Sinusoidal endothelial cells of the liver: Fine structure and function in relation to age

Liver endothelial cells form a continuous lining of the liver capillaries, or sinusoids, separating parenchymal cells and fat-storing cells from sinusoidal blood. Liver sinusoidal endothelial cells differ in fine structure from endothelial cells lining larger blood vessels and from other capillary endothelia in that they lack a distinct basement membrane and also contain open pores, or fenestrae, in the thin cytoplasmic projections which constitute the sinusoidal wall. This distinctive morphology supports the protective role played by liver endothelium, the cells forming a general barrier against pathogenic agents and serving as a selective sieve for substances passing from the blood to parenchymal and fat-storing cells, and vice versa. Sinusoidal endothelial cells, furthermore, significantly participate in the metabolic and clearance functions of the liver. They have been shown to be involved in the endocytosis and metabolism of a wide range of macromolecules, including glycoproteins, lipoproteins, extracellular matrix components, and inert colloids, establishing endothelial cells as a vital link in the complex network of cellular interactions and cooperation in the liver. Fine structural studies in combination with the development of cell isolation and culture techniques from both experimental animal and human liver have greatly contributed to the elucidation of these endothelial cell functions. Morphological and biochemical investigations have both revealed little changes with age except for an accumulation of iron ferritin and a decrease in the activities of glucose-6-phosphatase, Mg-ATPase, and in glucagon-stimulated adenylcyclase. Future studies are likely to disclose more fully the role of sinusoidal endothelial cells in the regulation of liver hemodynamics, in liver metabolism and blood clearance, in the maintenance of hepatic structure, in the pathogenesis of various liver diseases, and in the aging process in the liver.     

Indentation modulus and hardness of viscoelastic thin films by atomic force microscopy: A case study

We propose a nanoindentation technique based on atomic force microscopy (AFM) that allows one to deduce both indentation modulus and hardness of viscoelastic materials from the force versus penetration depth dependence, obtained by recording the AFM cantilever deflection as a function of the sample vertical displacement when the tip is pressed against (loading phase) and then removed from (unloading phase) the surface of the sample. Reliable quantitative measurements of both indentation modulus and hardness of the investigated sample are obtained by calibrating the technique through a set of different polymeric samples, used as reference materials, whose mechanical properties have been previously determined by standard indentation tests. By analyzing the dependence of the cantilever deflection versus time, the proposed technique allows one to evaluate and correct the effect of viscoelastic properties of the investigated materials, by adapting a post-experiment data processing procedure well-established for standard depth sensing indentation tests. The technique is described in the case of the measurement of indentation modulus and hardness of a thin film of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate), deposited by chronoamperometry on an indium tin oxide (ITO) substrate.     

Polymer composites in 2000: structure, performance, cost and compromise

Polymer matrix composites are based on the combination of stiff, strong reinforcing fibres with either thermosetting or thermoplastic polymer matrices. Since their introduction in the early 1940s, the world market has increased to some 5 million tonnes per annum, and some composites may now be considered commodity materials. The spectrum of fibre-reinforced plastics ranges from very high-performance speciality materials costing more than $1000/kg to these commodity composites, with more modest properties, at less than $10/kg. The performance of composites is determined by the properties of the fibre, the fraction of fibre in the composite and the structure, or fibre architecture. Processing technologies have been developed which maximise fibre content and precisely control the fibre architecture allowing for the manufacture of components with mechanical properties tailored to service requirements. Many composites offer significant advantages in specific stiffness and/or specific strength over metals. This makes them attractive for applications where high mechanical performance and minimum weight are important. However, the wider acceptance of composites is based on their ability to offer a more cost-effective alternative. In particular, composites also allow a dramatic reduction in the parts count in many applications, which leads to significant manufacturing advantages and greater economy.     

Structural and mechanical properties of (Cr,Ni) N single and gradient layer coatings deposited on mild steel by magnetron sputtering

Ternary single and gradient layer (Cr, Ni) N thin films were deposited on the mild steel substrate by unbalanced magnetron sputtering technique in order to evaluate mechanical properties for machine tools and automotive applications. Microstructure, chemical composition, surface morphology and phase analysis were carried out using field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray diffraction, respectively. Both single and gradient layer of (Cr, Ni) N coatings show a significant increment in mechanical properties such as hardness, adhesion strength and surface roughness along with the reduction of friction coefficient. Mechanical tests revealed that the hardness of the gradient layer increased up to 3.1 times due to the formation of Cr₂N and Ni phase whereas single layer showed the least friction. Single layer CrNiN layer exhibited 27.2% less surface roughness (R_a) in comparison with gradient layer. High values of surface roughness, hardness, thickness and friction could be correlated with high film-to-substrate adhesion (L_c2) for the gradient layer.     

Drying cells for SEM, AFM and TEM by hexamethyldisilazane: a study on hepatic endothelial cells

Critical point drying (CPD) is a common method of drying biological specimens for scanning electron microscopy (SEM). Drying by evaporation of hexamethyldisilazane (HMDS) has been described as a good alternative. This method, however, is infrequently used. Therefore, we reassessed HMDS drying. Cultured rat hepatic sinusoidal endothelial cells (LEC), possessing fragile fenestrae and sieve plates, were subjected to CPD and HMDS drying and evaluated in the scanning electron microscope, atomic force microscope (AFM) and transmission electron microscope (TEM). We observed no differences between the two methods regarding cellular ultrastructure. In contrast with CPD, HMDS drying takes only a few minutes, less effort, low costs for chemicals and requires no equipment. We conclude that HMDS-dried specimens have equal quality to CPD ones. Furthermore, the method also proved useful for drying whole-mount cells for TEM and AFM.     

Drosophila as a focus in olfactory research: mapping of olfactory sensilla by fine structure, odor specificity, odorant receptor expression, and central connectivity.

This review intends to integrate recent data from the Drosophila olfactory system into an up-to-date account of the neuronal basis of olfaction. It focuses on (1) an electron microscopic study that mapped a large proportion of fruitfly olfactory sensilla, (2) large-scale electrophysiological recordings that allowed the classification of the odor response spectra of a complete set of sensilla, (3) the identification and expression patterns of candidate odorant receptors in the olfactory tissues, (4) central projections of neurons expressing a given odorant receptor, (5) an improved glomerular map of the olfactory center, and (6) attempts to exploit the larval olfactory system as a model of reduced cellular complexity. These studies find surprising parallels between the olfactory systems of flies and mammals, and thus underline the usefulness of the fruitfly as an olfactory model system. Both in Drosophila and in mammals, odorant receptor neurons appear to express only one type of receptor. Neurons expressing a given receptor are scattered in the olfactory tissues but their afferents converge onto a few target glomeruli only. This suggests that in both phyla, the periphery is represented in the brain as a chemotopic map. The major difference between mammals and fruitflies refers to the numbers of receptors, neurons, and glomeruli, which are largely reduced in the latter, and particularly in larvae. Yet, if activated in a combinatorial fashion, even this small set of elements could allow discrimination between a vast array of odorants.     

On the complex three-dimensional amplitude point spread function of lenses and microscope objectives: theoretical aspects, simulations and measurements by digital holography

The point spread function is widely used to characterize the three‐dimensional imaging capabilities of an optical system. Usually, attention is paid only to the intensity point spread function, whereas the phase point spread function is most often neglected because the phase information is not retrieved in noninterferometric imaging systems. However, phase point spread functions are needed to evaluate phase‐sensitive imaging systems and we believe that phase data can play an essential role in the full aberrations' characterization. In this paper, standard diffraction models have been used for the computation of the complex amplitude point spread function. In particular, the Debye vectorial model has been used to compute the amplitude point spread function of ×63/0.85 and ×100/1.3 microscope objectives, exemplifying the phase point spread function specific for each polarization component of the electromagnetic field. The effect of aberrations on the phase point spread function is then analyzed for a microscope objective used under nondesigned conditions, by developing the Gibson model ( Gibson & Lanni, 1991 ), modified to compute the three‐dimensional amplitude point spread function in amplitude and phase. The results have revealed a novel anomalous phase behaviour in the presence of spherical aberration, providing access to the quantification of the aberrations. This work mainly proposes a method to measure the complex three‐dimensional amplitude point spread function of an optical imaging system. The approach consists in measuring and interpreting the amplitude point spread function by evaluating in amplitude and phase the image of a single emitting point, a 60‐nm‐diameter tip of a Near Field Scanning Optical Microscopy fibre, with an original digital holographic experimental setup. A single hologram gives access to the transverse amplitude point spread function. The three‐dimensional amplitude point spread function is obtained by performing an axial scan of the Near Field Scanning Optical Microscopy fibre. The phase measurements accuracy is equivalent to λ/60 when the measurement is performed in air. The method capability is demonstrated on an Achroplan ×20 microscope objective with 0.4 numerical aperture. A more complete study on a ×100 microscope objective with 1.3 numerical aperture is also presented, in which measurements performed with our setup are compared with the prediction of an analytical aberrations model.