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At least 487 records · Page 27Linked to original sources
PubMed1998

A capillary-driven root module for plant growth in microgravity.

A new capillary-driven root module design for growing plants in microgravity was developed which requires minimal external control. Unlike existing systems, the water supply to the capillary-driven system is passive and relies on root uptake and media properties to develop driving gradients which operate a suction-induced flow control valve. A collapsible reservoir supplies water to the porous membrane which functions to maintain hydraulic continuity. Sheet and tubular membranes consisting of nylon, polyester and sintered porous stainless steel were tested. While finer pore sized membranes allow greater range of operation, they also reduce liquid flux thereby constraining system efficiency. Membrane selection should consider both the maximum anticipated liquid uptake rate and maximum operating matric head (suction) of the system. Matching growth media water retention characteristics to the porous membrane characteristics is essential for supplying adequate liquid flux and gas exchange. A minimum of 10% air-filled porosity (AFP) was necessary for adequate aeration. The capillary-driven module maintained hydraulic continuity and proper gas exchange rates for more than 80 days in a plant growth experiment.

Capillary Action↗
PubMed1977

Determination of the configurations of lactic and glyceric acids from human serum and urine by capillary gas-liquid chromatography.

The separation of the enantiomers of lactic and glyceric acids can be achieved by capillary gas chromatography on SP-1000 using the corresponding O-acetylated methyl esters. The structures of the derivatives were proved by proton magnetic resonance spectroscopy and mass spectrometry. The method has been used for the determination of the absolute configuration of lactic and glyceric acids isolated from serum and urine from different patients.

Capillary Action↗
PubMed1996

Utility of NMR T2 distributions, connection with capillary pressure, clay effect, and determination of the surface relaxivity parameter rho 2.

Nuclear magnetic resonance magnetization decays are now used routinely to determine reservoir properties of economic significance to the oil and gas industry. Although individual features of relaxation time distributions are subject to degradation in the presence of measurement noise, integrated and average measures of those distributions are remarkably stable. Properties such as porosity, producible porosity, hydraulic permeability, and the capillary pressure curve can be measured rapidly and continuously. Laboratory comparisons of NMR T2 distributions with two different capillary pressure measurements enable the surface relaxivity parameter rho 2 to be determined for sandstones. Comparison with relaxivities of synthetic materials having well-defined surface areas strongly suggests that the NMR-effective internal surface area of rocks is closely connected with the hydraulic radius, and, surprisingly, is not greatly affected by the presence of clay, which dominates the pore space surface are as measured by gas adsorption.

Aluminum Silicates↗
PubMed2004

Mucoadhesive thiolated chitosans as platforms for oral controlled drug delivery: synthesis and in vitro evaluation.

The aim of the present study was to evaluate the influence of the degree of modification and the polymer chain length on the mucoadhesive properties and the swelling behavior of thiolated chitosan derivatives obtained via a simple one-step reaction between the polymer and 2-iminothiolane. The conjugates differing in molecular mass of the polymer backbone and in the amount of immobilized thiol groups were compressed into tablets. They were investigated for their mucoadhesive properties on freshly excised porcine mucosa via tensile studies and the rotating cylinder method. Moreover, the swelling behavior of these tablets in aqueous solutions was studied by a simple gravimetric method. The obtained results demonstrated that the total work of adhesion of chitosan-TBA (=4-thio-butyl-amidine) conjugates can be improved by an increasing number of covalently attached thiol groups; a 100-fold increase compared to unmodified chitosan was observed for a medium molecular mass chitosan-TBA conjugate exhibiting 264 microM thiol groups per gram polymer. Also, the polymer chain length had an influence on the mucoadhesive properties of the polymer. The medium molecular mass polymer displayed a fourfold improved adhesion on the rotating cylinder compared to the derivative of low molecular mass. These results contribute to the development of new delivery systems exhibiting improved mucoadhesive properties.

Adhesives↗
PubMed2003

Integrated capillary fluorescence DNA biosensor.

Covalent attachment of dsDNA molecules inside a glass capillary without the need for hybridization is described. It is shown that the glass capillary has a surface density of 2.5 x 10(13) molecules/cm(2) with specific binding capacity of 62.5%. The resulting substrate was used to develop a biosensor for determining fluorescent organic analytes and metal binding with DNA. The biosensor combines highly specific immobilization chemistry with a capillary-geometry flow cell arrangement. The results show that fluorescent dyes are retained in the dsDNA-modified surface and that exposure to concentrations of nickel and lead ions resulted in a recoverable, highly reproducible diminishment of the fluorescence intensity.

Adsorption↗
PubMed1998

Evaluation of ultrafiltration failure.

The evaluation of ultrafiltration failure is embarked upon when a patient has persistent problems with symptoms and signs of fluid overload. Fluid overload is a common problem in peritoneal dialysis (PD) patients and the risk of its occurrence increases with time on dialysis. Although often attributed to changes in peritoneal membrane function (membrane failure), there are a number of potential, and frequently more common factors that can contribute to the failure of adequate fluid removal in patients on PD. Many of the causes of ultrafiltration failure may be apparent after an initial informal evaluation. However, if after this the etiology remains unexplained, a systematic approach to the differential diagnosis of this problem can be utilized with the use of the peritoneal equilibration test. Once a diagnosis is confirmed, a logical therapeutic plan can be formulated.

Biological Transport↗
PubMed2005

Passive microfluidic control of two merging streams by capillarity and relative flow resistance.

In the progress of microfluidic devices, a simple and precise control of multiple streams has been essential for complex microfluidic networks. Consequently, microfluidic devices, which have a simple structure, typically use external energy sources to control the multiple streams. Here, we propose a pure passive scheme that uses capillarity without using external force or external regulation to control the merging of two streams and even to regulate their volumetric flow rate (VFR). We accomplish this process by controlling the geometry of two inlets and a junction, and by regulating the hydrophilicity of a substrate. Additionally, we use the relative flow resistance to control the VFR ratio of the merged two streams. Our results will significantly simplify the control of multiple streams without sacrificing precision.

Capillary Action↗
PubMed2005

Photochemical patterning of biological molecules inside a glass capillary.

A simple way for photochemical patterning of biological molecules onto the inner wall of fused-silica capillary is described. The method is based on a modification of the inner capillary surface with photoactive benzophenone (BP) derivative. The UV irradiation at 365 nm of the capillary filled with a sample solution results in cross-linking of the solutes to the BP moiety via a stable covalent bond. As a proof of concept, oligonucleotides and proteins were arrayed inside the capillary using an inverted microscope as an irradiation device. We demonstrated that the capillary arrays produced in this way are functional and could be used in different bioassays including DNA hybridization, protein interaction studies, and immunoassays. Having a sensitivity comparable to the fluorophore-based assays in a planar format, the capillary array possesses several advantages including submicroliter sample volume and a short assay time. The capillary format should therefore be considered as a possible alternative to a planar format in a number of low-density array applications such as mutation detection and diagnostic immunoassays.

Benzophenones↗
PubMedDate not supplied

Comparison of three common amine reactive fluorescent probes used for conjugation to biomolecules by capillary zone electrophoresis.

The conjugation of three amine reactive fluorescent probes, each containing the fluorophore fluorescein but different reactive moieties, was compared using the protein myoglobin and the amino acid L-lysine as reagents. The three different reactive moieties were an isothiocyanate group (FITC), a succinimidyl ester group (CFSE), and a dichlorotriazine group (DTAF). The relative performance was based on the degree of conjugation to myoglobin, the rate of reaction, freedom from hydrolysis, and the stability of a conjugate with lysine. Performance was evaluated by separating the conjugation reaction reagents and products on-line, using capillary zone electrophoresis, and assessing relative amounts by absorbance detection. Each of the reactive probes demonstrated the ability to achieve a similar degree of conjugation, which depended mostly on allowed conjugated reaction time, and a rate of conjugation that rendered hydrolysis of the reactive moiety insignificant. For the relative rate of conjugation between probes and stability of the resulting conjugate, CFSE demonstrated superior performance, followed by DTAF and then FITC, for both the protein myoglobin and the amino acid L-lysine. The FITC conjugation reaction was much easier to control, however, which may be significant for applications that require a precise degree of conjugation. With regard to conjugate-bond stability, the FITC conjugate demonstrated inferior performance when subjected to incubation at 37 degrees C.

Capillary Action↗
PubMed1995

Inhibition of prothrombinase at macroscopic lipid membranes: competition between antithrombin and prothrombin.

The kinetics of inhibition of prothrombinase during prothrombin conversion by antithrombin and antithrombin-heparin complexes was studied in a tubular flow reactor. Prothrombinase was assembled at a macroscopic phospholipid membrane, composed of 25 mol % phosphatidylserine and 75 mol % phosphatidylcholine, deposited on the inner wall of a glass capillary, by perfusion with a factor Xa-factor Va mixture. Measurement of thrombin production allowed estimation of the amount of prothrombinase present at the capillary wall. Perfusion with a mixture of prothrombin and antithrombin or antithrombin-heparin complexes caused a progressive decline of the prothrombinase activity. The rate of inactivation steeply decreased with increasing prothrombin concentrations, indicating competitive inhibition. Analysis of competitive inhibition data requires estimation of the time-dependent substrate concentration, Co, near the prothrombin converting surface using earlier developed transport theory [Billy, D., et al. (1995) J. Biol. Chem. 270, 1029-1034]. It appears that the inhibition rate is proportional to the fraction of enzyme, Km/(Km+Co), not occupied by substrate. The value of Km of prothrombinase estimated from the dependence of the inhibition rate on the prothrombin concentration (Km = 2-3 nM) is in excellent agreement with the value estimated from the substrate conversion rate (Km = 3 nM). Therefore inhibition of prothrombinase by antithrombin and antithrombin-heparin complexes is fully competitive with the substrate: prothrombin. Our results show that prothrombinase assembled on macroscopic lipid surfaces by virtue of its low Km value is protected for inhibition due to highly effective competition of prothrombin with antithrombin for the active site of factor Xa.

Animals↗
PubMed1993

Specificity studies on the heparin lyases from Flavobacterium heparinum.

An understanding of the substrate specificity study of the heparin lyases (heparinase and heparitinases) is crucial for elucidation of the sequence of heparin and heparan sulfate. Four chemically modified heparins have been used to study the substrate specificity of the three heparin lyases. These modified heparins include the N- and O-desulfated and then specifically N-sulfated or N-acetylated derivatives of heparin and a modified heparin containing L-galactopyranosyluronic acid residues. These chemically modified heparins were degraded to various extents by the three heparin lyases. Differences in degree of sulfation have profound impact on the ease of cleavage of glycosidic linkages. Heparin lyase I (EC 4.2.2.7) is selective in cleaving highly sulfated polysaccharide chains containing linkages to 2-O-sulfated alpha-L-idopyranosyluronic acid residues. Heparin lyase III (EC 4.2.2.8) cleaves linkages that have reduced density of sulfation and that contain beta-D-glucopyranosyluronic acid residues. The ability of heparin lyase III to act on linkages to unsulfated alpha-L-idopyranosyluronic acid residues is observed for the first time. Heparin lyase II (no assigned EC number) demonstrates an unparalleled, wide specificity for substrates comprised of linkages containing both alpha-L-idopyranosyluronic and beta-D- glucopyranosyluronic acid residues. Heparin lyase II can also act on substrates containing linkages to unnatural alpha-L-galactopyranosyluronic acid residues. The high level of specificity of heparin lyase I makes it particularly suitable for use in the sequencing of heparin and heparan sulfate, while caution must be exercised in using heparin lyases II and III to sequence heparin and heparan sulfate because of their relatively broad specificity.

Acetylation↗