging of lysosomes in living cells.

Hydrogen-sieving single-layer graphene membranes obtained by crystallographic and morphological optimization of catalytic copper foil

Gas separation membranes based on single-layer-graphene are highly attractive because the size of graphene nanopores can be tuned to separate gases by the size-sieving mechanism. A prerequisite for this, the synthesis of high-quality polycrystalline single-layer graphene film by chemical vapor deposition (CVD), is extremely crucial. The quality of graphene in the context of membranes is reflected by the size and the density of the intrinsic vacancy defects, and is affected by the catalytic metal substrate and the CVD environment. Generally, expensive high-purity Cu foil is used to obtain gas-sieving performance from single-layer graphene. For the eventual scale-up of graphene membranes, it is highly attractive to use low-cost Cu foils, however, as we show here, these Cu foils are rough and graphene membranes derived from these foils do not yield gas-sieving performance. Herein, we conduct a systematic high-temperature annealing study on two separate, commercial, low-cost Cu foils leading to their transformation to Cu(111). The annealing process smoothened the Cu surface, decreasing the root mean square (RMS) surface roughness from over 200 nm to close to 100 nm. The RMS roughness on the individual Cu step, measured using the scanning tunneling microscopy (STM), was only 0.23 nm. The smooth, oriented Cu grains yielded single-layer graphene with a significantly lower defect density with ID/IG ratio decreasing from 0.18 ± 0.02 to 0.04 ± 0.01. Finally, single-layer graphene films, synthesized on the annealed low-purity Cu foil, yielded H2-selective membranes with H2 permeance reaching 1000 gas permeation units (GPU) in combination with attractive H2/CH4 and H2/C3H8 selectivities of 13 and 26, respectively.

Production and characterization of alginate bilayer membranes for releasing simvastatin to treat wounds.

This study aims to produce and characterize alginate bilayer membranes composed of single membranes with varying cross-linking degrees to modulate simvastatin release, with potential to be used for wound-dressing. The single-layer and bilayer membranes were characterized by weight, thickness, surface pH, equilibrium-humidity, swelling degree, solubility, infrared spectroscopy (attenuated total reflectance Fourier-transform infrared), scanning electron microscopy, and water vapor transmission. Simvastatin diffusion and release rates were analyzed using Franz's cells; its indirect cytotoxicity was analyzed using human keratinocyte cells. The difference in the cross-linking degree (bottom and top layers) influenced the morphology of the membrane, and consequently its physical barrier properties. An in vitro release study demonstrated that the bilayer membrane could sustain drug-release for longer time as compared to the single-layer membrane, which could be potentially beneficial for long-term treatment of chronic wounds. A cell viability assay showed that simvastatin-loaded alginate membranes could be characterized as noncytotoxic, demonstrating their potential for use in wound-dressing applications.

Ultrathin single and multiple layer electrospun fibrous membranes of polycaprolactone and polysaccharides

Electrospinning was used to produce fibrous membranes, in single and multiple layers, from poly(ε-caprolactone), pullulan, and from mixtures of poly(ε-caprolactone) with potato modified starch and β-glucan. It was possible to obtain single-layer membranes from solutions of pullulan in water, poly(ε-caprolactone) in chloroform, and from mixtures of poly(ε-caprolactone)/β-glucan and poly(ε-caprolactone)/potato modified starch in chloroform. Scanning electron microscopy images showed the formation of ultrathin homogeneous fibers from electrospun poly(ε-caprolactone) and pullulan, whereas the fibers obtained from mixtures of poly(ε-caprolactone)/ β -glucan and poly(ε-caprolactone)/potato modified starch had different sizes and morphologies, as well as irregular microstructures, characterized by the presence of beads. Contact angle analyses showed that pullulan membranes were extremely hydrophilic, while poly(ε-caprolactone) membranes were predominantly hydrophobic. Subsequently, poly(ε-caprolactone)-pullulan-poly(ε-caprolactone) multilayer membranes, with intermediate wettability, were prepared by successive electrospinning steps. Infrared spectroscopy and calorimetric analyses showed the presence of both polymers and the absence of changes in their structure and stability due to electrospinning, indicating adequate compatibility between the two polymers. We foresee that the polyester-polysaccharide multilayer membrane might be used as a biodegradable vehicle for active agents with different hydrophobicity, with applications as food packaging and biocompatible scaffold materials.

Single-layer BSA-NH<sub>2</sub>/PNIPAAm membrane with modulated lipase biocatalytic reaction

Biocatalysis, utilizing enzymes or live microbial cultures to catalyze or speed up specific or cascade reactions, has broad applications in the manufacturing of fine chemicals, pharmaceuticals, and agrochemical intermediates. However, how to effectively adjust the biocatalytic process and the dose of enzymes during the reaction becomes one intriguing issue to be addressed. Smart porous membranes are desirable candidates for regulating substance permeability, which provides the possibility to adjust the biocatalysis. Herein, inspired by the temperature-sensitive stomatal size of plant leaves, we prepare a free-standing single-layer membrane through the self-assembly at oil-water interface, which is composed of thermosensitive amphiphilic protein-polymer conjugates, i.e., BSA-NH2/PNIPAAm (poly(N-isopropylacrylamide)). The membrane thickness is only about 4 nm, with a wide range of molecular cut-offs by tuning the molecular weight of PNIPAAm. Moreover, by virtue of the property of PNIPAAm, the pore size of the membrane could be tunable by changing temperature, through which the catalytic reaction of triglyceride by lipase was successfully controlled. Taken together, this work not only provides a simple method for preparing single-layer protein hybrid membranes, but also offers great potential applications in the controlled biocatalysis, smart gating systems and molecular separation.

Layer-by-layer assembly of bio-inspired borate/graphene oxide membranes for dye removal

Dye wastewater is harmful to the ecological environment because of its potential biological toxicity, teratogenicity, carcinogenicity, and mutagenicity. We fabricated a layered graphene oxide (GO) membrane through layer-by-layer (LBL) self-assembly. We used borate to crosslink with GO on a polyethyleneimine (PEI)-coated hydrolyzed polyacrylonitrile (hPAN) support. Fourier transform infrared (FTIR) spectrometry, Raman spectra, and x-ray photoelectron spectroscopy (XPS) confirmed the presence of a crosslinking reaction. The dynamic thermomechanical analysis (DMA) results indicated that the introduction of borate can significantly improve the mechanical properties of the membrane. The Young’s modulus, ultimate tensile strength, and proportional limit of borate that was assembled twice as the outermost layer were increased by 110.81%, 62.37%, and 53.72%, respectively, as compared to those of a single-layered GO membrane. Moreover, the pure water fluxes of the layered GO membrane did not obviously decrease with an increase in the number of layers. The flux of the membrane with an outermost layer of borate was greater than that of the previous GO layer. The salt and dye rejection of the membranes was augmented with an increase in the number of layers. For the GO membrane assembled three times, rejection to methyl orange (MO), methylene blue (MB), NaCl, MgCl2, and MgSO4 reached 74.02%, 88.56%, 14.55%, 27.50%, and 41.95%, respectively. The use of borate as an inorganic crosslinker can avoid the environmental pollution caused by organic agents, and improve the mechanical properties as well as the filter capability of the layered GO membrane. Therefore, this study presents a novel method of membrane preparation for dye removal.

An Integrative Dual-Layer Poly-L-Lactic Acid Fibrous Membrane Prevents Peritendinous Adhesions.

Anti-adhesion membranes are prospective scaffolds for preventing peritendinous adhesion after injury. However, currently available scaffolds have some limitations, such as low efficacy for anti-adhesion, low quality of tendon healing, and unknown drug interactions. Thus, in this study, we designed an innovative structure involving an integrated dual-layer poly(L-lactic acid) (PLLA) electrospun membrane for preventing peritendonous adhesion by promoting tendon gliding. We investigated the surface morphology and wettability of the fiber scaffold. The adhesion and proliferation of fibroblasts were low on the PLLA fibrous membrane. Compared with single-layer membranes, the dual-layer PLLA fiber scaffold reduced adhesion to the tissues. The gliding space persisted until recovery in chicken extensor flexor tendons in vivo. Thus, this innovative PLLA membrane scaffold could prevent adhesion and promote gliding to facilitate tendon healing.

Water desalination performance of h-BN and optimized charged graphene membranes

Water desalination using pressure-driven flow in hexagonal boron nitride (h-BN) and charged nanoporous graphene membranes are investigated using molecular dynamics (MD) simulations. Nanoporous h-BN membranes with pore diameters of 10.1 A, 12.2 A, and 14.7 A were selected to compare with the desalination performance of uncharged nanoporous graphene membranes with similar pore diameters. Salt rejection efficiency of uncharged graphene membranes is superior to that of h-BN, and the pressure drop for both materials exhibits the same inverse-cubic dependence on the pore diameter, regardless of the hydrophobic versus hydrophilic nature of graphene and h-BN, respectively. Charged graphene membranes with pore diameters of 15.9 A, 18.9 A, and 20.2 A were also considered, and 15.9 A pore diameter with total fixed charge of 12e was found to be the optimum setting for single-layer graphene membrane, resulting in 100% and 98% rejection efficiencies for Na+ and Cl− ions, respectively. The corresponding pressure drop is 51.8% lower than that obtained with 9.9 A pore diameter uncharged graphene with 100% salt rejection. To maintain perfect salt removal, 15.9 A pore diameter charged bilayer graphene membranes with 12e total charge on the first layer, and − 1e on the second one was simulated at different separation distances between the two membranes. The associated pressure drop is 35.7% lower than that obtained in 9.9 A pore diameter uncharged base-line case. These findings confirm the potential application of using charged bilayer nanoporous graphene membranes in improving the performance of reverse osmosis desalination systems.

Improving CO2/CH4 and O2/N2 separation by using surface-modified polysulfone hollow fiber membranes

Membrane technology for industrial gas separation was begun in the 1980s and has shown significant advantages over conventional techniques such as cryogenic distillation and solvent absorption in terms of energy consumption and operational cost. The main objective of this work is to develop a simple yet effective coating technique to modify the surface properties of polysulfone (PSF) hollow fiber membranes for enhanced separation of CO2/CH4 and O2/N2. The hollow fiber membranes made of different polymer concentration (15–35 wt%) were coated with different materials (polydimethylsiloxane (PDMS) or polyether-block-amide (Pebax) or PDMS followed by Pebax) through a simple dip-coating method before subjecting to pure gases testing and instrumental characterization. Results showed that the multilayer coated membranes exhibited better performance compared to the single-layer PDMS-coated and single-layer Pebax-coated membranes. It is also found that the Pebax concentration could affect the performance of the multilayer coated membranes in which the gas permeance decreased while its selectivity decreased with increasing Pebax concentration from 1 to 3 wt.%. Further increase in Pebax concentration from 3 to 9 wt% however negatively affected selectivities as high Pebax concentration tended to cover the membrane surface with tighter polymer chain packing which led to lower free volume. Experimental results also showed that the optimized multilayer coated membrane (3 wt.% Pebax) could achieve the highest gas pair selectivity, recording 34.28 and 6.65 for CO2/CH4 and O2/N2 separation, respectively. As a comparison, the membrane coated with 1 wt% Pebax only showed selectivity of 29.47 and 6.07, respectively. The findings of this work demonstrated that multilayered coating could be performed on the outer layer of hollow fiber membranes and is not limited to the flat sheet membranes as previously reported in the literature, provided a good combination of two coating solutions were used.

Power generation by reverse electrodialysis in a single-layer nanoporous membrane made from core-rim polycyclic aromatic hydrocarbons.

Nanoporous graphene and related atomically thin layered materials are promising candidates in reverse electrodialysis research owing to their remarkable ionic conductivity and high permselectivity. The synthesis of atomically thin nanoporous membranes with a narrow pore size distribution, however, remains challenging. Here, we report the fabrication of nanoporous carbon membranes via the thermal crosslinking of core-rim structured monomers, that is, polycyclic aromatic hydrocarbons. The mechanically robust, centimetre-sized membrane has a pore size of 3.6 ± 1.8 nm and a thickness of 2.0 ± 0.5 nm. When applied to reverse electrodialysis, the nanoporous carbon membrane offers a high short-circuit current with an output power density of 67 W m-2, which is about two orders of magnitude beyond that of the classic ion-exchange membranes and current prototype nanoporous membranes reported in the literature. Crosslinked and atomically thin porous polycyclic aromatic hydrocarbon membranes therefore represent new scaffolds that will revolutionize the rapidly developing fields of sustainable energy and membrane technology.

Control of Sequential MTO Reactions through an MFI-Type Zeolite Membrane Contactor.

A membrane for controlling methanol-to-olefin (MTO) reactions was developed, which featured an MFI-type zeolite membrane (Si/Al = 25) that was synthesized on a porous α-alumina substrate using a secondary growth method. Here, the H2/SF6 permeance ratios were between 150 and 450. The methanol conversion rate was 70% with 38% ethylene selectivity and 28% propylene selectivity as determined using a cross-flow membrane contactor. In order to improve the olefin selectivity of the membrane, the MFI zeolite layer (Si/Al = ∞) was coated on an MFI-type zeolite membrane (Si/Al = 25). Using this two-layered membrane system, the olefin selectivity value increased to 85%; this was 19% higher than the value obtained during the single-layer membrane system.

Thin film composite polyesteramide nanofiltration membranes fabricated from carboxylated chitosan and trimesoyl chloride

Thin film composite polyesteramide nanofiltration membranes were fabricated with interfacial polymerization from carboxylated chitosan and trimesoyl chloride on a microporous polysulfone support membrane. Salt rejection was improved by building a multiple-layer structure that was formed by sequentially repeating the cycles of the interfacial reactions. The chemical structure, surface morphology and charge were characterized for the polyesteramide top layer. The effects of the concentrations of the reactant solutions and the number of cycles of reactant depositions and reactions on the separation performance were investigated. The single-layer polyesteramide membrane produced from 3.5 wt% carboxylated chitosan and 0.7 wt% TMC has a negatively charged surface and shows favorable separation performance: pure water permeation flux of 7.3 L/(m2 h) at 0.6 MPa gauge feed pressure, and salt rejection of 95.0% for Na2SO4, 65.7% for MgSO4, 33.2% for MgCl2 and 66.3% for NaCl. The multiple-layer polyesteramide membranes show a more negatively charged surface and higher salt rejection than the single-layer polyesteramide membranes. The single-layer polyesteramide membrane PS-[(C-CS)1.0/TMC] with a relatively loose structure shows good retention for the reactive black 5 anionic dye. This study opens an interesting research area to explore a new type of thin film composite nanofiltration membrane.

Retention of organics and degradation of micropollutants in municipal wastewater using impregnated ceramics

Pesticides, personal care products, industrial chemicals often pollute surface- and groundwater sources. With trace concentrations and low molecular weights, these micropollutants (MPs) easily penetrate through treatment systems and impose a real health threat on drinking water consumers. The absence of a dedicated MP-retaining treatment technology at water treatment plants results in a constant consumption of MP-contaminated water. Advanced oxidation processes, and in particular the Fenton reaction, can successfully degrade MPs if other, larger, fractions of organics are retained. Here, we suggest a novel combined two-stage retention–degradation approach. Ceramic membranes retain large organics such as bovine serum albumin (BSA). Fenton processes disintegrate nonretained MPs such as methylene blue (MB) and bisphenol A (BPA) that penetrate through the membrane. The efficiency of the suggested approach is high. Single-layered ultrafiltration membrane retains more than 96% BSA and degrades 40–50% of MB and BPA. The degree of degradation depends on both the impregnated metal oxide and the concentration of hydrogen peroxide. Vanadium-based catalysts retain more than 90% MPs but leach into permeate. Ferric oxides were the only stable catalysts that performed better in membranes than when impregnated on α-Al2O3 pellets. A combined retention–degradation can be optimized to result in superior degree of retention. Catalytic ceramic membranes can retain large organic molecules and decompose MPs simultaneously. Three parameters affect the process efficiency: the dynamics of the influent fluid, the catalyst dose and the contact time.Graphic abstract

The effect of chemical functional groups and salt concentration on performance of single-layer graphene membrane in water desalination process: A molecular dynamics simulation study

In this study, the mechanisms of passing water and salt ions through nanoporous single-layer graphene membrane are simulated using classical molecular dynamics. The effects of functional groups placed in nanopores and feed water's salt concentration on water desalination are investigated. In order to understand the role of functional groups in desalination process, Methyl, Ethyl and a combination of Fluorine and Hydrogen molecules are distributed around the nanopores. In all cases, different number of functional molecules is employed in order to find an optimum distribution of the groups at hand. The results show that an appropriate distribution of Alkyl groups can properly stop the salt ions from passing through the graphene, where the flow rate of water molecules is sufficient. Moreover, the investigation of graphene membrane's performance in different salt concentrations reveals that with increase in salt concentration of feed water, the water flow rate falls and the number of salt ions on the other side of the membrane increases.

A Case of Fibrolipoma of the Hard Palate

An extremely rare case of fibrolipoma in the hard palate is presented and discussed with reference to the literature. An 85-year-old woman visited the Tokyo Dental College Chiba hospital in September 2016 with the chief complaint of a mass in the hard palate. The patient had first become aware of this mass several years earlier. An examination at another hospital in June 2009 resulted in a clinical diagnosis of lipoma. Regular examinations followed every 6 months until September 2014, at which time she stopped attending these appointments because there was no change. In August 2016, however, the patient realized that the tumor was increasing in size. Although there was no pain, awareness of a foreign body in the oral cavity when eating or talking was increasing, so she decided to visit our clinic for detailed examination and treatment. At this point, the mass extended from the center to the left side of the hard palate. It measured 15 mm along the major axis, and had a clear border; nearly spherical, its surface was smooth and glossy, and was of a slightly yellowish color. The mass was painless, elastic, and soft. Computed tomography and magnetic resonance imaging revealed a tumorous lesion. Based on a clinical diagnosis of lipoma, it was subsequently excised under general anesthesia in January 2017. The tumor lay under the palatal mucosa, extending from the center to the left side of the hard palate. It was surrounded by a single-layered membranous structure, and had not adhered to the surrounding tissues. Healthy palatal mucosa and periosteum were also removed en bloc with the tumor within a safety margin of approximately 5 mm. No pressure absorption of palatine bone was seen. Histopathologically, proliferation of mature adipose tissue was observed. This was surrounded by a thin, single-layer membrane within the subepithelial connective tissue, which was covered by stratified squamous epithelium. Proliferation of fibrotic connective tissue was seen between the adipocytes. The final diagnosis was fibrolipoma. To date, at 18 months postoperatively, no recurrence has been observed and progress has been satisfactory.