Biomedical subjects

L E Scriven

Publications and source records attributed to L E Scriven.

14 recordsLinked to original sources

PubMed1999

A patch coating method for preparing biocatalytic films of Escherichia coli.

A method has been developed for immobilizing viable but nongrowing Escherichia coli in highly uniform patches. The patches consist of a thin layer of bacteria in acrylate vinyl acetate covered with a thin layer of the same polymer devoid of bacteria and sealed by the edges. This method permits study of immobilized cell physiology in biocatalytic films by the assay methods used for suspended cells. Large numbers of patches of immobilized E. coli can be generated on metal or polyester sheets. Those described here are 12.7 mm in diameter; in them the cell layer is 30 microm thick and contains more than 5 x 10(8) viable cells. The method allows the cell-plus-polymer layer and the polymer sealant to be varied in thickness from 5 to 60 microm and from 7 to 80 microm, respectively. No leakage of cells was detected from 87% of the patches during 15 days of rehydration. Culturability of the immobilized cells, released by shaking the cells out of the porous polymer layer, was 80% of pre coating culturability. E. coli beta-galactosidase activity and measurements of total RNA and DNA from immobilized and suspended cells indicated that cells immobilized in the thin polymer layer have higher specific beta-galactosidase activity and a slower total RNA degradation rate than suspended cells over 15 days.

Bacterial Proteins↗

PubMed1998

Paramagnetic tracer concentration evolution by NMR relaxation time mapping: application to Aris-Taylor dispersion.

A procedure to study tracer dispersion was proposed and tested for the case of tracer spreading in tube flow. Concentration maps of paramagnetic tracers Gd3+ were measured in time through direct measurements of spin lattice relaxation time T1 obtained by using a two-point stimulated echo pulse sequence. The procedure was used to test the linear dependence of Peclet number on inverse velocity in the range of flow rates 0.3-1.2 cc/min.

Contrast Media↗

PubMed1996

Dispersion of paramagnetic tracers in bead packs by T1 mapping: experiments and simulations.

NMR imaging was used to study dispersion in 6 mm bead pack. T1 maps were employed to measure the rate of axial spreading of paramagnetic tracers (GdCl3) inside the bead pack in the range of flow rate from 0.015 mL/s to 0.175 mL/s. From the T1 maps, tracer concentration profiles were obtained, which yielded dimensionless axial dispersion coefficient and mean transit time. Spatial variations in the dispersion coefficient were observed at flow rates above 0.08 mL/s. We hypothesized that the observed spatial oscillations in the dispersion coefficient arise from the spatial variations of the velocity distribution. To validate this mechanism we showed by simulation that similar dispersion coefficient variation occur in a layered network.

Contrast Media↗

PubMed1988

Controlled environment vitrification system: an improved sample preparation technique.

The controlled environment vitrification system (CEVS) permits cryofixation of hydrated biological and colloidal dispersions and aggregates from a temperature- and saturation-controlled environment. Otherwise, specimens prepared in an uncontrolled laboratory atmosphere are subject to evaporation and heat transfer, which may introduce artifacts caused by concentration, pH, ionic strength, and temperature changes. Moreover, it is difficult to fix and examine the microstructure of systems at temperatures other than ambient (e.g., biological systems at in vivo conditions and colloidal systems above room temperature). A system has been developed that ensures that a liquid or partially liquid specimen is maintained in its original state while it is being prepared before vitrification and, once prepared, is vitrified with little alteration of its microstructure. A controlled environment is provided within a chamber where temperature and chemical activity of volatile components can be controlled while the specimen is being prepared. The specimen grid is mounted on a plunger, and a synchronous shutter is opened almost simultaneously with the release of the plunger, so that the specimen is propelled abruptly through the shutter opening into a cryogenic bath. We describe the system and its use and illustrate the value of the technique with TEM micrographs of surfactant microstructures in which specimen preparation artifacts were avoided. We also discuss applications to other instruments like SEM, to other techniques like freeze-fracture, and to novel "on the grid" experiments that make it possible to freeze successive instants of dynamic processes such as membrane fusion, chemical reactions, and phase transitions.

Microscopy, Electron↗

PubMed1982

Imaging vesicular dispersions with cold-stage electron microscopy.

A fast-freeze, cold-stage transmission electron microscopy technique which can incorporate in situ freeze-drying of the sample is described. Its use in elucidating structure in unstained and stained, hydrated and freeze-dried, aqueous vesicular dispersions of biological and chemical interest is demonstrated with vesicles of L-alpha-phosphatidylcholine (bovine phosphatidylcholine) and of the synthetic surfactant sodium 4-(1'-heptylnonyl)benzenesulfonate (SHBS). The contrast features observed in transmission electron microscope images of frozen, hydrated samples are identified and explained with the dynamical theory of electron diffraction. Radiolysis by the electron beam is shown to increase contrast in vesicle images and to change their structure and size. Micrographs illustrate the freeze-drying of a dispersion in the microscope; the process causes vesicles to shrink and collapse.

Animals↗

PubMed1974