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1.
Nature ; 579(7798): 229-232, 2020 03.
Artículo en Inglés | MEDLINE | ID: mdl-32161387

RESUMEN

Despite being only one-atom thick, defect-free graphene is considered to be completely impermeable to all gases and liquids1-10. This conclusion is based on theory3-8 and supported by experiments1,9,10 that could not detect gas permeation through micrometre-size membranes within a detection limit of 105 to 106 atoms per second. Here, using small monocrystalline containers tightly sealed with graphene, we show that defect-free graphene is impermeable with an accuracy of eight to nine orders of magnitude higher than in the previous experiments. We are capable of discerning (but did not observe) permeation of just a few helium atoms per hour, and this detection limit is also valid for all other gases tested (neon, nitrogen, oxygen, argon, krypton and xenon), except for hydrogen. Hydrogen shows noticeable permeation, even though its molecule is larger than helium and should experience a higher energy barrier. This puzzling observation is attributed to a two-stage process that involves dissociation of molecular hydrogen at catalytically active graphene ripples, followed by adsorbed atoms flipping to the other side of the graphene sheet with a relatively low activation energy of about 1.0 electronvolt, a value close to that previously reported for proton transport11,12. Our work provides a key reference for the impermeability of two-dimensional materials and is important from a fundamental perspective and for their potential applications.

2.
Nat Commun ; 11(1): 1097, 2020 02 27.
Artículo en Inglés | MEDLINE | ID: mdl-32107369

RESUMEN

Manipulating the surface energy, and thereby the wetting properties of solids, has promise for various physical, chemical, biological and industrial processes. Typically, this is achieved by either chemical modification or by controlling the hierarchical structures of surfaces. Here we report a phenomenon whereby the wetting properties of vermiculite laminates are controlled by the hydrated cations on the surface and in the interlamellar space. We find that vermiculite laminates can be tuned from superhydrophilic to hydrophobic simply by exchanging the cations; hydrophilicity decreases with increasing cation hydration free energy, except for lithium. The lithium-exchanged vermiculite laminate is found to provide a superhydrophilic surface due to its anomalous hydrated structure at the vermiculite surface. Building on these findings, we demonstrate the potential application of superhydrophilic lithium exchanged vermiculite as a thin coating layer on microfiltration membranes to resist fouling, and thus, we address a major challenge for oil-water separation technology.

3.
Nature ; 559(7713): 236-240, 2018 07.
Artículo en Inglés | MEDLINE | ID: mdl-29995867

RESUMEN

Controlled transport of water molecules through membranes and capillaries is important in areas as diverse as water purification and healthcare technologies1-7. Previous attempts to control water permeation through membranes (mainly polymeric ones) have concentrated on modulating the structure of the membrane and the physicochemical properties of its surface by varying the pH, temperature or ionic strength3,8. Electrical control over water transport is an attractive alternative; however, theory and simulations9-14 have often yielded conflicting results, from freezing of water molecules to melting of ice14-16 under an applied electric field. Here we report electrically controlled water permeation through micrometre-thick graphene oxide membranes17-21. Such membranes have previously been shown to exhibit ultrafast permeation of water17,22 and molecular sieving properties18,21, with the potential for industrial-scale production. To achieve electrical control over water permeation, we create conductive filaments in the graphene oxide membranes via controllable electrical breakdown. The electric field that concentrates around these current-carrying filaments ionizes water molecules inside graphene capillaries within the graphene oxide membranes, which impedes water transport. We thus demonstrate precise control of water permeation, from ultrafast permeation to complete blocking. Our work opens up an avenue for developing smart membrane technologies for artificial biological systems, tissue engineering and filtration.

4.
Indian J Nephrol ; 28(1): 28-34, 2018.
Artículo en Inglés | MEDLINE | ID: mdl-29515298

RESUMEN

Suspicion and subsequent detection of renal disease is by an assessment of the urinalysis and renal function in the clinical context. Our attempt in this study is to correlate initial presenting features of urinalysis and renal function to the final histopathological diagnosis. A retrospective analysis of 1059 native kidney biopsies performed from January 2002 to June 2015 at Amrita Institute of Medical Sciences was conducted. Correlative patterns between urinalysis, renal function, and final histopathological diagnosis were studied. Five hundred and eleven (48%) patients had nephrotic syndrome. Out of these, 193 (38%) had pure: nephrotic syndrome, 181 (35.8%) had associated microhematuria, 110 (21.7%) had microhematuria and renal failure, and 27 (5.3%) had only associated renal failure. Minimal change disease (MCD) (30%), membranous nephropathy (30%), and IgA nephropathy (29%) were the major diseases in the respective groups. Five hundred and five (47.6%) patients had subnephrotic proteinuria. Out of these, 29 (5.6%) had only subnephrotic proteinuria, 134 (27%) had additional microhematuria, 300 (59%) had subnephrotic proteinuria, microhematuria, and renal failure, and 42 (8%) had subnephrotic proteinuria with renal failure. Lupus Nephritis (45% and 40%) and IgA Nephropathy (32% and 21%) were the major disorders in the subgroups respectively. Forty-two patients (3.7%) were biopsied for isolated renal failure with bland urinary sediment. Cast nephropathy and acute interstitial nephritis were the major diseases. Out of 89 patients with diabetes who were biopsied, 15 (16.8%) had diabetic nephropathy, 45 (50.5%) had no diabetic nephropathy, and 29 (32.5%) had diabetic nephropathy along with a non-diabetic renal disease. Postinfectious glomerulonephritis was the major glomerular disease. IgA nephropathy (22.2%) and membranous nephropathy (15.5%) were the major diseases in patients with diabetes with no diabetic nephropathy. In our population, MCD and membranous nephropathy formed the majority of diseases in biopsied nephrotic syndrome. Added microhematuria did not seem to decrease the incidence of either disease on the whole. We found a significant number of patients with membranous nephropathy with nephrotic syndrome, microhematuria, and additional renal failure. IgA nephropathy formed a majority of cases with nephrotic syndrome, microhematuria, and renal failure. The presence of renal failure regardless of other abnormalities in urinalysis showed a trend toward IgA nephropathy. Membranous nephropathy may have a more varied presentation than was originally thought and IgA nephropathy presenting as nephrotic syndrome may not be uncommon. MCD is the major subgroup of diseases in the pediatric population and presents both as nephrotic syndrome as well as nephrotic syndrome with microhematuria. Thus, urinalysis and renal failure may be a valuable tool in assessing renal disease.

5.
Nat Mater ; 16(12): 1198-1202, 2017 12.
Artículo en Inglés | MEDLINE | ID: mdl-29170556

RESUMEN

Graphene oxide (GO) membranes continue to attract intense interest due to their unique molecular sieving properties combined with fast permeation. However, their use is limited to aqueous solutions because GO membranes appear impermeable to organic solvents, a phenomenon not yet fully understood. Here, we report efficient and fast filtration of organic solutions through GO laminates containing smooth two-dimensional (2D) capillaries made from large (10-20 µm) flakes. Without modification of sieving characteristics, these membranes can be made exceptionally thin, down to ∼10 nm, which translates into fast water and organic solvent permeation. We attribute organic solvent permeation and sieving properties to randomly distributed pinholes interconnected by short graphene channels with a width of 1 nm. With increasing membrane thickness, organic solvent permeation rates decay exponentially but water continues to permeate quickly, in agreement with previous reports. The potential of ultrathin GO laminates for organic solvent nanofiltration is demonstrated by showing >99.9% rejection of small molecular weight organic dyes dissolved in methanol. Our work significantly expands possibilities for the use of GO membranes in purification and filtration technologies.

6.
Science ; 358(6362): 511-513, 2017 10 27.
Artículo en Inglés | MEDLINE | ID: mdl-29074772

RESUMEN

In the field of nanofluidics, it has been an ultimate but seemingly distant goal to controllably fabricate capillaries with dimensions approaching the size of small ions and water molecules. We report ion transport through ultimately narrow slits that are fabricated by effectively removing a single atomic plane from a bulk crystal. The atomically flat angstrom-scale slits exhibit little surface charge, allowing elucidation of the role of steric effects. We find that ions with hydrated diameters larger than the slit size can still permeate through, albeit with reduced mobility. The confinement also leads to a notable asymmetry between anions and cations of the same diameter. Our results provide a platform for studying the effects of angstrom-scale confinement, which is important for the development of nanofluidics, molecular separation, and other nanoscale technologies.

7.
Crit Rev Ther Drug Carrier Syst ; 34(3): 185-208, 2017.
Artículo en Inglés | MEDLINE | ID: mdl-28845759

RESUMEN

There have been remarkable improvements in our understanding of cancer biology. However, therapeutic improvements, with a few exceptions, have been minimal. Also, significant challenges remain in translating fundamental discoveries in cancer biology and genetics into effective drugs and cures. Traditional two-dimensional monolayer cell cultures lack predictive value, resulting in a >90% failure rate of compounds in clinical trials. A developing cancer is a symbiotic tissue consisting of cancer cells, including cancer stem cells (CSCs), and cohabitating with the components of its environment to form a tumor microenvironment (TME) niche. Throughout the process of tumorigenesis, ubiquitous autocrine and paracrine signaling between the cellular and noncellular components of the TME dictates the milieu and structure of this niche. Arising out of such interactions are the cancer cell's phenotypic characteristics, such as stemness, epithelial mesenchymal transformation (EMT), and drug resistance which in turn greatly affect the response of these cells to drug therapy. For these reasons, in order to delineate the mechanism of tumorigenesis and in the process discover drugs that will have greatest impact on tumor growth, it becomes imperative to study the cancer cell in context of its microenvironment. In the present review, we enumerate the advantages of three- and four-dimensional (3D and 4D) cell cultures and describe the various cell culture platforms that are being used to study tumorigenesis in vitro. These culture systems will not only aid in the study of tumor progression complexities in a cost-effective and rapid manner; they also are expected to facilitate the discovery and delivery of therapeutic regimens that will have more success making it to the clinic.


Asunto(s)
Descubrimiento de Drogas , Antineoplásicos , Humanos , Células Madre Neoplásicas , Microambiente Tumoral
8.
Nat Commun ; 8: 15844, 2017 06 16.
Artículo en Inglés | MEDLINE | ID: mdl-28621311

RESUMEN

Van der Waals (vdW) interaction between two-dimensional crystals (2D) can trap substances in high pressurized (of order 1 GPa) on nanobubbles. Increasing the adhesion between the 2D crystals further enhances the pressure and can lead to a phase transition of the trapped material. We found that the shape of the nanobubble can depend critically on the properties of the trapped substance. In the absence of any residual strain in the top 2D crystal, flat nanobubbles can be formed by trapped long hydrocarbons (that is, hexadecane). For large nanobubbles with radius 130 nm, our atomic force microscopy measurements show nanobubbles filled with hydrocarbons (water) have a cylindrical symmetry (asymmetric) shape which is in good agreement with our molecular dynamics simulations. This study provides insights into the effects of the specific material and the vdW pressure on the microscopic details of graphene bubbles.

9.
Nat Commun ; 7: 12168, 2016 07 07.
Artículo en Inglés | MEDLINE | ID: mdl-27385262

RESUMEN

Van der Waals assembly of two-dimensional crystals continue attract intense interest due to the prospect of designing novel materials with on-demand properties. One of the unique features of this technology is the possibility of trapping molecules between two-dimensional crystals. The trapped molecules are predicted to experience pressures as high as 1 GPa. Here we report measurements of this interfacial pressure by capturing pressure-sensitive molecules and studying their structural and conformational changes. Pressures of 1.2±0.3 GPa are found using Raman spectrometry for molecular layers of 1-nm in thickness. We further show that this pressure can induce chemical reactions, and several trapped salts are found to react with water at room temperature, leading to two-dimensional crystals of the corresponding oxides. This pressure and its effect should be taken into account in studies of van der Waals heterostructures and can also be exploited to modify materials confined at the atomic interfaces.

10.
Sci Rep ; 6: 23254, 2016 Mar 16.
Artículo en Inglés | MEDLINE | ID: mdl-26979564

RESUMEN

Despite graphene's long list of exceptional electronic properties and many theoretical predictions regarding the possibility of superconductivity in graphene, its direct and unambiguous experimental observation has not been achieved. We searched for superconductivity in weakly interacting, metal decorated graphene crystals assembled into so-called graphene laminates, consisting of well separated and electronically decoupled graphene crystallites. We report robust superconductivity in all Ca-doped graphene laminates. They become superconducting at temperatures (Tc) between ≈4 and ≈6 K, with Tc's strongly dependent on the confinement of the Ca layer and the induced charge carrier concentration in graphene. We find that Ca is the only dopant that induces superconductivity in graphene laminates above 1.8 K among several dopants used in our experiments, such as potassium, caesium and lithium. By revealing the tunability of the superconducting response through doping and confinement of the metal layer, our work shows that achieving superconductivity in free-standing, metal decorated monolayer graphene is conditional on an optimum confinement of the metal layer and sufficient doping, thereby bringing its experimental realization within grasp.

11.
ACS Nano ; 9(12): 12004-10, 2015 Dec 22.
Artículo en Inglés | MEDLINE | ID: mdl-26516987

RESUMEN

We report the dynamics of photoinduced carriers in a free-standing MoS2 laminate consisting of a few layers (1-6 layers) using time-resolved optical pump-terahertz probe spectroscopy. Upon photoexcitation with the 800 nm pump pulse, the terahertz conductivity increases due to absorption by the photoinduced charge carriers. The relaxation of the non-equilibrium carriers shows fast as well as slow decay channels, analyzed using a rate equation model incorporating defect-assisted Auger scattering of photoexcited electrons, holes, and excitons. The fast relaxation time occurs due to the capture of electrons and holes by defects via Auger processes, resulting in nonradiative recombination. The slower relaxation arises since the excitons are bound to the defects, preventing the defect-assisted Auger recombination of the electrons and the holes. Our results provide a comprehensive understanding of the non-equilibrium carrier kinetics in a system of unscreened Coulomb interactions, where defect-assisted Auger processes dominate and should be applicable to other 2D systems.

12.
Opt Express ; 23(2): 1265-75, 2015 Jan 26.
Artículo en Inglés | MEDLINE | ID: mdl-25835885

RESUMEN

The dense packing of two dimensional flakes by van der Waals forces has enabled the creation of new metamaterials with desirable optical properties. Here we assemble graphene oxide sheets into a three dimensional metamaterial using a microfluidic technique and confirm their ordering via measurements of ellipsometric parameters, polarized optical microscopy, polarized transmission spectroscopy, infrared spectroscopy and scanning electron microscopy. We show that the produced metamaterials demonstrate strong in-plane optical anisotropy (Δn≈0.3 at n≈1.5-1.8) combined with low absorption (k<0.1) and compare them with as-synthesized samples of graphene oxide paper. Our results pave the way for engineered birefringent metamaterials on the basis of two dimensional atomic crystals including graphene and its derivatives.

13.
Nature ; 519(7544): 443-5, 2015 Mar 26.
Artículo en Inglés | MEDLINE | ID: mdl-25810206

RESUMEN

Bulk water exists in many forms, including liquid, vapour and numerous crystalline and amorphous phases of ice, with hexagonal ice being responsible for the fascinating variety of snowflakes. Much less noticeable but equally ubiquitous is water adsorbed at interfaces and confined in microscopic pores. Such low-dimensional water determines aspects of various phenomena in materials science, geology, biology, tribology and nanotechnology. Theory suggests many possible phases for adsorbed and confined water, but it has proved challenging to assess its crystal structure experimentally. Here we report high-resolution electron microscopy imaging of water locked between two graphene sheets, an archetypal example of hydrophobic confinement. The observations show that the nanoconfined water at room temperature forms 'square ice'--a phase having symmetry qualitatively different from the conventional tetrahedral geometry of hydrogen bonding between water molecules. Square ice has a high packing density with a lattice constant of 2.83 Å and can assemble in bilayer and trilayer crystallites. Molecular dynamics simulations indicate that square ice should be present inside hydrophobic nanochannels independently of their exact atomic nature.

14.
Nature ; 516(7530): 227-30, 2014 Dec 11.
Artículo en Inglés | MEDLINE | ID: mdl-25470058

RESUMEN

Graphene is increasingly explored as a possible platform for developing novel separation technologies. This interest has arisen because it is a maximally thin membrane that, once perforated with atomic accuracy, may allow ultrafast and highly selective sieving of gases, liquids, dissolved ions and other species of interest. However, a perfect graphene monolayer is impermeable to all atoms and molecules under ambient conditions: even hydrogen, the smallest of atoms, is expected to take billions of years to penetrate graphene's dense electronic cloud. Only accelerated atoms possess the kinetic energy required to do this. The same behaviour might reasonably be expected in the case of other atomically thin crystals. Here we report transport and mass spectroscopy measurements which establish that monolayers of graphene and hexagonal boron nitride (hBN) are highly permeable to thermal protons under ambient conditions, whereas no proton transport is detected for thicker crystals such as monolayer molybdenum disulphide, bilayer graphene or multilayer hBN. Protons present an intermediate case between electrons (which can tunnel easily through atomically thin barriers) and atoms, yet our measured transport rates are unexpectedly high and raise fundamental questions about the details of the transport process. We see the highest room-temperature proton conductivity with monolayer hBN, for which we measure a resistivity to proton flow of about 10 Ω cm(2) and a low activation energy of about 0.3 electronvolts. At higher temperatures, hBN is outperformed by graphene, the resistivity of which is estimated to fall below 10(-3) Ω cm(2) above 250 degrees Celsius. Proton transport can be further enhanced by decorating the graphene and hBN membranes with catalytic metal nanoparticles. The high, selective proton conductivity and stability make one-atom-thick crystals promising candidates for use in many hydrogen-based technologies.

15.
Nat Commun ; 5: 4843, 2014 Sep 11.
Artículo en Inglés | MEDLINE | ID: mdl-25208890

RESUMEN

Flexible barrier films preventing permeation of gases and moistures are important for many industries ranging from food to medical and from chemical to electronic. From this perspective, graphene has recently attracted particular interest because its defect-free monolayers are impermeable to all atoms and molecules. However, it has been proved to be challenging to develop large-area defectless graphene films suitable for industrial use. Here we report barrier properties of multilayer graphitic films made by gentle chemical reduction of graphene oxide laminates with hydroiodic and ascorbic acids. They are found to be highly impermeable to all gases, liquids and aggressive chemicals including, for example, hydrofluoric acid. The exceptional barrier properties are attributed to a high degree of graphitization of the laminates and little structural damage during reduction. This work indicates a close prospect of graphene-based flexible and inert barriers and protective coatings, which can be of interest for numerous applications.

16.
Indian J Nephrol ; 24(4): 257-9, 2014 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-25097343

RESUMEN

Takayasu arteritis (TA), a chronic inflammatory arteritis affecting the aorta and its main branches, is a rare condition mainly affecting young women in the second and third decades of life. Occurrence of TA in infants is extremely rare, with only less than 10 cases reported all over the world until date. We report a case of a 2-year-old girl who presented with hypertension and was diagnosed to have TA with bilateral renal artery stenosis and this is probably the youngest case reported from India.

17.
Indian J Nephrol ; 24(3): 178-80, 2014 May.
Artículo en Inglés | MEDLINE | ID: mdl-25120297

RESUMEN

Arteriovenous fistula (AVF) is an anomalous communication between an artery and a vein, caused by an iatrogenic or traumatic etiology. Surgically created upper limb AVF remains the preferred vascular access for patients on maintenance hemodialysis. Nonetheless central vein cannulation for hemodialysis is a common procedure done in patients who need hemodialysis. We incidentally detected a thyrocervical artery - jugular fistula in a patient on maintenance hemodialysis. He underwent a successful intra arterial coil embolization of the feeding vessel. Review of literature has shown that, a thyrocervical artery - internal jugular vein arteriovenous fistula following a central venous catheterization has not been reported so far.

18.
Science ; 343(6172): 752-4, 2014 Feb 14.
Artículo en Inglés | MEDLINE | ID: mdl-24531966

RESUMEN

Graphene-based materials can have well-defined nanometer pores and can exhibit low frictional water flow inside them, making their properties of interest for filtration and separation. We investigate permeation through micrometer-thick laminates prepared by means of vacuum filtration of graphene oxide suspensions. The laminates are vacuum-tight in the dry state but, if immersed in water, act as molecular sieves, blocking all solutes with hydrated radii larger than 4.5 angstroms. Smaller ions permeate through the membranes at rates thousands of times faster than what is expected for simple diffusion. We believe that this behavior is caused by a network of nanocapillaries that open up in the hydrated state and accept only species that fit in. The anomalously fast permeation is attributed to a capillary-like high pressure acting on ions inside graphene capillaries.

19.
Int J Immunogenet ; 41(1): 41-3, 2014 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-23442095

RESUMEN

C+3953T IL-1 B single-nucleotide polymorphism (SNP) genotyping was carried out in 140 unrelated early pregnancy loss (EPL) patients and in 198 fertile healthy control women and in chorionic villous samples by PCR-RFLP. In Indian population, this is the first report on association of IL-1 B SNP C+3953T polymorphism and EPL.


Asunto(s)
Aborto Espontáneo/genética , Interleucina-1beta/genética , Polimorfismo Genético , Adulto , Alelos , Estudios de Casos y Controles , Femenino , Frecuencia de los Genes , Predisposición Genética a la Enfermedad , Genotipo , Humanos , India , Oportunidad Relativa , Polimorfismo de Nucleótido Simple , Embarazo , Riesgo
20.
Placenta ; 34(9): 824-7, 2013 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-23850136

RESUMEN

Altered expression of inflammatory molecule at the maternal fetal interface is associated with early pregnancy loss. S100A8 and S100A9 are inflammatory proteins and they exhibit cytokine like function enhancing leukocyte recruitment to the inflammatory site. Reports from mouse model suggest the role of S100A8 with the vasculature of the decidual tissue and leukocyte recruitment during early pregnancy. Hence we hypothesized that maternal overexpression of S100A8 & S100A9 might increase the recruitment of inflammatory leukocytes in maternal-fetal interface resulting in uteroplacental perfusion deficiency, development of thrombotic events, and placental hypoxia, eventually embryo abortion. In the present study we investigated altered expression of S100A8 and S100A9 in 25 recurrent early pregnancy loss (REPL) patients compared to 40 induced abortion subjects as controls. S100A8 and S100A9 mRNA were evaluated using semi-quantitative RT-PCR and quantitative real-time PCR. To determine if differential expression pattern of these transcripts is translated to protein western blot analysis was performed.S100A8 and S100A9 mRNA and protein level were significantly increased in endometrial decidua tissue (p < 0.05) of REPL patients as compared to controls. This is the first report predicting the role of inflammatory molecules S100A8 & S100A9 in REPL. It opens a new perspective for understanding significance of S100A8 and S100A9 in pregnancy maintenance and outcome.


Asunto(s)
Aborto Habitual/metabolismo , Calgranulina A/biosíntesis , Calgranulina B/biosíntesis , Decidua/metabolismo , Regulación del Desarrollo de la Expresión Génica , Regulación hacia Arriba , Aborto Habitual/inmunología , Aborto Inducido , Adulto , Calgranulina A/genética , Calgranulina A/metabolismo , Calgranulina B/genética , Calgranulina B/metabolismo , Corion/inmunología , Corion/metabolismo , Decidua/inmunología , Pérdida del Embrión/inmunología , Pérdida del Embrión/metabolismo , Femenino , Humanos , Proyectos Piloto , Embarazo , Mantenimiento del Embarazo , Primer Trimestre del Embarazo , ARN Mensajero/metabolismo , Reproducibilidad de los Resultados
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