Structural,optical and magnetic characterizations of Mn-doped MgO nanoparticles

Structural, optical and room temperature magnetic properties of Mn-doped MgO nanoparticles with Mn fractions (5–50 at.%), were investigated. The as-prepared pure MgO, with grain size of about 15 nm, exhibits two magnetization components, one is diamagnetic and another is superparamagnetic. After removing the diamagnetic contribution, the magnetization curve exhibits superparamagnetic behavior which may be attributed to vacancy defects. As the Mn content increases, the lattice parameter decreases, the ferromagnetism appears and the emission bands were considerably blue shifted. First principle electronic structure calculations reveal the decrease of both the gap and the Curie temperature with increasing Mn concentration. The obtained results suggest that both Mn doping and oxygen vacancies play an important role in the development of room temperature ferromagnetism.     

Structural and optical characterizations of nitrogen-doped ZnO nanowires grown by MOCVD

One dimensional nitrogen-doped ZnO nanowires were deposited on C-plane sapphire using metal organic chemical vapour deposition. Nanowires have been characterized by scanning electron microscopy, transmission electron microscopy, micro-Raman scattering and micro-photoluminescence spectroscopy. The structural analysis has shown a high crystalline quality. In N-doped ZnO nanowires nitrogen incorporation was emphasized by Raman spectral analysis and reduction of nitrogen concentration along the wire, from the bottom to the top was found by local analysis. Low temperature micro-photoluminescence spectra exhibit donor-acceptor pair transitions.     

Structural and optical characterizations of chemically deposited cadmium selenide thin films

Synthesis of cadmium selenide thin films by CBD method has been presented. The deposited film samples were subjected to XRD, SEM, UV-vis-NIR and TEP characterization. X-ray diffraction analysis showed that CdSe film sample crystallized in zinc blende or cubic phase structure. SEM studies reveal that the grains are spherical in shape and uniformly distributed all over the surface of the substrates. The optical band gap energy of as deposited film sample was found to be in the order of 1.8 eV. The electrical conductivity of the film sample was found to be 10⁻⁶ (Ω cm)⁻¹ with n-type of conduction mechanism.     

Structural and microstructural characterizations of nanocrystalline hydroxyapatite synthesized by mechanical alloying

Single phase nanocrystalline hydroxyapatite (HAp) powder has been synthesized by mechanical alloying the stoichiometric mixture of CaCO₃ and CaHPO₄ powders in open air at room temperature, for the first time, within 2 h of milling. Nanocrystalline hexagonal single crystals are obtained by sintering of 2 h milled sample at 500 °C. Structural and microstructural properties of as-milled and sintered powders are revealed from both the X-ray line profile analysis and transmission electron microscopy. Shape and lattice strain of nanocrystalline HAp particles are found to be anisotropic in nature. Particle size of HAp powder remains almost invariant up to 10 h of milling and there is no significant growth of nanocrystalline HAp particles after sintering at 500 °C for 3 h. Changes in lattice volume and some primary bond lengths of as-milled and sintered are critically measured, which indicate that lattice imperfections introduced into the HAp lattice during ball milling have been reduced partially after sintering the powder at elevated temperatures. We could achieve ~ 96.7% of theoretical density of HAp within 3 h by sintering the pellet of nanocrystalline powder at a lower temperature of 1000 °C. Vickers microhardness (VHN) of the uni-axially pressed (6.86 MPa) pellet of nanocrystalline HAp is 4.5 GPa at 100 gm load which is close to the VHN of bulk HAp sintered at higher temperature. The strain-hardening index (n) of the sintered pellet is found to be > 2, indicating a further increase in microhardness value at higher load.     

Comparison of linear and non-linear monotonicity-based shape reconstruction using exact matrix characterizations

Detecting inhomogeneities in the electrical conductivity is a special case of the inverse problem in electrical impedance tomography, that leads to fast direct reconstruction methods. One such method can, under reasonable assumptions, exactly characterize the inhomogeneities based on monotonicity properties of either the Neumann-to-Dirichlet map (non-linear) or its Fréchet derivative (linear). We give a comparison of the non-linear and linear approach in the presence of measurement noise, and show numerically that the two methods give essentially the same reconstruction in the unit disk domain. For a fair comparison, exact matrix characterizations are used when probing the monotonicity relations to avoid errors from numerical solution to PDEs and numerical integration. Using a special factorization of the Neumann-to-Dirichlet map also makes the non-linear method as fast as the linear method in the unit disk geometry.     

High-throughput SEM preparation of proteinaceaous extracellular matrix

Adhesives of aquatic organisms are of high scientific interest with a view to biomimicry. The visualization of their fine-structure, however, is difficult due to the fragility of the extracellular matrix (ECM). Care must be taken in its preparation for high-resolution SEM. Relating matrix structures to substrate properties demands a high throughput of samples for reliable comparisons. In order to acquaint ourselves with a suitable method we found an easy way to manage the critical steps of preparation for SEM. We show that thin layers of proteinaceous matrix can be satisfactorily prepared by combining freeze-drying and sputtering in a conventional sputter coater after one-step fixation (2.5% glutaraldehyde). The results were superior to CPD.     

Structural characterizations of diglycerol monomyristate reverse micelles in aromatic solvent ethylbenzene

Using small-angle X-ray scattering (SAXS) we have investigated the shape and size of diglycerol monomyristate (designated as C14G2) nonionic surfactant reverse micelles in aromatic solvent ethylbenzene as a function of surfactant concentration, temperature, and water. When C14G2 is added into ethylbenzene globular type reverse micelles with maximum core diameter ca. 4.5 nm are formed under ambient conditions. The micellar structure (shape and size) did not change with the surfactant concentration. However, an increase in temperature decreased the micellar size due to an increase in the critical packing parameter (cpp). Surfactant becomes more lipophilic upon heating and the micellar curvature tends to become more negative at higher temperature. Addition of a small amount of water caused a significant micellar growth. For instance, incorporation of 0.3% water in the 5% C14G2/ethylbenzene system resulted in the formation of 2.1 time bigger micelles with a small water pool in the micellar core. Besides the micellar shape is modified into an ellipsoidal prolate, whose scenario can be understood in terms of hydration of the surfactant's headgroup. Hydration decreases the cpp and favors micellar growth. An increase of temperature of a water incorporated system decreased the micellar size due to dehydration, which is equivalent to rod-to-sphere type transition.     

Structural and thermoelectric characterizations of high pressure sintered nanocrystalline Bi2Te3 bulks

Using Bi₂Te₃ nanopowders prepared from ball milling of elemental Bi and Te, nanocrystalline Bi₂Te₃ bulks were fabricated with high pressure sintering technique under variable pressures. The structural and thermoelectric properties were characterized, revealing a strong correlation with the sintering pressure. The nanocrystalline Bi₂Te₃ bulk fabricated under 2 GPa exhibits good thermoelectric properties with ZT over 0.8 from 300 to 460 K and a peak ZT of 1.03 occurring at 403 K, which can be attributed to the small thermal conductivity from enhanced phonon scattering by grain boundaries and defects, as well as to the good electrical property comparable to that of the zone melting material.     

Structural and optical characterizations of ZnO aerogel nanopowder synthesized from zinc acetate ethanolic solution

ZnO aerogel powder has been synthesized by a modified sol–gel process using zinc acetate ethanolic solution. XRD, SEM, EDAX, FTIR, UV–visible absorption and photoluminescence (PL) techniques have been used to characterize the as-prepared and the annealed ZnO aerogel powders. The as-prepared ZnO powder has a well-defined polycrystalline hexagonal wurtzite structure. This measurement has demonstrated that the lattice parameters are lower than the standard ones indicating that drying in supercritical conditions of ethanol does not affect the crystallinity but acts as a compressive agent. EDAX measurements show that the obtained aerogel contains only O and Zn elements. Annealing improves the crystallinity in the low DRX angles and decreases the crystalline quality in the high diffraction angles. Also, annealing acts as a tensile agent and increases the lattice parameters. FTIR spectra confirm the annealing effect by the apparition of the strong Zn–O vibration band. The ZnO absorption band shifts to lower wave numbers after annealing indicating an increase in the Zn–O bond length and confirms the XRD results. UV–visible results show a decrease of the ZnO aerogel optical band gap after annealing and confirm the thermal decompression effect on the lattice parameters. The photoluminescence measurements show that the annealing of ZnO aerogel favors the thermal generation of zinc interstitials and oxygen vacancies defects existing in the as-prepared zinc oxide aerogel and shifts the emission toward lower energies.     

Effects of sterilization on an extracellular matrix scaffold: Part II. Bioactivity and matrix interaction

Small intestinal submucosa (SIS) has been successfully used to treat a variety of damaged or diseased tissues in human patients. As a biologic scaffold, SIS stimulates repair of damaged or diseased tissues and organs with tissue that is similar in structure and function to the material it was meant to replace. To meet clinical safety requirements, biologic materials from animal tissues must undergo processing treatments to minimize host immune response and to eliminate the possibility of disease transmission. The effect of peracetic acid disinfection, lyophilization, and ethylene oxide sterilization on the in vitro bioactivity of the processed SIS was therefore examined in murine fibroblasts and pheochromocytoma (PC12) cells. Specifically, the ability of processed SIS to support fibroblast attachment, to stimulate PC12 cell differentiation, and to upregulate fibroblast VEGF secretion was examined. Fibroblasts attach to the sterilized SIS, remain viable, and more than double their secretion of VEGF as a result of interacting with the SIS matrix components. Additionally, PC12 cells exhibit increased neurite outgrowth following stimulation by SIS matrix proteins versus controls. We conclude that a biologic scaffold can be prepared for human use and still retain significant bioactivity.     

Effects of sterilization on an extracellular matrix scaffold: Part I. Composition and matrix architecture

The impact of peracetic acid (PAA), lyophilization, and ethylene oxide (EO) sterilization on the composition and three dimensional matrix structure of small intestinal submucosa (SIS), a biologic scaffold used to stimulate the repair of damaged tissues and organs, was examined. Fibronectin and glycosaminoglycans are retained in SIS following oxidation by peracetic acid and alkylation using ethylene oxide gas. Significant amounts of FGF-2 are also retained, but VEGF is susceptible to the effects of PAA and is dramatically reduced following processing. Further, matrix oxidation, lyophilization, and sterilization with EO can be performed without irreversibly collapsing the three dimensional structure of the native SIS. These structural features and growth promoting extracellular matrix constituents are likely to be important variables underlying cellular attachment, infiltration and eventual incorporation of SIS into healing host tissues.     

The cytoprotective capacity of processed human cardiac extracellular matrix

Freshly isolated human cardiac extracellular matrix sheets (cECM) have been shown to support stem cell proliferation and tissue-specific lineage commitment. We now developed a protocol for standardized production of durable, bio-functional hcECM microparticles and corresponding hydrogel, and tested its cytoprotective effects on contractile cells subjected to ischemia-like conditions. Human ventricular myocardium was decellularized by a 3-step protocol, including Tris/EDTA, SDS and serum incubation (cECM). Following snap-freezing and lyophilization, microparticles were created and characterized by laser diffraction, dynamic image analysis (DIA), and mass spectrometry. Moreover, cECM hydrogel was produced by pepsin digestion. Baseline cell-support characteristics were determined using murine HL-1 cardiomyocytes, and the cytoprotective effects of ECM products were tested under hypoxia and glucose/serum deprivation. In cECM, glycoproteins (thrombospondin 1, fibronectin, collagens and nidogen-1) and proteoglycans (dermatopontin, lumican and mimecan) were preserved, but residual intracellular and blood-borne proteins were also detected. The median particle feret diameter was 66 μm (15–157 μm) by laser diffraction, and 57 μm (20–182 μm) by DIA with crystal violet staining. HL-1 cells displayed enhanced metabolic activity (39 ± 12 %, P < 0.05) and proliferation (16 ± 3 %, P < 0.05) when grown on cECM microparticles in normoxia. During simulated ischemia, cECM microparticles exerted distinct cytoprotective effects (MTS conversion, 240 ± 32 %; BrdU uptake, 45 ± 14 %; LDH release, ?72 ± 7 %; P < 0.01, each). When cECM microparticles were solubilized to form a hydrogel, the cytoprotective effect was initially abolished. However, modifying the preparation process (pepsin digestion at pH 2 and 25 °C, 1 mg/ml final cECM concentration) restored the cytoprotective cECM activity. Extracellular matrix from human myocardium can be processed to yield standardized durable microparticles that exert specific cytoprotective effects on cardiomyocyte-like cells. The use of processed cECM may help to optimize future clinical-grade myocardial tissue engineering approaches.     

Structural and frequency dependencies of a.c. and dielectric characterizations of epitaxial InSb-based heterojunctions

In this work, heterojunction of InSb/InP was grown by liquid phase epitaxy (LPE). Surface morphology and crystalline structure of the heterojunction were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The frequency and temperature dependences of a.c. conductivity and dielectric properties of the heterojunctions were investigated in the ranges of 100 kHz–5 MHz and 298–628 K, respectively. The a.c. conductivity and its frequency exponents were interpreted in terms of correlated barrier hopping model (CBH), as the dominant conduction mechanism for charge carrier transport. The calculated activation energy, from the Arrhenius plot, was found to decrease with increasing frequency. Experimental results of both dielectric constant ε ₁ and dielectric loss ε ₂ showed a remarkable dependence of both frequency and temperature.     

Structural performance of discontinuous metal matrix composites

Abstract

Discontinuous metal matrix composites (i.e. short fibre and particle reinforced materials) have attained a significant degree of scientific and technological maturity as advanced structural materials. Initial commercialisation has been achieved, with the unique combinations of mechanical and physical properties afforded by metal-ceramic systems proving appropriate for a variety of structural and semistructural applications. In recent years there has been important consolidation in the understanding of basic structural properties in such composites, which are addressed in the present review. The outstanding requirement for an improved understanding of damage tolerance characteristics in these materials is particularly noted. ‘Mesoscopic’ materials architectures (e.g. laminated and functionally graded materials) are also discussed, and the associated potential for development offracture resistant discontinuous metal composite materials highlighted.     

京尼平交联脱细胞猪真皮基质材料的研究

分别采用0、2%、4%、8%、16%(质量分数)的京尼平(GP)交联脱细胞猪真皮基质(pADM),检测交联后材料(GP-pADM)的基本性能。研究结果表明,随着交联剂GP用量的增加,材料的收缩温度逐渐提高,抗张强度降低;电镜扫描图显示交联后材料的孔隙有缩小的趋势,并导致了吸附水率、吸湿率和溶胀率的逐渐下降;红外图谱表明交联后材料中含有共轭双键;细胞毒性试验显示,GP-pADM细胞毒性为0级,急性经口毒性实验未见明显急性毒性。     

Controlling stem cell behavior with decellularized extracellular matrix scaffolds

Decellularized tissues have become a common regenerative medicine platform with multiple materials being researched in academic laboratories, tested in animal studies, and used clinically. Ideally, when a tissue is decellularized the native cell niche is maintained with many of the structural and biochemical cues that naturally interact with the cells of that particular tissue. This makes decellularized tissue materials an excellent platform for providing cells with the signals needed to initiate and maintain differentiation into tissue-specific lineages. The extracellular matrix (ECM) that remains after the decellularization process contains the components of a tissue specific microenvironment that is not possible to create synthetically. The ECM of each tissue has a different composition and structure and therefore has unique properties and potential for affecting cell behavior. This review describes the common methods for preparing decellularized tissue materials and the effects that decellularized materials from different tissues have on cell phenotype.     

Tailoring material properties of a nanofibrous extracellular matrix derived hydrogel

In the native tissue, the interaction between cells and the extracellular matrix (ECM) is essential for cell migration, proliferation, differentiation, mechanical stability, and signaling. It has been shown that decellularized ECMs can be processed into injectable formulations, thereby allowing for minimally invasive delivery. Upon injection and increase in temperature, these materials self-assemble into porous gels forming a complex network of fibers with nanoscale structure. In this study we aimed to examine and tailor the material properties of a self-assembling ECM hydrogel derived from porcine myocardial tissue, which was developed as a tissue specific injectable scaffold for cardiac tissue engineering. The impact of gelation parameters on ECM hydrogels has not previously been explored. We examined how modulating pH, temperature, ionic strength, and concentration affected the nanoscale architecture, mechanical properties, and gelation kinetics. These material characteristics were assessed using scanning electron microscopy, rheometry, and spectrophotometry, respectively. Since the main component of the myocardial matrix is collagen, many similarities between the ECM hydrogel and collagen gels were observed in terms of the nanofibrous structure and modulation of properties by altering ionic strength. However, variation from collagen gels was noted for the gelation temperature along with varied times and rates of gelation. These discrepancies when compared to collagen are likely due to the presence of other ECM components in the decellularized ECM based hydrogel. These results demonstrate how the material properties of ECM hydrogels could be tailored for future in vitro and in vivo applications.     

Characterization of and host response to tyramine substituted-hyaluronan enriched fascia extracellular matrix

Naturally-occurring biomaterial scaffolds derived from extracellular matrix (ECM) have been previously investigated for soft tissue repair. We propose to enrich fascia ECM with high molecular weight tyramine substituted-hyaluronan (TS-HA) to modulate inflammation associated with implantation and enhance fibroblast infiltration. As critical determinants of constructive remodeling, the host inflammatory response and macrophage polarization to TS-HA enriched fascia were characterized in a rat abdominal wall model. TS-HA treated fascia with cross-linking had a similar lymphocyte (P = 0.11) and plasma cell (P = 0.13) densities, greater macrophage (P = 0.001) and giant cell (P < 0.0001) densities, and a lower density of fibroblast-like cells (P < 0.0001) than water treated controls. Treated fascia, with or without cross-linking, exhibited a predominantly M2 pro-remodeling macrophage profile similar to water controls (P = 0.82), which is suggestive of constructive tissue remodeling. Our findings demonstrated that HA augmentation can alter the host response to an ECM, but the appropriate concentration and molecular weight needed to minimize chronic inflammation within the scaffold remains to be determined.