Tensile experiments and SEM fractography on bovine subchondral bone

Subchondral bone undecalcified samples, extracted from bovine femoral heads, are subjected to a direct tensile load. The Young's modulus of each sample is determined from repeated tests within the elastic limit. In a last test, the tensile load is increased up to the specimen failure, determining the ultimate tensile strength. The investigation is performed on both dry and wet specimens. The measured Young's modulus for dry samples is 10.3+/-2.5GPa, while that of wet samples is 3.5+/-1.2GPa. The ultimate tensile strengths are 36+/-10 and 30+/-7.5MPa for dry and wet specimens, respectively. SEM micrographs of failure surfaces show characteristic lamellar bone structures, with lamellae composed of calcified collagen fibers. Rudimentary osteon-like structures are also observed. Failure surfaces of wet samples show a marked fiber pull-out, while delamination predominates in dry samples. The obtained results are interpreted on the basis of the deformation mechanisms typical of fiber-reinforced laminated composite materials.     

Human bone marrow CFU-GM and BFU-E localized by light scatter cell sorting

Flow cytometric separation was performed on the normal human bone marrow (BM) by using the low-angle (0 degrees) or high-angle (90 degrees) light scatter. Four distinct subpopulations of cells can be enriched from normal human BM and these fractions were subsequently evaluated for their morphological properties as well as their clonogenic capacity in various progenitor cell assays. Our results indicate that human erythroid and granulocyte-macrophage progenitor cells can be separated from BM low-density cells by cell sorting, and these cells show similar 0 degrees and 90 degrees light scatter properties to those observed with murine bone marrow studies. Flow cytometric analysis also suggests that the majority of sorted BFU-E and CFU-GM resides in the blast cell subset of human BM mononuclear cells.     

香茶菜属3种植物花粉形态的扫描电镜观察

应用扫描电子显微镜对香茶菜(Isodon amethystoides)、大萼香茶菜(I. macrocalyx)、显脉香茶菜(I. nervosa)8个居群的花粉进行了形态观察.结果表明,不同居群的香茶菜的花粉在形态上具有一定共同特性 ,但在外壁纹饰、大小、穴的形状上存在差异.香茶菜属不同种在花粉形态、大小、外壁纹饰、穴分布情况存在较明显的差异.这些花粉表面微观形态的差异可为品种鉴定提供依据.     

Preparation of human leukocytes for SEM observation: a modified technique

Variations in the mode of preparation, type of fixation and leukocyte collection can plan an important part in the determination of the surface structure of a given population, and can result in modifications of the microprojections, and their number, evident on the cell surface. We present preparatory modes that circumvent these difficulties, and the results obtained clearly show that the techniques are profitable, appear essential for the preservation of cell population and integrity, and allow accurate scanning electron microscopy observations without resort to time consuming procedures. Indeed, the entire process can be completed in one day.     

Simple and rapid methods for SEM observation and TEM immunolabeling of rubber particles.

We developed a method involving air-drying of a rubber suspension after fixation in glutaraldehyde-tannic acid and postfixation in osmium tetroxide for SEM observation. For TEM immunolabeling the suspension was air-dried after osmium-only fixation. Whereas conventional methods failed to satisfactorily stabilize rubber particles, the methods described here proved successful in preserving their integrity.     

Seed morphology under SEM and light microscopy in Kansas Juncus (Juncaceae)

Seed morphology was studied in 15 species of four subgenera ofJuncus occurring in Kansas, to determine if seeds provide traits useful in assessing systematic relations within the genus. In this study seed size and shape were of limited value, while surface ornamentation of the hard inner seed coat provided encouraging results. SubgenusPoiophylli showed little variation in surface ornamentation among taxa; similar ornamentation was observed in subgenusGenuini. SubgeneraGraminifolii andSeptati were separately distinct with the taxa in theSeptati forming a continuum of variation.     

四种补血草属植物叶片泌盐结构的扫描电镜观察

利用扫描电镜技术,对4种补血草属植物大叶补血草（Limonium gmelinii (Willd.) Kuntze）、耳叶补血草（Limoniu otolepis (Schrenk) Kuntze）、繁枝补血草（Limonium myrianthum (Schrenk) Kuntze）和簇枝补血草（Limonium auream）的叶表面进行了研究,以探讨植物微形态结构与生态环境的关系。结果表明,这4种植物的上下表皮都分布有盐腺,且上表皮的盐腺密度大于下表皮,盐腺的基本结构相同,多由20个细胞构成,其中4个分泌细胞顶端的角质层中央有一小孔,植物体靠盐腺的泌盐孔泌盐。但4种植物在盐腺的密度、盐腺的大小、盐腺与周围表皮细胞的位置等方面存在差异。植物在对盐碱生境的长期适应过程中,促使其强烈地分化出泌盐结构,因而,具有明显的生态适应性。     

A rapid digestive technique to expose networks of vascular elastic fibers for SEM observation

The NaOH sonication digestion technique permits rapid isolation and exposure of intact networks of elastic fibers in vascular tissue for 3-dimensional observation with the SEM. The configuration of the network of elastic fibers within the vascular wall of large elastic arteries (aorta) is generally agreed to be a flexible framework through which smooth muscle cells and collagenous fibers are interwoven. However, the configuration of elastic fiber networks in muscular arteries, medium sized veins and smaller vessels remains unknown. When the lengthy standard biochemical elastin purification techniques were applied to vessels containing lesser amounts of elastic tissue and finer elastic fibers, the vessels were completely digested. In contrast, the digestion and sonication technique isolated and exposed intact networks of delicate elastic fibers in blood vessels which do not contain large amounts of elastic tissue. Unfixed vessels were cut into short segments, placed in 0.5 N NaOH and sonicated for 20-40 min. The specimens were rinsed in deionized distilled H2O, then autoclaved for 30 min. The tissue was rinsed a second time, fixed and processed routinely for SEM. Elastic stains and enzymatic digestion with chromatographically purified elastase and collagenase confirmed that the digestion and sonication technique produced clean, isolated networks of elastic fibers. Knowledge of the configuration of the networks of elastic fibers in different vessels enhances understanding of distensibility characteristics of individual vessels and serves as a baseline for studying alterations in the elastic framework which occur during aging and disease processes such as atherosclerosis, arterial hypertension and aneurysms.     

Thymic anlage is colonized by progenitors restricted to T, NK, and dendritic cell lineages

It remains controversial whether the thymus-colonizing progenitors are committed to the T cell lineage. A major problem that has impeded the characterization of thymic immigrants has been that the earliest intrathymic progenitors thus far identified do not necessarily represent the genuine thymic immigrants, because their developmental potential should have been influenced by contact with the thymic microenvironment. In the present study, we examined the developmental potential of the ontogenically earliest thymic progenitors of day 11 murine fetus. These cells reside in the surrounding mesenchymal region and have not encountered thymic epithelial components. Flow cytometric and immunohistochemical analyses demonstrated that these cells are exclusively Lin(-)c-kit(+)IL-7R(+). Limiting dilution analyses disclosed that the progenitors with T cell potential were abundant, while those with B cell potential were virtually absent in the region of day 11 thymic anlage. Clonal analyses reveled that they are restricted to T, NK, and dendritic cell lineages. Each progenitor was capable of forming a large number of precursors that may clonally accommodate highly diverse TCRbeta chains. These results provide direct evidence that the progenitors restricted to the T/NK/dendritic cell lineage selectively immigrate into the thymus.     

Preparation of chromosome spreads for electron (TEM,SEM, STEM), light and confocal microscopy

In the past, ultrastructural studies on chromosome morphology have been carried out using light microscopy, scanning electron microscopy and transmission electron microscopy of whole mounted or sectioned samples. Until now, however, it has not been possible to use all of these techniques on the same specimen. In this paper we describe a specimen preparation method that allows one to study the same chromosomes by transmission, scanning-transmission and scanning electron microscopy, as well as by standard light microscopy and confocal microscopy. Chromosome plates are obtained on a carbon coated glass slide. The carbon film carrying the chromosomes is then transferred to electron microscopy grids, subjected to various treatments and observed. The results show a consistent morphological correspondence between the different methods. This method could be very useful and important because it makes possible a direct comparison between the various techniques used in chromosome studies such as banding, in situ hybridization, fluorescent probe localization, ultrastructural analysis, and colloidal gold cytochemical reactionsAbbreviations CLSM confocal laser scanning microscope - EM electron microscopy - kV kilovolt(s) - LM light microscope - SEM scanning electron microscope - STEM scanning-transmission electron microscope - TEM transmission electron microscope     

Medieval example of metastatic carcinoma: a dry bone, radiological, and SEM study.

An elderly male skeleton from medieval Canterbury displayed evidence of DISH and metastatic carcinoma. The dry bone findings, SEM, and radiography suggest a primary focus in the prostate. A review of the palaeopathological literature has shown that such a finding is extremely rare in archaeological remains. This is the first reported case of prostatic carcinoma from medieval England.     

Lignin distribution in wood cell walls determined by TEM and backscattered SEM techniques

The lignin distribution in cell walls of spruce and beech wood was determined by high-voltage transmission-electron-microscopy (TEM) in sections stained with potassium permanganate as well as by field-emission-scanning-electron-microscopy (FE-SEM) combined with a back-scattered electron detector on mercurized specimens. The latter is a new technique based on the mercurization of lignin and the concomitant visualization of mercury by back-scattered electron microscopy (BSE). Due to this combination it was possible to obtain a visualized overview of the lignin distribution across the different layers of the cell wall. To our knowledge, this combined method was used the first time to analyse the lignin distribution in cell walls. In agreement with previous work the highest lignin levels were found in the compound middle lamella and the cell corners. Back-scattered FE-SEM allows the lignin distribution in the pit membrane of bordered pits as well as in the various cell wall layers to be shown. In addition, by using TEM as well as SEM we observed that lignin closely follows the cellulose microfibril orientation in the secondary cell wall. From these observations, we conclude that the polymerisation of monolignols is affected by the arrangement of the polysaccharides which constitute the cell wall.     

Polarized light scattering for rapid observation of bacterial size changes.

The effect of changing growth conditions on the diameter of rod-shaped bacteria was studied in vivo with the use of polarized light scattering. The value of a ratio of scattering matrix elements was measured as a function of scattering angle at various times after nutritional "upshift" for two strains of Escherichia coli cells. The peak locations of the scattering function were calibrated against the diameter for rod-shaped bacteria. The peaks moved toward smaller angles as a function of time after upshift, indicating that the diameter was increasing. Under special conditions, substantial peak shifts occurred within a few minutes of growth condition change, indicating a rapid onset of growth in diameter. The rate of increase of the diameters after upshift was obtained from the angular shift of peak location. This rate was approximately 14 nm/min for E. coli K12 and approximately 9 nm/min for E. coli B/r at 37 degrees C. The rate of diameter increase is smaller at lower temperatures. Experiments with Bacillus megaterium showed that any diameter change after nutritional upshift at 37 degrees C is limited to at most a very small increase, at least for the strain and medium tested.     

Direct observation of mammalian cell growth and size regulation

We introduce a microfluidic system for simultaneously measuring single-cell mass and cell cycle progression over multiple generations. We use this system to obtain over 1,000 h of growth data from mouse lymphoblast and pro-B-cell lymphoid cell lines. Cell lineage analysis revealed a decrease in the growth rate variability at the G1-S phase transition, which suggests the presence of a growth rate threshold for maintaining size homeostasis.     

Update on Wnt signaling in bone cell biology and bone disease

For more than a decade, Wnt signaling pathways have been the focus of intense research activity in bone biology laboratories because of their importance in skeletal development, bone mass maintenance, and therapeutic potential for regenerative medicine. It is evident that even subtle alterations in the intensity, amplitude, location, and duration of Wnt signaling pathways affects skeletal development, as well as bone remodeling, regeneration, and repair during a lifespan. Here we review recent advances and discrepancies in how Wnt/Lrp5 signaling regulates osteoblasts and osteocytes, introduce new players in Wnt signaling pathways that have important roles in bone development, discuss emerging areas such as the role of Wnt signaling in osteoclastogenesis, and summarize progress made in translating basic studies to clinical therapeutics and diagnostics centered around inhibiting Wnt pathway antagonists, such as sclerostin, Dkk1 and Sfrp1. Emphasis is placed on the plethora of genetic studies in mouse models and genome wide association studies that reveal the requirement for and crucial roles of Wnt pathway components during skeletal development and disease.     

Experimental cryosurgery on bone: A light and electron microscopical investigation

Three rabbits were treated with cryosurgery on the lateral surface of the mandible. Osteocytes with normal appearance were not detected in the cortex after 2 or 7 days following cryosurgery. In the marrow cavity, cells appeared more resistant and often showed a normal morphology as studied with both light and electron microscopy. The reason why cells survived in the marrow cavity is probably due to a combination of sheltering bone and the near proximity to an intact circulation due to a patent alveolar artery.The uncertain extension of the cold front beyond the cortex may indicate that cryosurgery alone is not suitable if a tumor has invaded the marrow cavity, while more superficially located tumors can be eradicated. However, tumor invasion itself destroys the cortex and thus the marrow cavity will be more readily exposed to the more extensive cryosurgical techniques used in clinical cryosurgery.     

A mathematical model of bone remodeling dynamics for normal bone cell populations and myeloma bone disease

Background  

Multiple myeloma is a hematologic malignancy associated with the development of a destructive osteolytic bone disease.