Osteogenic behavior of alginate encapsulated bone marrow stromal cells: An in vitro study

Sodium alginate is a useful polymer for the encapsulation and immobilization of a variety of cells in tissue engineering because it is biocompatible, biodegradable and easy to process into injectable microbeads. Despite these properties, little is known of the efficacy of calcium cross-linked alginate gel beads as a biodegradable scaffold for osteogenic cell proliferation and differentiation. In this study, we investigated the ability of rabbit derived bone marrow cells (BMCs) to proliferate and differentiate in alginate microbeads and compared them with BMCs cultured in poly-l-lysine (PLL) coated microbeads and on conventional 2D plastic surfaces. Results show that levels of proliferation and differentiation in microbeads and on tissue culture plastics were comparable. Cell proliferation in microbeads however diminished after fortification with a coating layer of PLL. Maximum cell numbers observed were, 3.32 × 10⁵ ± 1.72 × 103; 3.11 × 10⁵ ± 1.52 × 10³ and 3.28 × 10⁵ ± 1.21 × 10³ for the uncoated, PLL coated and plastic surface groups respectively. Alkaline phosphatase and protein expressions reflected the stage of cell differentiation. We conclude that calcium cross-linked alginate microbeads can act as a scaffold for BMC proliferation and osteogenic differentiation and has potential for use as 3D degradable scaffold.     

Aerodynamic quality management for the NACA 23012 airfoil model using the surface high-frequency discharge

The effect of the surface capacity HF discharge on airfoil flow-around has been studied in the situation when the oncoming flow velocity is 20 m/s and the Reynolds numbers are Re = 10⁵. The power delivered to discharge was modulated with a frequency of 3 × 10²–2 × 10⁴ Hz, which corresponds to a Strouhal number of St = 1.2–80, and the average electric power (W _av) was 50–400 W. It has been indicated that the aerodynamic drag decreased and the lift increased at stall and post-stall angles of attack when the HF dielectric barrier discharge was turned on. A nonstationary stochastic change in the C _x and C _y aerodynamic characteristics was observed at a stall angle in the St = 4–10 range of Strouhal numbers when the power was insufficient (W _av ≈ 100 W).     

Enhanced electrochemiluminescence behavior of C,N quantum dots embedded g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanosheets and its sensing application for copper (II)

Electrochemiluminescence (ECL) is a very sensitive method for trace analysis because of its background interference and high signal-to-noise ratio. In the past decade, the determination of Cu²⁺ in environment has attracted considerable attention since it plays an essential role in many physiological processes. Herein, a novel ECL sensor based on C,N quantum dots embedded g-C₃N₄ nanosheets (C,N-QDs@NSs) was constructed for the detection of Cu²⁺. The nanocomposite was rapidly obtained via the oxidation of normal g-C₃N₄ in H₂O₂ solution using sonochemical synthesizing method. Due to the abundant surface defects on C,N-QDs@NSs, the ECL intensity was magnified 2.5 times for using a C,N-QDs@NSs electrode in comparision to a g-C₃N₄ modified electrode. Besides, C,N-QDs@NSs could accelerate the rate of electron transfer in ECL reaction and thus resulted in the lower cathodic peak potential. Significantly, Cu²⁺ could effectively quench the ECL of C,N-QD@NSs, which endowed C,N-QD@NSs with a great advantage in the ECL detection of Cu²⁺. under optimum conditions, C,N-QDs@NSs modified electrode exhibited a linear detection range from 5 × 10^?4 to 10 µM with a detection limit of 2 × 10^?4 µM (S/N?=?3) for Cu²⁺, and was finally applied to detect Cu²⁺ in real samples with satisfactory results.     

Mixed Lead Halide Passivation of Quantum Dots

Infrared‐absorbing colloidal quantum dots (IR CQDs) are materials of interest in tandem solar cells to augment perovskite and cSi photovoltaics (PV). Today's best IR CQD solar cells rely on the use of passivation strategies based on lead iodide; however, these fail to passivate the entire surface of IR CQDs. Lead chloride passivated CQDs show improved passivation, but worse charge transport. Lead bromide passivated CQDs have higher charge mobilities, but worse passivation. Here a mixed lead‐halide (MPbX) ligand exchange is introduced that enables thorough surface passivation without compromising transport. MPbX–PbS CQDs exhibit properties that exceed the best features of single lead‐halide PbS CQDs: they show improved passivation (43 ± 5 meV vs 44 ± 4 meV in Stokes shift) together with higher charge transport (4 × 10^‐2 ± 3 × 10^‐3 cm² V^‐1 s^‐1 vs 3 × 10^‐2 ± 3 × 10^‐3 cm² V^‐1 s^‐1 in mobility). This translates into PV devices having a record IR open‐circuit voltage (IR V_oc) of 0.46 ± 0.01 V while simultaneously having an external quantum efficiency of 81 ± 1%. They provide a 1.7× improvement in the power conversion efficiency of IR photons (>1.1 µm) relative to the single lead‐halide controls reported herein.     

Proton conductivity of zirconium tricarboxybutylphosphonate/PBI nanocomposite membrane

The preparation process and proton transport properties of zirconium tricarboxybutylphosphonate Zr(O₃PC(CH₂)₃(COOH)₃)₂ (Zr(PBTC))/polybenzimidazole (PBI) composite membranes have been investigated with a view to developing a novel electrolyte for direct methanol fuel cells. A compacted Zr(PBTC) powder sample and a Zr(PBTC)/PBI composite membrane with 50 wt.% Zr(PBTC) content show conductivities of 6.74 × 10^–2 S cm^–1 and 3.82 × 10^–3 S cm^–1 at 200 °C under a fully humid condition, respectively. Post-sulfonation thermal treatment, which has a great effect on the ligand structure of PBI, gives a marked increase in the conductivity of the membrane by a factor of 2 in the same condition. This effect is mainly attributed to the proton transport via sulfonic acid groups bonded to the PBI unit.     

Determining early adhesion of cells on polysaccharides/PCL surfaces by a quartz crystal microbalance

The early adhesions of cells to various biopolymers are important to their growths and proliferations. Here, the adhesion of cells (e.g., fibroblasts) on the electrode of a quartz crystal microbalance (QCM) that was coated by PCL or PEG/PCL and further adsorbed by chitosan (CS) or CS/hyaluronic acid (HA) layers, was examined by cell-counting technique, QCM method and MTS assay under a serum-free condition for 3 h. The surfaces on electrodes of the QCM were confirmed to have been modified by measuring their contact angles, FT-IR spectra and the weights of biopolymers affected the frequency shifts of the QCM. Among tested surfaces on electrodes, the adhesion of fibroblasts on a HA/CS/PCL surface was the most (e.g., 3.08 × 10⁵ cells/cm²) while that on a PEG/PCL surface was the least (e.g., 0.7 × 10⁵ cells/cm²), as determined by cell-counting technique. The frequency shift and the mass of adhering fibroblasts on HA/CS/PCL electrodes were ?3,537 ± 770 Hz and 3.78 ± 0.22 μg (n = 3), respectively, that were significantly exceeded those on other electrodes (?393 ± 58 Hz and 0.32 ± 0.06 μg, n = 3, respectively, for PEG/PCL electrodes). These results were consistent with cell-counting technique. Although MTS assay yielded similar results, it was less sensitive than the two aforementioned methods. In conclusion, modified electrodes of a QCM provide a convenient and sensitive method for examining the early adhesion of cells (e.g., 3 h) to biopolymer surfaces.     

Determination,par diffraction des rayons X,du coefficient de magnetostriction spontanee du grenat de fer-terbium a 77 et 4.2 °K

During an X-ray low temperature topographic study of magnetic domains in Tb₃Fe₅O₁₂, we found a new method to measure the λ₁₁₁ magnetostriction coefficient of that compound. The method is based on the misorientation between reflecting planes in two adjacent domains, due to rhomboedric magnetostrictive deformation along two different {111} magnetisation directions. The results (λ₁₁₁ = 2175 × 10^?6 at 4.2°K, λ₁₁₁ = 520 × 10^?6 at 77°K) are in good agreement with previous ones, obtained by different other methods.     

Effect of strain rate on interfacial fracture behaviors of Sn-58Bi/Cu solder joints

The interfacial reactions and mechanical properties of Sn-58Bi/Cu solder joints reflowed at different temperatures ranging from 180 to 220 °C for constant time of 10 min were investigated with various strain rates. Only a continuous Cu₆Sn₅ intermetallic compound (IMC) layer was formed at the interface between the Sn-58Bi solder and the Cu substrate during reflow. The equivalent thickness of the Cu₆Sn₅ layer increased with increasing reflow temperature, and the relationship between Cu₆Sn₅ layer equivalent thickness (X) and reflow temperature (T) is obtained by using method of linear regression and presented as $ X = 0.01 \times T + 0.187 $ . For the tensile property, the tensile strength of solder joint gradually decreased as the reflow temperature it increased, whereas it increased with increasing strain rate. Moreover, the fracture behavior of Sn-58Bi/Cu solder joint indicated the ductile fracture with low strain rate (5 × 10^?4 and 1 × 10^?3 s^?1), while toward brittle fracture with high strain rate (2 × 10^?3 and 1 × 10^?2 s^?1). The strain rate sensitivities of the solder joints fractured with various modes were also investigated, and it is found that the tensile strength of the solder is more sensitive to the strain rate than that of the IMC layer.     

Novel wet-chemical synthesis and characterization of nanocrystalline CeO2 and Ce0.8Gd0.2O1.9 as solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications

Novel wet-chemical methods of synthesis have been adopted to synthesize nano-crystalline CeO₂ and Gd-substituted compositions aiming to explore an efficient oxide ion conducting solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Nano-crystalline CeO₂ powders were synthesized by combustion method using redox mixture of cerric ammonium nitrate or cerium nitrate and maleic acid or 1,3-dimethylurea and compared with high surface area CeO₂ powders prepared by hydrothermal technique with microwave precipitated precursor from aqueous solutions of (NH₄)₂Ce(NO₃)₆ and urea. The grain size achieved by the hydrothermal technique is ∼7 nm which is smaller than that of commercial nano CeO₂ powders. Conventional or microwave sintering was used to prepare dense Ce_0.8Gd_0.2O_1.9 pellets from the ceria powders made of redox mixture of cerium nitrate, 1,3-dimethylurea (DMU) and Gd₂O₃ as the starting ingredients. The samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and ac impedance spectroscopy. The ionic conductivity measured for the pellet sintered at 1400 °C is 1 × 10⁻² and 2.4 × 10⁻² S/cm at 700 °C and 800 °C respectively.     

Fabrication,characterization and comparison of DSSC using anatase TiO2 synthesized by various methods

In this study, anatase TiO₂ nanoparticles were synthesized by three techniques, namely, sol–gel, acid-base co-catalyst and room temperature colloidal methods. The synthesized materials were characterized by X-ray diffraction, scanning electron microscopy, pore diameter, pore volume and surface area. The dye-sensitized solar cells were fabricated using the synthesized materials and characterized for incident photon to current conversion efficiency, photocurrent density to photo voltage measurement and electrochemical impedance analysis. Among the studied materials, TiO₂ synthesized by sol–gel method displayed highest photon to current conversion of 76.8% and a maximum solar cell efficiency of 7.85% with J_sc of 14.75 mA/cm², V_oc of 0.76 V and FF of 0.7. This is the first study to report a high power conversion efficiency of DSSC using a sol–gel synthesized titania and its comparison with other two synthesized materials. The high power conversion efficiency of the solar cell using TiO₂ synthesized by sol–gel method is attributed to its characteristic properties such high surface area, larger pore diameter and larger pore volume and highest dye loading capacity.     

Thermal Conductivity and Interfacial Thermal Resistance: Measurements of Thermally Oxidized SiO2 Films on a Silicon Wafer Using a Thermo-Reflectance Technique

This article describes the development of a method to measure the normal-to-plane thermal conductivity of a very thin electrically insulating film on a substrate. In this method, a metal film, which is deposited on the thin insulating films, is Joule heated periodically, and the ac-temperature response at the center of the metal film surface is measured by a thermo-reflectance technique. The one-dimensional thermal conduction equation of the metal/film/substrate system was solved analytically, and a simple approximate equation was derived. The thermal conductivities of the thermally oxidized SiO₂ films obtained in this study agreed with those of VAMAS TWA23 within ± 4%. In this study, an attempt was made to estimate the interfacial thermal resistance between the thermally oxidized SiO₂ film and the silicon wafer. The difference between the apparent thermal resistances of the thermally oxidized SiO₂ film with the gold film deposited by two different methods was examined. It was concluded that rf-sputtering produces a significant thermal resistance ((20 ± 4.5) × 10⁻⁹ m²·K·W⁻¹) between the gold film and the thermally oxidized SiO₂ film, but evaporation provides no significant interfacial thermal resistance (less than ± 4.5 × 10⁻⁹ m²·K·W⁻¹). The apparent interfacial thermal resistances between the thermally oxidized SiO₂ film and the silicon wafer were found to scatter significantly (± 9 × 10⁻⁹ m²·K·W⁻¹) around a very small thermal resistance (less than ± 4.5 × 10⁻⁹ m²·K·W⁻¹).     

Platinum deposition from hydrogen-ion beam irradiated solid precursor

We report a particular method of Pt/glassy carbon (GC) surface formation, based on a 15 keV H^+/? ion beam irradiation of thin H₂PtCl₆ × nH₂O layer placed over the GC surface. Hydrogen-ion beam irradiation provided an excellent adherence of Pt deposit, unlike to any other Pt-deposition method. Furthermore, the morphology and electrochemical activity of GC/Pt catalyst obtained at the fluence of 5 × 10¹⁷ cm^? 2 was found to be sensitive to the sign of charge of hydrogen ions. The electrochemical activity of such obtained Pt/GC surface toward oxygen reduction and ethanol oxidation was compared with the activity of the Pt deposits obtained by other more common reduction procedures.     

DNA‐Driven Two‐Layer Core–Satellite Gold Nanostructures for Ultrasensitive MicroRNA Detection in Living Cells

It is a significant challenge to achieve controllable self‐assembly of superstructures for biological applications in living cells. Here, a two‐layer core–satellite assembly is driven by a Y‐DNA, which is designed with three nucleotide chains that hybridized through complementary sequences. The two‐layer core–satellite nanostructure (C₃₀S₅S₁₀ NS) is constructed using 30 nm gold nanoparticles (Au NPs) as the core, 5 nm Au NPs as the first satellite layer, and 10 nm Au NPs as the second satellite layer, resulting in a very strong circular dichroism (CD) and surface‐enhanced Raman scattering. After optimization, the yield is up to 85%, and produces a g‐factor of 0.16 × 10^?2. The hybridization of the target microRNA (miRNA) with the molecular probe causes a significant drop in the CD and Raman signals, and this phenomenon is used to detect the miRNA in living cells. The CD signal has a good linear range of 0.011–20.94 amol ng_RNA^?1 and a limit of detection (LOD) of 0.0051 amol ng_RNA^?1, while Raman signal with the range of 0.052–34.98 amol ng_RNA^?1 and an LOD of 2.81 × 10^?2 amol ng_RNA^?1. This innovative dual‐signal method can be used to quantify biomolecules in living cells, opening the way for ultrasensitive, highly accurate, and reliable diagnoses of clinical diseases.     

High Aspect Ratio Sub‐Micrometer Channels Using Wet Etching: Application to the Dynamics of Red Blood Cell Transiting through Biomimetic Splenic Slits

Nanoparticles delivering drugs, disseminating cancer cells, and red blood cells (RBCs) during splenic filtration must deform and pass through the sub‐micrometer and high aspect ratio interstices between the endothelial cells lining blood vessels. The dynamics of passage of particles/cells through these slit‐like interstices remain poorly understood because the in vitro reproduction of slits with physiological dimensions in devices compatible with optical microscopy observations requires expensive technologies. Here, novel microfluidic PDMS devices containing high aspect ratio slits with sub‐micrometer width are molded on silicon masters using a simple, inexpensive, and highly flexible method combining standard UV lithography and anisotropic wet etching. These devices enabled revealing novel modes of deformations of healthy and diseased RBCs squeezing through splenic‐like slits (0.6–2 × 5–10 × 1.6–11 µm³) under physiological interstitial pressures. At the slit exit, the cytoskeleton of spherocytic RBCs seemed to be detached from the lipid membrane whereas RBCs from healthy donors and patients with sickle cell disease exhibited peculiar tips at their front. These tips disappeared much slower in patients' cells, allowing estimating a threefold increase in RBC cytoplasmic viscosity in sickle cell disease. Measurements of time and rate of RBC sequestration in the slits allowed quantifying the massive trapping of spherocytic RBCs.     

Stochastic modelling for gradient sensing by chemotactic cells

Chemotaxis, the process by which cells move toward attractant molecules, operates in a range of biological processes including immunity, neuronal patterning, and morphogenesis. Dictyostelium discoideum cells display a strong chemotactic response to cyclic adenosine 3^',5^'-monophosphate (cAMP), which binds to a cell surface receptor. Each Dictyostelium has ca. 80000 cAMP receptors, and can transduce shallow spatial chemoattractant gradients into strongly localized intracellular responses in spite of large statistical fluctuation of receptor occupancy even in the case of very low cAMP concentration. In this study, we develop a stochastic model for gradient sensing by chemotactic cells. We simulate the binding of cAMP molecules to receptors by a Monte-Carlo method in order to account for statistical fluctuation of receptor occupancy and treat intracellular signal processing by a diffusion–translocation model, which includes the production of second-messenger molecules and positive feedback mechanisms mediated by effector molecules. Our simulation results show that the fluctuation of second-messenger concentration is much smaller than that of receptor occupancy, and that a shallow chemoattractant gradient are transduced into a large second-messenger concentration gradient through nonlinear signal amplification.     

Nitrogen ion implantation effects on the structural,optical and electrical properties of CdSe thin film

In the present study, thin films of cadmium selenide (CdSe) are deposited on ITO substrate by electrodeposition method using aqueous solution of 3CdSO₄·8H₂O and SeO₂. These films are implanted with 40 keV N⁺ ions with different fluencies i.e. 1?×?10¹⁵, 5?×?10¹⁵, 1?×?10¹⁶ and 5?×?10¹⁶ ions/cm² using a beam current of 0.9 µA. The structural, morphological, optical and electrical properties of pristine and nitrogen ion-implanted CdSe thin films are analyzed using XRD, SEM, AFM, UV-PL Spectrophotometer and I–V four probes setup. XRD analysis revealed the effects of nitrogen ions on the structural parameters such as grain size, FWHM, micro strain and dislocation density etc. Crystallanity of the material increased with increase in implantation dose. SEM and AFM analysis show decrease in the surface roughness with implantation. From the optical studies, band gap value decreased from 2.50 to 2.29 eV with increase in N⁺ implantation doses. Noticeable changes in the electrical properties are also reported. The effect of N⁺ ion implantation on the properties of CdSe thin films are discussed on the basis of lattice disorder.     

Dimensionality-dependent photocatalytic activity of TiO2-based nanostructures: nanosheets with a superior catalytic property

TiO₂-based nanostructures usually possess excellent photochemical properties. However, the relationship between their dimensionality and photocatalytic activity was rarely investigated. In this study, a series of TiO₂-based nanostructures in various dimensionalities (such as nanosheets, nanotubes) were obtained by hydrothermal treatment of P25, and the process of structural evolution was also systematically investigated by TEM, BET, Raman, and XRD analysis. Much higher rate constant (3.7 × 10^?2 min^?1) for the degradation of rhodamine B was found for nanosheets, comparing with those of three-dimensional P25 nanoparticles (0.59 × 10^?2 min^?1) and one-dimensional nanotubes (0.85 × 10^?2 min^?1). It is found that the hydrothermally prepared TiO₂-based nanosheets possess small thickness (ca. 5 nm) and plentiful surface hydroxyl groups, and the reason why TiO₂-based nanosheets possess superior photocatalytic activity is also discussed in detail from the microstructure and surface chemical states. In addition, TiO₂-based nanosheets exhibit good reusability in the cyclic experiments, implying a potential application for photocatalytic degradation of organic pollutants.     

Oxidation behaviour of nanocrystalline Fe–Ni–Cr–Al alloy coatings

Abstract

Nanocrystalline Fe–Ni–Cr–Al alloy coatings with ～4 wt-%Al were produced using the unbalanced magnetron sputter deposition technique with a composite 310S stainless steel target embedded with aluminium plugs. The oxidation behaviour of the coatings was studied, during which complete external α-Al₂O₃ scales were formed. During isothermal oxidation tests at 950, 1000, and 1050°C, the oxidation kinetics followed an essentially parabolic rate law, and the oxidation constants were measured to be 2·06 × 10^-3, 4·23 × 10^-3, and 1·14 × 10^-2 mg² cm^-4 h^-1 respectively. During a cyclic oxidation test at 1000°C the α-Al₂O₃ scale showed good scale spallation resistance. The surface hardness of the coatings was measured with a Knoop indentor before and after oxidation. After oxidation, the coating surface hardness was still significantly higher than that of the uncoated specimen, demonstrating the potential this coating has in the improvement of high temperature erosion resistance.     

Quantification of vital adherent <Emphasis Type="Italic">Streptococcus sanguinis</Emphasis> cells on protein-coated titanium after disinfectant treatment

The quantification of vital adherent bacteria is challenging, especially when efficacy of antimicrobial agents is to be evaluated. In this study three different methods were compared in order to quantify vital adherent Streptococcus sanguinis cells after exposure to disinfectants. An anaerobic flow chamber model accomplished initial adhesion of S. sanguinis on protein-coated titanium. Effects of chlorhexidine, Betadine^®, Octenidol^®, and ProntOral^® were assessed by quantifying vital cells using Live/Dead BacLight^?, conventional culturing and isothermal microcalorimetry (IMC). Results were analysed by Kruskal–Wallis one-way analysis of variance. Live/dead staining revealed highest vital cell counts (P < 0.05) and demonstrated dose-dependent effect for all disinfectants. Microcalorimetry showed time-delayed heat flow peaks that were proportioned to the remaining number of viable cells. Over 48 h there was no difference in total heat between treated and untreated samples (P > 0.05), indicating equivalent numbers of bacteria were created and disinfectants delayed growth but did not eliminate it. In conclusion, contrary to culturing, live/dead staining enables detection of cells that may be viable but non-cultivable. Microcalorimetry allows unique evaluation of relative disinfectant effects by quantifying differences in time delay of regrowth of remaining vital cells.     

CTAB assisted immobilization of RuO2 nanoparticles on graphene oxide for electrochemical sensing of hydrazine

A novel method has been presented to modify glassy carbon electrode (GCE) with graphene oxide (GO) nanocomposite without introducing any electrode binder such as chitosan and Nafion. First, modify GCE with RuO₂ nanoparticles which have been dispersed in cetyltrimethyl ammonium bromide (CTAB) aqueous solution. Then, highly adhesive RuO₂/CTAB/GO nanocomposite membrane formed on GCE by immersing RuO₂/CTAB modified GCE in GO suspension. CTAB plays significant roles not only in the preparation of the nanocomposite but also in the immobilization of nanocomposite on GCE surface. First, CTAB was used as the dispersant of RuO₂ nanoparticles. Second, CTAB acted as the molecular linker to bind RuO₂ nanoparticles on graphene sheets. Third, CTAB formed CTAB/GO nanocomposite which is highly adhesive on the surface of electrodes such as GCE and ITO (indium tin oxide). The obtained RuO₂/CTAB/GO/GCE shows excellent electrocatalytic ability towards the oxidation of hydrazine. The oxidation of hydrazine on RuO₂/CTAB/GO/GCE is an adsorption-controlled process and the oxidation current is linear with the concentration of hydrazine in the range of 1 × 10^?5～1 × 10^?3 M with a detection limit of 2.3 × 10^?6 M. The application of this sensor in the sensing of hydrazine in real water samples confirmed its reliability and accuracy.