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 21,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An injectable composite material based on biphasic calcium phosphate (BCP) and a nonionic cellulose ether has been elaborated for use in percutaneous surgery for spine fusion. This paper reports the characterization results of this material by spectroscopic techniques including X-ray diffraction (XRD), infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) fitted with an energy dispersive X-Ray analysis system and high-resolution transmission electron microscopy (HR-TEM). From FTIR and XPS results, it was observed that the adhesion between the polymer and the ceramic might be insured by oxygen bridging developed through an ionic bonding between calcium ions and (C-O) groups of the polymer. Moreover, XPS showed attraction of Ca2+ ions in the polymer matrix, while the ceramic surface was modified in a HPO4(2-) -rich layer. These results suggest a possible dissolution/precipitation process at the interface ceramic/polymer. HR-TEM observations supported this hypothesis, showing a light contrasted fringe at the surface of the ceramic grains in the composite paste. As well, changes in the XRD spectra could indicate a small decrease in the crystal size of the BCP powder through the contact to polymer solution. In addition, SEM observation showed a decrease of the initial BCP granulometry. Aggregates of 80-200 microm seemed to be mostly dissociated in micrograins. The ceramic grains were coated with and bonded between each other by the polymer matrix, which acted as spacer in between the ceramic grains, creating a macroporous-like material structure.
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PMID:Influence of a cellulosic ether carrier on the structure of biphasic calcium phosphate ceramic particles in an injectable composite material. 1020 9

Ultrafine mixed Fe-Mo oxide particles are prepared by the sol-gel technique using citric acid as a complex agent. The formation process of the ultrafine oxides is studied by using XRD, DTA-TG, FT-IR, TEM, and BET surface area measurement. It is found that the morphology and structure of the oxide particles are significantly dependent on the process parameters such as thermal treatment temperature (T), pH of the starting solution, and the molar ratio of citric acid to metallic ions (L/M). The formation temperature of crystalline Fe(2)(MoO(4))(3) by the sol-gel process is much lower than that by the coprecipitation method. The catalytic properties of ultrafine Fe-Mo oxide particles are tested and compared with those of large oxide particles having the same composition. It is shown that for selective oxidation of toluene to benzaldehyde the ultrafine Fe-Mo oxide particles exhibit higher benzaldehyde selectivity and toluene conversion than the large oxide particles. The unique catalytic properties of ultrafine Fe-Mo oxide particles may be correlated to the higher mobility of lattice oxygen species in the ultrafine oxide particles and their higher BET surface area. Copyright 1999 Academic Press.
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PMID:Preparation, Characterization, and Catalytic Properties of Ultrafine Mixed Fe-Mo Oxide Particles. 1041 72

Methods of electron-probe microanalysis (EPMA), with some input from scanning and transmission electron microscopy (SEM/TEM), are applied for the identification of micro-scale constituents in a solid matrix. The subject of the study is a magnesium alloy composite, which contains silicon carbide-based fibres made by a liquid metal infiltration process. Backscattered electron imaging of the composite in the SEM showed that during composite manufacture, fibres were chemically attacked by the metal, many of the fibres exhibiting three distinct grey levels, indicative of different reaction zones, and others appearing uniformly black. EPMA measurements showed that each region contained approximately 12wt.% oxygen and that penetration of the fibre by magnesium was accompanied by a reduction in the concentration of silicon and carbon. From studying the position and shape of specific X-ray lines it was shown that magnesium penetration involved a chemical reaction with silicon oxycarbide, established in earlier EPMA studies as one of the fibre constituents. Also, in the outermost region, aluminium in the alloy reacted with free carbon in the fibre to form aluminium carbide and with magnesium to produce a Mg-Al intermetallic. The composition of black fibres was quite different from the grey ones, with negligible silicon and only a small amount of aluminium. Oxygen levels in black fibres were consistent with complete oxidation, indicating these fibres were subjected, locally, to severe oxidising conditions during composite manufacture. In the metal matrix itself, particles of a mixed magnesium/aluminium oxide, silicon carbide and magnesium silicide were observed, the latter two phases forming as silicon and carbon were ejected from fibres.
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PMID:Phase identification of microfeatures using EPMA methods, especially high-resolution X-ray spectroscopy 1093 55

Whole gland perfusion technique was applied to rat parotid glands to assess whether amylase affects fluid secretion. Control perfusion without any secretagogue evoked no spontaneous secretion. Carbachol (CCh 1 microM) induced both amylase and fluid secretion with distinctive kinetics. Fluid secretion occurred constantly at 40-120 microliter/g-min (average plateau was 60 microliter/g-min), whereas amylase secretion exhibited an initial peak (10 mg maltose/30 s per g wet w. of the gland), followed by a rapid decrease to reach a plateau level of 1 mg maltose/30 s later than 1.5-2 min. Isoproterenol (Isop 1 microM) alone did not induce fluid secretion although it evoked amylase secretion as measured in isolated perfused acini. Addition of Isop during CCh stimulation evoked a rapid and large rise in amylase secretion to 15 mg maltose/30 s accompanied by the increase in oxygen consumption. However, the fluid secretion exhibited a rather gradual decrease. These findings suggest that control of salivary fluid secretion is independent of the amylase secretion system induced by CCh and/or Isop. Morphological observations carried out by HR SEM and TEM revealed exocytotic profiles following Isop stimulation. CCh stimulation alone seldom showed -exocytotic profiles, suggesting a low incidence of amylase secretion during copious fluid secretion. Combined stimulation of CCh and Isop induced both vacuolation and exocytosis along intercellular canaliculi. During washout of secretagogues, lysosomal digestion of excess membrane took place.
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PMID:Relationship between amylase and fluid secretion in the isolated perfused whole parotid gland of the rat. 1098 Jun 75

Whole gland perfusion technique was applied to rat parotid glands to assess whether amylase affects fluid secretion. Control perfusion without any secretagogue evoked no spontaneous secretion. Carbachol (CCh 1 microM) induced both amylase and fluid secretion with distinctive kinetics. Fluid secretion occurred constantly around 60 microL/g-min, whereas amylase secretion exhibited an initial peak, followed by a rapid decrease to reach a plateau. Isoproterenol (Isop 1 microM) alone did not induce fluid secretion although it evoked amylase secretion as measured in isolated perfused acini. Addition of Isop during CCh stimulation evoked a rapid and large rise in amylase secretion accompanied by small increase in oxygen consumption. Morphological observations carried out by HR SEM and TEM revealed exocytotic profiles following Isop stimulation. CCh stimulation alone seldom showed exocytotic profiles, suggesting a low incidence of amylase secretion during copious fluid secretion. Combined stimulation of CCh and Isop induced both vacuolation and exocytosis along intercellular canaliculi. These findings suggest that control of salivary fluid secretion is independent of the amylase secretion system induced by CCh and/or Isop.
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PMID:Fluid and amylase secretion by perfused parotid gland: physio-morphological approach. 1098 8

Acquisition of a great number of energy-filtered images in a TEM (EFTEM) around the characteristic signal with a low energy-selecting slit allows display of the electron energy loss (EEL)-spectrum of regions of interest (ROIs) of a sample. These EEL-spectra can be submitted to the different treatments already in use for electron energy loss spectroscopy (EELS). In particular, it is possible to fit the experimental background with different mathematical models, using images acquired below and above a characteristic ionization edge. After this fitting, elemental maps can be computed by subtraction of the extrapolated/interpolated background from the characteristic images. In this work, we compared two mathematical models for background fitting-the Egerton power law and the log-polynomial law. We studied the low-energy region (40-150 eV) and a higher-energy region (350-600 eV) with the aid of software for interactive processing of EFTEM image series that we developed. The analyzed elements were the constitutive elements: iron, phosphorus, nitrogen, and oxygen in several biological materials. Two analytical TEMs, one equipped with a post-column and the other with an in-column spectrometer, were used. Our experimental results confirm that the power law is very sensitive to the value of the energy loss of the pre-edge images when the background is computed by extrapolation. The log-polynomial model is less sensitive than the power law model to the value of the energy loss of the pre-edge images in the low energy region. For the oxygen K edge at 535 eV, it gives the best fit when it is combined with the interpolation method. The use of programs that facilitate the handling of EFTEM image series, and the controlled calculation of the background under the characteristic images, represent a step forward in the generation of elemental maps.
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PMID:Elemental maps from EFTEM images using two different background subtraction models. 1130 90

Four adult female Japanese newts, Cynops pyrrhogaster, were carried for 15 days aboard the orbiting space shuttle, Columbia, in July of 1994, as part of the Second International Microgravity Laboratory, IML-2 aquatic animal experiments. These previously fertilized newts, after stimulation with chorionic gonadotropin by a spaceflight adapted injection procedure, deposited numerous eggs for study of early development during weightlessness. The primitive saccular lungs of the two newts which survived the spaceflight revealed by TEM marked pulmonary cytopathologic changes including basal laminar separation, microvillar degeneration, and cytoplasmic granular changes in the primary granulated pneumocytes. Also, intracellular edema in the pulmonary collagenous matrix and vacuolar changes in the ciliated pulmonary lining cell type and in vascular endothelial cells were observed. These changes, triggered by the spaceflight, and not seen in controls also relying on respiration via the skin, may reflect a chronic mild hypoxia as it is known that newts undergoing oviposition are subject to increased oxygen demand.
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PMID:Cytopathologic observations of the lung of adult newts (Cynops pyrrhogaster) on-board the space shuttle, Columbia, during the Second International Microgravity Laboratory experiments. 1153 33

This paper describes the usefulness of electron microscopy in the investigation of the cause of opacification of an intraocular artificial lens (IOL), which affected both the anterior and posterior surfaces of the IOL. The explanted lenses were remarkably similar and were uniformly opaque, with "reticulated" surfaces under dissecting and ordinary light microscopes. TEM showed that the surfaces of the explanted lenses were irregular, and there was a layer of electron-dense granular deposits that extended to a depth of approximately 5 microm into the lens substance. SEM showed a "cerebriform" lens surface with elevated areas alternating with depressed crevices, which corresponded nicely to the TEM appearance. Energy-dispersive x-ray analysis showed that the deposit was composed of calcium, oxygen, and phosphorus, which was later shown to be calcium hydroxyapatite by x-ray diffraction study. Electron microscopy has proven to be an essential tool in the investigation of the cause of this mysterious outbreak of opacification of the surfaces of the artificial lenses. Apart from directly visualizing the lens surfaces in a 2- and 3-dimensional manner, it also provides information on the elemental composition of the deposit. Such findings enable the clinicians and manufacturer to search for the underlying pathogenesis of the abnormal calcium hydroxyapatite crystals deposit.
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PMID:Opacification of artificial intraocular lens: an electron microscopic study. 1157 71

The decomposition, either thermal or under H2, of [O(AuIPR3)3](CF3SO3) (R = Ph 1, R = Me 2) in organic solvents has been studied by 31P(1H) NMR, UV-vis spectroscopy and TEM; during the reaction, the phosphine acts as an efficient oxygen trap and gold nanoparticles are produced which may be stabilized by PVP in acetonitrile (mean diameter 4.5 nm) or oleylamine in toluene (mean diameter 9 nm).
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PMID:Aurophilic complexes as gold atom sources in organic media. 1212 Jan 41

Analytical electron microscopy was used to characterize aquatic iron-rich colloids. We focused our attention on a redox transition medium in the drainage water of a peat soil. In the anoxic peat water, observations by transmission electron microscopy and associated energy dispersive analyses (TEM-EDS) highlight the presence of spherical entities (approximately 100-600 nm), containing only traces of iron. The increase of dissolved oxygen concentration favours the formation of iron oxy(hydr)oxides. In the oxygenated drain, particles with the same morphology and size range are present. Statistical TEM-EDS analyses show that they represent the only colloidal form of iron in the drain samples. Nevertheless, although Fe-K peaks appear clearly on EDS spectra, the proportion of iron in these colloids reaches at most 4% at. (whereas C + O > 90% at.). Structural information completes this study. Both electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS) reveal the disparity between element distributions within the drain entities. Iron and calcium are preferably distributed on the outer sphere of the particle, whereas carbon and oxygen follow the theoretical variation of the signal intensity within a plain sphere. The implication of organic matter as nucleation site for iron precipitation is spectacularly demonstrated by the presence of nanometre-sized iron-rich phases highlighted by EELS line scans.
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PMID:Analytical electron microscopy as a tool for accessing colloid formation process in natural waters. 1223 Apr 88


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