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At least 775 records · Page 43Linked to original sources
PubMed1995

Nitric acid passivation of Ti6Al4V reduces thickness of surface oxide layer and increases trace element release.

Passivation of Ti6Al4V and cpTi implants using methods based on the ASTM-F86 nitric acid protocol are used with the intention of reducing their surface reactivity, and consequently the corrosion potential, in the highly corrosive biologic milieu. The ASTM-F86 passivation protocol was originally developed for surgical implants made of stainless steel and chrome cobalt alloy. Using X-ray photoelectron spectroscopy (XPS) to examine the effect of nitric acid passivation on the surface oxide layer of mill-annealed Ti6Al4V and cpTi, we have found that such treatment actually reduced the oxide thickness on the alloy while having no significant effect on the pure metal. These results correlated with observations obtained using graphite furnace atomic absorption spectrophotometry (GFAAS) to detect trace element release from solid, mill-annealed, Ti6Al4V and cpTi into serum-containing culture medium. We detected significantly greater levels of Ti, Al, and V in the presence of passivated compared to nonpassivated Ti6Al4V. In contrast, nitric acid passivation did not influence Ti release from mill-annealed cpTi. These results, derived from two mill-annealed Ti-based metals, would indicate that re-examination of ASTM-F86-based passivation protocols with respect to Ti6Al4V should be considered in view of the widespread use of this alloy for biomedical devices.

Alloys↗
PubMed2004

Surface modification of titanium implant by microarc oxidation and hydrothermal treatment.

Surface modification of titanium implant is processed by microarc oxidation and hydrothermal treatment. A porous surface with a biologically active bone-like apatite layer was formed. The apatite layer consists of very fine crystals and high crystallinity and is integrated with the titanium alloy substrate with a graded structure without a distinct interface. Such a bioactive layer is expected not only to enhance the bony ingrowth into the porous structure, but also to improve the interlocking between implant and bone.

Alloys↗
PubMed1993

The effect of aluminium coating on elemental signals in X-ray microanalysis.

It has been determined that, in the normal range of aluminium coating thicknesses used to remove charge from non-conducting specimens in the electron microscope, no detectable influence on the elemental signals obtained in X-ray microanalysis is observed. This is in contrast to a previous report (Hopkins et al., J. Electron Microsc. Tech., 18:176-182, 1991) of a reduction in elemental signal with increasing aluminium coating thickness. An explanation of errors in the previous interpretation is provided.

Aluminum↗
PubMed1993

Microanalysis near particles and voids at grain boundaries.

Some of the problems of using high spatial resolution microanalysis in the vicinity of particles and voids in metal grain boundaries are discussed. New analytical results are presented for nickel based alloys, which suggest that elemental distributions in the region immediately adjacent to growing grain boundary particles and voids are often anisotropic.

Electron Probe Microanalysis↗
PubMed2005

Evolution of nanocrystallinity in periodic mesoporous anatase thin films.

Herein we report the first kinetic study of the intrachannel wall phase-transition of amorphous titania to nanocrystalline anatase for periodic mesoporous titania thin films, monitored by time-resolved in situ high-temperature X-ray diffraction. Structural transformations associated with the phase transition are further probed by high-resolution scanning electron microscopy and transmission electron microscopy. The model found to be most consistent with the kinetic data involves 1D diffusion-controlled growth of nanocrystalline anatase within the spatial confines of the channel walls of the mesostructure. The observation of anisotropic, rod-shaped anatase nanocrystals preferentially aligned along the channel axis implies that the framework of the liquid-crystal-templated mesostructure guides the crystal growth.

Anisotropy↗
PubMed1998

Visualization of NMDA receptor-induced mitochondrial calcium accumulation in striatal neurons.

Ca2+ influx through NMDA receptor-gated channels and the subsequent rise in intracellular Ca2+ concentration ([Ca2+]i) have been implicated in cytotoxic processes that lead to irreversible neuronal injury. While many studies have focused on cytosolic Ca2+ homeostasis, much less is known about Ca2+ fluxes in subcellular organelles, such as mitochondria. The mitochondria play an important role in Ca2+ homeostasis by sequestering cytosolic Ca2+ loads. However, mitochondrial Ca2+ overload can impair ATP synthesis, induce free radical formation, and lead to lipid peroxidation. Thus, it is also important to understand the mitochondrial Ca2+ fluxes induced by NMDA. In this study, changes in mitochondrial Ca2+ concentration ([Ca2+]m) in cultured striatal neurons were monitored with a Ca(2+)-binding fluorescent probe, rhod-2, and laser scanning confocal microscopy. The rhod-2 fluorescence signal was highly localized in mitochondrial areas of confocal images. A rapid increase of [Ca2+]m was observed when neurons were treated with 100 microM NMDA. The increased [Ca2+]m induced by NMDA could not be observed in the presence of ruthenium red, an inhibitor of the mitochondrial Ca2+ uniporter, or CCCP, a protonophore that breaks down the mitochondrial membrane potential necessary for Ca2+ uptake. The magnitude and reversibility of changes in [Ca2+]m induced by NMDA were variable. In neurons receiving multiple pulses of NMDA, [Ca2+]m did not return to baseline. The elevated [Ca2+]m may persist indefinitely and may rise further after successive NMDA exposures. These data demonstrate that Ca2+ accumulates in mitochondria in response to NMDA receptor activation. This Ca2+ accumulation may play a role in the excitotoxic mitochondrial dysfunction induced by NMDA.

Animals↗
PubMed1993

In vitro interactions of c-ANCA (antibodies to proteinase 3) with human endothelial cells.

Several concepts concerning the pathogenicity of antineutrophil cytoplasmic antibodies (ANCA) exist, but till now only sparse data about ANCA-endothelial interactions are available. In this study we have investigated the expression of proteinase 3 (PR-3) in human umbilical endothelial cells (HEC) using purified anti-PR-3 antibodies (C-ANCA) of patients with Wegener's granulomatosis (WG) and monoclonal antibodies to PR-3 (human and murine) as probes. Performing cyto-ELISAs, laser scanning microscopy and Western blot we were able to show that treatment of HEC with IL-1-alpha led to an increased PR-3 expression in the cytoplasm and to a transient translocation into the EC-membrane. Representing an important missing link of ANCA-endothelial interactions, our data give a hint at a possible direct pathogenicity of anti-PR-3 antibodies in WG and other vasculitides.

Antibodies, Antineutrophil Cytoplasmic↗
PubMed2000

Labeled probes inserted in the macrophage membrane are transferred to the parasite surface and internalized during cell invasion by Toxoplasma gondii.

Tachyzoites of Toxoplasma gondii attach to the macrophage surface and are internalized either by a phagocytic process, which can be inhibited by cytochalasin D, or by an active process, independent of host cell actin. Previous studies have shown that parasite attachment induces the secretion of macromolecules found in the apical organelles (micronemes and rhoptries) and subsequent/concomitant parasite internalization with the formation of a membrane-bound vacuole known as the parasitophorous vacuole. In the present study we labeled the macrophage surface with fluorescent probes that bind to proteins (DiIC16) and lipids (DTAF) and then allowed control or cytochalasin-D-treated cells to interact with untreated or antibody-coated tachyzoites of T. gondii. The interaction was interrupted at different time points by fixation and the distribution of the probes was analyzed by confocal laser scanning microscopy. Following attachment of the parasites to the macrophage surface, intense labeling of the parasite surface was observed, suggesting transfer of components of the macrophage surface to the parasite surface. Nonadherent parasites were not labeled. Immediately after attachment, most of the parasites were internalized and labeling of the internalized parasites as well as of the parasitophorous vacuole, probably of its membrane, was evident, indicating that surface components of the macrophage are involved in the formation of the parasitophorous vacuole.

Animals↗
PubMed2003

Transformation behavior, chemical composition, surface topography and bending properties of five selected 0.016" x 0.022" NiTi archwires.

PURPOSE: The aim of this study was to characterize five selected commercial NiTi archwires in terms of their transformation behavior, chemical composition, surface topography and mechanical properties (at temperatures of 22 degrees C, 37 degrees C and 60 degrees C). MATERIAL AND METHODS: The rectangular orthodontic archwires investigated were Neo Sentalloy F80 (GAC, Central Islip, NY, USA), 35 degrees C Thermo-Active Copper NiTi (A-Company/Ormco, Glendora, CA, USA), Rematitan "Lite" (Dentaurum, Pforzheim, Germany), Titanol SE S (Forestadent, Pforzheim, Germany) and Titanal (Lancer, San Marcos, CA, USA) in size 0.016" x 0.022". The chemical composition and surface topography were analyzed by energy dispersive X-ray spectroscopy using an analytical scanning electron microscope (XL30, EDAX SUTW Saphire Detector; Philips, Eindhoven, Netherlands). The transition temperatures were measured by means of differential scanning calorimetry (DSC; Perkin-Elmer Pyris 1, Perkin-Elmer, Fremont, CA, USA) in a range of - 80 degrees C to + 80 degrees C. The mechanical properties and their dependence on temperature were determined by means of 3-point bending tests. The binary archwire materials were characterized by a two-phase structure (NiTi matrix and Ni3Ti4 precipitates). RESULTS: The SEM analyses revealed abradant residues in virtually all archwires, while DSC revealed complex transformation properties. In addition to the martensitic and austenitic transformations, an R-phase transformation was also detected. The bending tests showed pronounced loading and unloading plateaus. The martensitic archwires (Neo Sentalloy F80, 35 degrees C Thermo-Active Copper NiTi) were found to have a lower strength than the martensitic-austenitic (Rematitan "Lite") and the austenitic archwires (Titanol SE S, Titanal). With increasing temperature (in the range from 22 degrees C to 60 degrees C) a linear rise in the plateau forces was recorded. CONCLUSIONS: When assessing the quality of archwires, account should be taken of the surface quality, as it is this that determines corrosion resistance, biocompatibility and friction characteristics. The mechanical properties depend on the initial state; moderate plateau forces and plateau moments can only be achieved with martensitic archwires. In contrast to conventional steel alloys, the strength characteristics are heavily dependent on temperature and need to be known if NiTi archwires are to be used to optimal effect. In addition, the superelastic plateau is used only partially, if at all, when minimum leveling is required.

Calorimetry, Differential Scanning↗
PubMed2000

Silica deposition in Demosponges: spiculogenesis in Crambe crambe.

Transmission electron-microscopy images coupled with dispersive X-ray analysis of the species Crambe crambe have provided information on the process of silica deposition in Demosponges. Sclerocytes (megasclerocytes) lie close to spicules or surround them at different stages of growth by means of long thin enveloping pseudopodia. Axial filaments occur free in the mesohyl, in close contact with sclerocytes, and are triangular in cross section, with an internal silicified core. The unit-type membrane surrounding the growing spicule coalesces with the plasmalemma. The axial filament of a growing spicule and that of a mature spicule contain 50%-70% Si and 30%-40% Si relative to that contained in the spicule wall, respectively. The extracellular space between the sclerocyte and the growing spicule contains 50%-65%. Mitochondria, vesicles and dense inclusions of sclerocytes exhibit less than 10%. The cytoplasm close to the growing spicule and that far from the growing spicule contain up to 50% and less than 10%, respectively. No Si has been detected in other parts of the sponge. The megascleres are formed extracellularly. Once the axial filament is extruded to the mesohyl, silicification is accomplished in an extracellular space formed by the enveloping pseudopodia of the sclerocyte. Si deposition starts at regularly distributed sites along the axial filament; this may be related to the highly hydroxylated zones of the silicatein-alpha protein. Si is concentrated in the cytoplasm of the sclerocyte close to the plasmalemma that surrounds the growing spicules. Orthosilicic acid seems to be pumped, both from the mesohyl to the sclerocyte and from the sclerocyte to the extracellular pocket containing the growing spicule, via the plasmalemma.

Animals↗
PubMed2006

Ultrastructural and physico-chemical heterogeneities of yeast surfaces revealed by mapping lateral-friction and normal-adhesion forces using an atomic force microscope.

Scanning force microscopy has been used to probe the surface of the emerging pathogenic yeast Candida parapsilosis, in order to get insight into its surface structure and properties at submicrometer scales. AFM friction images eventually show patches with a very strong contrast, showing high lateral interaction with the tip. Adhesion force measurement also reveals a high normal interaction with the tip, and patches show extraordinarily high pull off values. The tip eventually sticks completely at the center of the patches. While an extraordinarily high interaction is measured by the tip at those zones, topographic images show extraordinarily flat topography over those zones, both of which characteristics are consistent with a liquid-like area. High resolution friction images show those zones to be surrounded by microfibrillar structures, concentrically oriented, of a mean width of about 25 nm, structures that become progressively less defined as we move away from the center of the patches. No structure can be appreciated inside the zones of maximum contrast. Also some helical or ribbon-like structure can be resolved from friction images. There is not only an ordered disposition of the microfibrillar structures, but also the adhesion force increases radially in the direction towards the center of the patches. These structures responsible for the high adhesion are thought to be incipient-emerging budding zones. Microfibrillar structures are thought to represent the first steps of chitin biosynthesis and cell wall digestion, with chitin polymers being biosynthesized, associated with other macromolecules of the yeast cell wall. They can be also beta glucan helical structures, made visible in the zone of yeast division due to the action of autolysins. The observed gradient in surface adhesion and elastic properties correlates well with that expected from a biochemical point of view. The higher adhesion force measured could be either due to the different macromolecular nature of the patches, or to a mechanical adhesion effect due to the different plasticity of that zone. This work reveals the importance of taking into account the dynamic nature of the cell wall physico-chemical properties. Processes related to the normal cell-cycle, as division, can strongly alter the surface morphology and physico-chemical properties and cause important heterogeneities that might have a profound impact on the adhesion behavior of a single cell, which could not be detected by more macroscopic methods.

Candida↗
PubMed1986

Interface corrosion in amalgam-to-amalgam and amalgam-to-nonprecious metal crown couplings.

This study examined the contact surface area in the coupling of a class II amalgam restoration with another class II amalgam restoration or with a stainless steel or nickel-chrome crown in 1% NaCl solution. The characterization of interfaces was carried out by using SEM and EDX microanalysis. The results indicate that the coupling of an amalgam-stainless steel crown and an amalgam-inconel crown in NaCl solution forms a deposit on the crown surfaces. This deposit contains all the constituents of corrodible phases of amalgam, including Zn. If amalgam restorations in adjoining teeth are contemplated, non-Zn-containing amalgam alloys of the same composition should be considered.

Chemical Phenomena↗
PubMed1988

Corrosion of dental burs in sterilizing and disinfecting solutions.

Potentiodynamic anodic polarization, SEM, and energy dispersive microanalysis techniques were used to determine electrochemical aggressiveness of disinfecting and sterilizing solutions on carbide and stainless steel burs. The importance of galvanic cell formation in carbide burs caused by mixed metal coupling was examined. The following conclusions were reached. 1. Anodic polarization methods are an effective means for discriminating among the relative corrosiveness of sterilizing and disinfecting agents on dental instruments, particularly dental burs. 2. The relative degree of corrosiveness on stainless steel burs shows Omni II and Omnicide solutions the best, Sterall and Sporicidin solutions the poorest, and Glutarex solution intermediate. Omnicide and Glutarex solutions show the least degree of corrosiveness on the carbide burs. 3. SEM analysis of ground, polished, and treated surfaces shows corrosion deposition over the soldered joint of the carbide burs. The stainless steel shank is a cathodic component of a three-way galvanic cell, whereas the silver soldered joint is an anodic component.

Carbon↗
PubMedDate not supplied

Use of coincidence techniques to improve the detection limits of electron spectroscopy in STEM.

A method of improving the detection limits of microanalysis using electron energy losses due to inner-shell excitation is proposed. This is based on coincidence detection of the energy-loss electrons with another signal which also results from inner-shell excitations, i.e., Auger electrons or characteristic X-rays. It is concluded that there will be a significant improvement in the detection of monolayers on a homogeneous monatomic substrate by using coincidence of energy-loss electrons with Auger electrons.

Electron Probe Microanalysis↗