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PubMed2006

Modification of poly(dimethylsiloxane) microfluidic channels with silica nanoparticles based on layer-by-layer assembly technique.

A hydrophilic poly(dimethylsiloxane) (PDMS) microchip with stable electroosmotic flow (EOF) was prepared by a simple and reproducible coating procedure with silica nanoparticles. The microchannel wall of PDMS chip was coated with a layer of poly(diallyldimethylammonium chloride) (PDDA) and then collected silica nanoparticles. The assembly was followed by contact angle, charge-coupled device (CCD) imaging, electroosmotic flow (EOF) measurements and electrophoretic separation experiments. Contact angle measurements revealed the coated surface was hydrophilic; the water contact angle for coated chips was 64 degrees compared with a water contact angle for native PDMS chips of 113 degrees . CCD images indicated a substantially more hydrophilic microchannel than native PDMS. We carried out a comparison and concluded that the EOF values on the coated PDMS chip were close to those values on the glass chip above pH 7.0. The coated channel had an excellent stability and reproducibility, RSD of EOF values (n=6) on native and coated PDMS microchip was 1.58 and 0.57%, respectively. Separation of dopamine and epinephrine was performed on the coated chip generated 1.40 x 10(5), 1.39 x 10(5) theoretical plates/m compared with the native PDMS chip of 0.79 x 10(5), 0.88 x 10(5), high resolution of 1.7 was achieved with a channel of 3.60 cm length.

Dimethylpolysiloxanes↗

PubMed1992

Cell death in the rat retina after a pressure-induced ischaemia-reperfusion insult: an electron microscopic study. I. Ganglion cell layer and inner nuclear layer.

In rats, a pressure-induced ischaemia-reperfusion insult can lead to retinal cell death. In order to elucidate the underlying mechanisms, we performed a qualitative study of the ultrastructural morphology of degenerating retinal cells in the ganglion cell and inner nuclear layers at several time points after the insult. Three morphologically distinct types of cell death could be individualized. Type I was characterized by progressive karyo- and cytolysis and was consistent with necrosis. Type II exhibited progressive shrinkage and condensation of the nuclear and cytoplasmic components followed by heterophagic elimination, thus resembling apoptosis. Type III was characterized mainly by homogenization of the nucleoplasm and cytoplasm and dilation of the perinuclear cisternae and endoplasmic reticulum, thus showing features of 'non-lysosomal vesiculate' cell death. This study lends support to the concept that there may exist a fair but limited number of types of cell death in the retina.

Animals↗

PubMed2000

A comparison of optical coherence tomography and retinal nerve fiber layer photography for detection of nerve fiber layer damage in glaucoma.

PURPOSE: To compare optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) thickness measurements with established methods for assessment of glaucomatous damage using RNFL photography and visual field testing. DESIGN: Cross-sectional study. PARTICIPANTS: Fifty-eight eyes of 58 healthy volunteer ocular hypertensive patients, glaucoma suspect patients, and glaucoma patients were included. METHODS: Optical coherence tomography 3.4-mm diameter circular scans were obtained within 3 months of RNFL photography and standard achromatic visual field testing. Three independent observers graded RNFL photographs using two standardized protocols. For each method, superior and inferior arcuate bundles were scored separately, and interobserver and intraobserver variation was measured. Standard achromatic visual field mean deviation in the superior and inferior hemifields was compared with RNFL damage as assessed by photography and OCT RNFL thickness measurements. MAIN OUTCOME MEASURES: Visual field mean deviation and severity of glaucomatous RNFL damage as assessed by photography. RESULTS: Optical coherence tomography RNFL thickness decreased with increasing RNFL damage as assessed by photography using both methods of photographic assessment. Standard achromatic perimetry mean deviation was significantly associated with OCT RNFL thickness (R(2) = 35%-43%) and RNFL photography severity score (R(2) = 18%-29%). CONCLUSIONS: These results suggest that the OCT shows promise for providing quantitative measures of RNFL thickness for diagnosing and monitoring glaucoma.

Adult↗

PubMed2000

Electrochemical behavior of polyphenol oxidase immobilized in self-assembled structures layer by layer with cationic polyallylamine.

We report here a novel bioelectrode based on self-assembled multilayers of polyphenol oxidase intercalated with cationic polyallylamine built up on a thiol-modified gold surface. We use an immobilization strategy previously described by Hodak J. et al. (Langmuir 1997, 13, 2708-2716) Quartz crystal microbalance with electroacustic impedance experiments were carried out to follow quantitatively the multilayer film formation. The response of the self-assembly polyphenol oxidase-polyallylamine electrodes toward different metabolically related catecholamines was studied, to evaluate enzyme kinetics. For the analyzed compounds, only dopamine and its metabolite Dopac gave catalytic currents at applied potential close to 0 V. These responses were proportional to the number of polyphenol oxidase-immobilized layers and were also controlled by the enzymatic reaction. The combination of microgravimetric and electrochemical techniques allowed us to determine the kinetic enzymatic constants, showing that the decomposition rate for the enzyme-substrate complex is slower than the enzymatic reoxidation step.

Catechol Oxidase↗

PubMed2004

Diffusion boundary layer of a rotating disk electrode as a thin-layer spectroelectrochemical cell.

A UV-visible rapid scan spectrophotometer (RSS) was coupled to a Au rotating disk electrode (RDE) for monitoring at near-normal incidence the reflection-absorption spectrum of the diffusion boundary layer in [Fe(CN)(6)](4)(-) aqueous solutions over a potential region in which [Fe(CN)(6)](4-) oxidizes, generating highly absorbing [Fe(CN)(6)](3-) (lambda(max) = 420 nm). Measurements were performed under steady-state conditions at rotation rates, omega, in the range 300 <or= omega <or= 2500 rpm, yielding well-defined spectra displaying characteristic features of [Fe(CN)(6)](3-). In agreement with theoretical predictions, the absorbance A at lambda(max), using as a reference A(lambda(max)) for the spectrum recorded at a potential negative to the onset of [Fe(CN)(6)](4-) oxidation, was found to be proportional both to the current and also to omega(1/2) under conditions in which E was positive enough for the reaction to proceed under diffusion-limited control.

Journal Article↗

PubMed1999

Layered double hydroxide stability. 1. Relative stabilities of layered double hydroxides and their simple counterparts.

Solutions containing di- and trivalent metal chlorides [M(II) = Mg2+, Zn2+, Co2+, Ni2+, Mn2+; M(III) = Al3+, Fe3+] were titrated with NaOH to yield hydrotalcite-like layered double hydroxides (LDH), [[M(II)]1-x[M(III)]x(OH)2][Cl]x yH2O, by way of M(III) hydroxide/hydrous oxide intermediates. Analysis of the resultant titration curves yields nominal solubility constants for the LDH. The corresponding LDH stabilities are in the order Mg < Mn < Co approximately Ni < Zn for M(II) and Al < Fe for M(III). The stability of LDH relative to the separate metal hydroxides/hydrous oxides is discussed.

Aluminum↗

PubMed1999

Layered double hydroxide stability. 2. Formation of Cr(III)-containing layered double hydroxides directly from solution.

Solutions containing divalent metal [M(II) = Mg2+, Zn2+, Co2+, Ni2+, Mn2+] chlorides and CrCl3 6H2O were titrated with NaOH to yield, for M(II) = Zn, Co, and Ni, hydrotalcite-like layered double hydroxides (LDHs), [[M(II)]1-z[Cr(III)]z(OH)2][Cl]z yH2O, in a single step, without intermediate formation of chromium hydroxide. Analysis of the resultant titration curves yields solubility constants for these compounds. These are in the order Zn < Ni approximately Co, with a clear preference for formation of the phase with z = 1/3. With Mg2+ as chloride, titration gives a mixture of Cr(OH)3 and Mg(OH)2, but the metal sulfates give Mg2Cr(OH)6 1/2(SO4) by a two-step process. Titrimetric and spectroscopic evidence suggests short-range cation order in the one-step LDH systems.

Anions↗

PubMed2003

Nanocoatings onto arteries via layer-by-layer deposition: toward the in vivo repair of damaged blood vessels.

The deposition of polysaccharide-based self-assembled nanocoatings onto damaged arteries is described as a means not only to protect a damaged artery against thrombogenesis, but also to control the healing processes by incorporating biologically active components within the multilayer. As shown by confocal microscopy, the polysaccharide multilayer was retained on the artery in physiological condition and prevented platelet adhesion. Diffusion of the polysaccharides within the artery was also observed and may be used to efficiently target the vascular wall. The NO-precursor l-arginine was used a drug model and incorporated within the self-assembled layers.

Animals↗

PubMed2004

Layer by layer self-assembled polyelectrolyte multilayers with embedded phospholipid vesicles.

We describe a method to embed phospholipid vesicles into polyelectrolyte multilayers built up by the alternate deposition of polyanions and polycations. Before deposition, the vesicles are rigidified by polycation adsorption onto their surface avoiding their fusion once deposited on the multilayer surface. The vesicles adsorb to form a compact and "hard" monolayer as imaged by atomic force microscopy. The thickness of the adsorbed vesicle layer, of the order of 250 nm, is very close to the diameter of the vesicles in solution. This work should open the route to the buildup of multilayer films containing phospholipid vesicles that could act as "reservoirs" for drugs or enzymatic nanoreactors.

Adsorption↗

PubMed2006

Redox properties of the ferricyanide ion on electrodes coated with layer-by-layer thin films composed of polysaccharide and poly(allylamine).

Polyelectrolyte multilayer thin films were prepared by an alternate deposition of poly(allylamine hydrochloride) (PAH) and anionic polysaccharides {carboxymethylcellulose (CMC) and alginic acid (AGA)} on the surface of a gold (Au) disk electrode, and the binding of ferricyanide [Fe(CN)(6)](3)(-) and hexaammine ruthenium ions [Ru(NH(3))(6)](3+) to the films was evaluated. Poly(acrylic acid) (PAA) was also employed as a reference polyanion bearing carboxylate side chains. A quartz-crystal microbalance study showed that PAH-CMC and PAH-AGA multilayer films grow exponentially as the number of depositions increases. The thicknesses of five bilayers of (PAH-CMC)(5) and (PAH-AGA)(5) films were estimated to be 150 +/- 20 and 90 +/- 15 nm, respectively, in the dry state. The PAH/polysaccharide multilayer film-coated Au electrodes exhibited a redox response to the [Fe(CN)(6)](3)(-) ion dissolved in solution, irrespective of the sign of the surface charge of the film, suggesting the high permeability of the films to the [Fe(CN)(6)](3)(-) ion. In contrast, the PAH-PAA film-coated Au electrodes exhibited a redox response only when the outermost surface of the film was covered with a positively charged PAH layer. However, the permeation of the [Ru(NH(3))(6)](3+) cation was severely suppressed for all of the multilayer films. It was possible to confine the [Fe(CN)(6)](3)(-) ion in the films by immersing the film-coated electrodes in a 1 mM [Fe(CN)(6)](3)(-) solution for 15 min. Thus, the [Fe(CN)(6)](3)(-)-confined electrodes exhibited a cyclic voltammetric response in the [Fe(CN)(6)](3)(-) ion-free buffer solution. The loading of the [Fe(CN)(6)](3)(-) ion in the films was higher when the surface charge of the film was positive and increased with increasing film thickness. It was also found that the [Fe(CN)(6)](3)(-) ion confined in the films serves as an electrocatalyst that oxidizes ascorbic acid in solution.

Catalysis↗

PubMed1999

Distribution of TNF-alpha, TNF-R55 and TNF-R75 in the rheumatoid synovial membrane: TNF receptors are localized preferentially in the lining layer; TNF-alpha is distributed mainly in the vicinity of TNF receptors in the deeper layers.

The expression of TNF-alpha and its receptors in the rheumatoid synovial membrane was investigated using immunohistochemistry and immunocytofluorescence. TNF-alpha+ cells (< 10% of all cells) were found in all regions, predominantly in sublining and diffuse infiltrates. The highest percentage of TNF-R+ cells was found in the lining layer (50-90%), with a slight predominance of TNF-R55. In the sublining, fewer cells expressed TNF-R (approximately 50%), mostly TNF-R75. TNF-R75+ cells were also detectable in diffuse infiltrates and lymphoid aggregates (10-50%). These contained only individual TNF-R55+ cells. In diffuse infiltrates, there were slightly more TNF-R55+ cells than in lymphoid aggregates (in both cases < 10%). In sequential sections, TNF-alpha+ cells localized mostly in the vicinity of TNF-R+ cells. Macrophage-like cells appeared to be the predominant TNF-R+ cell type. CD3+ T cells in lymphoid aggregates expressed exclusively TNF-R75. Subsequently, the expression of membrane-bound TNF-alpha, TNF-R55 and TNF-R75 was tested by FACS analysis in isolated RA synoviocytes (n = 7 patients). Only four specimens expressed mTNF-alpha, and that on a low percentage of cells (2 +/- 2.4%; mean +/- SD). In contrast, all specimens expressed higher percentages of TNF-R55 and TNF-R75 (21 +/- 1% and 14 +/- 7.1%, respectively). These results demonstrate that: (1) the percentage of cells expressing soluble/transmembrane TNF-alpha is greatly outnumbered by the percentage of cells expressing TNF receptors; and (2) TNF-alpha-expressing cells are localized in regions expressing substantial levels of TNF receptors. Therefore, the known pro-inflammatory and pro-arthritic effects of TNF-alpha are probably mediated by local interactions between the receptors and their soluble and transmembrane ligands.

Adult↗

PubMed2000

Double-layer porcelain veneers: effect of layering on resulting veneer color.

STATEMENT OF PROBLEM: Densely sintered aluminum oxide veneered with feldspathic porcelain seems to be a promising technology for the fabrication of porcelain laminate veneers, which provide both strength and esthetics. To effectively use this approach for porcelain veneers, practitioners should know how the resulting color is affected by adding a layer of veneering porcelain onto the aluminum oxide. PURPOSE: This study compared changes in CIE L*a*b* color coordinates of simulated stained teeth when covered with the aluminum oxide core disks alone and after the disks had been veneered with 3 different shades of porcelain. MATERIAL AND METHODS: Fifteen aluminum oxide disks were divided into 3 groups. Each of 5 disks was veneered with porcelain of the Vita shades A1, A2, and B4, respectively. The colors of the substrate covered with the nonveneered disks and the veneered disks were measured separately, and the color differences were calculated. Measurements of the disks on a white background were also performed and used as controls. The extracted data were compared with Vita shade values available from the literature. RESULTS: Statistically significant differences in color coordinates of dark substrates were recorded between the substrate covered by an aluminum oxide disk and the addition of veneering porcelain to the aluminum oxide disks. Veneering the aluminum oxide disks with A1, A2, and B4 porcelain produced significant differences in the resulting color when placed on a dark substrate. The direction of the color modifications correlated with values obtained from the literature. The resulting color was also affected by the color of the underlying structures. CONCLUSION: Although aluminum oxide alone does have a degree of masking capability, the resulting color of porcelain veneers with the use of this material can successfully be modified with the veneering porcelain.

Aluminum Oxide↗

PubMed2006

Effects of conjugated linoleic acid supplementation in layer diet on fatty acid compositions of egg yolk and layer performances.

Conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers of linoleic acid with conjugated double bonds. Conjugated linoleic acids have been reported to have a wide range of health-beneficial effects, including anticarcinogenic, antiatherogenic, antidiabetic, and immune stimulatory effects. The objective of this study was to investigate the incorporation of CLA into eggs. Three hundred 27-wk-old layers were allocated to 5 dietary treatments (0, 1, 2, 3, and 4% CLA) with 5 replicates. The results of the study showed that average daily feed intakes were similar in all treatment groups, although hens fed with 4% CLA tended to consume less feed than other hens. Body weight gain and mortality rate were not significantly different (P > 0.05). Hens fed 4% dietary CLA had reduced egg, yolk, and albumen weights (P < 0.05). Yolk color significantly decreased as dietary CLA increased (P < 0.01). Shell thickness and Haugh units were not influenced by the dietary CLA. Concentrations of CLA and saturated fatty acids in egg yolk lipids increased as dietary CLA increased (P < 0.01), whereas concentrations of monounsaturated fatty acids and polyunsaturated fatty acids decreased as dietary CLA increased (P < 0.01). It can be concluded from the present experiments that increasing the amount of CLA fed to hens will increase the amount of CLA in egg yolk and that this increase is accompanied by a reduction in the amount of yolk polyunsaturated fatty acids but an increase in yolk saturated fatty acids. Egg size, yolk weight, and Roche-fan determined yolk color significantly decreased at the highest level of CLA supplementation.

Animal Feed↗

PubMed2006

Optical studies on the surface-induced tilted layers in freestanding films of two no-layer-shrinkage liquid crystal compounds.

Null transmission ellipsometry has been employed to study the molecular arrangements in freestanding films of two no-layer-shrinkage liquid crystal homologous compounds above the bulk smectic A-smectic C* (Sm C*) transition temperature. An unusual nonplanar-parallel or nonplanar-antiparallel-parallel transition has been observed in both compounds under a proper electric field. With the addition of one CH2 group, while the SmC* phase is more stable thermally, the magnitude of the critical field needed to induce a parallel-antiparallel transition decreases dramatically.

Journal Article↗

PubMed2006

Octakis(3-propylammonium) octadecaiodopentaplumbate(II): a new layered stucture based on layered perovskites.

The title compound, (C3H10N)8[Pb5I18], crystallizes as an inorganic-organic hybrid. As such, the structure consists of two-dimensional sheets of corner- and face-sharing [PbI6]4- octahedra, separated by layers of 3-propylammonium cations, which hydrogen bond to the I atoms. The asymmetric unit contains six independent Pb atoms; four are on general positions and the other two are on special positions, viz. a centre of inversion and a twofold axis. The inorganic sheets show a never before seen motif.

Journal Article↗

PubMed1991

A layer-recursive formula for the medium filter for volume conductor problems in radially symmetric layered media.

Simplified algorithms for the computation of the filter coefficients used in solutions of the forward and inverse volume conductor problems in a multilayered cylindrical geometry are derived. The new algorithms are layer-recursive, as opposed to previous algorithms which were specific for the structure studied. The new algorithms not only eliminate the need to derive algebraically cumbersome filter expressions, but also speed up their numerical evaluation.

Algorithms↗

PubMed1985

The structure of the stalk surface layer of a brine pond microorganism: correlation averaging applied to a double layered lattice structure.

The surface layer of the stalk of a prosthecate halophilic microorganism is a periodic array (space group p3m1) comprised of electron dense trimers with a centre to centre spacing of 9.0 nm. The structure is reminiscent of E. coli porin. We have demonstrated that the method of correlation averaging can be effectively used to separate overlapping lattices, and that this results in a higher fidelity reconstruction, when compared to the established method of Fourier filtration. Two statistical methods are used to determine the resolution of the correlation average as a function of the number of 'windows' averaged. (i) The phase residual of spatial frequencies in Fourier space is computed between independently obtained subaverages, and (ii) a new method of Q factor analysis examines the cumulative vector sum in Fourier space as a function of the number of windows averaged. Both methods give a resolution of 1/2.1 nm-1.

Bacteria↗

PubMed1979

Cumulative effect of surfactants on cutaneous horny layers: adsorption onto human keratin layers in vivo.

An attempt has been made to determine the adsorption ability of surfactants by the human horny layers in vivo. For this purpose, a technique utilizing an acidic dye such as indigo carmine was applicable and convenient. Our in vivo study estimating adsorbing residual amounts of surfactants has revealed that there is a positive correlation between adsorbing and roughening effects. It is suggested that the pathogenesis of hand roughness is primarily related to the cumulative injury of the stratum corenum by adsorbing residual surfactant molecules.

Detergents↗