<Emphasis Type="Italic">In vitro</Emphasis> microhardness of glass ionomer cements

This study evaluated the surface microhardness of four glass ionomer cements and a composite resin (Fuji IX, Ketac Molar, Vidrion R, Vitromolar and Z 250). Ten specimens of each glass ionomer cement with 8.0 mm diameter and 5.0 mm high dimensions were made and Vicker’s microhardness measurements were taken at 1 day and 1 week after initial setting reaction. The results were analyzed using Student’s T test and Tukey test (p < 0.05) and demonstrated that the values of microhardness increased after 1 week, with the exception of Fuji IX. Resin composite Z250 presented the greatest values for microhardness.     

The Activation Energy <Emphasis Type="Italic">U</Emphasis>(<Emphasis Type="Italic">T</Emphasis>,<Emphasis Type="Italic">H</Emphasis>) in Y-based Superconductors

Based on the Arrhenius equation, a method to calculate the activation energy from the resistance transition is proposed for high temperature superconductors. This method is applied to the Y-based superconductors. The activation energy is found to be U(T,H)∼(1−T/T _c )^4.8(H/H ₀)^−3.8 of YBCO crystal, and U(T,H)∼(1−T/T _c )^3.3(H/H ₀)^−2.2 of Er doped MTG YBCO crystal, respectively. With the obtained activation energy U(T,H), the lower part of the experimental curve ρ(T,H) and its derivative can be reproduced.      

Evaluation of hydrogels for soft tissue adhesives <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis> analyses

In this study, natural materials (sodium alginate, dextran, gelatin and carboxymethyl chitosan) were modified to get aldehyde components and amino components. Upon mixing the two-component solutions together, four kinds of Schiff base hydrogels formed successfully within 5-300 s and could seal the wound tissue. The cytotoxicity tests of hydrogel extraction solution confirmed that the hydrogels are nontoxic materials. The adhesive ability was evaluated in vivo by measuring the adhesive strength after sealing the skin incisions on the back of rats. All the hydrogels showed higher adhesive strength than that of commercial fibrin glue and the blank control. The histological staining observation by hematoxylin and eosin staining (HE) and Masson’s trichrome staining (MTC) methods suggested that the hydrogels had good biocompatibility and biodegradation in vivo. They have only normal initial inflammation to skin tissue and could improve the formation of new collagen in the incision section. So, the prepared hydrogels were both safe and effective tissue adhesive, which had the great potentials to be used as skin tissue adhesive.     

Long-wavelength photodiodes based on <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb/<Emphasis Type="Italic">p</Emphasis>-AlGaAsSb heterostructures

Photodiodes sensitive in the wavelength ranges 1–2.5 μm and 1–4.8 μm at room temperature have been created on the basis of n-GaSb/n-GaInAsSb/p-AlGaAsSb double-junction heterostructures of two types. The broadband photosensitivity of the diode structures of both types is indicative of the complete separation of photogenerated electron-hole pairs in the staggered n-p heterojunction (n-GaInAsSb/p-AlGaAsSb). The noise characteristics of photodetectors based on the proposed diode structures have been studied. Prospects of the use of these devices in thermophotovoltaic cells for low-temperature radiation sources are considered.     

Porous-conductive chitosan scaffolds for tissue engineering II. <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis> degradation

Porous-conductive chitosan scaffolds were fabricated by blending conductive polypyrrole (PPy) particles with chitosan solution and employing an improved phase separation method. In vitro and in vivo degradation behaviors of these scaffolds were investigated. In the case of in vitro degradation, an enzymatic degradation system was employed and lysozyme was used as a working enzyme. Meanwhile, the degradation products of scaffolds, glucosamine and N-acetyl-glucosamine, were also analyzed with a HPLC method. In vivo degradation of scaffolds was performed by subcutaneously implanting these scaffolds in rat for prescheduled time intervals. In the both cases, the weight-loss of scaffolds was monitored during the whole degradation process for evaluating the degradation of scaffolds. The changes in conductivity of scaffolds afterin vitro or in vivo degradation were also measured using a four-point technique. It was observed that the pore parameters of scaffolds themselves could significantly influence the degradation behaviors of scaffolds but the PPy content in the scaffolds seemed not to impart its effect to the degradation of scaffolds. Degradation dynamics of scaffolds and conductivity measurements indicated that these scaffolds shown fairly different behaviors in their in vitro and in vivo degradation process. According to the results obtained from in vitro and in vivo degradation of scaffolds and based on some requirements of practical tissue engineering application, it was suggested that the PPy content in the scaffold should be slightly higher than 3 wt.% but lower than 6 wt.%.     

Impact-ionization-stimulated electroluminescence in isotype <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-AlGaAsSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb heterostructures

We have studied electroluminescence in n-GaSb/n-AlGaAsSb/n-GaInAsSb heterostructures with isotype heterojunctions, in which the quantum efficiency of emission is increased due to the additional production of electron-hole pairs as a result of the impact ionization that takes place near the heterointerface. The impact ionization in such heterostructures is possible due to the presence of deep wells in the energy band structure.     

<Emphasis Type="Italic">In vitro</Emphasis> studies of polyethyleneimine coated miRNA microspheres as anticancer agents

RNA plays important roles as a gene-silencing agent, a therapeutic agent for clinical treatment, and in the differentiation, proliferation, and development of cells. However, RNA is very difficult to work with due to its sensitivity and fragility. Another obstacle in using RNA for gene delivery/silencing is its negative charge, which causes its repulsion by cell membranes, which are also negatively charged. Our recent study showed that miR-125b is upregulated in glioblastoma (GMB) and plays an oncogenic role in GMB cells by promoting cell proliferation and inhibiting apoptosis. Endogenous miR-125b can be blocked by transfection of its antisense RNA molecule, miR-125b antisense (miR-125b-AS). Thus, miR- 125b-AS can be developed as an RNA-based agent for cancer treatment. However, instability during storage and difficulty in delivery into cells has limited the use of RNA-based therapies thus far. In the current work, we demonstrate a short and simple one-step technique for the preparation of positively charged RNA nanospheres (miR-125b-RNS and miR-125b-AS-RNS) coated with a bioavailable polymer, polyethylenimine (PEI). These RNA nanospheres are able to penetrate the cell directly without the use of liposomes. Our study confirmed that converting miR-125b and miR-125b-AS into nanospheres is a viable approach for storing RNA. In addition, this study provides evidence that PEI-coated RNA nanospheres have the potential to be used as a novel class of anticancer agents.

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Speed of sound in <Emphasis Type="Italic">n</Emphasis>-hexane, <Emphasis Type="Italic">n</Emphasis>-octane, <Emphasis Type="Italic">n</Emphasis>-decane,and <Emphasis Type="Italic">n</Emphasis>-hexadecane in the liquid state

This paper describes an improved experimental facility for measuring the speed of sound in liquids with an accuracy of up to 0.1%. Measurements of the speed of sound in liquid n-hexane, n-octane, n-decane, and n-hexadecane at temperatures of 298–433 K and pressures of 0.1–100 MPa have been made. It has been shown that in the possible comparison range the obtained values of the speed of sound are in good agreement with the literature data. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 732–736, July–August, 2008.     

The search for novel superhard and incompressible materials on the basis of higher borides of <Emphasis Type="Italic">s</Emphasis>, <Emphasis Type="Italic">p</Emphasis>, <Emphasis Type="Italic">d</Emphasis> metals

The state of the art in the search for novel superhard and (or) incompressible materials on the basis of higher borides of s, p, d metals has been briefly reviewed. The information has been considered about experimental and theoretical studies of the following groups of borides: diborides of 4d, 5d heavy metals (Tc, Ru, Rh, Re, Os, and Ir), hexagonal tetraborides with the WB₄-type structure, and AMB₁₄ borides (where A, M are s, p metals) as well as of a number of related systems.     

Highly efficient gene silencing and bioimaging based on fluorescent carbon dots <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis>

Small interfering RNA (siRNA) is an attractive therapeutic candidate for sequencespecific gene silencing to treat incurable diseases using small molecule drugs.However,its efficient intracellular delivery has remained a challenge.Here,we have developed a highly biocompatible fluorescent carbon dot (CD),and demonstrate a functional siRNA delivery system that induces efficient gene knockdown in vitro and in vivo.We found that CD nanoparticles (NPs) enhance the cellular uptake of siRNA,via endocytosis in tumor cells,with low cytotoxicity and unexpected immune responses.Real-time study of fluorescence imaging in live cells shows that CD NPs favorably localize in cytoplasm and successfully release siRNA within 12 h.Moreover,we demonstrate that CD NP-mediated siRNA delivery significantly silences green fluorescence protein (GFP) expression and inhibits tumor growth in a breast cancer cell xenograft mouse model of tumor-specific therapy.We have developed a multi functional siRNA delivery vehicle enabling simultaneous bioimaging and efficient downregulation of gene expression,that shows excellent potential for gene therapy.     

<Emphasis Type="Italic">In vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis> evaluation of bone morphogenetic protein-2 (BMP-2) immobilized collagen-coated polyetheretherketone (PEEK)

Polyetheretherketone (PEEK) is regarded as one of the most potential candidates of biomaterials in spinal implant applications. However, as a bioinert material, PEEK plays a limited role in osteoconduction and osseointegration. In this study, recombinant human bone morphogenetic protein-2 (rhBMP-2) was immobilized onto the surface of collagen-coated PEEK in order to prepare a multi-functional material. After adsorbed onto the PEEK surface by hydrophobic interaction, collagen was cross-linked with N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). EDC/NHS system also contributed to the immobilization of rhBMP-2. Water contact angle tests, XPS and SEM clearly demonstrated the surface changes. ELISA tests quantified the amount of rhBMP-2 immobilized and the release over a period of 30 d. In vitro evaluation proved that the osteogenesis differentiation rate was higher when cells were cultured on modified PEEK discs than on regular ones. In vivo tests were conducted and positive changes of major parameters were presented. This report demonstrates that the rhBMP-2 immobilized method for PEEK modification increase bioactivity in vitro and in vivo, suggesting its practicability in orthopedic and spinal clinical applications.     

Short-term <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis> biocompatibility of a biodegradable polyurethane foam based on 1,4-butanediisocyanate

In this study short-term in vitro and in vivo biocompatibility apects of a biodegradable polyurethane (PU) foam were evaluated. The PU consists of hard urethane segments and amorphous soft segments based on a copolyester of dl-lactide and -caprolactone. The urethane segments are of uniform length and synthesized with 1,4-butanediisocyanate. The foam has good mechanical properties and will be used for tissue regeneration applications. Degradation tests were carried out in a buffer solution for twelve weeks. Cytotoxicity was determined using extract and direct contact test methods with incubation periods varying form 24 to 72 h. The foam was implanted subcutaneously for one, four and twelve weeks and the tissue response to the material was histologically evaluated.In vitro, the mass loss was 3.4% after twelve weeks. In the cytotoxicity tests the PU caused no abnormal growth behaviour, nor morphological changes or inhibition in metabolic activity. The in vivo studies showed no toxic tissue response to the PU. Connective tissue ingrowth, accompanied by vascular ingrowth was complete at twelve weeks. In vivo degradation had started within four to twelve weeks.In conclusion, the PU shows a good in vitro and in vivo biocompatibility in these short-term experiments.     

<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">z</Emphasis></Subscript> constraints of semi-elliptical surface cracks in elastic plates subjected to uniform tension loading

The out-of-plane constraints T_z around the semi-elliptical surface cracks in an elastic plate subjected to uniform tension loading have been investigated through detailed three-dimensional (3D) finite element (FE) analyses. The distributions of T_z are obtained in the vicinity of the crack border with aspect ratios of 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0. T_z drops from Poissons ratio at the crack tip to approximate zero beyond certain radial distance in the normal plane of the crack front line, and increases gradually from the free surface to the mid-plane at the same radial distance. By fitting the numerical results, empirical formulae are obtained to describe the 3D distributions of T_z for semi-elliptical surface cracks with a sufficient accuracy in the wide aspect ratio range of 0.2a/c 1.0 except very near the free surface, where T_z is extremely low. T_z, combining with the corresponding K and T or J and Q, can be applied to establish the three-parameter dominated stress field, which can characterize the 3D crack front field completely as an attempt.     

Synthesis,growth, optical,mechanical and electrical properties of <Emphasis Type="Italic">L</Emphasis>-lysine <Emphasis Type="Italic">L</Emphasis>-lysinium dichloride nitrate (<Emphasis Type="Italic">L</Emphasis>-LLDN) single crystal

Semi-organic nonlinear optical material, L-lysine L-lysinium dichloride nitrate (2C₆H₁₅N₂O₂⁺_{2}^{+} · H⁺ · NO₃^-_{3}^{-} · 2Cl⁻) was synthesized at room temperature. Single crystals of L-LLDN were grown by slow cooling solution growth technique. The grown crystal was confirmed by powder X-ray diffraction analysis. The crystalline perfection of the grown single crystal was characterized by high-resolution X-ray diffraction (HRXRD) studies. The cut-off wavelength was determined by UV-vis transmission spectral analysis. The frequency doubling of the grown crystal was confirmed by powder second harmonic generation (SHG) measurement. The refractive index and birefringence of the crystal were determined using He–Ne laser source. Mechanical property of the crystal was determined by Vickers hardness tester. The frequency and temperature dependence of dielectric constant (ε _r), dielectric loss (tan δ) and a.c. conductivity (σ _ac) were also measured.     

Project of laser-pumped quantum <Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">X</Emphasis></Subscript> magnetometer

The possibility of creating a new scheme of a laser-pumped quantum magnetometric device based on a double-beam M _X magnetometer is considered. The proposed system ensures the simultaneous measurement of the modulus of the Earth’s magnetic field vector (with an absolute accuracy of 0.02 nT) and two angles of deviation of this vector with an absolute accuracy and sensitivity of not worse than 0.4″ (0.1 nT) at a measurement time of τ = 1 s. In contrast to the known analogous systems, the proposed scheme does not require generating additional magnetic fields.     

Investigation of mechanical and superconducting properties of iron diffusion-doped <Emphasis Type="Italic">Bi</Emphasis>-<Emphasis Type="Italic">2223</Emphasis> superconductors

The mechanical and superconducting properties of the Fe diffusion-doped (Bi-Pb)-2223 superconductor have been investigated. First, iron was evaporated on Bi-2223 superconductor and then the Fe layered superconductor was annealed at 830 °C for 10, 30 and 60 h. Static Vickers hardness, dc electrical resistivity, X-ray diffraction and scanning electron microcopy have been carried out to assess the effects of Fe doping. These measurements indicates that Fe doping, in comparison with the undoped samples, increased the critical transition temperature, and improved formation of high T _c phase, while decreasing the number and size of voids. Moreover, both microhardness and grain size were also enhanced by increasing the amount of diffusion. The values of microhardness were found to be load dependent. In addition, we have investigated the indentation size effect (ISE) behavior using some models such as the Kick’s law, modified proportional specimen resistance (MPRS) model and the Hays- Kendall (HK) approach. Among them, both HK and MPRS models are successful. In this study, the possible reasons of noticed improvement on mechanical and physical properties due to iron diffusion are discussed.     

Inference with progressively censored <Emphasis Type="Italic">k</Emphasis>-out-of-<Emphasis Type="Italic">n</Emphasis> system lifetime data

A system with n independent components which works if and only if a least k of its n components work is called a k-out-of-n system. For exponentially distributed component lifetimes, we obtain point and interval estimators for the scale parameter of the component lifetime distribution of a k-out-of-n system when the system failure time is observed only. In particular, we prove that the maximum likelihood estimator (MLE) of the scale parameter based on progressively Type-II censored system lifetimes is unique. Further, we propose a fixed-point iteration procedure to compute the MLE for k-out-of-n systems data. In addition, we illustrate that the Newton–Raphson method does not converge for any initial value. Finally, exact confidence intervals for the scale parameter are constructed based on progressively Type-II censored system lifetimes.     

Nernst Signal in High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

The time-dependent Ginzburg–Landau equation with thermal noise is used to calculate the Nernst signal e _N , describing the Nernst effect, in type-II superconductor in the vortex-liquid regime. The Gaussian method used is an elaboration of the Hartree–Fock method. An additional assumption often made in analytical calculations that only the lowest Landau level significantly contributes to physical quantities of interest in the high-field limit is lifted by including all the Landau levels. The values of e _N are in good quantitative agreement with experimental data for temperature close to T _c on Bi₂Sr₂CaCu₂O_8+δ and Bi₂Sr₂Ca₂Cu₃O_10+δ .     

Investigation on the <Emphasis Type="Italic">in vitro</Emphasis> cytocompatibility of Mg-Zn-Y-Nd-Zr alloys as degradable orthopaedic implant materials

Mg-Zn-Y-Nd-Zr alloy has been developed as a new type of biodegradable orthopaedic implant material by the authors’ research group with its excellent mechanical properties and controllable degradation rate. In this study, the cytocompatibility of Mg-Zn-Y-Nd-Zr alloy was systematically evaluated through in vitro cell culture method. MTT assay was applied to evaluate the cytotoxicity of Mg-Zn-Y-Nd-Zr alloy and no toxic effect was observed on L929 and MC3T3-E1 cells followed the protocol of ISO 10993 standard. Considering the potential ion accumulation in the bony environment, this study further investigated the cytotoxic effect of accumulated metallic ions during the alloy degradation by extending the extract preparation time. When the extract preparation time was prolonged to 1440?h, the accumulated metallic ions leaded to severe cell apoptosis, of which the combined ion concentration was determined as 39.5–65.8?µM of Mg²⁺, 3.5–5.9?µM of Zn²⁺, 0.44–0.74?µM of Y³⁺, 0.3–0.52?µM of Nd³⁺ and 0.11–0.18?µM of Zr⁴⁺ for L929, and 65.8–92.2?µM of Mg²⁺, 5.9–8.3?µM of Zn²⁺, 0.74–1.04?µM of Y³⁺, 0.52–0.73?µM of Nd³⁺ and 0.18–0.25?µM of Zr⁴⁺ for MC3T3-E1 cells. Besides the cell viability assessment, high expression of ALP activity and calcified nodules implied that metal elements in Mg-Zn-Y-Nd-Zr alloys can promote the osteogenic differentiation. Hence, excellent cytocompatibility has equipped Mg-Zn-Y-Nd-Zr alloy as a promising candidate for orthopaedic implant application, which can remarkably guide the magnesium-based alloy design and provide scientific evidence for clinical practice in future.     

Electrical and photoelectric properties of electrodeposited <Emphasis Type="Italic">n</Emphasis>-Si/<Emphasis Type="Italic">n</Emphasis>-Cd<Subscript>1 - <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>x</Subscript>S heterojunctions

n-Si/n-Cd_{1 - x} Zn_xS heterojunctions are produced by electrodepositing Cd_{1 - x} Zn_xS (0 x 0.6) films on silicon substrates, and their electrical and photoelectric properties are studied. The results demonstrate that the spectral response of the heterojunctions depends strongly on the film composition and heat-treatment conditions. The highest photosensitivity is achieved at x = 0.6 by heat treatment at 350°C for 7 min: V _OC = 0.5 V and I _SC = 3.8 mA/cm² under illumination of 1500 lx at 300 K.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 276–280.Original Russian Text Copyright © 2005 by Mamedov, Gasanov, Amirova.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.