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At least 73 records · Page 4

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NASA NTRS1976

Electrophoretic characterization of aldehyde-fixed red blood cells, kidney cells, lynphocytes and chamber coatings

Ground-based electrokinetic data on the electrophoresis flight experiment to be flown on the Apollo-Soyuz Test Project experiment MA-011 are stipulated. Aldehyde-fixed red blood cells, embryonic kidney cells and lymphocytes were evaluated by analytical particle electrophoresis. The results which aided in the interpretation of the final analysis of the MA-011 experiment are documented. The electrophoresis chamber surface modifications, the buffer, and the material used in the column system are also discussed.

Source record↗

NASA NTRS1976

Detailed results of ASTP experiment MA-011

This experiment was developed in order to conduct engineering and operational tests of electrokinetic equipment in a micro-gravity environment. The experimental hardware in general functioned as planned and electrophoretic separations were obtained in space. The results indicated the development of satisfactory sample collection, return, and preservation techniques. The application of a near-zero zeta potential interior wall coating to the experimental columns, confirmation of biocompatibility of all appropriate hardware components, and use of a sterile operating environment provided a significant step forward in the development of a biological processing facility in space. A separation of a test of aldehyde-fixed rabbit, human, and horse red blood cells was obtained. Human kidney cells were separated into several components and viable cells returned to earth. The isotachophoretic separation of red cells was also demonstrated. Problems associated with the hardware led to a lack of success in the attempt to separate subpopulations of human lymphocytes.

Seaman, G. V. F.↗

NASA NTRS1979

Preparative cell electrophoresis at 1 and 0 gravity

It is attempted to show that the use of heavy water (D2O) as starting cushion for the cells combines the advantages of the required density difference, with no lasting biochemical or physiochemical influence on the cells. Phosphate buffers of low ionic strength were prepared in distilled water or heavy water. A vertical starch gel electrophoresis was used to support a cylindrical polystyrene electrophoresis tube used for lymphocyte separations, 25 cm in length and 0.75 cm I.D., prepared from a 10 ml disposable pipet. Erythrocyte separations were carried out in a jacketed rectangular plexiglas chamber. It is pointed out that the described preparative D2O gradient electrophoresis method cannot be readily used for the measurement of electrophoretic mobilities for analytical purposes. However, for the preparative separation of cells with only slightly different electrokinetic properties the method appears promising, simple, and entirely inocuous to the cells.

Van Oss, C. J.↗

NASA NTRS1980

Electrophoretic cell separation using microspheres

Methods of cell separation based on the electrokinetic properties of the cell membrane offer a degree of discrimination among cell populations which is not available with methods based on cell size or density alone. Studies aimed at extending red cell separations using microspheres to purification of lymphocytes.

Smolka, A.↗

NASA NTRS1982

Electrophoresis tests on STS-3 and ground control experiments - A basis for future biological sample selections

Static zone electrophoresis is an electrokinetic method of separating macromolecules and small particles. However, its application for the isolation of biological cells and concentrated protein solutions is limited by sedimentation and convection. Microgravity eliminates or reduces sedimentation, floatation, and density-driven convection arising from either Joule heating or concentration differences. The advantages of such an environment were first demonstrated in space during the Apollo 14 and 16 missions. In 1975 the Electrophoresis Technology Experiment (MA-011) was conducted during the Apollo-Soyuz Test Project flight. In 1979 a project was initiated to repeat the separations of human kidney cells. One of the major objectives of the Electrophoresis Equipment Verification Tests (EEVT) on STS-3 was to repeat and thereby validate the first successful electrophoretic separation of human kidney cells. Attention is given to the EEVT apparatus, the preflight electrophoresis, and inflight operational results.

Morrison, D. R.↗

NASA NTRS1983

Electrochemical Studies of Redox Systems for Energy Storage

Particular attention was paid to the Cr(II)/Cr(III) redox couple in aqueous solutions in the presence of Cl(-) ions. The aim of this research has been to unravel the electrode kinetics of this redox couple and the effect of Cl(1) and electrode substrate. Gold and silver were studied as electrodes and the results show distinctive differences; this is probably due to the role Cl(-) ion may play as a mediator in the reaction and the difference in state of electrical charge on these two metals (difference in the potential of zero charge, pzc). The competition of hydrogen evolution with CrCl3 reduction on these surfaces was studied by means of the rotating ring disk electrode (RRDE). The ring downstream measures the flux of chromous ions from the disk and therefore separation of both Cr(III) and H2 generation can be achieved by analyzing ring and disk currents. The conditions for the quantitative detection of Cr(2+) at the ring electrode were established. Underpotential deposition of Pb on Ag and its effect on the electrokinetics of Cr(II)/Cr(III) reaction was studied.

Wu, C. D.↗

NASA NTRS1982

Countercurrent distribution of biological cells

Detailed physiochemical studies of dextran/poly(ethylene glycol) (PEG) two phase systems were carried out to characterize and provide understanding of the properties of the systems which determine cell partition and the electrophoretic behavior of phase drops responsible for electric field driven phase separation. A detailed study of the electrostatic and electrokinetic potentials developed in these systems was carried out. The salt partition was examined both in phase systems and with pure polymer solutions via equilibrium dialysis and mechanism of sulfate, chloride and phosphate partition shown to be exclusion by PEG rather than binding by dextran. Salt partition was shown to have a strong effect on the polymer compositions of the phases as well, an effect which produces large changes in the interfacial tension between them. These effects were characterized and the interfacial tension shown to obey a power law with respect to its dependence on the length of the tie line describing the system composition on a phase diagram. The electrostatic potential differences measured via salt bridges were shown to obey thermodynamic predictions. The electrophoretic mobilities measured were utilized to provide a partial test of Levine's incomplete theory of phase drop electrophoresis. The data were consistent with Levine's expression over a limited range of the variables tested.

Brooks, D. E.↗

NASA NTRS1985

Free-zone electrophoresis of animal cells. 1: Experiments on cell-cell interactions

The electrophoretically migrating zones wasa monitored. The absence of fluid flows in the direction of migration permits direct measurement of electrophoretic velocities of any material. Sedimentation is orthogonal to electrokinetic motion and the effects of particle-particle interaction on electrophoretic mobility is studied by free zone electrophoresis. Fixed erythrocytes at high concentrations, mixtures of fixed erythrocytes from different animal species, and mixtures of cultured human cells were studied in low ionic strength buffers. The electrophoretic velocity of fixed erythrocytes was not altered by increasing cell concentration or by the mixing of erythrocytes from different species. When zones containing cultured human glial cells and neuroblastoma cells are permitted to interact during electrophoresis, altered migration patterns occur. It is found that cell-cell interactions depends upon cell type.

Todd, P. W.↗

NASA NTRS1985

Recommendations and calculations concerning physical characteristics of the EEVT apparatus

Several issues arose during the course of preparing for the flight of EEVT on STS-3. Documents concerning the issues are presented in the following order: (1) the possibility of mixing latex spheres with kidney cells as standard electrokinetic markers; (2) tube breakage and the potential for the development of leaks and bubbles; (3) effects of the shape of the sample gate on the electric field and the outward migration of cells; (4) suggestions for reducing electroosmosis by decreasing the diameter of the sample; and (5) predictions of the effects of modified sample dimensions on electroosmotic band spreading.

Source record↗

NASA NTRS1987

Stability and rheology of dispersions of silicon nitride and silicon carbide

The relationship between the surface and colloid chemistry of commercial ultra-fine silicon carbide and silicon nitride powders was examined by a variety of standard characterization techniques and by methodologies especially developed for ceramic dispersions. These include electrokinetic measurement, surface titration, and surface spectroscopies. The effects of powder pretreatment and modification strategies, which can be utilized to augment control of processing characteristics, were monitored with these technologies. Both silicon carbide and nitride were found to exhibit silica-like surface chemistries, but silicon nitride powders possess an additional amine surface functionality. Colloidal characteristics of the various nitride powders in aqueous suspension is believed to be highly dependent on the relative amounts of the two types of surface groups, which in turn is determined by the powder synthesis route. The differences in the apparent colloidal characteristics for silicon nitride powders cannot be attributed to the specific absorption of ammonium ions. Development of a model for the prediction of double-layer characteristics of materials with a hybrid site interface facilitated understanding and prediction of the behavior of both surface charge and surface potential for these materials. The utility of the model in application to silicon nitride powders was demonstrated.

Feke, Donald L.↗

NASA NTRS1986

Polystyrene latex separations by continuous flow electrophoresis on the Space Shuttle

The seventh mission of the Space Shuttle carried two NASA experiments in the McDonnell Douglas Astronautics Corporation continuous flow electrophoresis system. The objectives were to test the operation of continuous flow electrophoresis in a reduced gravity environment using stable particles with established electrokinetic properties and specifically to evaluate the influence of the electrical properties of the sample constituents on the resolution of the continuous flow electrophoretic device. Polystrene latex microspheres dispersed in a solution with three times the electrical conductivity of the curtain buffer separated with a significantly larger band spread compared to the second experiment under matched conductivity conditions. It is proposed that the sample of higher electrical conductivity distorted the electric field near the sample stream so that the polystyrene latex particles migrated toward the chamber walls where electroosmosis retarded and spread the sample.

Snyder, R. S.↗

NASA NTRS1986

Mathematical models of continuous flow electrophoresis: Electrophoresis technology

Two aspects of continuous flow electrophoresis were studied: (1) the structure of the flow field in continuous flow devices; and (2) the electrokinetic properties of suspended particles relevant to electrophoretic separations. Mathematical models were developed to describe flow structure and stability, with particular emphasis on effects due to buoyancy. To describe the fractionation of an arbitrary particulate sample by continuous flow electrophoresis, a general mathematical model was constructed. In this model, chamber dimensions, field strength, buffer composition, and other design variables can be altered at will to study their effects on resolution and throughput. All these mathematical models were implemented on a digital computer and the codes are available for general use. Experimental and theoretical work with particulate samples probed how particle mobility is related to buffer composition. It was found that ions on the surface of small particles are mobile, contrary to the widely accepted view. This influences particle mobility and suspension conductivity. A novel technique was used to measure the mobility of particles in concentrated suspensions.

Saville, Dudley A.↗

NASA NTRS1987

Bioseparations - Flight experiment support research

While important principles of electrokinetic technology, such as electrophoresis, have been demonstrated for microgravity environments and promise to be able to alleviate many of the practical limitations imposed by gravity, the minimal crew time and sample-handling facilities available in orbit call for almost total reliance on postflight analysis of separated fractions. Since cell separations are the most difficult to accomplish in 1-g, two model cell types have been studied intensively to determine the basic relationships between cell surface charge and secretory functions. A rationale has been developed for selecting and qualifying new cell types and proteins that warrant processing in microgravity.

Morrison, Dennis R.↗

NASA NTRS1989

Physical phenomena and the microgravity response

The living biological cell is not a sack of Newtonian fluid containing systems of chemical reactions at equilibrium. It is a kinetically driven system, not a thermodynamically driven system. While the cell as a whole might be considered isothermal, at the scale of individual macromolecular events there is heat generated, and presumably sharp thermal gradients exist at the submicron level. Basic physical phenomena to be considered when exploring the cell's response to inertial acceleration include particle sedimentation, solutal convection, motility electrokinetics, cytoskeletal work, and hydrostatic pressure. Protein crystal growth experiments, for example, illustrate the profound effects of convection currents on macromolecular assembly. Reaction kinetics in the cell vary all the way from diffusion-limited to life-time limited. Transport processes vary from free diffusion, to facilitated and active transmembrane transport, to contractile-protein-driven motility, to crystalline immobilization. At least four physical states of matter exist in the cell: aqueous, non-aqueous, immiscible-aqueous, and solid. Levels of order vary from crystalline to free solution. The relative volumes of these states profoundly influence the cell's response to inertial acceleration. Such subcellular phenomena as stretch-receptor activation, microtubule re-assembly, synaptic junction formation, chemotactic receptor activation, and statolith sedimentation were studied recently with respect to both their basic mechanisms and their responsiveness to inertial acceleration. From such studies a widespread role of cytoskeletal organization is becoming apparent.

Todd, Paul↗

NASA NTRS1990

The fluid mechanics of continuous flow electrophoresis

The overall objective is to establish theoretically and confirm experimentally the ultimate capabilities of continuous flow electrophoresis chambers operating in an environment essentially free of particle sedimentation and buoyancy. The efforts are devoted to: (1) studying the effects of particle concentration on sample conductivity and dielectric constant. The dielectric constant and conductivity were identified as playing crucial roles in the behavior of the sample and on the resolving power and throughput of continuous flow devices; and (2) improving the extant mathematical models to predict flow fields and particle trajectories in continuous flow electrophoresis. A dielectric spectrometer was designed and built to measure the complex dielectric constant of a colloidal dispersion as a function of frequency between 500 Hz and 200 kHz. The real part of the signal can be related to the sample's conductivity and the imaginary part to its dielectric constant. Measurements of the dielectric constants of several different dispersions disclosed that the dielectric constants of dilute systems of the sort encountered in particle electrophoresis are much larger than would be expected based on the extant theory. Experiments were carried out to show that, in many cases, this behavior is due to the presence of a filamentary structure of small hairs on the particle surface. A technique for producing electrokinetically ideal synthetic latex particles by heat treating was developed. Given the ubiquitous nature of hairy surfaces with both cells and synthetic particles, it was deemed necessary to develop a theory to explain their behavior. A theory for electrophoretic mobility of hairy particles was developed. Finally, the extant computer programs for predicting the structure of electro-osmotically driven flows were extended to encompass flow channels with variable wall mobilities.

Saville, D. A.↗

NASA NTRS1992

Mathematical modeling of a thermovoltaic cell

A new type of battery named 'Vaporvolt' cell is in the early stage of its development. A mathematical model of a CuO/Cu 'Vaporvolt' cell is presented that can be used to predict the potential and the transport behavior of the cell during discharge. A sensitivity analysis of the various transport and electrokinetic parameters indicates which parameters have the most influence on the predicted energy and power density of the 'Vaporvolt' cell. This information can be used to decide which parameters should be optimized or determined more accurately through further modeling or experimental studies. The optimal thicknesses of electrodes and separator, the concentration of the electrolyte, and the current density are determined by maximizing the power density. These parameter sensitivities and optimal design parameter values will help in the development of a better CuO/Cu 'Vaporvolt' cell.

White, Ralph E.↗

NASA NTRS1992

A mathematical model of a CuO/Cu Vaporvolt cell

Kawanami, Makoto↗

NASA NTRS1993

FNAS phase partitions

Project NAS8-36955 D.O. #100 initially involved the following tasks: (1) evaluation of various coatings' ability to control wall wetting and surface zeta potential expression; (2) testing various methods to mix and control the demixing of phase systems; and (3) videomicroscopic investigation of cell partition. Three complementary areas were identified for modification and extension of the original contract. They were: (1) identification of new supports for column cell partition; (2) electrokinetic detection of protein adsorption; and (3) emulsion studies related to bioseparations.

Vanalstine, James M.↗