Carrier Beads Research Articles

Flow-through microfluorometry of immobilized enzymes

The turnover of bioreactors is commonly determined from the total consumption or production rates of substrates and products. However, conventional techniques provide no information about the dispersion of catalytic particles such as cells or enzyme carrier beads. Flow-through microfluorometry enables the dispersive measurement on-line of static parameters (e.g. distribution of size and enzyme load), and of dynamic parameters of particle suspensions (e.g. distribution of individual turnover rates in bioreactors). This allows the influence of heterogeneity of the carrier matrix or cells on the kinetics of the system to be estimated.

Extraction-chromatographic separation of137mBa from137Cs

The possibilities of extraction-chromatographic separation of137mBa from137Cs in genetic succession were studied, using columns filled with support beads loaded with the extractant H+[π)−(3)−1,2−B9C2H11]2Co−, further referred to as dicarbolide-H+, in nitrobenzene. The dependence of the amount of separable activities on experimental conditions was established. Optimal conditions were selected for the separation process. The effects of isotopic and nonisotopic carriers of137mBa on the separation and the degree on saturation of extraction-chromatographic column with Ba2+ ions were evaluated. The effects of acidity of the elution solutions, of flow-through velocity, the amount of elution solution and the quality of carrier beads on the separation process were assessed. The extraction-chromatographic yield was calculated and the number of possible repeated elution cycles for137mBa with saline and some other eluents was determined.

Electrical Properties of Conductive Two-Component Xerographic Developer

Xerographic development with a conductive two-component magnetic brush depends on the electrical properties of a developer mixture consisting of insulative toner particles and conductive carrier beads. The electric field driving toner deposition onto an image receiver is affected by the carrier bead conductivity, toner concentration, magnetic field strength, developer thickness, and developer agitation due to the relative motion between the developer and image receiver. To elucidate the dependence of the electrical properties on these parameters, the measurements on an electroded cell of developer under conditions simulating magnetic brush development systems are described. The measurements provide insight into the solid area and line development process with conductive xerographic developer.

In vitro delayed hypersensitivity granuloma formation: development of an antigen-coated bead model.

Previously, we have described an in vitro model of granulomatous hypersensitivity around Schistosoma mansoni eggs in both the murine model of schistosomiasis and in human schistosomiasis. These studies describe a new model of in vitro granuloma formation that complexes soluble egg antigen from S. mansoni eggs, a partially purified protein derivative of Mycobacterium tuberculosis (PPD), or bovine serum albumin to carrier beads. Ultrastructural and morphologic evaluations demonstrate that there are initial macrophage interactions, followed by the recruitment of antigen-specific T cells that interact with and recruit macrophages, lymphocytes, granulocytes, and fibroblasts. Finally, there is a stage of granulomatous organization involving fibroblast proliferation and collagen deposition. The in vitro reactivity, defined by a quantitative granuloma index, correlates with in vivo granulomas around S. mansoni eggs in the livers of infected cell donor animals. In vitro granuloma formation against PPD-coated beads correlated with delayed cutaneous hypersensitivity against PPD, which was judged by footpad swelling. The reactions demonstrate antigenic specificity and were intrinsically modulated in a manner that is analogous to that previously shown with the in vitro egg granuloma model. This model of in vitro granuloma formation promises to be a useful tool for elucidating mechanisms of cellular immunity and regulation.

Measurement of Carrier Bead Velocity Distribution in Cascade Flow

A miniature piezoelectric impact probe is described for measuring the impact velocity of carrier beads in a cascade flow. The probe can sense a force of a few dynes. It has a response time of about 1 μs and a total settling time of less than 40 μs. The impacts of a few microgram particles due to a free-fall under gravity of a distance of about 50 μm and at a count rate in excess of 20 000/s have been measured. The probe has been used in measuring the impact velocity distribution of carrier beads in a cascade flow. The impact velocity distributions have been measured at different flow conditions and compared with theoretical predictions. The characteristics of the cascade flow are briefly discussed in terms of the two parameters: the number density of the carrier beads in the flow and the diffusion constant of the flow.

Generation Mechanism of Contact Pressure in Magnetic Brush Developer

This paper describes theoretical and experimental studies on contact pressure between the recording paper and the magnetic brush in the magnetic brush development process. Compression of the magnetic brush caused by contacting the paper is modeled as a powder compressed by a fixed-area piston. The relation between the surface sunken depth of the magnetic brush versus the compressin pressure is found. In addition, the carrier bead density distribution in the compressed magnetic brush is described. It is found that the contact pressure is related to the ratio of the magnetic brush velocity to the recording paper velocity. It has a maximum contact pressure when the ratio is 1.

Immobilized xanthine oxidase: Kinetics, (in)stability, and stabilization by coimmobilization with superoxide dismutase and catalase

AbstractMilk xanthine oxidase was immobilized by covalent attachment to CNBr‐activated Sepharose 4B and by adsorption to n‐octylamine‐substituted Sepharose 4B. The amounts of activity immobilized for the two preparations were 30 and 90%, respectively. The pH optima for free and adsorbed xanthine oxidase were at 8.6 and 8.2, respectively. Both free and immobilized xanthine oxidase show substrate inhibition. The apparent inhibition constant (Ki′) found for adsorbed xanthine oxidase with xanthine as substrate was higher than the Ki for the free enzyme, which was shown to be due to substrate diffusion limitation in the pores of the carrier beads (internal diffusion limitation). Higher substrate concentrations, as desirable for practical application in organic synthesis, can therefore be used with the immobilized enzyme without decreasing the rate. As a result of the internal diffusion limitation the apparent Michaelis constant (Km′) for adsorbed xanthine oxidase was also higher than the Km for the free enzyme. Immobilized xanthine oxidase was more stable than the free enzyme during storage at 4 and 30°C. Both forms rapidly lost activity during catalysis. The loss was proportional to the amount of substrate converted. Coimmobilization of xanthine oxidase with superoxide dismutase and catalase improved the operational stability, suggesting that O2− and H2O2 side‐products of the enzymatic reaction were involved in the inactivation. Coimmobilization with albumin also had some stabilizing effect. Complete surrounding of xanthine oxidase by protein, however, by means of etrapment in a glutaraldehyde‐crosslinked gelatin matrix, considerably enhanced the operational half‐life. This system was less efficient than the Sepharose preparations either because much activity was lost during the immobilization procedure and/or because it had poor flow properties. Xanthine (15 mg)was converted by an adsorbed xanthine oxidase preparation and product (uric acid) was isolated in high yield (84%).

Human natural cell-mediated cytotoxicity against fetal fibroblasts: II. Isolation and target cell specificity of the effector cells

Human peripheral Wood lymphocytes were depleted of natural killer cells cytotoxic against human fetal fibroblasts by allowing them to attack the fibroblast targets grown on plastic beads followed by gravity sedimentation under conditions in which single cells floated but the attacker cells sedimented with the carrier beads. The attacker cells could be released from the bead-grown targets and shown to be greatly enriched in natural cytotoxic activity. The effector cells depleted by fibroblast adsorption were also depleted of cytotoxic activity against other monolayer targets whereas suspension grown lymphoma and leukemia cells (MOLT-4, RAJI, and K-562) were killed as effectively as by non-depleted effector cells. In competition assays other monolayer cells inhibited the natural cytotoxicity against fetal fibroblasts but the suspension-grown cells were unable to compete. The results suggested that different effector cell populations were probably involved when monolayer vs suspension targets were used in assays for human natural cell-mediated cytotoxicity. The separation was not, however, functionally complete since in competition assays with suspension-grown target cells also monolayer cells were able to compete. Preliminary morphological characterization of the natural killer cells against fetal fibroblasts is also presented.

Neutralization of electrophotographic developer

In many electrophotographic development systems, the developer consists of toner particles (∼10 μ) triboelectrically charged by carrier beads (∼100–250 μ). Since development onto a photoconductor continually removes charged toner from the development system, the carrier-bead charge would continue to increase with use unless, as happens, the developer net charge is limited by some neutralization mechanism. From a series of measurements on typical developer materials, we rule out electrical conduction and air breakdown as straightforward dominant neutralization mechanisms and find that the neutralization of developer is a multistep process. When the net-charged developer is agitated, toner migrates through the developer, reducing the net charge in its bulk and leaving a toner-starved bead layer adhering to any conducting boundary surface. When the developer is further agitated, the surface layer of highly charged adhering beads can be released by either of two charge neutralizing mechanisms. If the beads have conducting cores coated with a polymer, the carrier beads are neutralized by triboelectric charging in the presence of the high electric field due to the net charge on the beads. But if the bead coating integrity is poor, the beads can be neutralized by charge flow from the boundary surface to the conducting bead cores.

Studies of the distribution of proteins bound to CNBr-activated Sepharose 6B at the electron-microscopic level.

Proteins were covalently attached to Sepharose by the CNBr method. Their distribution across the carrier beads was studied at the electron microscopic level. The approach has been to ferritinstain and to section the gel beads. Ferritin was either coupled directly to the polysaccharide backbone of the carrier or conjugated with pure rabbit anti-aminopeptidase in order to visualize covalently bound leucine aminopeptidase by the immunferritin technique. The results corroborate earlier fluorescence microscopic findings of a uniform protein distribution, provided that a number of conditions are fulfilled.

The effects of electric fields on toner—Carrier adhesion in xerographic development

Centrifuge measurements and electrostatic charge measurements have shown that the force of adhesion of xerographic toner particles to carrier beads can be described by an electrostatic model. In this model the triboelectric charge on the toner particle is attracted by its countercharge residing on the bead surface and during the process of electrostatic development this force of attraction between toner and carrier must be overcome by a competing process. In this paper it is suggested that the applied field lowers the Coulomb barrier that normally constrains the toner to the bead surface, so that under the combined effects of the mechanical impulse and the applied electric field, the less tightly held particles are stripped from the carrier bead surface. A calculation has been made on the potential function adjacent to the bead surface in the presence of an electric field, and an equation is derived for toner detachment. Measurements have been made on xerographic toner of the efficiency of toner release for various drop heights, with field applied, and without field. The results are somewhat difficult to interpret because of the wide distribution in toner mass and charge. Nonetheless, a comparison can be made between theory and experiment, and there is reasonable agreement.

Isopycnometric serology: a new technique based on buoyant density changes in latex beads.

WE wish to describe new serological techniques based on changes in buoyant density occurring when antibodies, or antigens, or both, are attached to latex beads. For the density change to be observed, the mass of the attached particles must be an appreciable fraction of the total mass. Using very small carrier beads less than one hundred antibody molecules or one virus particle per bead can be detected. The speed and sensitivity of the method make it directly applicable to the clinically important problem of rapid identification of infectious agents.