Biomedical and biological applications of scanning electron microscopy

This article summarizes the basic principles of scanning electron microscopy and the capabilities of the technique with different examples ofapplications in biomedical and biological research.

Scanning electron microscopy of the interaction between Cryptococcus magnus and Colletotrichum gloeosporioides on papaya fruit

The objective of this work was to investigate possible modes of action of the yeast Cryptococcus magnus in controlling anthracnose (Colletotrichum gloeosporioides) on post harvested papaya fruits. Scanning electron microscopy was used to analyze the effect of the yeast on inoculations done after harvest. Results showed that C. magnus is able to colonize wound surfaces much faster than the pathogen, outcompeting the later for space and probably for nutrients. In addition, C. magnus produces a flocculent matrix, which affects hyphae integrity. The competition for space and the production of substances that affect hyphae integrity are among the most important modes of action of this yeast.

Alterations of Na, K and Rb concentrations in Mycenaean pottery and a proposed explanation using X-ray diffraction

One of the most important reference groups for Mycenaean pottery is the Mycenae/Berbati (MB). In several studies, a second group has been identified (MBKR). The chemical compositions were similar to MB, but with important differences in the Na, K and Rb contents. The present study suggests that these differences are due to selective alteration and contamination processes that are indirectly determined by the original firing temperature. Therefore, groups MB and MBKR should be considered as a single reference group.

Combined experimental powder X-ray diffraction and DFT data to obtain the lowest energy molecular conformation of friedelin

Friedelin molecular conformers were obtained by Density Functional Theory (DFT) and by ab initio structure determination from powder X-ray diffraction. Their conformers with the five rings in chair-chair-chair-boat-boat, and with all rings in chair, are energy degenerated in gas-phase according to DFT results. The powder diffraction data reveals that rings A, B and C of friedelin are in chair, and rings D and E in boat-boat, conformation. The high correlation values among powder diffraction data, DFT and reported single-crystal data indicate that the use of conventional X-ray diffractometer can be applied in routine laboratory analysis in the absence of a single-crystal diffractometer.

Nanoporous materials: pillared clays and regular silicas as an example of synthesis and their porosity characterization by X-ray diffraction

Because of their practical applications, porous materials attract the attention of undergraduate students in a way that can be used to teach techniques and concepts in various chemistry disciplines. Porous materials are studied in various chemistry disciplines, including inorganic, organic, and physical chemistry. In this work, the syntheses of a microporous material and a mesoporous material are presented. The porosity of the synthesized materials is characterized by X-ray diffraction analysis. We show that this technique can be used to determine the pore dimensions of the synthesized materials.

Studies of the small bowel surface by scanning electron microscopy in infants with persistent diarrhea

We describe the ultrastructural abnormalities of the small bowel surface in 16 infants with persistent diarrhea. The age range of the patients was 2 to 10 months, mean 4.8 months. All patients had diarrhea lasting 14 or more days. Bacterial overgrowth of the colonic microflora in the jejunal secretion, at concentrations above 10(4) colonies/ml, was present in 11 (68.7%) patients. The stool culture was positive for an enteropathogenic agent in 8 (50.0%) patients: for EPEC O111 in 2, EPEC O119 in 1, EAEC in 1, and Shigella flexneri in 1; mixed infections due to EPEC O111 and EAEC in 1 patient, EPEC O119 and EAEC in 1 and EPEC O55, EPEC O111, EAEC and Shigella sonnei in 1. Morphological abnormalities in the small bowel mucosa were observed in all 16 patients, varying in intensity from moderate 9 (56.3%) to severe 7 (43.7%). The scanning electron microscopic study of small bowel biopsies from these subjects showed several surface abnormalities. At low magnification (100X) most of the villi showed mild to moderate stunting, but on several occasions there was subtotal villus atrophy. At higher magnification (7,500X) photomicrographs showed derangement of the enterocytes; on several occasions the cell borders were not clearly defined and very often microvilli were decreased in number and height; in some areas there was a total disappearance of the microvilli. In half of the patients a mucus-fibrinoid pseudomembrane was seen partially coating the enterocytes, a finding that provides additional information on the pathophysiology of persistent diarrhea.

The measured variation of the Debye-Waller factor of aluminum from 295K to 815K by using the energy dispersive x-ray diffraction technique

The Energy Dispersive X-ray Diffraction System at Brock University has been used to measure the intensities of the diffraction lines of aluminum powder sample as a function of temperature. At first, intensity measurements at high temperature were not reproducible. After some modifications have been made, we were able to measure the intensities of the diffraction lines to 815K, with good accuracy and reproducibility. Therefore the changes of the Debye-Waller factor from room temperature up to 815K for aluminum were determined with precision. Our results are in good agreement with those previously published.

X-ray diffraction studies of muscle : observations on the anterior byssus retractor muscle of Mytilus edulis and the insect flight muscle from Sarcophaga bullata

The interfilament spacing of the anterior byssus retractor muscle from Mytilus edulis was studied as the muscle was extended. It was found that variations in this spacing were very small and consistent with the hypothesis that the interfilament spacing was independent of the extension of the muscle. It was observed that the interfilament spacing was dependent on the osmolarity of the bathing medium. In concentrated solutions of the artificial seawater, the interfilament spacing decreased; while in dilute solutions of artificial seawater, it was observed that the interfilament spacing was increasing. X-ray diffraction patterns were obtained from fresh, and glutaraldehyde fixed, specimens of insect flight muscle from Sarcophaga bullata. There patterns were in general agreement with previous X-ray diffraction studies of insect flight muscle. A reflexion G at 93A was observed and interpreted as arising from diffraction in the mitochondria. Specimens of dried insect flight muscle produced a diffraction pattern consisting of arc and ring reflexions. This was interpreted as suggesting an ordered arrangement of cristae, in the mitochondria from these muscles.

X-ray diffraction from Al powder using energy dispersive technique

Using the energy dispersive x ...ray diffraction (EDXD) technique, the room temperature diffraction pattern of Al powder was obtained at diffraction angles ~ 30° and 50°. From the small angle diffraction pattern the average relative intensities (IR) of the (111), (200), and (220) lines were measured to be equal to 100, 62, and 32 respectively. From the large diffraction angle IR for the (220), (311+222), (400), (331+420), and (422) lines were measured to be 100,201,17,90, and 19.5 respectively. The diffraction pattern at those two angles were obtained at several higher temperatures to measure the change in the intensities of the Al lines. From the intensity changes the increase of the Debye- Waller temperature factor, i.e ~B(T), with respect to the value at room temperature was determined to be 0.6+0.1 at 250°C, 1.10+0.15 at 350°C, 1.45+0.20 at 450°C, and 2.20±0.35 at 550°C.

Applying scanning electron microscopy for the ultrastructural and clinical analysis of periprosthetic capsules in implant-based breast reconstruction

La reconstruction en deux étapes par expanseur et implant est la technique la plus répandue pour la reconstruction mammmaire post mastectomie. La formation d’une capsule périprothétique est une réponse physiologique universelle à tout corps étranger présent dans le corps humain; par contre, la formation d’une capsule pathologique mène souvent à des complications et par conséquent à des résultats esthétiques sous-optimaux. Le microscope électronique à balayage (MEB) est un outil puissant qui permet d’effectuer une évaluation sans pareille de la topographie ultrastructurelle de spécimens. Le premier objectif de cette thèse est de comparer le MEB conventionnel (Hi-Vac) à une technologie plus récente, soit le MEB environnemental (ESEM), afin de déterminer si cette dernière mène à une évaluation supérieure des tissus capsulaires du sein. Le deuxième objectif est d‘appliquer la modalité de MEB supérieure et d’étudier les modifications ultrastructurelles des capsules périprothétiques chez les femmes subissant différents protocoles d’expansion de tissus dans le contexte de reconstruction mammaire prothétique. Deux études prospectives ont été réalisées afin de répondre à nos objectifs de recherche. Dix patientes ont été incluses dans la première, et 48 dans la seconde. La modalité Hi-Vac s’est avérée supérieure pour l’analyse compréhensive de tissus capsulaires mammaires. En employant le mode Hi-Vac dans notre protocole de recherche établi, un relief 3-D plus prononcé à été observé autour des expanseurs BIOCELL® dans le groupe d’approche d’intervention retardée (6 semaines). Des changements significatifs n’ont pas été observés au niveau des capsules SILTEX® dans les groupes d’approche d’intervention précoce (2 semaines) ni retardée.

Scanning Electron Microscopy Studies on Tear and Wear Failure of Short Kevlar Fiber-Thermoplastic- Polyurethane Composite

Tear and wear properties of short kevlar fiber, thermoplastic polcurethane (TPU) composite with respect to fiber loading-and fiber onentation has been studied and the fracture surfaces were examined under scanning electron microscope (SEM). Tear strength first decreased up to 20 phr fiber loading and then gradually increased with increasing fiber loading. Anisotropy in tear strength was evident beyond a fiber loading of 20 phr. Tear fracture surface of unfilled TPU showed sinusoidal folding characteristics of high strength matrix. At low fiber loading the tear failure was mainly due to fibermatrix failure whereas at higher fiber loading the failure occurred by fiber breakage. Abrasion loss shows a continuous rise with increasing fiber loading, the loss in the transverse orientation of fibers being higher than that in the longitudinal orientation. The abraded surface showed lone cracks and ridges parallel to the direction of abrasion indicating an abrasive wear mechanism. In the presence of fber the abrasion loss was mainly due to fiber low.

X-ray diffraction, thermal analysis, and Raman scattering study of K2BeF4 and comparation to other member of the (beta)-K2SO4 family with ferroelectric -paraelectric transition

Thermal analysis, powder diffraction, and Raman scattering as a function of the temperature were carried out on K2BeF4. Moreover, the crystal structure was determined at 293 K from powder diffraction. The compound shows a transition from Pna21 to Pnam space group at 921 K with a transition enthalpy of 5 kJ/mol. The transition is assumed to be first order because the compound shows metastability. Structurally and spectroscopically the transition is similar to those observed in (NH4)2SO4, which suggests that the low-temperature phase is ferroelectric. In order to confirm it, the spontaneous polarization has been computed using an ionic model.

Microstructure and random magnetic anisotropy in Fe–Ni based nanocrystalline thin films

Nanocrystalline Fe–Ni thin films were prepared by partial crystallization of vapour deposited amorphous precursors. The microstructure was controlled by annealing the films at different temperatures. X-ray diffraction, transmission electron microscopy and energy dispersive x-ray spectroscopy investigations showed that the nanocrystalline phase was that of Fe–Ni. Grain growth was observed with an increase in the annealing temperature. X-ray photoelectron spectroscopy observations showed the presence of a native oxide layer on the surface of the films. Scanning tunnelling microscopy investigations support the biphasic nature of the nanocrystalline microstructure that consists of a crystalline phase along with an amorphous phase. Magnetic studies using a vibrating sample magnetometer show that coercivity has a strong dependence on grain size. This is attributed to the random magnetic anisotropy characteristic of the system. The observed coercivity dependence on the grain size is explained using a modified random anisotropy model