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PubMed2003

SEM/EDS comparison of polar and seasonal temperate ice.

We have developed a method employing a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy for examining uncoated ice specimens. By permitting the ice to sublimate in the SEM at temperatures between -115 degrees and -60 degrees C, enough ions are produced to prevent specimen charging. The absence of a conductive coating permits both the acquisition of uncompromised X-ray spectra, and a dynamic view of impurities as the ice sublimates. The method has enabled us to examine the microstructure and impurities in ice in ways not possible through standard melt chemistry measurements or even through using a SEM to study coated samples. Soluble impurities appeared either as white spots in grain interiors, grain boundaries, and triple junctions, or as filaments in grain boundaries. Inclusions of insoluble impurities have also been observed in natural ice. Thus, we have been able to compare the microstructural location and concentration of impurities in ice from different terrestrial locations. Even when ion chromatography of the melt from two core sections reveals similar levels of impurities, the morphology and location of the impurity aggregates can be quite different. Analysis of impurity type and location can provide clues to the depositional environment and history of the ice.

Cold Climate↗
PubMed2005

Effects of buccal versus lingual surfaces, enamel conditioning procedures and storage duration on brackets debonding characteristics.

OBJECTIVES: To determine the influence of two enamel conditioning techniques on buccal and lingual tooth surfaces at two different times on debonding strength and tooth damage. METHODS: The study included 50 premolars. Buccal and lingual surfaces of 10 teeth were scanned using SEM before (N=4) and after enamel conditioning by either acid etching or sandblasting prior to acid etching (N=6) for their morphology. The remaining 40 teeth were divided into 2 equal groups, differing in enamel conditioning prior to metallic bracket bonding on the buccal and lingual surfaces. Each group was equally subdivided into short-term (48h) or long-term (12m) water storage. Debonding strength was measured followed by SEM and EDAX for adhesive remnant index (ARI) and calcium remnant index (CRI) left on bracket bases. ANOVA with repeated measures was applied to the results. RESULTS: The buccal enamel was rougher than the lingual one. The surface morphology after the two types of conditioning showed a different pattern. A significantly higher debonding strength was needed to debond the buccal brackets compared to the lingual ones (p<0.05). A significantly higher ARI (p<0.002) and higher CRI (p<0.005) were found in the lingual surface compared with the buccal. No differences were found in debonding strength ARI or CRI regarding the different conditioning or storage duration. CONCLUSIONS: Lingual bonding leads to higher ARI and CRI than buccal bonding. Sandblasting prior to etching does not improve bonding strength for lingual or buccal bonding.

Acid Etching, Dental↗
PubMed1998

Bacterial biofilm formation, encrustation, and antibiotic adsorption to ureteral stents indwelling in humans.

Encrustation and urinary tract infection are problematic complications of ureteral stent usage. The objective of our first study was to use surface science techniques to examine three ureteral stent types for encrustation, biofilm formation, and antibiotic adsorption after use in patients. Black Beauty (N = 16), LSe (N = 16), and SofFlex (N = 32) ureteral stents were recovered from patients who had received trimethoprim or ciprofloxacin while the stent was indwelling. These stents were examined with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDX) for the presence and composition of encrustation or biofilm. Conditioning films and encrustations were found on all stents. Encrustation elements (Ca, Mg, P) were identified on 11 of 16 Black Beauty (69%), 7 of 16 LSe (44%), and 12 of 32 SofFlex (38%) stents. The stent type, duration of insertion, and age or sex of the patient did not correlate significantly with the amount of encrustation. Bacterial biofilms were found on 1 of 7 Black Beauty stents (14%) and 7 of 32 SofFlex stents (22%). In a second study, an additional 28 patients with SofFlex stents were treated with ciprofloxacin (N = 16) or ofloxacin (N = 12). Their stents were subjected to high-performance liquid chromatography to determine if oral antibiotic therapy can lead to drug adsorption to the stent. Analysis showed that both ciprofloxacin and ofloxacin adsorbed to the stent surfaces. The mean concentrations of the two antibiotics within the conditioning film of the stents were 0.99 microg/mL and 0.34 microg/mL, respectively. These surface science techniques provide a comprehensive method of evaluating ureteral stents and other prosthetic devices in vivo.

Administration, Oral↗
PubMed1994

Distribution of electrical potential, pH, free Ca2+, and volume inside cultured adult rabbit cardiac myocytes during chemical hypoxia: a multiparameter digitized confocal microscopic study.

Exploiting the optical sectioning capabilities of laser scanning confocal microscopy and using parameter-specific fluorescent probes, we determined the distribution of pH, free Ca2+, electrical potential, and volume inside cultured adult rabbit cardiac myocytes during ATP depletion and reductive stress with cyanide and 2-deoxyglucose ("chemical hypoxia"). During normoxic incubations, myocytes exhibited a cytosolic pH of 7.1 and a mitochondrial pH of 8.0 (delta pH = 0.9 units). Sarcolemmal membrane potential (delta psi) was -80 mV, and mitochondrial delta psi was as high as -100 mV, yielding a mitochondrial protonmotive force (delta p) of -155 mV (delta P = delta psi - 60 delta pH). After 30 min of chemical hypoxia, mitochondrial delta pH decreased to 0.5 pH units, but mitochondrial delta psi remained essentially unchanged. By 40 min, delta pH was collapsed, and mitochondrial and cytosolic free Ca2+ began to increase. Mitochondrial and sarcolemmal delta psi remained high. as Ca2+ rose, myocytes shortened, hypercontracted, and blebbed with a 30% decrease of cell volume. After hypercontraction, extensive mitochondrial Ca2+ loading occurred. After another few minutes, mitochondrial depolarized completely and released their load of Ca2+. After many more minutes, the sarcolemmal permeability barrier broke down, and viability was lost. These studies demonstrate a sequence of subcellular ionic and electrical changes that may underlie the progression to irreversible hypoxic injury.

Animals↗
PubMed1992

Localization of a 230-kD parasitophorous vacuole membrane antigen of Plasmodium berghei exoerythrocytic schizonts (LSA-2) by immunoelectron and confocal laser scanning microscopy.

Using antiserum to a 230-kD parasitophorous vacuole membrane (PVM) antigen of Plasmodium berghei exoerythrocytic schizonts as a specific probe for the PVM, we studied the three-dimensional structure of this membrane within infected host cells by immunoelectron microscopy and confocal laser scanning microscopy at 3, 4, and 50 hr after sporozoite invasion. Fluorescent label was not detected at 3 hr, but was associated with the cytoplasm of 24-hr-old exoerythrocytic parasites. Specific labeling of the PVM was not observed by immunoelectron microscopy until 50 hr, when numerous vesicles and finger-like projections of the PVM were found in the cytoplasm of infected host cells. Labeled vesicles were often isolated and located at the periphery of the infected hepatocyte. Confocal microscopy demonstrated that these vesicles formed discontinuous chains that extended from 3-10 microns away from the parasite. These structures appear to be similar to the membranous clefts of Plasmodium-infected erythrocytes, and may be important in the movement of host or parasite proteins within infected hepatocytes.

Animals↗
PubMed1996

Bone bonding behavior of titanium and its alloys when coated with titanium oxide (TiO2) and titanium silicate (Ti5Si3).

It has been proposed that the essential requirement for artificial materials to bond to living bone is the formation of bonelike apatite on their surfaces in the body. Recent studies have shown that titanium hydrogel and silica gel induce apatite formation on their surface in a simulated body fluid. In this study, the influence of titanium oxide and titanium silicate on the bonding of titanium alloys to bone was studied. Rectangular implants (15 x 10 x 2.2 mm) of titanium, Ti-6Al-4V, Ti-6Al-2Nb-Ta, Ti-6Al-4V coated with TiO2, and Ti-6Al-4V coated with Ti5Si3 were implanted into the tibial metaphyses of mature rabbits. At 8 and 24 weeks after implantation, the tibiae containing the implants were dissected out and subjected to a detaching testing. The failure load for titanium, Ti-6Al-4V, Ti-6Al-2Nb-Ta, Ti-6Al-4V coated with TiO2, and Ti-6Al-4V coated with Ti5Si3 were, respectively, 0.68 +/- 0.48, 0.22 +/- 0.46, 0.67 +/- 0.59, 2.18 +/- 0.71 and 2.03 +/- 0.41 kgf at 8 weeks, and 2.7 +/- 0.91, 2.58 +/- 1.29, 2.38 +/- 0.41, 3.79 +/- 1.7, and 2.79 +/- 0.87 kgf at 24 weeks after implantation. Histological examination by Giemsa surface staining, CMR, and SEM-EPMA revealed the coated titanium alloy implants directly bonded to bone tissue during early implantation. A Ca-P layer was observed at the interface of the coated implants and the bone. The results of this study indicated that TiO2 and Ti5Si3 can enhance the early bonding of titanium alloys to bone by inducing a Ca-P layer (chemical apatite) on the surface of titanium alloys. It also is suggested that the direct bone contact occurs in relation to the calcium and phosphorus adsorption onto the surface of the titanium passive layer formed during long-term implantation.

Alloys↗
PubMed1998

Analysis of titanium dental implants after failure of osseointegration: combined histological, electron microscopy, and X-ray photoelectron spectroscopy approach.

A multitechnique approach has been used to characterize the surface of nonosseointegrated titanium implants and the surrounding biological tissues. Five pure titanium dental implants were used as reference, and 25 removed implants were studied. Surface and in-depth chemical compositions of the implants (from a total of 16 patients) were investigated by X-ray photoelectron spectroscopy (XPS). Histological slides of the surrounding tissues were examined by light microscopy, XPS, and electron microprobe analysis. None of the failed implants presented the regular surface composition and depth profile of the TiO2 overlayer; foreign elements (Ca, Na, P, Si, Cl, Zn, Pb, and Al) were observed on some implants. Fibrosis, lymphocytic and plasmocytic infiltrates, and granulomatous lesions were detected in the surrounding tissues. XPS and electron microprobe analysis indicated the presence of Zn, Fe, Sn, and Ti in the tissues. As a possible scenario for implant failure, we propose and discuss a oxidoreduction mechanism, leading to a partial dissolution or the complete dissociation of the protective titanium dioxide overlayer and to ion diffusion through the surrounding tissues.

Connective Tissue↗
PubMed1999

Optimal conditions for alumina coating formation on the MA956 superalloy for prosthetic bearing applications.

An experimental study of the oxidation treatment at high temperature of the ODS MA956 superalloy was conducted in an attempt to achieve a protective alumina scale for biomedical applications. A quadratic response-surface model was developed in order to study the effects of treatment time and temperature (in the range of 1000 degrees C to 1250 degrees C) on scale thickness. The obtained model adequately represents the experimental response and shows that the thickness gradients of the layer increase with the temperature for each exposure time and decrease steadily to zero as the treatment time increases. The microstructural characterization reveals that the alumina scale formed at or above 1000 degrees C consists of an alpha-alumina phase. Treatments at temperatures above 1150 degrees C give rise to an alumina scale with some defect probability. An increase in the temperature up to 1200 degrees C gives rise to the appearance of some blistering of the superficial scale. An oxidation treatment of 100 h at 1100 degrees C was found to be the best for guaranteeing the formation of a defect-free, compact, adherent, and continuous alpha-alumina scale thick enough to support satisfactory wear and biological conditions.

Alloys↗
PubMed2003

Fabrication of porous polymer monoliths covalently attached to the walls of channels in plastic microdevices.

UV-initiated grafting of plastic tubes and microfluidic chips with ethylene diacrylate followed by the preparation of porous polymer monoliths has been studied. The first step affords a thin grafted layer of polymer with a multiplicity of pendent double bonds that are then used in the second step for covalent attachment of the monolith to the wall. As clearly seen on scanning electron micrographs, this procedure prevents the formation of voids at the monolith-channel interface a problem that has always plagued approaches involving bulk polymerization in nontreated channels due to the shrinkage of the monolith during the polymerization process and its lack of compatibility with the material of the device. Irradiation with UV light through a photomask allows precise patterning specifying both the area subjected to surface modification and the location of the monolith within specific areas of the device.

Microfluidics↗
PubMed2003

Microfluidic device for capillary electrochromatography-mass spectrometry.

A novel microfabricated device that integrates a monolithic polymeric separation channel, an injector, and an interface for electrospray ionization-mass spectrometry detection (ESI-MS) was devised. Microfluidic propulsion was accomplished using electrically driven fluid flows. The methacrylate-based monolithic separation medium was prepared by photopolymerization and had a positively derivatized surface to ensure electroosmotic flow (EOF) generation for separation of analytes in a capillary electrochromatography (CEC) format. The injector operation was optimized to perform under conditions of nonuniform EOF within the microfluidic channels. The ESI interface allowed hours of stable operation at the flow rates generated by the monolithic column. The dimensions of one processing line were sufficiently small to enable the integration of 4-8 channel multiplexed structures on a single substrate. Standard protein digests were utilized to evaluate the performance of this microfluidic chip. Low- or sub-fmol amounts were injected and detected with this arrangement.

Electrophoresis, Capillary↗
PubMed2006

In vivo performance of two different hydroxyapatite coatings on titanium prepared by discharging in electrolytes.

This study reports a discharging method for bone-like carbonated HA (cHA)-coating (Ca/P 1.71) and stoichiometric HA (sHA)-coating (Ca/P 1.67) with micrometer order thicknesses on titanium plates, using modified body fluid and acidic calcium phosphate solutions, respectively. In vivo histological performance of the HA coatings prepared by discharging in electrolytes was evaluated. Bone-contact indexes of HA coatings were measured microscopically. Additionally, bone-coating interface was analyzed by scanning electron microscopy and the use of an electron probe microanalyzer. Results demonstrated that there was no significant difference in contact index between HA coatings. However, the cHA coating was practically replaced by immature bone, and the titanium metal substrate was directly connected to the bone structure whereas the sHA coating layer remained and was partially detached from the titanium metal substrate. Since detached coating particles are pathogens, and can cause peri-implantitis, the cHA coating was more favorable than the sHA coating even if contact index was equivalent to that of the sHA coating. It is thought that coating thickness and chemical composition of coatings are important for biological stability of implants. In conclusion, since bone-like thin cHA coating showed high osteoconductivity and bone replacement, bone-like HA is superior to sHA coating for use in dental implants.

Coated Materials, Biocompatible↗
PubMed1995

Uranium-contaminated soils: ultramicrotomy and electron beam analysis.

Uranium-contaminated soils from the U.S. Department of Energy (DOE) Fernald Site, Ohio, have been examined by a combination of backscattered electron imaging (BSE) and analytical electron microscopy with electron diffraction (AEM). The inhomogeneous distribution of particulate uranium phases in the soil required the development of a method for using ultramicrotomy to prepare transmission electron microscopy (TEM) thin sections from the SEM mounts. A water-miscible resin was selected that allowed comparison between SEM and TEM images, permitting representative sampling of the soil. Uranium was found in iron oxides, silicates (soddyite), phosphates (autunites), and uraninite (UO2 + x). No uranium was detected in association with phyllosilicates in the soil.

Electron Probe Microanalysis↗
PubMed1984

Regulation of the permeability of the medaka fish embryo chorion by exogeneous sodium and calcium ions.

We questioned if the optically transparent noncellular chorion, or egg envelope, which encapsulates the entire medaka fish (Oryzias latipes) embryo might in some way constitute a permeability barrier to high concentrations of the diuretic called amiloride. More specifically, we questioned if removal of cations from the exogenous environment of the medaka embryo might make the chorion more permeable to amiloride and thereby make the fish embryos more sensitive to the inhibitory and lethal effects of this drug. To test this question, chorion-encapsulated medaka embryos were exposed to: deionized-distilled water, to Yamamoto-Ringer's (Y-R) solution, to Yamamoto-Ringer's containing choline chloride as a substitute for NaCl, and to isotonic NaCl solution in the presence of and in the absence of amiloride. Briefly, the prediction that the medaka embryos would be most sensitive to amiloride's inhibitory effects in distilled water was confirmed. Further studies showed that the presence of Na+ or of Ca2+ alone in the culture solution gave partial protection against the lethal effects of the amiloride. Electron probe X-ray microanalysis studies indicated that addition of Ca2+ and other cations to the culture solution caused the concentrations of cations to increase in the chorion, and that increase was correlated to a visible decrease in the permeability of the chorion to the amiloride. This decreased permeability of the chorion apparently protected the embryo from the amiloride. The decreased permeability of the chorion to amiloride, which occurred in the presence of the cations present in Y-R solution, was found to be reversible once the cations were washed from the chorion. Key words medaka, chorion, Na+, Ca2+ permeability, x-ray microanalysis, Oryzias latipes, egg envelope.

Amiloride↗
PubMedDate not supplied

Measures for spectral quality in low-voltage X-ray microanalysis.

Characteristic x-ray production with energetic electrons depends strongly on the overvoltage, the ratio of the incident beam energy to the critical excitation energy for the atomic species of interest. Low-voltage x-ray microanalysis (beam energy < or = 5 keV) is especially susceptible to artifacts due to sample charging because the overvoltage is low and even slight charging can strongly affect peak intensities. The Duane-Hunt bremsstrahlung limit is a good diagnostic to detect sample charging. Dynamic charging effects, however, can influence spectra despite an apparently satisfactory Duane-Hunt limit. Dynamic charging effects must be examined by time series experiments, or through use of dynamic energy windows continuously measuring count rates placed across the spectrum. When charging is a problem, conductive surface coatings can eliminate the effects. When pristine surfaces must be examined without coating, the use of a conductive grid can control charging so that useful x-ray spectra can be obtained.

Artifacts↗