Inhibition of adhesion of Plasmodium falciparum-infected erythrocytes by structurally defined hyaluronic acid dodecasaccharides.
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We recently reported that Plasmodium falciparum-infected erythrocytes (IRBCs) can adhere to hyaluronic acid (HA), which appears to be a receptor, in addition to chondroitin sulfate A (CSA), for parasite sequestration in the placenta. Further investigations of the nature and specificity of this interaction indicate that HA oligosaccharide fragments competitively inhibit parasite adhesion to immobilized purified HA in a size-dependent manner, with dodecasaccharides being the minimum size for maximum inhibition. Rigorously purified and structurally defined HA dodecasaccharides, free of contamination by CSA or other glycosaminoglycans, effectively inhibited IRBC adhesion to HA but not CSA, providing compelling evidence of a specific interaction between IRBCs and HA. (+info)
A microcantilever device to assess the effect of force on the lifetime of selectin-carbohydrate bonds.
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A microcantilever technique was used to apply force to receptor-ligand molecules involved in leukocyte rolling on blood vessel walls. E-selectin was adsorbed onto 3-microm-diameter, 4-mm-long glass fibers, and the selectin ligand, sialyl Lewis(x), was coupled to latex microspheres. After binding, the microsphere and bound fiber were retracted using a computerized loading protocol that combines hydrodynamic and Hookean forces on the fiber to produce a range of force loading rates (force/time), r(f). From the distribution of forces at failure, the average force was determined and plotted as a function of ln r(f). The slope and intercept of the plot yield the unstressed reverse reaction rate, k(r)(o), and a parameter that describes the force dependence of reverse reaction rates, r(o). The ligand was titrated so adhesion occurred in approximately 30% of tests, implying that >80% of adhesive events involve single bonds. Monte Carlo simulations show that this level of multiple bonding has little effect on parameter estimation. The estimates are r(o) = 0.048 and 0.016 nm and k(r)(o) = 0.72 and 2.2 s(-1) for loading rates in the ranges 200-1000 and 1000-5000 pN s(-1), respectively. Levenberg-Marquardt fitting across all values of r(f) gives r(o) = 0.034 nm and k(r)(o) = 0.82 s(-1). The values of these parameters are in the range required for rolling, as suggested by adhesive dynamics simulations. (+info)
Vascular endothelium-leukocyte interaction; sticking shear force in venules.
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To determine the shear force acting on a white blood cell sticking to the endothelium of a blood vessel, the flow field about a single white blood cell in a venule was determined by hign-speed motion picture photomicrography. The force acting on the white blood cell was then calculated according to the principles of fluid mechanics. In this paper, the calculation was made using an experimentally determined dimensionless shear force coefficient obtained from a kinematically and dynamically similar model. The large physical model of the hemodynamic system could be easily instrumented, and the shear force acting on the model cell and the flow field around it were measured. The data were then used to calculate a shear force coefficient. On the basis of dynamic similarity, this shear force coefficient was applied to the white blood cell in the venule. The shear force coefficient was strongly influenced by the hematocrit, so in vivo hematocrits were measured from electron micrographs. It was found that in the venules of the rabbit omentum a white blood cell sticking to the endothelial wall was subjected to a shear force in the range of 4 times 10--5 dynes to 234 times 10--5 dynes; the exact value depended on the size and motion of the white blood cell, the size of the blood vessel, the velocity of the blood flow, and the local hematocrit, which varied between 20% and 40% in venules of about 40 mum in diameter. The contact area between the white blood cell and the endothelial cell was estimated, and the shear stress was found to range between 50 dynes/cm-2 and 1060 dynes/cm-2. The normal stress of interaction between the white blood cell and the endothelium had a maximum value that was of the same order of magnitude as the shear stress. The accumulated relative error of the experimental procedure was about 49%. The instantaneous shear force was a random function of time because of random fluctuations of the hematocrit. (+info)
Effect of the adhesive layer thickness on the fracture toughness of dental adhesive resins.
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We investigated how the thickness of an adhesive layer between two Co-Cr alloy plates affected the mode I fracture toughness of dental adhesive resin by varying the type of resin using a double cantilever beam (DCB) test. Two typical adhesive resins (PV and SB) were used. The adhesive layers of the DCB test specimens were 20, 100 and 200 microns thick. The fracture modes of PV differed with the thickness of the adhesive layer, such as interface fracture at 20 microns thickness, and similar cohesive fracture at 100 and 200 microns thickness. In the case of SB, crack-propagating areas were observed as cohesive fractures in all test specimens with different adhesive layer thickness, and the surfaces of these areas became remarkably rougher as the thickness of the adhesive layer increased. The fracture toughness of PV was not affected by the differences in thickness between the 100 and 200 microns adhesive layers, but there was a notable decrease in fracture toughness when the adhesive layer decreased to a thickness of 20 microns. That of SB showed a tendency to increase as the adhesive layer became thicker. (+info)
Retinal adhesion in light- and dark-adapted rabbits.
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The effects of pigmentation and light exposure on retinal adhesion in rabbits have been investigated in a complete factorial experiment. Ocular pigmentation did not significantly influence retinal adhesion. A significant difference in retinal adhesive forces was found between light and dark adaptation. The force required to detach the retina from the retinal pigment epithelium was 20 per cent greater in light-adapted eyes than in dark-adapted eyes. These observations suggest that the positional change of rhodopsin molecules in the outer segment disk membranes occurring with light exposure and the resultant alteration in interdisk electrostatic forces may play an important role in retinal adhesion. (+info)
Silicone oil-intraocular lens interaction: which lens to use?
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AIM: To determine a suitable intraocular lens for implantation in patients at high risk of lens exposure to silicone oil in their lifetime. METHODS: PMMA, AcrySof, AR40, AQUA-Sense, and Raysoft lenses were examined. Each lens was immersed for 5 minute intervals in balanced salt solution (BSS), in stained silicone oil, and again in BSS before being photographed in air and in BSS. Percentage silicone oil coverage of the lens optic was determined. RESULTS: The mean percentage coating (MPC) for the lens biomaterials ranged from 5.2% to 21.5%. The Raysoft lens had significantly less oil coverage when statistically compared with the other lens types (p < 0.001). CONCLUSION: A Raysoft (Rayner) lens is a suitable lens for implantation in patients who are at risk of severe vitreoretinal disease. (+info)
A ligand-receptor model for the cohesive behaviour of Dictyostelium discoideum axenic cells.
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Axenically grown cells of D. discoideum Ax-2 harvested in the log phase of growth, cohere rapidly when shaken in phosphate buffer. After 3.5 days in the stationary phase of growth, cells become completely non-cohesive. Although they do not stick to each other, stationary phase cells do stick to both log phase cells and aggregation-competent cells. The cohesion of stationary phase cells with these other 2 cell types is inhibited by both EDTA and the low-molecular-weight factor which we have previously demonstrated in stationary-phase growth medium. There is a decline in the sensitivity of slime mould cell cohesion to the low-molecular-weight inhibitory factor as the cells become aggregation-competent. This effect parallels the developmentally-regulated decline in sensitivity to EDTA. The low-molecular-weight inhibitor is not a chelating agent, however. The effect of the inhibitor seems to be specifically against contact sites-B mediated cohesion. We suggest that the simplest cohesive mechanism which can explain our results, is that the EDTA-sensitive cohesion of log phase cells could be dependent on a ligand-receptor system. (+info)
Mechanism of adhesion between 4-META resin and alloys based on Bolger's acid-base interaction.
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The water durability at adhesion interfaces between 4-META resin and Au-In or Au-Si alloys was investigated by the peeling test and by surface analysis using X-ray photoelectron spectroscopy (XPS) as well as theoretical consideration based on Bolger's acid-base theory. XPS spectra demonstrated that several-nm thick layers of In2O3 and SiO2 were formed on the Au-In and Au-Si alloys. The water durability of the Au-In alloys increased with increases in In content. The Au-Si alloy and quartz glass specimens showed a total absence of water durability. Bolger's theory suggested that the interaction of 4-MET with In2O3 was considered to be ionic and stable in the presence of water while that of 4-MET with SiO2 was due to hydrogen bonds, which can easily be dissociated in the presence of water. These findings suggest that Bolger's theory is useful for evaluating chemical interactions between an adhesive monomer and oxides on a precious metal alloy. (+info)