Monolayer Configuration Research Articles

SIMULATION STUDY OF THE ADSORPTION DYNAMICS OF CYLINDRICAL SILICA GEL PARTICLES

The paper presents a simulation study of loose cylindrically shaped particles packed within a copper plate and aluminum fins. The model presented solves coupled heat and mass transfer equations using the finite volume method based on ANSYS FLUENT medium. Three different arrangements of cylindrical particles are considered. The model is validated with experimental data. It is found that the arrangements which represented monolayer configurations are only marginally better in heat transfer and uptake efficiency than the tri-layer configuration in the presence of fins. However, there is an appreciable difference in the uptake curve between mono-and tri-layer configurations in the absence of fins. Finally, it is found that the fin pitch also plays an important role in determining the time constant for the adsorber design.

Establishment and Characterization of an In Vitro Model of Fas-Mediated Hepatocyte Cell Death.

Fas-mediated apoptosis underlies a plethora of liver pathologies and toxicities. As a consequence, this process is a major research topic in the field of experimental and clinical hepatology. The present chapter describes the setup of an in vitro model of hepatocellular apoptotic cell death. In essence, this system consists of freshly isolated hepatocytes cultured in a monolayer configuration, which are exposed to a combination of Fas ligand and cycloheximide. This in vitro model has been characterized by using a set of well-acknowledged cell death markers. This experimental system allows the study of the entire course of Fas-mediated hepatocellular cell death, going from early apoptosis to secondary necrosis, and hence can serve a broad range of in vitro pharmaco-toxicological purposes.

Effect of Molecular Fluctuations on Hole Diffusion within Dye Monolayers

Measured hole diffusion coefficients in dye monolayers are larger than can be explained by a charge hopping model with a static distribution of parameters describing intermolecular hole transfer. We show that large amplitude fluctuations of the tethered dye configurations on the surface could explain the observed diffusion rates by enabling charges trapped in particular configurations to escape as the dye orientation changes. We present a multiscale model of hole transport that includes the effect of dynamic rearrangement of the monolayer of anchored dyes. Conformations of pairs of indolene dye molecules (both D102 and D149) were generated by a rigid molecular packing algorithm and Car–Parrinello molecular dynamics to mimic the conformational and configurational disorder of a dye monolayer adsorbed to an anatase (101) titanium dioxide surface. The electronic coupling (Jij) for each pair of neighboring dyes was calculated to build distributions representing the disorder in a real system. These values were used as inputs to Marcus’ non-adiabatic equation for charge transfer to calculate the rate of hole hopping for each pair. Hole diffusion was simulated with a continuous time random walk, accounting for different time scales of molecular rearrangement (changes in the dye geometry). The dynamic nature of configurational disorder was captured by reassigning the values of Jij, drawn from the aforementioned distributions, after a fixed renewal time. We found hole diffusion coefficients of 3.3 × 10–8 and 9.2 × 10–8 cm2 s–1 for D102 and D149, respectively, for a renewal time of 10–7 s. This is in good agreement with the corresponding measured coefficients for D102 and D149 of 9.6 × 10–8 and 2.5 × 10–7 cm2 s–1, whereas the diffusion coefficients are underestimated by at least a factor of 15 if the dynamics are ignored. Fast rearrangement of dye monolayer configuration may explain the high lateral hole diffusion coefficients determined experimentally. Our results indicate that both chemical structure and the availability of different packing configurations must be considered when designing conductive molecular monolayers.

Exciton complexes in low dimensional transition metal dichalcogenides

We examine the excitonic properties of layered configurations of low dimensional transition metal dichalcogenides (LTMDCs) using the fractional dimensional space approach. The binding energies of the exciton, trion, and biexciton in LTMDCs of varying layers are analyzed, and linked to the dimensionality parameter α, which provides insight into critical electro-optical properties (relative oscillator strength, absorption spectrum, exciton-exciton interaction) of the material systems. The usefulness of α is highlighted by its independence of the physical mechanisms underlying the confinement effects of geometrical structures. Our estimates of the binding energies of exciton complexes for the monolayer configuration of transition metal dichalcogenides suggest a non-collinear structure for the trion and a positronium-molecule-like square structure for the biexciton.

XCELLigence system for real-time label-free monitoring of growth and viability of cell lines from hematological malignancies.

The xCELLigence system is a new technological approach that allows the real-time cell analysis of adherent tumor cells. To date, xCELLigence has not been able to monitor the growth or cytotoxicity of nonadherent cells derived from hematological malignancies. The basis of its technology relies on the use of culture plates with gold microelectrodes located in their base. We have adapted the methodology described by others to xCELLigence, based on the pre-coating of the cell culture surface with specific substrates, some of which are known to facilitate cell adhesion in the extracellular matrix. Pre-coating of the culture plates with fibronectin, compared to laminin, collagen, or gelatin, significantly induced the adhesion of most of the leukemia/lymphoma cells assayed (Jurkat, L1236, KMH2, and K562). With a fibronectin substrate, nonadherent cells deposited in a monolayer configuration, and consequently, the cell growth and viability were robustly monitored. We further demonstrate the feasibility of xCELLigence for the real-time monitoring of the cytotoxic properties of several antineoplastic agents. In order to validate this technology, the data obtained through real-time cell analysis was compared with that obtained from using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. This provides an excellent label-free tool for the screening of drug efficacy in nonadherent cells and discriminates optimal time points for further molecular analysis of cellular events associated with treatments, reducing both time and costs.

Beyond graphene: stable elemental monolayers of silicene and germanene.

Two-dimensional materials are one of the most active areas of nanomaterials research. Here we report the structural stability, electronic and vibrational properties of different monolayer configurations of the group IV elemental materials silicene and germanene. The structure of the stable configuration is calculated and for planar and low (<1 Å) atomic buckling configurations, analysis of the electronic band structure reveals linear band dispersion giving rise to massless Dirac Fermions with a Fermi velocity about two-thirds that of graphene. Monolayer stability is shown to be directly attributed to the phonons present with the instability being driven by the out-of-plane ZA and ZO phonon modes. Long momentum relaxation lengths and high carrier mobilities are predicted for silicene and germanene based devices as carrier relaxation via phonon scattering is found to be inhibited as the electron-optical phonon coupling matrix elements are calculated to be small, being about a factor of 25 times smaller than in graphene. The consequences for phonon scattering, high energy electrical transport and integration of elemental monolayers into electronic devices are further discussed.

Sorption and desorption of tetracycline on layered manganese dioxide birnessite

Birnessite is one of the most common manganese oxides in the clay-sized fraction (<2 μm) of soils and has high cation exchange capacity and larger surface area. Birnessite was previously studied for decomposition of selected antibiotics from water. In this study, the removal of tetracycline (TC) by birnessite from aqueous solution was investigated as a function of initial tetracycline concentration, solution pH, temperature, and equilibrium time. Changes in solid phase after TC adsorption and desorption were characterized by X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and Fourier transform infrared analyses. Desorption of exchangeable cations accompanying TC removal and partial desorption of TC from birnessite by AlCl3 confirmed that cation exchange was responsible for TC removal at low initial concentrations. Both the external and internal surface areas were readily available for TC uptake by birnessite. The intercalated TC formed a horizontal monolayer configuration in the interlayer of birnessite as deduced from XRD analyses.

Perfusion enhanced polydimethylsiloxane based scaffold cell culturing system for multi‐well drug screening platform

Conventional two-dimensional cultures in monolayer and sandwich configuration have been used as a model for in vitro drug testing. However, these culture configurations do not present the actual in vivo liver cytoarchitecture for the hepatocytes cultures and thus they may compromise the cells liver-specific functions and their cuboidal morphology over longer term culture. In this study, we present a three-dimensional polydimethylsiloxane (PDMS) scaffold with interconnected spherical macropores for the culturing of rat liver cells (hepatocytes). The scaffolds were integrated into our perfusion enhanced bioreactor to improve the nutrients and gas supply for cell cultures. The liver-specific functions of the cell culture were assessed by their albumin and urea production, and the changes in the cell morphology were tracked by immunofluorescence staining over 9 days of culture period. N-Acetyl-Para-Amino-Phenol (acetaminophen) was used as drug model to investigate the response of cells to drug in our scaffold-bioreactor system. Our experimental results revealed that the perfusion enhanced PDMS-based scaffold system provides a more conducive microenvironment with better cell-to-cell contacts among the hepatocytes that maintains the culture specific enzymatic functions and their cuboidal morphology during the culturing period. The numerical simulation results further showed improved oxygen distribution within the culturing chamber with the scaffold providing an additional function of shielding the cell cultures from the potentially detrimental fluid induced shear stresses. In conclusion, this study could serve a crucial role as a platform for future preclinical hepatotoxicity testing.

Density functional study of CaN mono and bilayer on Cu(001)

Density functional - pseudopotential calculations are performed to provide first-principles insights into magnetic behaviour of bulk CaN and CaN monolayers on Cu(001) in the rock-salt (RS) and zinc-blende (ZB) structures. Our results indicate that both RS- and ZB-CaN exhibit half-metallic ferromagnetism originated from the incomplete 2p shell of the nitrogen ion. In contrast to the bulk CaN, the CaN monolayers on Cu(001) generally favor ZB structure. We argue that the more stable ZB-CaN thin films on Cu(001) are nonmagnetic, because of strong Cu-N bonding at the interface, while the less stable Ca terminated ZB-CaN thin films exhibit half-metallic ferromagnetism. The transition path between the high energy ferromagnetic and the stable nonmagnetic configurations of the ZB-CaN monolayer on Cu(001) are studied by using the nudged elastic band method. We observe a two stages transition and an activation barrier of about 1.18 eV in the minimum energy path of this transition.

Preparation and Characterization of Guar-Montmorillonite Nanocomposites.

Polymer-clay nanocomposites are highly sought-after materials, mainly due to their applicability in a variety of avenues. From the standpoint of the preparation of these nanocomposites, however, organic compatibility with clay and adherence to “green chemistry” concepts and principles can be limiting factors. As such, the objective was to prepare a biopolymer-modified clay nanocomposite using a simple and environmentally friendly method of preparation, whereby pre-treatment of the clay for organic compatibility was bypassed. Novel montmorillonite nanocomposites were prepared using neutral guar gum and cationic guar gum. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of intercalated structures. A monolayer configuration of cationic guar within the interlayer space was indicated by XRD results, while treatment with neutral guar gum resulted in the observance of both monolayer and bilayer configurations. Additionally, TEM results indicated partial exfoliation. Results attributed from 13C cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS NMR) of the nanocomposites indicated peaks corresponding to the guar constituent, confirming the adsorption of the biopolymer. Inductively coupled plasma emission spectrometry (ICP-ES) results indicated the exchange of cations present in neutral guar gum with the sodium cations of montmorillonite, in the case of the neutral guar nanocomposites.

A surface‐tethered spheroid model for functional evaluation of 3T3‐L1 adipocytes

In order to effectively treat obesity, it must be better understood at the cellular level with respect to metabolic state and environmental stress. However, current two-dimensional (2D) in vitro cell culture methods do not represent the in vivo adipose tissue appropriately due to the absence of complex architecture and cellular signaling. Conversely, 3D in vitro cultures have been reported to have optimal results mimicking the adipose tissue in vivo. The main aim of this study was to examine the efficacy of a novel conjugate of a genetically engineered polymer, elastin-like polypeptide (ELP) and a synthetic polymer, polyethyleneimine (PEI), toward creating a 3D preadipocyte culture system. We then used this 3D culture model to study the preadipocyte differentiation and adipocyte maintenance processes when subjected to various dosages of nutritionally relevant free fatty acids with respect to total DNA and protein content, cell viability, and intracellular triglyceride accumulation. Our results showed that 3T3-L1 preadipocytes cultured on the ELP-PEI surface formed 3D spheroids within 72 h, whereas the cells cultured on unmodified tissue culture polystyrene surfaces remained in monolayer configuration. Significant statistical differences were discovered between the 3D spheroid and 2D monolayer culture with respect to the DNA and protein content, fatty acid consumption, and triglyceride accumulation, indicating differences in cellular response. Results indicated that the 3D culture may be a more sensitive modeling technique for in vitro adipocyte culture and provides a platform for future evaluation of 3D in vitro adipocyte function.

Role of squalene in the organization of monolayers derived from lipid extracts of Halobacterium salinarum.

We have studied interfacial compressibility and lateral organization in monolayer configurations of total (squalene containing) and polar (squalene-devoid) lipid extracts of Halobacterium salinarum NRC-1, an extremely halophilic archaeon. Pressure-area isotherms derived from Langmuir experiments reveal that packing characteristics and elastic compressibility are strongly influenced by the presence of squalene in the total lipid extract. In conjunction with control experiments using mixtures of DPhPC and squalene, our results establish that the presence of squalene significantly extends elastic area compressibility of total lipid extracts, suggesting it has a role in facilitating tighter packing of archaeal lipid mixtures. Moreover, we find that squalene also influences spatial organization in archaeal membranes. Epifluorescence and atomic force microscopy characterization of Langmuir monolayers transferred onto solid hydrophilic substrates reveal an unusual domain morphology. Individual domains of microscopic dimensions (as well as their extended networks) exhibiting a peculiar bowl-like topography are evident in atomic force microscopy images. The tall rims outlining individual domains indicate that squalene accumulates at the domain periphery in a manner similar to the accumulation of cholesterol at domain boundaries in their mixtures with phospholipids. Taken together, the results presented here support the notion that squalene plays a role in modulating molecular packing and lateral organization (i.e., domain formation) in the membranes of archaea analogous to that of cholesterol in eukaryotic membranes.

Improving RhoA-mediated Intestinal Epithelial Permeability by Continuous Blood Purification in Patients with Severe Acute Pancreatitis

Early dysfunction of the intestinal mucosal barrier contributes to increasing intestinal permeability. It may play an important role in the pathophysiology of severe acute pancreatitis (SAP). A rising number of clinical data have showed that continuous blood purification (CBP) may improve the prognosis of SAP. However, the therapeutic effects of CBP on intestinal epithelial permeability have been rarely reported. Intestinal epithelial monolayer (Caco-2) was incubated with serum samples collected at specific time points from SAP patients during CBP. Changes in intestinal epithelial monolayer permeability and configuration, and levels of cellular tight junction structural proteins including occludin and ZO-1, and RhoA mRNA expression level were recorded, respectively. In addition, serum tumor necrosis factor-alpha (TNF-α) levels at specific time points during CBP were determined. Before CBP initiation, intestinal epithelial permeability was increased and tight junction structural protein level was decreased and reorganized, but RhoA mRNA expression and serum TNF-α were increased. However, after CBP treatment, intestinal epithelial permeability was reduced and tight junction protein levels were increased, with reorganization attenuated. Meanwhile, RhoA mRNA expression and serum TNF-α level was decreased. After CBP treatment, intestinal epithelial permeability was reduced by increasing occludin and ZO-1 protein level and attenuating reorganization. This beneficial effect of CBP on intestinal epithelial permeability is associated with down-regulation of RhoA mRNA expression, and it may be related to the removal of TNF-α by CBP.

Functional expression and regulation of drug transporters in monolayer- and sandwich-cultured mouse hepatocytes

Primary hepatocyte cultures are now considered as convenient models for in vitro analyzing liver drug transport. However, if primary human and rat hepatocytes have been well-characterized with respect to drug transporter expression and regulation, much less is known for primary mouse hepatocytes. The present study was therefore designed to gain insights about this point. The profile of sinusoidal and canalicular drug transporter mRNA expression in short time (4h)-cultured mouse hepatocytes was found to be highly correlated with that of freshly isolated hepatocytes; by contrast, those of counterparts cultured for a longer time (until 4days) either in monolayer configurations on plastic or collagen or in sandwich configuration with matrigel were profoundly altered: uptake drug transporters such as Oct1, Oatps and Oat2 were thus down-regulated, whereas most of efflux transporters such as Mdr1a/b, Mrp3, Mrp4 and Bcrp were induced. Moreover, short time-cultured hepatocytes exhibited the highest levels of sinusoidal influx transporter activities. Transporter-mediated drug secretion into canalicular networks was however only observed in sandwich-cultured hepatocytes. Mouse hepatocytes cultured either in monolayer or sandwich configurations were finally shown to exhibit up-regulation of referent transporters in response to exposure to prototypical activators of the drug sensing receptors pregnane X receptor, aryl hydrocarbon receptor or constitutive androstane receptor. Taken together, these data demonstrate the feasibility of using primary mouse hepatocytes for investigating potential interactions of xenobiotics with hepatic transporter activity or regulation, provided that adequate culture conditions are retained.

Pre-culturing islets with mesenchymal stromal cells using a direct contact configuration is beneficial for transplantation outcome in diabetic mice.

We recently showed that co-transplantation of mesenchymal stromal cells (MSCs) improves islet function and revascularization in vivo. Pre-transplant islet culture is associated with the loss of islet cells. MSCs may enhance islet cell survival or function by direct cell contact mechanisms and soluble mediators. We investigated the capacity of MSCs to improve islet cell survival or β-cell function in vitro using direct and indirect contact islet-MSC configurations. We also investigated whether pre-culturing islets with MSCs improves islet transplantation outcome. The effect of pre-culturing islets with MSCs on islet function in vitro was investigated by measuring glucose-stimulated insulin secretion. The endothelial cell density of fresh islets and islets cultured with or without MSCs was determined by immunohistochemistry. The efficacy of transplanted islets was tested in vivo using a syngeneic streptozotocin-diabetic minimal islet mass model. Graft function was investigated by monitoring blood glucose concentrations. Indirect islet-MSC co-culture configurations did not improve islet function in vitro. Pre-culturing islets using a direct contact MSC monolayer configuration improved glucose-stimulated insulin secretion in vitro, which correlated with superior islet graft function in vivo. MSC pre-culture had no effect on islet endothelial cell number in vitro or in vivo. Pre-culturing islets with MSCs using a direct contact configuration maintains functional β-cell mass in vitro and the capacity of cultured islets to reverse hyperglycemia in diabetic mice.

A Printed Single-Layer UWB Monopole Antenna With Extended Ground Plane Stubs

In this letter, a compact coplanar-waveguide-fed single-layer printed antenna with an ultrawideband (UWB) rectangular monopole radiator etched with a half-elliptical slot is presented. Collaborating with the UWB radiator, two symmetrical open-circuit stubs are extended from the ground plane to jointly achieve an ultrawideband impedance match with a compact size. The proposed antenna is fabricated and tested in an anechoic chamber, showing an ultrawide operating frequency range from 3.7 to 10.1 GHz with a quasi-omnidirectional gain from 2.0 to 7.3 dBi. With the advantages of a reduced size, an improved voltage standing wave ratio (VSWR), and a monolayer configuration without any back ground plane, the proposed antenna can be used in a wide range of UWB applications.

Tunable electronic and dielectric behavior of GaS and GaSe monolayers

Here we present first-principles calculations to investigate systematically the electronic behavior and the electron energy low-loss spectra (EELS) of monolayer, bilayer, four-layer, and bulk configurations of periodic GaX (X = S, Se), as well as the effect of mechanical strain on the electronic properties of the GaX monolayer. We predicate that the GaX monolayer is a semiconductor with an indirect band gap, however, the difference between the direct and indirect gaps is so small that electrons can transfer easily between this minimum with a small amount of thermal energy. Owning to strong surface effects, the electronic and dielectric properties of GaX vary drastically with number of layers in a sheet. In detail, the band gap increases from multilayer-to-single layer and EELS shifts towards larger wavelengths with a decrease in the layer thickness. Moreover, we demonstrate that the band gaps of GaX monolayers can be widely tuned by mechanical deformation, making them potential candidates for tunable nanodevices. The present study provides theoretical insight leading to a better understanding of these novel 2D structures.

Modeling of isobaric stages of adsorption cooling cycle: Transient and quasi-stationary regimes

Isobaric water ad-/desorption on/from a spherical adsorbent grain of 1.5 mm in diameter, which is in thermal contact with a metal plate, is studied by numerical simulation based on a Fickian diffusion model. The plate is subjected to a fast temperature drop/jump (60 °C ↔ 70 °C) that initiates changing the adsorbed water uptake/release. Several model adsorption isobars (linear, exponential and stepwise) are used to describe the adsorbent–water equilibrium.We have investigated the formation of quasi-stationary ad-/desorption regimes which are established after a short transient period right after the temperature drop/jump. The instant rate of water ad-/desorption is found to be a linear function of the difference of the metal plate temperature and the current temperature of the grain. As a result, the water ad-/desorption is faster when this average temperature difference is larger. Under studied conditions, the vapor pore diffusivity affects the overall ad-/desorption dynamics, although the dynamics is more sensitive to variation of heat transfer parameters. For a monolayer configuration, the heat transfer from the plate to the grain is the main rate limiting process at most realistic situations. Intraparticle water diffusion is the main rate limiting factor at unfeasible values of the pore diffusivity (lower than 10−10–10−11 m2/s).

A thermo-mechanical analysis of functionally graded beams via hierarchical modelling

In this work, functionally graded beams subjected to thermal loadings are analysed. To this end, several beam models are hierarchically derived by means of a unified formulation that makes the formulation independent from the displacements polynomial approximation order over the cross-section. The temperature profile is determined by solving Fourier’s heat conduction equation. The governing equations are, then, derived from the Principle of Virtual Displacements considering the temperature field as an external load. A Navier-type, closed form solution is used. Simply supported beams are, therefore, considered. Functionally graded mono-layer and sandwich cross-section configurations are investigated. Numerical results in terms of temperature, displacement and stress distributions are provided for different beam slenderness ratios. Results are assessed towards three-dimensional finite element solutions demonstrating that accurate results can be obtained with reduced computational costs.

Cross-sectional configuration analysis and magnetic properties of SmFe2/Fe exchange-coupled multilayers

In this study, SmFe2 monolayer and SmFe2/Fe multilayers were fabricated by the IBSD method. It scored a first by analyzing the TEM images of SmFe2 monolayer and cross-sectional configuration of SmFe2/Fe multilayers. The soft magnetic properties of the samples were measured by an alternating gradient magnetometer (AGM). The results showed that both SmFe2 monolayer and the SmFe2 layers in the multilayers were amorphous, while Fe layers were polycrystalline. Compact and high cohesion scale can be observed in all layers for the multilayers. In addition, an obvious transitional area between the film and substrate existed in the multilayers. Due to the strong exchange-coupled interaction among the layers of SmFe2/Fe, the easy axis turned to the direction parallel to the applied magnetic field, and the much smaller coercive force of the x direction compared with that of the SmFe2 monolayer (10.80 vs. 23.96kA/m) contributed to the excellent soft magnetic properties of SmFe2/Fe multilayers.