Effect of human astrocytes on the characteristics of human brain-microvascular endothelial cells in the blood-brain barrier

A blood-brain barrier (BBB) model in vitro was established by cultivating human brain-microvascular endothelial cells (HBMECs) with the regulation of human astrocytes (HAs) (HBMEC/HA). Astrocyte-conditioned medium (ACM) was employed to constitute a confluent monolayer of HBMECs without directly conjugated HAs. HBMECs exhibited an orientated multiplication on the supporting membrane; while HAs grew in an overlapping fashion. In addition, HBMECs could propagate over the membrane pore, and the end-feet of HAs extended into the membrane pore to improve the integral feature of the BBB. HBMEC/HA demonstrated a high transendothelial electrical resistance (TEER) about 230 Ω cm2 and low permeability of propidium iodide (PI) about 4 × 10?? cm/s. The order in TEER was HBMEC/HA>HBMECs with 100% ACM>HBMECs with 50% ACM > HBMECs. The reverse order was valid for the permeability of PI and uptake of calcein-AM by HBMECs. The tranwell culture of HBMECs and HAs displays appropriate characteristics of the BBB and can be applied to estimate the delivery efficiency of therapeutic chemicals for the brain-related disease.     

Evaluation of sphingomyelin,cholester, and phosphatidylcholine-based immobilized artificial membrane liquid chromatography to predict drug penetration across the blood-brain barrier

Over the past decades, several in vitro methods have been tested for their ability to predict drug penetration across the blood-brain barrier. So far, in high-performance liquid chromatography, most attention has been paid to micellar liquid chromatography and immobilized artificial membrane (IAM) LC. IAMLC has been described as a viable approach, since the stationary phase emulates the lipid environment of a cell membrane. However, research in IAMLC has almost exclusively been limited to phosphatidylcholine (PC)-based stationary phases, even though PC is only one of the lipids present in cell membranes. In this article, sphingomyelin and cholester stationary phases have been tested for the first time towards their ability to predict drug penetration across the blood-brain barrier. Upon comparison with the PC stationary phase, the sphingomyelin- and cholester-based columns depict similar predictive performance. Combining data from the different stationary phases did not lead to improvements of the models. Figure

Schematic representation of how IAM-LC is used to predict drug penetration across the blood-brain barrier.     

Thermodynamic analysis of the high-temperature stability of silicon nitride and silicon carbide

A thermodynamic analysis of the stability of Si₃N₄ and SiC is presented which can be employed to assess their suitability for use at high temperatures in various environments. Specifically, the decomposition and the volatilization of Si₃N₄ and SiC, and of SiO₂, which is the major constituent in the oxide scales formed on their surfaces in oxidizing atmospheres, are discussed in terms of ambient environment and temperature. The calculated values of the lowest oxygen partial pressure up to which a protective SiO₂ layer should be maintained on the surface of Si₃N₄ and SiC are also presented.     

Iron mediates endothelial cell damage and blood-brain barrier opening in the hippocampus after transient forebrain ischemia in rats

Blood cells are transported into the brain and are thought to participate in neurodegenerative processes following hypoxic ischemic injury. We examined the possibility that transient forebrain ischemia (TFI) causes the blood-brain barrier (BBB) to become permeable to blood cells, possibly via dysfunction and degeneration of endothelial cells in rats. Extravasation of Evans blue and immunoglobulin G (IgG) was observed in the hippocampal CA1-2 areas within 8 h after TFI, and peaked at 48 h. This extravasation was accompanied by loss of tight junction proteins, occludin, and zonula occludens-1, and degeneration of endothelial cells in the CA1-2 areas. Iron overload and mitochondrial free radical production were evident in the microvessel endothelium of the hippocampus before endothelial cell damage occurred. Administration of deferoxamine (DFO), an iron chelator, or Neu2000, an antioxidant, blocked free radical production and endothelial cell degeneration. Our findings suggest that iron overload and iron-mediated free radical production cause loss of tight junction proteins and degeneration of endothelial cells, opening of the BBB after TFI.     

血脑屏障药物筛选模型的建立及丹参活性成分筛选分析

ECV304细胞在C6细胞的诱导下生长,通过细胞培养时间优化、渗透系数测定和细胞形态学观察等,建立ECV304/C6共培养血脑屏障(BBB)药物筛选模型.将该模型应用于从丹参提取液中筛选可能作用于中枢神经系统(CNS)的活性成分,结合液相色谱-质谱联用技术(LC-MS)分析,发现丹参提取液中至少有16种成分能够穿越BBB模型,其中4种成分被确认为隐丹参酮、丹参酮Ⅰ、丹参素和原儿茶酸.通过定量构效关系(QASR)分析,进一步从理论上证明所确认的4种化合物均符合CNS靶向药物的特征.研究结果表明,ECV304/C6共培养BBB模型能够在模拟生理状态下从中药复杂体系中筛选分离跨越BBB的活性成分组,可用于CNS药物开发的早期快速筛选,服务于中药现代化研究.     

Kinetic studies of the reactions between silicon nitride and carbon

The reactions between silicon nitride and carbon take place in two stages, the surface silica of silicon nitride powders reacts with carbon first followed by the decomposition of silicon nitride and the residual silicon reacting with carbon. The kinetics of the two stage reactions has been studied by isothermal thermogravimetric analysis. Physico-geometric models for both of the reaction stages have been proposed, and the kinetic parameters have been calculated. The implications of the kinetic models and parameters are discussed.     

AFM study of forces between silica, silicon nitride and polyurethane pads

Interaction of silica and silicon nitride with polyurethane surfaces is rather poorly studied despite being of great interest for modern semiconductor industry, e.g., for chemical-mechanical planarization (CMP) processes. Here we show the results from the application of the atomic force microscopy (AFM) technique to study the forces between silica or silicon nitride (AFM tips) and polyurethane surfaces in aqueous solutions of different acidity. The polyurethane surface potentials are derived from the measured AFM data. The obtained potentials are in rather good agreement with measurements of zeta-potentials using the streaming-potentials method. Another important parameter, adhesion, is also measured. While the surface potentials of silica are well known, there are ambiguous results on the potentials of silicon nitride that is naturally oxidized. Deriving the surface potential of the naturally oxidized silicon nitride from our measurements, we show that it is not oxidized to silica despite some earlier published expectations.     

Computational chemistry of the silicon nitride surface. 1. Water,ammonia, and water-ammonia complex

This paper deals with computational modeling of structure and properties of the silicon nitride surface zone using combined computational and real experiments. The computational experiment implies quantum chemical calculations of structure and vibrational spectra of polyatomic clusters. The real experiment suggests measurement and analysis of vibrational spectra. For quantum chemical calculations, semiempirical methods (MNDO and AM1) were chosen. In most calculations, the MNDO/H method was preferred because of the presence of many H-bonds in the surface zone. For verification of calculations, we calculated the structures and vibrational spectra of water and ammonia molecules and the water-ammonia complex and compared the results with experimental and ab initio (extended basis) data; MNDO/H proved to be an optimal method giving reliable results. Russian Peoples' Friendship University. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 1, pp. 58–69, January–February, 1995. Translated by L. Smolina     

Characterisation of thin sputtered silicon nitride films by NRA, ERDA, RBS and SEM

Summary Thin, amorphous silicon nitride (a-SIN_x) films were deposited on n-type (100) silicon substrates using an argon ion beam for sputtering a HPSN block under high vacuum conditions. The substrates were kept at room temperature. Nitrogen depth distributions were determined by NRA using the resonance reaction ¹⁵N(p,)¹²C at 429 keV. Hydrogen profiles were analysed by NRA (¹H(¹⁵N,)¹²C at E_o=6.385 MeV) and by ERDA (²⁰Ne²⁺, E_o=10 MeV). The NRA was used to determine the depth distributions (concentration vs. areal density) of nitrogen and hydrogen taking calibration standards into consideration. The silicon depth distributions and the N/Si ratios of the deposited a-SiN_x films were determined by RBS (⁴He⁺, E_o=2.0 MeV). Film thicknesses were obtained by SEM. The density of the deposited a-SiN_x films was found to be =2.7 (±0.1) g/cm³ by correlating RBS data and real film thicknesses as obtained by SEM.     

Optical trapping of microparticles using silicon nitride waveguide junctions and tapered-waveguide junctions on an optofluidic chip

We study optical trapping of microparticles on an optofluidic chip using silicon nitride waveguide junctions and tapered-waveguide junctions. We demonstrate the trapping of single 1 μm-sized polystyrene particles using the evanescent field of waveguide junctions connecting a submicrometer-sized input-waveguide and a micrometer-sized output-waveguide. Particle trapping is localized in the vicinity of the junction. We also demonstrate trapping of one and two 1μm-sized polystyrene particles using tapered-waveguide junctions connecting a submicrometer-sized singlemode input-waveguide and a micrometer-sized multimode output-waveguide. Particle trapping occurs near the taper output end, the taper center and the taper input end, depending on the taper aspect ratio.     

Effects of boron nitride nanopowder on thermal,chemical and gas barrier properties of starch

Starch/boron nitride （starch/BN） bionanocomposites were prepared with the reinforcement of boron nitride nano powder by solution technique. The dispersion of BN in the starch was achieved by a continuous sonication process. The interaction between starch and boron nitride nanopowder was investigated by Fourier transform infrared （FTIR） spectroscopy. The structural properties of starch/BN bionanocomposites was studied by X-ray diffraction （XRD）. The high resolution transmission electron microscopy （HRTEM） was used for the study of dispersion of boron nitride in starch matrix and diffraction patterns were studied by selected area electron diffraction （SAED）. Thermal stability of the starch was increased with rising concentrations of boron nitride due to incorporation of rigid nano BN with starch matrix. The substantial reduction in oxygen permeability was obtained by increasing the concentration of BN. The biodegradability of synthesized bionanocomposites was measured by using activated sludge water. Further, it was noticed that, starch/BN bionanocomposites are resistant towards inorganic acids and bases. The tensile strength of starch/BN bionanocomposites was increased whereas; the water resistance property of the materials was decreased with increasing BN loading.     

Development of a blood-brain barrier model in a membrane-based microchip for characterization of drug permeability and cytotoxicity for drug screening

Since most of the central nervous system (CNS) drug candidates show poor permeability across the blood-brain barrier (BBB), development of a reliable platform for permeability assay will greatly accelerate drug discovery. Herein, we constructed a microfluidic BBB model to mimic drug delivery into the brain to induce cytotoxicity at target cells. To reconstitute the in vivo BBB properties, human cerebral microvessel endothelial cells (hCMEC/D3) were dynamically cultured in a membrane-based microchannel. Sunitinib, a model drug, was then delivered into the microchannel and forced to permeate through the BBB model. The permeated amount was directly quantified by an electrospray ionization quadrupole time-of-flight mass spectrometer (ESI-Q-TOF MS) after on-chip SPE (μSPE) pretreatment. Moreover, the permeated drug was incubated with glioma cells (U251) cultured inside agarose gel in the downstream to investigate drug-induced cytotoxicity. The resultant permeability of sunitinib was highly correlated with literature reported value, and it only required 30 min and 5 μL of sample solution for each permeation experiment. Moreover, after 48 h of treatment, the survival rate of U251 cells cultured in 3D scaffolds was nearly 6% higher than that in 2D, which was in accordance with the previously reported results. These results demonstrate that this platform provides a valid tool for drug permeability and cytotoxicity assays which have great value for the research and development of CNS drugs.     

An emulsion membrane extraction of strontium and its separation from calcium utilizing crowns and picric acid

The selective separation ability of the cyclic crowns, known for liquid-liquid extraction, e.g. alkali metals, is found to be effective for emulsion membrane extraction. 18-C-6, DB-18-C-6, DC-18-C-6 crowns were used as carriers. The co-transport of the ionic pair SrL²⁺. 2A through the membrane has been studied. Calcium was considered as a main competing ion. Even in the case of 20-fold preconcentration, there have been found conditions under which the pertraction process can reach Sr/Ca separation factors of about 500 and the yield of strontium is high (95–98%). The presence of calcium up to 1000-fold excess has no influence on the yield of strontium (1.10^–5M). The calcium content in the isolated emulsion was caused by second emulsification of the outer solution. The influence of potassium on strontium pertraction has been studied and some transport data of Cs and Y have been obtained.     

Expression of ornithine decarboxylase during the transport of saquinavir across the blood-brain barrier using composite polymeric nanocarriers under an electromagnetic field

The expression of human ornithine decarboxylase (ODC) and permeability of saquinavir (SQV) across the blood-brain barrier were studied using nanoparticles (NPs) composed of poly(lactide-co-glycolide) (PLGA), poly-(γ-glutamic acid) (γ-PGA), and polyethyleneimine (PEI). SQV was encapsulated in the particle core to traverse a monolayer of human brain-microvascular endothelial cells (HBMECs) with the regulation of human astrocytes under an electromagnetic field (EMF). An increase in the weight percentage of PEI enhanced the particle size, zeta potential, and permeability of SQV. However, the viability of HBMECs reduced when the weight percentage of PEI increased. In addition, an increment in the molecular weight of γ-PGA enhanced the particle size and viability of HBMECs, and reduced the zeta potential. The permeability of SQV and expression of ODC were in the order: an EMF with amplitude modulation (AM)>an EMF with frequency modulation>no EMF. At 0.04% PEI, the AM EMF increased 2.38 times the uptake of NPs and 2.72 times the expression of ODC. The combination of PEI/γ-PGA/PLGA NPs and EMF can be an innovative strategy for delivering SQV into the brain.     

Simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by slurry-sampling graphite furnace AAS.

A fast and accurate analytical method was established for the simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by graphite furnace atomic absorption spectrometry using a slurry sampling technique and a Hitachi Model Z-9000 atomic absorption spectrometer. The slurry samples were prepared by the ultrasonication of silicon carbide or silicon nitride powders with 0.1 M nitric acid. Calibration curves were prepared by using a mixed standard solution containing aluminum, calcium, iron and 0.1 M nitric acid. The analytical results of the proposed method for aluminum, calcium and iron in silicon carbide and silicon nitride reference materials were in good agreement with the reference values. The detection limits for aluminum, calcium and iron were 0.6 microg/g, 0.15 microg/g and 2.5 microg/g, respectively, in solid samples, when 200 mg of powdered samples were suspended in 20 ml of 0.1 M nitric acid and a 10 microl portion of the slurry sample was then measured. The relative standard deviation of the determination of aluminum, calcium and iron was 5 - 33%.     

A correlation between the virulence and the adhesion of Listeria monocytogenes to silicon nitride: An atomic force microscopy study

Listeria monocytogenes is a facultative intracellular Gram-positive bacterium that is widely distributed in the environment. Despite being pathogenic at the species level, L. monocytogenes in fact comprises a diversity of strains from pathogenic ones that can result in disease and/or mortality to others that are relatively avirulent. The main goal of the current study was to answer the question on whether enhanced binding or attachment of L. monocytogenes to inert surfaces bears any relationship to pathogenicity in food-borne isolates. To answer this question, the nanoscale adhesion forces of eight L. monocytogenes strains that vary in their pathogenicity levels to a model surface of silicon nitride were quantified using atomic force microscopy. The strains used were the highly pathogenic (EGDe, 874, 1002, ATCC 19115), the intermediate pathogenic (ATCC 19112, ATCC 19118), and the non pathogenic (ATCC 15313 and HCC25). Our results indicate that the average nanoscale adhesion (in nN) and the 50% lethal dose (LD50) of strain virulence quantified in mice are logarithmically correlated according to: (nN) = −0.032 ln (LD50) + 1.040, r² = 0.96. Such correlation indicates that nanoscale adhesion could potentially be used as a design criterion to distinguish between virulent and avirulent L. monocytogenes strains. Finally, stronger adhesion of virulent strains to inert surfaces modeled by silicon nitride might be a way for pathogenic strains to survive better in the environment and thus increase their likelihood of infecting animals or humans.     

Contribution of nanoclays to the barrier properties of a model proton exchange membrane for fuel cell application

Direct methanol fuel cells (DMFCs) that use a proton exchange membrane (PEM) as electrolyte, is a promising alternative source of energy for the future. However, methanol crossover from the anodic side to the cathodic one is a major problem in DMFC. Proper dispersion of layered silicates within the fuel cell membrane has been proposed as a strategy for improving the barrier properties of the membrane. The validity of this approach has been tested in case of a model membrane consisting of phosphotungstic acid doped poly(vinyl alcohol). A solvent casting technique has been used, which allows the nanofiller to be delaminated by an ultrasonic pre-treatment, as confirmed by TEM and XRD analysis. The layered silicates have a favourable impact on the methanol permeability, whose the decrease overcompensates some loss in ionic conductivity.     

Surface-near analyses of ultra thin silicon nitride layers by NRA, channeling RBS, FT IR ellipsometry and AFM

Homogeneous ultra thin silicon nitride layers (SiN_x layers) close to the surface have been produced by 10 keV ¹⁵N ₂ ⁺ molecular ion implantation and an ion current density of 10 A/cm², into single crystal silicon at room temperature. Stoichiometric SiN_x layers with thicknesses of about 28 nm (analyzed by NRA) were obtained at fluences of 1.5×10¹⁷ at/cm². NRA analyses of samples annealed by EB-RTA at T=1150° C for 15 s indicated that the N/Si ratio and the layer thickness did not change drastically. FT IR ellipsometry analyses indicated the existence of Si₃N₄ bonds in as-implanted specimens. A disordered Si layer (d-Si, typically 15 nm thick) underneath the implantation region caused by the ion implantation was found by channeling RBS analyses. The d-Si layer partly recrystallized during EB-RTA showing a thickness of 6 nm afterwards. The SiN_x layers showed no decomposition and detachment after EB-RTA. Due to EB-RTA, however, the smooth surface of the as-implanted specimens changed into a surface with remaining whisker-like structures surrounded by circular recesses as shown by AFM analyses. A model for the growth of these whisker-liker structures caused by low energy ion implantation and EB-RTA is presented on the basis of the thickness of the SiN_x layer, the existence of the d-Si layer and the special annealing process.