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At least 217 records · Page 12Linked to original sources
PubMed2004

Capillarity-driven assembly of two-dimensional cellular carbon nanotube foams.

Capillary forces arising during the evaporation of liquids from dense carbon nanotube arrays are used to reassemble the nanotubes into two-dimensional contiguous cellular foams. The stable nanotube foams can be elastically deformed, transferred to other substrates, or floated out to produce free-standing macroscopic fabrics. The lightweight cellular foams made of condensed nanotubes could have applications as shock-absorbent structural reinforcements and elastic membranes. The ability to control the length scale, orientation, and shape of the cellular structures and the simplicity of the assembly process make this a particularly attractive system for studying pattern formation in ordered media.

Manufactured Materials↗
PubMed2005

The electroosmotic droplet switch: countering capillarity with electrokinetics.

Electroosmosis, originating in the double-layer of a small liquid-filled pore (size R) and driven by a voltage V, is shown to be effective in pumping against the capillary pressure of a larger liquid droplet (size B) provided the dimensionless parameter sigmaR(2)/epsilon|zeta|VB is small enough. Here sigma is surface tension of the droplet liquid/gas interface, epsilon is the liquid dielectric constant, and zeta is the zeta potential of the solid/liquid pair. As droplet size diminishes, the voltage required to pump electroosmotically scales as V approximately R(2)/B. Accordingly, the voltage needed to pump against smaller higher-pressure droplets can actually decrease provided the pump poresize scales down with droplet size appropriately. The technological implication of this favorable scaling is that electromechanical transducers made of moving droplets, so-called "droplet transducers," become feasible. To illustrate, we demonstrate a switch whose bistable energy landscape derives from the surface energy of a droplet-droplet system and whose triggering derives from the electroosmosis effect. The switch is an electromechanical transducer characterized by individual addressability, fast switching time with low voltage, and no moving solid parts. We report experimental results for millimeter-scale droplets to verify key predictions of a mathematical model of the switch. With millimeter-size water droplets and micrometer-size pores, 5 V can yield switching times of 1 s. Switching time scales as B(3)/VR(2). Two possible "grab-and-release" applications of arrays of switches are described. One mimics the controlled adhesion of an insect, the palm beetle; the other uses wettability to move a particle along a trajectory.

Journal Article↗
PubMed2005

Evidence for capillarity contributions to gecko adhesion from single spatula nanomechanical measurements.

The hairy attachment system on a gecko's toes, consisting of one billion spatulae in the case of Gekko gecko [Ruibal, R. & Ernst, V. (1965) J. Morphol. 117, 271-294], allows it to adhere to nearly all surface topographies. The mechanistic basis for gecko adhesion has been intensely investigated, but the lowest hierarchical level, that of the spatula, has become experimentally accessible only recently. This report details measurements of the adhesion force exerted by a single gecko spatula for various atmospheric conditions and surface chemistries. Through judicious choice and modification of substrates, the short- and long-range adhesive forces are separated. In contrast to previous work [Autumn, K., Sitti, M., Liang, Y. C. A., Peattie, A. M., Hansen, W. R., Sponberg, S., Kenny, T. W., Fearing, R., Israelachvili, J. N. & Full, R. J. (2002) Proc. Natl. Acad. Sci. USA 99, 12252-12256], our measurements clearly show that humidity contributes significantly to gecko adhesion on a nanoscopic level. These findings are crucial for the development of artificial biomimetic attachment systems.

Adhesiveness↗
PubMed1970

A capillarity mechanism for diatom gliding locomotion.

It is proposed that the diatom raphe is a parallel-plate capillary containing a fluid which reacts at the trailing end, turning into a form which no longer "wets" the raphe walls, and which is left behind as a trail. More unreacted raphe fluid is drawn by capillary pressure from a source near the leading end of the raphe. This fluid sticks out from the raphe along its length, adhering to surfaces, thus causing gliding locomotion. Formulae are given for the maximum velocity and force of a moving diatom in terms of the raphe dimensions and the surface tension and viscosity of the fluid. An a priori estimate of the force exerted by a moving diatom, 1-50 millidynes, agrees with measured values. Five experimental tests of the theory are proposed.

Journal Article↗
PubMed2002

Focal rectal capillaritis: microscopic polyangiitis presenting as painless rectal bleeding.

Microscopic polyangiitis is a pauci-immune, necrotizing, small-vessel vasculitis without evidence of granulomatous inflammation. Gastrointestinal involvement is rare and is predominantly limited to abdominal pain. Until now, the gold standard for diagnosis has been an invasive lung or kidney biopsy. We report the case of a 59-year-old woman with microscopic polyangiitis presenting as painless rectal bleeding, which was diagnosed by rectal mucosal biopsy. This is the first reported case of microscopic polyangiitis with initial presentation of rectal bleeding and diagnosis made by rectal mucosal biopsy.

Biopsy↗
PubMed2006

Model of a liquid nanofilm on a solid substrate based on the van der Waals concept of capillarity.

Van der Waals attractive forces drastically change the material properties of thin liquid layers several nanometers when in contact with a solid. At this scale, the fluid is no longer homogeneous. Moreover, it has properties which are analogous to those of solids. In particular, in equilibrium the stress tensor is no longer spherical. For such fluids, we use a long-wave approximation to derive the evolution of a liquid nanofilm on a substrate. We establish that the driving pressure in the nanofilm should be associated with the mean value of the component of the pressure tensor tangential to the liquid interface (along the substrate). Finally, we derive the equation for nanofilm dynamics by using a mass conservation formulation. This is not a conventional, conservative equation for the position of the free surface normally used in the theory of thick films where the density is homogeneous, but rather a conservative equation for the liquid mass. The equation turns out to be a nonlinear parabolic equation with a diffusion coefficient of a "good" sign.

Journal Article↗
PubMed2006

Meandering rivulets on a plane: a simple balance between inertia and capillarity.

Experiments on streams of water flowing down a rigid substrate have been performed for various plate inclinations and flow rates, and we focused on the regime of stationary meanders. The outcome is that (i) the flow is highly hysteretic--the shape of the meanders varies with flow rate only for increasing flow rates, and the straight rivulet regime does not appear for decreasing flow rate, and (ii) a simple force balance, including inertia, capillary forces, and also hysteresis of wetting, accounts well for the experimental instability threshold flow rate and for the final radius of curvature of the meanders.

Journal Article↗
PubMed2004

Time-course changes in VEGF expression and capillarity in the early stage of exercise training with Co treatment in rat skeletal muscles.

AIM: Cobalt administration was reported to mimic hypoxia. This study was designed to examine the time-course changes in vascular endothelial growth factor (VEGF) expression and capillary geometry in skeletal muscles during endurance training with CoCl(2) administration in female Wistar rats. METHODS: Exercise training by running lasted for up to 10 days at 25 m min(-1) on a 20% gradient, 15-42 min day(-1). Rats in the Co(2+)-treated groups drank water containing 0.01% CoCl(2). Serial frozen sections were stained for alkaline phosphatase and dipeptidylpeptidase IV to identify capillary profiles and VEGF-A protein. RESULTS: In the soleus muscle, the density of VEGF-positive capillaries (VEGF-cap) was significantly increased after 6 and 10 days of the Co(2+) administration (by 27 and 65% respectively) while the capillary-to-fibre ratio (C : F) first increased after 10 days. The training with Co(2+) significantly increased VEGF-cap by 69, 44 and 60%, respectively, after 3, 6 and 10 days. The VEGF-cap was significantly increased after 6 and 10 days of training alone by 38 and 58%, respectively. In a similar extent, both training groups with and without Co(2+) showed a significant increase in the C : F ratio after 6 and 10 days. CONCLUSIONS: The present results suggest that activation of the cellular oxygen-sensing mechanism induced by Co(2+) administration slightly facilitates an expression of VEGF but does not facilitate exercise-induced microvascular remodelling in hind-leg muscles.

Animals↗
PubMed1992

Unilateral linear capillaritis.

We present four cases of a distinctive type of pigmented purpuric eruption occurring in a striking linear and pseudo-dermatomal distribution in young males. Whilst these cases share some of the clinical and histological features of other pigmented purpuric dermatoses, they are not readily classified with any of the entities so far defined in this group of disorders. We believe these cases represent a distinct group not previously described. Four patients with an unusual pigmented purpuric eruption are presented.

Adolescent↗
PubMedDate not supplied

Sinusoidal capillarization in small hepatocellular carcinoma.

The morphological and phenotypic changes of sinusoidal endothelial cells in hepatocellular carcinoma were investigated along with the hemodynamic changes. Hepatocellular carcinomas, which were 10-20 mm in diameter, were obtained by liver aspiration biopsy. Twenty specimens of well differentiated and 20 specimens of moderately differentiated hepatocellular carcinoma were used. These were classified into two groups of hepatocellular carcinoma: with and without hypervascularity. Electron microscopy, immunohistochemistry using antibodies against factor VIII-related antigen, type IV collagen and laminin and lectin histochemistry using Ulex europaeus agglutinin I (UEA-I) were performed. Factor VIII-related antigen and UEA-1 binding sites were present in the sinusoidal endothelial cells in two groups. In hepatocellular carcinoma with hypervascularity, type IV collagen and laminin were present corresponding to basement membranes along the endothelial cells, which had few fenestrae. In another group, although type IV collagen was present along the endothelial cells that had a few fenestrae, laminin and basement membranes were rarely observed. These results suggest that the sinusoidal endothelial cells tend to show phenotypic changes in the early stage of hepatocarcinogenesis. As the arterial blood supply for hepatocellular carcinoma increases, the sinusoidal endothelial cells may form basement membranes and take on the morphological appearance of capillaries.

Adult↗
PubMed1993

The effects of evening primrose oil on nerve function and capillarization in streptozotocin-diabetic rats: modulation by the cyclo-oxygenase inhibitor flurbiprofen.

1. The aims of this study were first, to examine whether deficits in nerve conduction in streptozotocin-diabetic rats could be reversed by a 10% dietary supplement of evening primrose oil. Second, to determine the time-course of reversal, and third, to assess whether the effects could be blocked by the cyclo-oxygenase inhibitor flurbiprofen (5 mg kg-1 day-1). 2. One-month diabetes produced 20% and 15% deficits in sciatic motor and saphenous sensory conduction velocity respectively, which were maintained over 2 months diabetes. 3. The effect of 1-month evening primrose oil treatment on abnormalities caused by an initial month of untreated diabetes was examined. Motor and sensory nerve conduction velocity were restored to the non-diabetic level. 4. Resistance to hypoxic conduction failure was investigated for sciatic nerve trunk in vitro. The 80% conduction failure times were 29% and 55% prolonged by 1- and 2-month diabetes respectively. Evening primrose oil did not reverse the increased hypoxic resistance following 1-month untreated diabetes. 5. Sciatic nerve endoneurial capillary density was not significantly affected by diabetes, but was 16% increased in diabetic rats with reversal by evening primrose oil treatment for 1 month compared to 2-month untreated diabetes. 6. Serial motor conduction velocity measurement after 3-month untreated diabetes revealed complete normalization by evening primrose oil within 4 days. Cessation of treatment resulted in a rapid decline in conduction velocity over 24 h. 7. In a preventive study of 2-month duration, 6 groups of rats were used. These comprised non-diabetic controls, diabetic rats, and evening primrose oil-treated diabetic rats, both with and without flurbiprofen treatment. Flurbiprofen had no significant effect in non-diabetic rats, but produced an 11% worsening of motor conduction velocity and a 21% reduction of sciatic capillary density in diabetic rats. Evening primrose oil prevented the decreases in conduction velocity and increased hypoxic resistance with diabetes, and caused a 23% increase in capillary density. Flurbiprofen completely blocked the effect of evening primrose oil on conduction velocity, resistance to hypoxia, and capillarization.8. Six main conclusions were reached. First, evening primrose oil rapidly reverses conduction deficits in diabetic rats. Second, the effects of treatment may be very short-lived, suggesting a primary metabolic action. Third, evening primrose oil cannot reverse established changes in hypoxic resistance over 1-month treatment. Fourth, long-term treatment causes angiogenesis, suggesting a vascular action. Fifth,products of cyclo-oxygenase-mediated metabolism are necessary for maintaining vasa nervorum integrity in diabetic rats. Sixth, evening primrose oil probably acts by providing substrate for vasodilator prostanoid synthesis by vasa nervorum.

Action Potentials↗
PubMed1998

Sample size required for the accurate determination of fiber area and capillarity of human skeletal muscle.

This study aimed to determine the skeletal muscle fiber sample size required for a reliable, valid representation of an individual's average fiber area and capillary contacts (CC) per fiber. Biopsies were obtained from the biceps brachii of 11 college-age, recreational resistance-trained men in conjunction with a study investigating how muscle morphology changed after 12 weeks of resistance training. The effect of additional measurements on the rolling cumulative means for fiber area and CC per fiber was evaluated using sequential estimation analysis. Results showed that group cumulative mean and standard deviation had stabilized by 50 fiber measurements per individual for type I and II fibers and CC per fiber. Significant correlations (.96-.99; p < .05) existed between the 50th and 95th/100th cumulative individual means. These results indicate that a typical skeletal muscle needle biopsy would be sufficient to characterize type I and II fiber areas and CC per fiber of an individual in most subject populations, although the required sample size for characterizing fiber subtypes might be different.

Adult↗