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At least 955 records · Page 53Linked to original sources
PubMed2002

Calcified nanostructured silicon wafer surfaces for biosensing: effects of surface modification on bioactivity.

The growth of known biologically-relevant mineral phases on semiconducting surfaces is one strategy to explicitly induce bioactivity in such materials, either for sensing or drug delivery applications. In this work, we describe the use of a spark ablation process to fabricate deliberate patterns of Ca(10)(PO4)6(OH)2 on crystalline Si (calcified nanoporous silicon). These patterns have been principally characterized by scanning electron microscopy in conjunction with elemental characterization by energy dispersive x-ray analysis. This is followed by a detailed comparison of the effects of fibroblast adhesion and proliferation onto calcified nanoporous Si, calcified nanoporous Si derivatized with alendronate, as well as control samples of an identical surface area containing porous SiO2. Fibroblast adhesion and proliferation assays demonstrate that a higher density of cells grow on the Ca3(PO4)2/porous Si/SiO2 structures relative to the alendronate-modified surfaces and porous Si/SiO2 samples.

Biosensing Techniques↗
PubMed1992

Comparative surface microanalysis of failed Brånemark implants.

The chemical composition and topography of an implant surface determine the human immunologic system response. This study compared the surfaces of 13 Brånemark oral implants, 11 that came from retrieved specimens which failed initially or did not osseointegrate and 2 that were never implanted (controls). The period of implantation in human jaws varied between 3 and 20 months. After cleaning and sterilization, the topography, surface chemical composition, and thickness of the oxide layer were studied. The results obtained with scanning electron microscopy did not show any significant topographic differences among the specimens. X-ray spectrographic microanalysis showed very similar composition (titanium and amounts less than 0.5% of other elements) in the outermost layer of the analyzed specimens. The Auger spectroscope revealed considerable percentage differences in the amount of carbon and silicon in the last monolayers, which could be attributed to handling or to an inadequate cleaning process. This places the retrieved specimens out of the acceptable statistical limits of contamination by introducing a factor of doubt for long-term prognosis in the hypothetical situation of their re-use.

Dental Implants↗
PubMed2006

The core of tau-paired helical filaments studied by scanning transmission electron microscopy and limited proteolysis.

In Alzheimer's disease and frontotemporal dementias the microtubule-associated protein tau forms intracellular paired helical filaments (PHFs). The filaments formed in vivo consist mainly of full-length molecules of the six different isoforms present in adult brain. The substructure of the PHF core is still elusive. Here we applied scanning transmission electron microscopy (STEM) and limited proteolysis to probe the mass distribution of PHFs and their surface exposure. Tau filaments assembled from the three repeat domain have a mass per length (MPL) of approximately 60 kDa/nm and filaments from full-length tau (htau40DeltaK280 mutant) have approximately 160 kDa/nm, compared with approximately 130 kDa/nm for PHFs from Alzheimer's brain. Polyanionic cofactors such as heparin accelerate assembly but are not incorporated into PHFs. Limited proteolysis combined with N-terminal sequencing and mass spectrometry of fragments reveals a protease-sensitive N-terminal half and semiresistant PHF core starting in the first repeat and reaching to the C-terminus of tau. Continued proteolysis leads to a fragment starting at the end of the first repeat and ending in the fourth repeat. PHFs from tau isoforms with four repeats revealed an additional cleavage site within the middle of the second repeat. Probing the PHFs with antibodies detecting epitopes either over longer stretches in the C-terminal half of tau or in the fourth repeat revealed that they grow in a polar manner. These data describe the physical parameters of the PHFs and enabled us to build a model of the molecular arrangement within the filamentous structures.

Alzheimer Disease↗
PubMed1984

The in vivo corrosion of Dispersalloy.

The in vivo corrosion of Dispersalloy amalgam restorations was characterized by scanning electron microscopy and energy dispersive X-ray analysis. It was observed that the corrosion of CuSn resulted in pitting on the restoration surface. Corrosion of Sn-rich grain boundaries led to intergranular separation of gamma 1 grains. The tin released through corrosion reacted with Ca, P, Cl and O forming various insoluble complexes on the external surface, at the tooth-amalgam interface, and within the interior of the restoration. The demineralization of the amalgam-adjacent margin has been attributed to corrosion.

Chemical Phenomena↗
PubMed1988

Restorative dental materials: scanning electron microscopy and x-ray microanalysis.

Restorative dental materials include the materials used to repair damaged teeth and/or replace missing teeth. The definition could be extended to include a much broader group of dental materials, but this paper concentrates only on those materials used to restore the crown portion of damaged teeth. Auxiliary materials, materials for removable denture prostheses, and root canal materials are excluded. Progress and recent research utilizing SEM (Scanning Electron Microscopy), EDS (Energy Dispersive Spectroscopy), and some related methods are presented for the following dental materials: dental amalgam, enamel and dentin bonding agents, dental composites, dental cements, casting alloys for crowns and bridges, and ceramic-metal and ceramic restorative materials. In addition to the basic characterization of these materials by SEM/EDS techniques, examples of replication methods for SEM study of restorative materials in situ are discussed. Some examples are also presented in the direct use of SEM/EDS for characterization of changes and degradation of restorative materials which occur during clinical use.

Dental Materials↗
PubMed1996

Morphometry, scanning electron microscopy and X-ray spectral microanalysis of protostylid pits on human lower third molars.

Protostylid pits on 50 lower third molars were studied. The depth and width of the pits, the thickness of the enamel at the pit bottom and the concavity of the dentino-enamel junction under the pit were measured by light microscopy. The pit content was examined by scanning electron microscopy and X-ray spectral microanalysis. The results show that the morphometric variables of protostylid pits are similar to those of occlusal fissures and pits. The protostylid pits were seen to contain globular formations, belonging mainly to dental calculus; organic rod-shaped bodies, which could represent remnants of the enamel organ--or more probably--foreign bodies, were frequently observed. The study suggests that the development of the most common form of protostylid is basically similar to that of an occlusal cusp, with variations attributable to the low expression of the protostylid and particularities of cusp development in the lateral tooth wall.

Calcium↗
PubMed1991

A classification of urinary calculi with respect to their composition and micromorphology.

Texture and micro-morphology of 1615 urinary calculi has been studied using scanning electron microscopy and X-ray micro analysis. Together with the results of X-ray diffractometry concerning their phase composition, a classification into five stone classes, 13 stone groups and 17 sub-groups could be evaluated. Especially the large and inhomogeneous class of the calcium-stones could be resolved into 13 stone types. Using this classification, the stone type is characterized by a three digit number containing the stone class, the stone group and in some cases the sub-group. Criteria for classification are typical texture patterns, the occurrence of special crystalline phases or both. These items are presented and clinical relationships discussed.

Calcium↗
PubMed2005

Probing charge transport at the single-molecule level on silicon by using cryogenic ultra-high vacuum scanning tunneling microscopy.

A cryogenic variable-temperature ultra-high vacuum scanning tunneling microscope is used for measuring the electrical properties of isolated cyclopentene molecules adsorbed to the degenerately p-type Si(100)-2x1 surface at a temperature of 80 K. Current-voltage curves taken under these conditions show negative differential resistance at positive sample bias, in agreement with previous observations at room temperature. Because of the enhanced stability of the scanning tunneling microscope at cryogenic temperatures, repeated measurements can be routinely taken over the same molecule. Taking advantage of this improved stability, we show that current-voltage curves on isolated cyclopentene molecules are reproducible and possess negligible hysteresis for a given tip-molecule distance. On the other hand, subsequent measurements with variable tip position show that the negative differential resistance voltage increases with increasing tip-molecule distance. By using a one-dimensional capacitive equivalent circuit and a resonant tunneling model, this behavior can be quantitatively explained, thus providing insight into the electrostatic potential distribution across a semiconductor-molecule-vacuum-metal tunnel junction. This model also provides a quantitative estimate for the alignment of the highest occupied molecular orbital of cyclopentene with respect to the Fermi level of the silicon substrate, thus suggesting that this experimental approach can be used for performing chemical spectroscopy at the single-molecule level on semiconductor surfaces. Overall, these results serve as the basis for a series of design rules that can be applied to silicon-based molecular electronic devices.

Electron Transport↗
PubMed2001

Probing the spatial dependence of the emission spectrum of single human retinal lipofuscin granules using near-field scanning optical microscopy.

The emission spectra of single lipofuscin granules are examined using spectrally resolved confocal microscopy and near-field scanning optical microscopy (NSOM). The emission spectrum varies among the granules examined revealing that individual granules are characterized by different distributions of fluorophores. The range of spectra observed is consistent with in vivo spectra of human retinal pigment epithelium cells. NSOM measurements reveal that the shape of the spectrum does not vary with position within the emissive regions of single lipofuscin granules. These results suggest that the relative distribution of fluorophores within the emissive regions of an individual granule is homogeneous on the spatial scale approximately 150 nm.

Humans↗
PubMed2004

Distribution of minerals in quinoa (Chenopodium quinoa Willd.) seeds.

The distribution of minerals in quinoa (Chenopodium quinoa Willd.) seed was examined using energy dispersive X-ray microanalysis (EDX) in combination with scanning electron microscopy (SEM). Phosphorus, K, and Mg coincided in localization in embryonic tissue. Since phytin globoids have been known to localize in protein bodies in embryonic cells of quinoa seed, it is thought that P is attributed to phytic acid and that K and Mg form to phytate. Calcium and K were present in the pericarp, where the cell wall is thickly developed, suggesting that these minerals are associated with pectin. Sulfur occurred in embryonic tissues, which would be derived from sulfur amino acid residues of storage proteins concentrated in the tissues. Abrasion of quinoa seeds resulted particularly in decrease in Ca content.

Calcium↗
PubMed2002

Effects of a potassium nitrate mouthwash on dentinal tubules--a SEM analysis using the dentine disc model.

The concept of tubular occlusion as a method of dentine desensitisation is a logical conclusion from the hydrodynamic hypothesis put forth by Brannström. The aim of this study was therefore to investigate qualitatively by SEM whether a 3% potassium nitrate/0.2% sodium fluoride mouthwash occluded tubule orifices, and by x-ray microanalysis, to characterise the nature of the deposits if any, following application. Following the 'dentine disc model' methodology 1mm thick tooth sections from unerupted molars were obtained. These were treated with the test and control mouthwashes and subjected to scanning electron microscopy. If any deposits were seen, they were to be subjected to elemental analysis using the energy dispersive x-ray analyser. Examination of all the dentine disc surfaces, treated by water (control), active and control mouthwashes demonstrated that none of the treatments, at any of the time intervals, had any visible effect on the dentinal tubule orifices i.e. there was no dentinal tubular occlusion seen. The results suggest that potassium nitrate does not reduce dentinal hypersensitivity, at least by tubule occlusion. This could mean that there is a different mechanism of action, which could not be detected by this in vitro model.

Dentin↗
PubMed1987

Scanning electron microscopic analysis of intraocular ossification in advanced retinal disease.

Chicken eyes from congenic blind (rd/rd) animals showing early, intermediate, and final stages of ossification, similar to the phthisis bulbi condition in man, were examined using scanning and transmission electron microscopy as well as light microscopy and X-ray microanalysis. Early stages of ossification were devoid of mineralized calcium apatite while intermediate and end stages of the disorder contained large amounts of calcium and phosphorus. This process resulted in metaplastic bone formation. An intact Bruch's membrane appeared to separate the choroid from the degenerated pigment epithelium and the developing bone suggesting that its possible origin was metaplasia of the retinal pigment epithelium and the degenerated sensory retina. The end-stage ossification resulted in "phthisic bone" formation which completely filled the vitreous cavity in a manner very similar to the human condition of phthisis bulbi.

Animals↗
PubMed1992

An evaluation of smear layer with various desensitizing agents after tooth preparation.

According to hydrodynamics, any agent blocking the dentinal tubules reduces the flow of fluids and diminishes hypersensitivity. The properties of the desensitizing agents that sponsor tubular occlusion and the barrier efficiency resulting from the interaction of the smear layer with test materials were examined with the scanning electron microscope and energy-dispersive x-ray microanalysis. Selected dentinal desensitizing was accomplished with burnishing procedures, cavity varnish, calcium hydroxide, and topical fluoride. Subjective evaluations were also recorded clinically after tooth preparation. This investigation indicated that the smear layer did not protect against zinc phosphate cement, and that cavity varnish prevented the formation of the smear plugs. The smear layer and plugs were basically composed of calcium and phosphorus, the major ingredients of dentin.

Adult↗
PubMed1984

Deposits on hydrophilic 'bandage' lenses. A scanning electronmicroscopic and x-ray microanalytic study.

Scanning electronmicroscopy of 34 continuously worn Sauflon PW 'bandage' lenses showed an initial deposition of cellular debris, followed by an increasing, general, non-penetrating, organic coating, particularly on the anterior lens surface. No microorganisms were found. X-ray microanalysis of the 34 Sauflon PW lenses as well as 11 daily worn Hydroflex m lenses showed that elements may be added to or 'washed out' from the lenses during storage before preparation for microscopy. The elements obtained were constituents of both normal tear fluid and lens storage solutions. Only sulphur appeared firmly bound in the deposits, probably as sulphur-containing macromolecules of ocular mucus. Calcium was only detected in a few cases.

Contact Lenses, Hydrophilic↗
PubMed1982

Corrosion of resin-bonded orthodontic brackets.

The objective was to identify the nature and origin of indelible black and green stains found in enamel after the removal of bonded orthodontic brackets. Several brackets were examined by scanning electron microscopy and energy-dispersive x-ray analysis. Irrespective of the type of bracket or resin, morphologic evidence of corrosion activity was found. Brackets were pitted, and in some cases large amounts of metal were missing. Cracks were found in the resin which led to sites of destruction in which structures resembling microorganisms were also found. X-ray analysis showed the presence of chromium, nickel, iron, and chlorine in significant amounts in the bonding, discolored resin. It was concluded that the cracks were favoring crevice corrosion. In the presence of organisms and a lowered pH, together with a chloride environment and an oxygen gradient, conditions conducive to corrosion are established.

Chemical Phenomena↗
PubMed2000

Structure and species composition of mercury-reducing biofilms.

Mercury-reducing biofilms from packed-bed bioreactors treating nonsterile industrial effluents were shown to consist of a monolayer of bacteria by scanning electron microscopy. Droplets of several micrometers in diameter which accumulated outside of the bacterial cells were identified as elemental mercury by electron-dispersive X-ray analysis. The monospecies biofilms of Pseudomonas putida Spi3 initially present were invaded by additional strains, which were identified to the species level by thermogradient gel electrophoresis (TGGE) and 16S rDNA sequencing. TGGE community fingerprints of the biofilms showed that they were composed of the effluent bacteria and did not contain uncultivable microorganisms. Of the 13 effluent bacterial strains, 2 were not mercury resistant, while all the others had resistance levels similar to or higher than the inoculant strain.

Bacteria↗