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PubMedDate not supplied

Is gravity on our way? The case of polyacrylamide gel polymerization.

Potential gravity-induced deformations of polyacrylamide matrices during gelling were investigated in two different initiator systems based on (i) photopolymerization with 100 microM methylene blue, 1 mM sodium toluene sulfinate (reducer) and 50 microM diphenyliodonium chloride (oxidizer) (photopolymerization) and (ii) chemical polymerization, utilizing the standard persulfate N,N,N',N'-tetramethylethylenediamine. In both systems, it is seen that convective flows are imprinted in the final gel structure above a critical gelling layer thickness, set at ca. 3 mm. In both systems, progressive increments of the solution density, from normodense (density = 1.0) up to isodense with the growing polymer chains (density = 1.3) do not inhibit the appearance of strong convective flows. However, gel inhomogeneities are completely abolished even in 10 mm gelling layers if polymerization is performed in presence of density gradients, notably of sucrose, from 0 to 20%, 0 to 40% and 0 to 60%. Even the shallower gradient (0-20% sucrose) is able to completely abolish convective flows in persulfate-driven polymerization. It is hypothesized that such disturbances are not created by sedimentation of the growing polymer chains in the gravitational field, but are produced by the reaction exothermality, which produces strong buoyancy-driven flows. It is additionally demonstrated that persulfate polymerization is sensitive to oxygen absorbed from the top liquid layers, which should be carefully protected by an overlay of organic solvent. Methylene blue-induced polymerization appears to offer a series of unique advantages over chemical initiation with persulfate.

Acrylic Resins↗

PubMed1989

Rapid detection of DNA-interstrand and DNA-protein cross-links in mammalian cells by gravity-flow alkaline elution.

Alkaline elution is a sensitive and commonly used technique to detect cellular DNA damage in the form of DNA strand breaks and DNA cross-links. Conventional alkaline elution procedures have extensive equipment requirements and are tedious to perform. Our laboratory recently presented a rapid, simplified, and sensitive modification of the alkaline elution technique to detect carcinogen-induced DNA strand breaks. In the present study, we have further modified this technique to enable the rapid characterization of chemically induced DNA-interstrand and DNA-protein associated cross-links in cultured epithelial cells. Cells were exposed to three known DNA cross-linking agents, nitrogen mustard (HN2), mitomycin C (MMC), or ultraviolet irradiation (UV). One hour exposures of HN2 at 0.25, 1.0, and 4.0 microM or of MMC at 20, 40, and 60 microM produced a dose-dependent induction of total DNA cross-links by these agents. Digestion with proteinase K revealed that HN2 and MMC induced both DNA-protein cross-links and DNA-interstrand cross-links. Ultraviolet irradiation induced both DNA cross-links and DNA strand breaks, the latter of which were either protein and nonprotein associated. The results demonstrate that gravity-flow alkaline elution is a sensitive and accurate method to characterize the molecular events of DNA cross-linking. Using this procedure, elution of DNA from treated cells is completed in 1 hr, and only three fractions per sample are analyzed. This method may be useful as a rapid screening assay for genotoxicity and/or as an adjunct to other predictive assays for potential mutagenic or carcinogenic agents.

Animals↗

PubMed2004

Gravity-induced coating flows of vaginal gel formulations: in vitro experimental analysis.

Efficacy of topical microbicidal drug delivery formulations against HIV depends in part on their coating distributions and retention on vaginal epithelium. This study focused on gravity-induced coating flows of vaginal gels, and effects of formulation composition and surface wettability on coating. We hypothesized that presence of a yield stress, and surface wettability, affect coating. Experiments imaged and analyzed coating flows of gels on inclined model hydrophilic or hydrophobic surfaces. The in vitro wettability conditions bracket those believed to exist on vaginal epithelium in vivo. Six commercial vaginal gels were studied: three polyacrylic acid-based (PAA) and three cellulose-based. Our research group uses these gels in complementary human in vivo studies and other in vitro experimental analyses; this study is a first step in linking the in vivo and in vitro measurements. Coating by PAA gels was different from cellulose-based gels: the former exhibited yield stresses, which prevented initial gel shape from deforming during sliding. Coating flows of cellulose gels depended upon surface wettability. The slipping rates of the PAA gels ranked inversely with fitted yield stress values. The coating flow rates of the cellulose gels (hydrophilic surface) did not correlate with consistency index, but ranked inversely with the shear-thinning index. This study introduces a simple methodology for comparing trial formulations and relating their flows to gel constituents and physical properties. It also suggests differences in coating by current commercial gels.

Administration, Intravaginal↗

PubMed1989

Center of gravity of drug level curves: a model-independent parameter useful in bioavailability studies.

The center of gravity (CG) of a drug level curve [c(t)] has the time coordinate AUMC/AUC and the concentration coordinate AUCC/2AUC, where AUC, AUMC, and AUCC are the integrals from time t = zero to t = infinity of c(t), tc(t), and c(t).c(t), respectively. An algorithm and computer program for determining CG when c(t) is given by a sum of exponentials is presented and its use is demonstrated with oral cimetidine data. Simulations indicate that the CG appears more suitable for comparison of absorption rates than mean absorption time (MAT) parameters. The limitation of the MAT parameter is due to the fact that this parameter is scale independent in that it only considers the shape and not the magnitude of the drug level or absorption rate curve. The MAT is therefore independent of the extent (F) of absorption. This limitation is not shared by the CG. When dealing with first-order absorption, the absorption rate of drug from product A will consistently (all t greater than 0) be larger than the absorption rate from product B (tested in the same subject) if MATA greater than MATB and AUCA/AUCB greater than MATA/MATB (assuming a time-invariant linear disposition). The above inequality relationships strongly contrast the common thinking about the "nonproblematic" use of MAT in absorption rate comparisons. Since both CG and MAT suffer some fundamental limitations, it is recommended that whenever problems arise, one should compare absorption rates by nonparametric system analysis methods (e.g., deconvolution) if possible.

Absorption↗

PubMed1994

Cell proliferation inhibition in reduced gravity.

Extended durations of spaceflight have been shown to be deleterious on an organismic level; however, mechanisms underlying cellular sensitivity to the gravitational environment remain to be elucidated. The majority of the gravitational studies to date indicates that cell regulatory pathways may be influenced by their gravitational environment. Still, few cell biology experiments have been performed in space flight and even fewer experiments have been repeated on subsequent flights. With flight opportunities on STS-50, 54, and 57, Sf9 cells were flown in the BioServe Fluids Processing Apparatus and cell proliferation was measured with and without exposure to a cell regulatory sialoglycopeptide (CeReS) inhibitor. Results from these flights indicate that the Sf9 cells grew comparable to ground controls, that the CeReS inhibitor bound to its specific receptor, and that its signal transduction cascade was not gravity sensitive.

Animals↗

PubMed1998

Gravity-Induced Coagulation of Spherical Particles of Different Size and Density

We consider a dilute homogeneous suspension of rigid spherical particles with different size and density in a motionless Newtonian fluid. These particles are moving under gravity at low Reynolds and Stokes numbers (negligible fluid and particle inertia) and high Peclet numbers (negligible Brownian diffusion). Doublets are formed when two particles in relative motion are brought into contact by the action of the attractive van der Waals force. Trajectory calculations for particles with different densities indicate that as the reduced density ratio increases above unity, the percentage of particles captured on the front hemisphere decreases, and this generally results in smaller collision efficiencies. Furthermore, in contrast to the case of particles with equal density, a maximum of the collision efficiency occurs for a particle size ratio smaller than unity. Above a critical value of the reduced density ratio, the occurrence of a closed region of relative trajectories confines the capture sites mostly to the "rear" hemisphere of each particle. As the reduced density ratio increases above the critical value, this region grows larger and the collision efficiency may be estimated by a closed-form asymptotic solution. Copyright 1998 Academic Press. Copyright 1998Academic Press

Journal Article↗

PubMed1998

Gravity and Inertia Effects in Plate Coating.

Coating processes are of technological interest. We focus here on the extraction of a vertical plate out of a wetting liquid. We first summarize the Landau-Levich-Derjaguin theory, including the gravity corrections which have been proposed in particular by White and Tallmadge. We propose a new numerical solution to the problem. Then, we discuss further developments: for liquids of low viscosity, it is shown that above a threshold in capillary number, the film is thickened because of inertia. A simple scaling argument is proposed for predicting the location of the threshold. Copyright 1998 Academic Press.

Journal Article↗

PubMed1999

First-Order Wetting Transitions under Gravity.

We discuss the effect of a gravitational field on the first-order wetting transition of a liquid layer on a horizontal surface. Gravity limits the thickness of the wetting layer and leads to a smooth first-order transition line Deltaµw(T, g) in the wetting phase diagram of chemical potential difference from bulk coexistence, Deltaµ identical with µ - µc, temperature T, and gravitational acceleration g. Consequences for the interpretation of wetting experiments are pointed out. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Stability of Magnetically Levitated Liquid Bridges of Arbitrary Volume Subjected to Axial and Lateral Gravity.

The paramagnetic fluid composed of manganese chloride tetrahydrate dissolved in water was used to form bridges held between two parallel collinear rods. Magnetic levitation was used to control the effective gravity felt by the bridges. Their stability was studied as a function of Bond number and volume of the supported liquid. Data are compared with theoretical predictions for liquid bridges as well as with experimental results, where available. Copyright 1999 Academic Press.

Journal Article↗

PubMed2000

Determination of Water-Oil Interfacial Area during 3-Phase Gravity Drainage in Porous Media.

Water-oil interfacial area in porous media was determined in laboratory experiments using sand columns consisting of either 2 (water and oil) or 3 (water, oil, and air) fluid phases. Surfactant sorption at the water-oil interface was directly measured for a wide range of water, oil, and air saturations undergoing gravity drainage. Differing values of the water-oil interfacial tension were also examined. The Gibbs adsorption equation was then used to obtain values for the water-oil interfacial area. Both 2- and 3-phase water-oil experiments showed a linear increase in interfacial area with decreasing water saturation. Results also showed that interfacial areas were not affected by changes in interfacial tension. The interfacial areas in the 3-phase experiments were less than half the calculated values of the corresponding 2-phase experiments, which contradicts predictions from a conventional pore level analysis of 3-phase flow. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

Unusual Interfacial Phase Behavior of Two Nonmiscible Liquids in a Cylindrical Test Tube: Equilibrium Shapes and Stability of Axisymmetric Liquid Bridges under Gravity.

In this paper the unusual interfacial phase behavior of two nonmiscible fluids contained in a cylindrical glass test tube is reported. Water, which is the lighter phase, takes up the upper part of the tube, whereas the denser compound (a hydrofluorocarbon) is in the bottom. However, below some critical volume of water, the denser phase emerges at the air surface, by forming an axisymmetric liquid bridge through the aqueous phase. Above the critical condition, the formation of the bridge, the evolution of the shape of this bridge, and its final breakdown can be visually inspected after shaking the tube. The minority liquid (water) is dispersed in the majority phase (HCFC) as an unstable dispersion of droplets. Droplets rise to the air surface under the action of the buoyant force, and coalesce on the glass wall: this leads to the formation of a bridge (made from the dispersion in the middle of a hollow axisymmetric water drop), whose height increases and thickness decreases during the coalescence process, until it breaks down. Using a free energy analysis, we state the exact variational problem via its Euler-Lagrange equation. However, since this nonlinear differential equation cannot be solved analytically, a simplified "mean-field" approach is developed, which provides a comprehensive insight into the physical origin of these capillary bridges and their stability under gravity. Copyright 2000 Academic Press.

Journal Article↗

PubMed1994

The effect of body orientation to gravity on early infant reaching.

The purpose of the study was to examine the effect of body orientation with respect to gravity on infant's reaching quantity and quality. Two groups, 12- to 19-week-old and 20- to 27-week-old infants, were seated in three positions: vertical (90 degrees from horizontal), recline (60 degrees), and supine (0 degrees). Nine balls on a black board were presented. Video recordings were used to measure quantity of reaching (number and duration of reaches) and quality of reaching (open or closed hand, starting position of the arm, and position of touched and grasped balls). On the quantity measure there was a significant age x body position interaction that indicated that the 12- to 19-week-olds showed reaching behavior in the vertical position equal to that of 20- to 27-week-old infants in all positions. A similar tendency, although not significant, was found for the quality measurements. These findings indicate that the development of reaching does not just reflect maturation of the central nervous system, but a changing interaction between organismic and environmental constraints.

Age Factors↗

PubMed1993

Influence of diffusion and gravity on the adhesion of a two-component mixture of hard spheres on a flat surface.

The adhesion of hard spheres, modeling particles of biological interest (proteins, bacteria, cells), on flat surfaces is investigated by means of Monte Carlo simulations. These computations include the Brownian diffusion of the particles in the bulk fluid, as well as the systematic displacement due to the gravitational field. The size of the particles influences directly both diffusion coefficient and net weight, with the consequence that the coverage at the jamming limit depends on this parameter. Results obtained in a former paper based on a lattice model are confirmed by the present continuous space model. In order to gain a better understanding of the adsorption competition of two types of particles, the proposed model is applied to the case of binary mixtures of spheres. For polydispersed suspensions, various parameters determine the final coverage, as well as the distribution of the small and large particles on the surface: the radii of the particles and the respective proportions of them in the infinitely large reservoir from which they are randomly selected. In this way, it is shown that the chronology of the adhesion of the small and large particles strongly influences the final number of each type of spheres fixed on the surface. Qualitatively, the present results resemble those obtained with disks placed by means of a classical random sequential adsorption mechanisms. Quantitatively, however, the number densities and coverage values determined in this way are significantly different due to the inclusion of the gravity and of the diffusion in the model.

Adhesiveness↗

PubMed2006

First clinical experiences in patients with idiopathic normal-pressure hydrocephalus with the adjustable gravity valve manufactured by Aesculap (proGAV(Aesculap)).

OBJECTIVE: Improved clinical outcomes after implantation of a low pressure valve in patients with idiopathic normal-pressure hydrocephalus is usually achieved at the expense of a higher overdrainage rate. Can an adjustable valve with a gravitational unit provide optimal results? METHOD: In a prospective clinical outcome study conducted in the Unfallkrankenhaus Berlin, 30 patients with idiopathic normal-pressure hydrocephalus were treated surgically between June 2004 and May 2005 with the valve combination described above, and reexamination 3 months or 6 months postoperatively. RESULTS: Clinical outcome correlates with opening pressure level of the valve. Controlled adjustment of the valve from 100 mmH2O to 70 mmH2O, and then to 50 mmH2O after 3 months, permits optimum adaptation of the brain to the implanted valve without overdrainage complications. CONCLUSIONS: Advantages of this programmable gravity valve include: 1) the absence of unintentional readjustment through external magnets, and 2) the possibility of controlling the valve setting using an accessory instrument without the need for x-ray monitoring. A significant disadvantage is adjusting the valve after implantation. From the clinical point of view, this new "proGAV(Aesculap)" valve is a necessary development in the right direction, but at the moment it is still beset with technical problems.

Cerebrospinal Fluid Shunts↗

PubMed2005

Gravity valves for idiopathic normal-pressure hydrocephalus: a prospective study with 60 patients.

OBJECTIVE: Are hydrostatic valves superior to conventional differential pressure shunts in patients with normal-pressure hydrocephalus, with regard to the postoperative results of treatment and possible complications? METHODS: From September 1997 to January 2002, 60 patients with idiopathic normal-pressure hydrocephalus were treated by surgical implantation of hydrostatic valve at the Unfallkrankenhaus Berlin. In a prospective study, the clinical examination and a CT examination were carried out preoperatively, postoperatively and 1 year after the operation. RESULTS: One year after the operation, the clinical picture was very good for 33% of the patients, good for 33% and satisfactory or poor for 17%, each, of the patients. 3 dislocations (5%) of ventricular or abdominal catheters and three valve infections were found as valve-independent. As valve-dependent complications, underdrainage was found in 4 patients (7%) and radiological signs of overdrainage in 2 patients (3%), while 1 patient (1.7%) showed symptomatic over-drainage. CONCLUSION: According to our experience, hydrostatic Dual-switch valves Aesulap are superior to conventional differential pressure shunts without an additional gravity unit especially with regard to the treatment of patients with idiopathic normal-pressure hydrocephalus, concerning both the postoperative results and the incidence of possible complications. A clinical improvement can be achieved for 83% of such patients.

Adult↗

PubMed1992

Detection of rotating gravity signals.

It is shown in the preceding paper that neurons with two-dimensional spatio-temporal properties to linear acceleration behave like one-dimensional rate sensors: they encode the component of angular velocity (associated with a rotating linear acceleration vector) that is normal to their response plane. During off-vertical axis rotation (OVAR) otolith-sensitive neurons are activated by the gravity vector as it rotates relative to the head. Unlike "one-dimensional" linear accelerometer neurons which exhibit equal response magnitudes for both directions of rotation, "two-dimensional" neurons can be shown to respond with unequal magnitudes to clockwise and counterclockwise off-vertical axis rotations. The magnitudes of the sinusoidal responses of these neurons is not only directionally selective but also proportional to rotational velocity. Thus, responses from such "two-dimensional" neurons may represent the first step in the computations necessary to generate the steady-state eye velocity during OVAR. An additional step involving a nonlinear operation is necessary to transform the sinusoidally modulated output of these neurons into a signal proportional to sustained eye velocity. Similarly to models of motion detection in the visual system, this transformation is proposed to be achieved through neuronal operations involving mathematical multiplication followed by a leaky integration by the velocity storage mechanism. The proposed model for the generation of maintained eye velocity during OVAR is based on anatomical and physiological properties of vestibular nuclei neurons and capable of predicting the experimentally observed steady-state characteristics of the eye velocity.

Acceleration↗

PubMed1977

Unit gravity sedimentation separation of cells comprising the caput epididymidis of the rat.

Cells from the rat caput epididymidis were separated by unit gravity sedimentation. Purest 12-ml fractions contained 88-95% basal cells or 64-76% principal cells. Ultrastructure of separated cells was similar to that of cells in intact tissue. Viability of separated cells was excellent as determined by dye exclusion tests and cellular ATP content. By combining fractions pools containing 4.0 +/- 0.9 X 10(6) cells (86 +/- 8% basal cells) and 1.4 +/- 0.4 X 10(6) cells (56 +/- 7% principal cells) were obtained. Thus, studies on the function of basal and principal cells from the rat caput epididymidis should be possible.

Animals↗

PubMed1977

Neuronal and synaptic organization in the gravity receptor system of the statocyst of Octopus vulgaris.

The neuronal and synaptic organization of the sensory epithelium (macula) of the gravity receptor system of Octopus vulgaris was investigated by serial electron microscopic reconstruction. Three different types of afferent neurons, unipolar, bipolar, and multipolar, are described. Afferent synapses exist between the secondary sensory cells (hair cells) and the afferent neurons. Consequently, the neurons are first-order neurons. Two morphologically distinct types of afferent synapses could be identified: the most common type, present on every hair cell, has a finger-like postsynaptic process; the second type, which does not occur on every hair cell, has a flat or somewhat curved postsynaptic process. As a rule, the hair cells each form synapses with more than one afferent neuron. The neurons, in turn, form synapses with more than one hair cell. A complicated arrangement of efferent synapses was found at the level of both the hair cells and the neurons. The results are discussed with reference to their physiological consequences.

Animals↗