Splitter Imperfections in Annular Split-Flow Thin Separation Channels: Experimental Study of Nonspecific Crossover

The separation performance of a split-flow thin (SPLITT) separation device depends on uniformity of channel thickness and the precise placement of the flow splitters at fixed distances between the channel walls. The observation of nonspecific crossover, that is, the transport of sample materials across the channel thickness without the influence of an applied field, has routinely been taken to indicate the presence of irregularities in splitter shape or placement. Computational fluid dynamics software may be used to predict the influence of splitter imperfections on nonspecific crossover, where it is assumed that sample transport is by convection alone. A previous study has shown how small inlet splitter imperfections can account for the relatively low levels of nonspecific crossover observed with typical annular SPLITT devices. This study, however, could not distinguish between the possible sources of nonspecific crossover; hydrodynamic lift or shear-induced diffusion could have contributed. To confirm the validity of the computational approach, a series of experiments has been carried out on a channel having a deliberately and severely bent splitter. Nonspecific crossover was measured for a range of inlet and outlet flow rate ratios, with the bent splitter placed at both the channel inlet and outlet. The severity of the splitter distortion was sufficient to produce significant nonspecific crossover over a wide range of flow conditions. Good agreement was found between experiment and prediction based on computational fluid dynamics, with experiment generally showing only slightly higher crossover than prediction. The quantitative agreement for this extreme case suggests that the contribution to nonspecific crossover due to geometrical imperfections can be well described using computational fluid dynamics.

Magnetophoretic cell sorting is a function of antibody binding capacity

Antibody binding capacity (ABC) is a term representing a cell's ability to bind antibodies, correlating with the number of specific cellular antigens expressed on that cell. ABC allows magnetically conjugated antibodies to bind to the targeted cells, imparting a magnetophoretic mobility on each targeted cell. This enables sorting based on differences in the cell magnetophoretic mobility and, potentially, a magnetic separation based on the differences in the cell ABC values. A cell's ABC value is a particularly important factor in continuous magnetic cell separation. This work investigates the relationship between ABC and magnetic cell separation efficiency by injection of a suspension of immunomagnetically labeled quantum simply cellular calibration microbeads of known ABC values into fluid flowing through a quadrupole magnetic sorter. The elution profiles of the outlet streams were evaluated using UV detectors. Optimal separation flow rate was shown to correlate with the ABC of these microbeads. Comparing experimental and theoretical results, the theory correctly predicted maximum separation flow rates but overestimated the separation fractional recoveries.

Genetic polymorphisms and personality in healthy adults: a systematic review and meta-analysis

A meta-analysis was conducted on studies reporting data on associations between candidate genes and human personality. Studies reporting data for psychiatric populations (including organic disease and substance abuse) were excluded. A total of 46 studies contributed to the analysis. Pooled data using a fixed-effects model suggested significant associations between the 5HTT LPR, DRD4 c>t, DRD4 length, DRD2 A1/A2, DRD3 A1/A2 polymorphisms and personality traits. A multivariate analysis using a mixed-effects model and including age, sex and predominant ethnicity as covariates was applied to the analyses of 5HTT LPR and DRD4 length polymorphism data. Only the association between the 5HTT LPR polymorphism and avoidance traits remained significant (P=0.038). However, sensitivity analyses excluding data from studies reporting allele frequencies not in Hardy-Weinberg equilibrium and unpublished data resulted in this association no longer being significant. Implications for the design of future association studies of human personality are discussed, including the likely sample sizes that will be required to achieve sufficient power and the potential role of moderating variables such as sex.

Red blood cell magnetophoresis

The existence of unpaired electrons in the four heme groups of deoxy and methemoglobin (metHb) gives these species paramagnetic properties as contrasted to the diamagnetic character of oxyhemoglobin. Based on the measured magnetic moments of hemoglobin and its compounds, and on the relatively high hemoglobin concentration of human erythrocytes, we hypothesized that differential migration of these cells was possible if exposed to a high magnetic field. With the development of a new technology, cell tracking velocimetry, we were able to measure the migration velocity of deoxygenated and metHb-containing erythrocytes, exposed to a mean magnetic field of 1.40 T and a mean gradient of 0.131 T/mm, in a process we call cell magnetophoresis. Our results show a similar magnetophoretic mobility of 3.86 x 10(-6) mm(3) s/kg for erythrocytes with 100% deoxygenated hemoglobin and 3.66 x 10(-6) mm(3) s/kg for erythrocytes containing 100% metHb. Oxygenated erythrocytes had a magnetophoretic mobility of from -0.2 x 10(-6) mm(3) s/kg to +0.30 x 10(-6) mm(3) s/kg, indicating a significant diamagnetic component relative to the suspension medium, in agreement with previous studies on the hemoglobin magnetic susceptibility. Magnetophoresis may open up an approach to characterize and separate cells for biochemical analysis based on intrinsic and extrinsic magnetic properties of biological macromolecules.

Splitter imperfections in annular split-flow thin separation channels: effect on nonspecific crossover

The separation performance of split-flow thin (SPLITT) separation channels generally falls short of ideal behavior. There are many possible contributing factors to the loss of separation resolution, and these are discussed in the text. The possibility that small imperfections in the splitters play a significant role is examined in this study. Computational fluid dynamics is used to determine the flow pattern within an annular SPLITT channel having small imperfections in the inlet splitter. These results are used to calculate the nonspecific crossover of particles from the inner annular inlet to the outer annular outlet under various flow rate regimes. Nonspecific crossover, obtained through convective transport alone, and not the result of field-induced transport, is often used as a check of channel behavior. The results of a typical experimental determination of nonspecific crossover are included for comparison. It is concluded that geometrical imperfections can indeed play a significant role in the loss of resolution observed for these systems.

Study of magnetic particles pulse-injected into an annular SPLITT-like channel inside a quadrupole magnetic field

Advantages of the continuous magnetic flow sorting for biomedical applications over current, batch-wise magnetic separations include high throughput and a potential for scale-up operations. A continuous magnetic sorting process has been developed based on the quadrupole magnetic field centered on an annular flow channel. The performance of the sorter has been described using the conceptual framework of split-flow thin (SPLITT) fractionation, a derivative of field-flow fractionation (FFF). To eliminate the variability inherent in working with a heterogenous cell population, we developed a set of monodisperse magnetic microspheres of a characteristic magnetization, and a magnetophoretic mobility, similar to those of the cells labeled with a magnetic colloid. The theory of the magnetic sorting process has been tested by injecting a suspension of the magnetic beads into the carrier fluid flowing through the sorter and by comparing the theoretical and experimental recovery versus total flow-rate profiles. The position of the recovery maxima along the total flow-rate axis was a function of the average bead magnetophoretic mobility and the magnetic field intensity. The theory has correctly predicted the position of the peak maxima on the total flow-rate axis and the dependence on the bead mobility and the field intensity, but has not correctly predicted the peak heights. The differences between the calculated and the measured peak heights were a function of the total flow-rate through the system, indicating a fluid-mechanical origin of the deviations from the theory (such as expected of the lift force effects in the system). The well-controlled elution studies using the monodisperse magnetic beads, and the SPLITT theory, provided us with a firm basis for the future sorter evaluation using cell mixtures.

The use of magnetite-doped polymeric microspheres in calibrating cell tracking velocimetry

Continuous magnetic separation, in which there is no accumulation of mass in the system, is an inherently dynamic process, requiring advanced knowledge of the separable species for optimal instrument operation. By determining cell magnetization in a well-defined field, we may predict the cell trajectory behavior in the well-characterized field environments of our continuous separators. Magnetization is determined by tracking the migration of particles with a technique known as cell tracking velocimetry (CTV). The validation of CTV requires calibration against an external standard. Furthermore, such a standard, devoid of the variations and instabilities of biological systems, is needed to reference the method against day-to-day shifts or trends. To this end, a method of synthesizing monodisperse, magnetite-doped polymeric microspheres has been developed. Five sets of microspheres differing in their content of magnetite, and each of approximately 2.7 microm diameter, are investigated. An average gradient of 0.18 T/mm induces magnetic microsphere velocities ranging from 0.45 to 420 microns/s in the CTV device. The velocities enable calculation of the microsphere magnetization. Magnetometer measurements permit the determination of magnetization at a flux density comparable to that of the CTV magnet's analysis region, 1.57 T. A comparison of the results of the CTV and magnetometer measurements shows good agreement.

Detection of rare MCF-7 breast carcinoma cells from mixtures of human peripheral leukocytes by magnetic deposition analysis

BACKGROUND

The presence of malignant breast cancer cells in bone marrow or peripheral blood is a prognostic factor. We tested the capacity of a novel magnetic cell analyzer to detect rare cancer cells in mixtures with human peripheral leukocytes.

METHODS

Human peripheral leukocytes were spiked with cells of the MCF-7 line, and the cell mixture was labeled with anti-epithelial membrane antigen antibody and a magnetic colloid. The MCF-7 cells were selectively captured on a magnetic deposition substrate from the flowing leukocyte and MCF-7 cell mixture.

RESULTS

The recovery of the MCF-7 cells from the original mixture ranged from 20% to 60%. The limit of detection of the MCF-7 cells was 10(-6) (n = 9). The morphology of the captured cancer cells was well preserved and comparable to that observed in cytospin smears. All deposited cells were located in a small area of 1.4 mm x 6 mm and could be quickly identified with an optical microscope following Wright's staining.

CONCLUSIONS

This is a proof-of-principle study using a simplified model of rare cancer cells in a leukocyte mixture. The clinical relevance of the method will be tested in the future by extension to patient bone marrow samples and using antibody cocktails to increase specificity against the breast carcinoma cells.

Rapid cell isolation by magnetic flow sorting for applications in tissue engineering

Rapid and efficient cell sorting methods are important for tissue progenitor cell isolation. We built and evaluated a laboratory prototype of a continuous flow, quadrupole magnetic cell sorter. The sorter was tested on a model cell system of human peripheral lymphocytes. The helper T cell subpopulation was targeted by primary, mouse anti-CD4 monoclonal antibody conjugated to a fluorochrome (FITC), and magnetized by secondary, anti-FITC antibody magnetic colloid. The purities and recoveries of the cell fractions were measured by flow cytometry and an automated cell counter. Cells were spread across the flow according to their magnetophoretic mobilities. The purity of the CD4 cell enriched fraction was 99.6%, and the purity of the CD4 cell depleted fraction was 2% for an initial CD4 cell purity of 36%; the corresponding recovery of the enriched CD4 cell fraction was 59% at a sorting speed of 4,200 cells/s (four experiments). The recovery could be increased to 90% with a concomitant decrease in the purity of CD4 cell enriched fraction to 66%. This type of sorting should be applicable to any cells in suspension for which a suitable antibody exists, in particular, to large, fragile cells.

Continuous, flow-through immunomagnetic cell sorting in a quadrupole field

A flow-through quadrupole magnetic cell separator has been designed, built, and evaluated by using a cell model system of human peripheral T lymphocytes (CD4+, CD8+, and CD45+ cells). The immunomagnetic labeling was accomplished by using a sandwich of mouse anti-human monoclonal antibody conjugated to fluorescein isothiocyanate and rat anti-mouse polyclonal antibody conjugated to a colloidal magnetic nanoparticle. The feed and sorted fractions were analyzed by FACScan flow cytometry. The magnetically labeled cells were separated from nonlabeled ones in a flow-through cylindrical column within a quadrupole field, which exerted a radial, outward force on the magnetic cells. The flow rate of the cell samples was 0.1-0.75 ml/min, and the flow rate of sheath fluid was 1.5-33.3 times that of the sample flow rate. The maximum shear stress exerted on the cell was less than 1 dyne/cm2, which was well below the level that would threaten cell integrity and membrane disruption. The maximum magnetic field was 0.765 T at the channel wall, and the gradient was 0.174 T/mm. The highest purity of selected cells was 99.6% (CD8 cells, initial purity of 26%), and the highest recovery of selected cells was 79% (CD4 cells, initial purity of 20%). The maximum throughput of the quadrupole magnetic cell separator was 7,040 cells/s (CD45 cells, initial purity of 5%). Theoretical calculations showed that the throughput can be increased to 10(6) cells/s by a scale-up of the current prototype.

Lymphocyte fractionation using immunomagnetic colloid and a dipole magnet flow cell sorter

The relationship between cell function and surface marker expression is a subject of active investigation in biology and medicine. These investigations require separating cells of a homogeneous subset into multiple fractions of varying marker expression. We have developed a novel cell sorter, the dipole magnet flow sorter (DMFS), which separates selected T lymphocyte subpopulations, targeted by immunomagnetic colloid, into multiple fractions according to cell surface marker expression, as determined by flow cytometry. A narrow stream of cells is introduced into a sheath of carrier fluid in a rectangular channel while subjected to a perpendicular magnetic force. The special design of the pole pieces ensures a constant magnetic force acting on the magnetically labeled cells in the separation area. Cells are spread across the flow in relation to their magnetophoretic mobility. Separation is achieved by control of the positions of the effluent stream boundaries, which separate fluid volumes with cells of different magnetophoretic mobility. CD4 and CD8 T lymphocytes labeled with primary antibody-fluorescein isothiocyanate (FITC) conjugate and anti-FITC-magnetic colloid are the chosen cell systems. Flow cytometry analysis shows that, for CD4 cells, a three-fold increase in total marker number per cell is observed when comparing the highest to the lowest fluorescence fractions. Similarly, a four-fold increase in total marker number is observed for CD8 cells. We also observed the separation of two dissimilar cell types that differed in expression of the CD4 marker, monocytes and T helper lymphocytes. We believe that this type of separation is applicable to any cells in suspension for which a suitable antibody exists and, due to the comparatively gentle nature of the process, is particularly suitable for the sorting of fragile cells.

Physiology and molecular phylogeny of coexisting Prochlorococcus ecotypes

The cyanobacterium Prochlorococcus is the dominant oxygenic phototroph in the tropical and subtropical regions of the world's oceans. It can grow at a range of depths over which light intensities can vary by up to 4 orders of magnitude. This broad depth distribution has been hypothesized to stem from the coexistence of genetically different populations adapted for growth at high- and low-light intensities. Here we report direct evidence supporting this hypothesis, which has been generated by isolating and analysing distinct co-occurring populations of Prochlorococcus at two locations in the North Atlantic. Co-isolates from the same water sample have very different light-dependent physiologies, one growing maximally at light intensities at which the other is completely photoinhibited. Despite this ecotypic differentiation, the co-isolates have 97% similarity in their 16S ribosomal RNA sequences, demonstrating that molecular microdiversity, commonly observed in microbial systems, can be due to the coexistence of closely related, physiologically distinct populations. The coexistence and distribution of multiple ecotypes permits the survival of the population as a whole over a broader range of environmental conditions than would be possible for a homogeneous population.

Magnetic flow sorting using a model system of human lymphocytes and a colloidal magnetic label

Cells of identical physical properties that differ in the expression of surface proteins can be sorted conveniently using immunospecific stains conjugated to fluorescent, or magnetic, labels. Immunomagnetic cell sorting using commercial batch sorters offers advantages of high sorting capacity, high viability of sorted fractions, and high depletion rates; its disadvantages are low enrichment rate and batch processing. The authors developed and tested a continuous, flow-through magnetic cell sorter for small volume, experimental cell enrichment. Freshly isolated human peripheral lymphocytes were labeled using an immunofluoromagnetic sandwich consisting of mouse anti human CD8 monoclonal antibody-fluorescein conjugate and rat anti mouse polyclonal antibody-colloidal iron-dextran conjugate. A total of 2-3 min lymphocytes were sorted per hour using a saturation magnetic field of 1.334 T and a five channel sorter. The fluorescent cells were distributed among the channels in relation to their fluorescence intensity and magnetic susceptibility. The purity (68-85%) and enrichment rates (16-34x) were comparable to those of commercial batch magnetic separators; sorting capacity and recovery of the enriched fractions (up to 32%) were limited by the small scale of the sorter. Future direction is focused on increasing the resolution, recovery, and sorting capacity of the enriched fractions, and testing the sorter on other cell systems.

Influence of family functioning on maternal-fetal attachment

Although the development of a positive relationship between the mother and infant most likely begins during pregnancy, the correlates of maternal-fetal attachment are poorly understood. This study examined the influence of family functioning on maternal-fetal attachment in a sample of varied ethnic and socioeconomic backgrounds. The authors surveyed 339 pregnant women in their last trimesters with the Family Adaptability and Cohesion Scales-III (FACES-III), Maternal-Fetal Attachment Scale (MFA), and a demographic interview. On the basis of correlational and regression analyses, the demographic variables of parity, ethnicity, age, education, and occupation of primary wage earner correlated significantly with maternal-fetal attachment. When entered in a multiple regression analysis, parity, ethnicity, and occupation explained 12% of the variance in the MFA scores. The FACES-III total score and the subscale scores of adaptability and cohesion also correlated significantly with scores on the MFA and explained an additional 3% of the variance in the MFA beyond that explained by the demographics. Support of positive family dynamics during pregnancy by health care workers may potentially increase the quality of maternal-fetal attachment.

Central venous catheterization in patients with coagulopathy

To explore the risk of bleeding complications during percutaneous central venous catheterization in patients with coagulopathy, 40 liver transplant recipients underwent 259 percutaneous central venous catheterizations. Two hundred two catheterizations were performed in patients with coagulopathy, as evidenced by their prothrombin times, activated partial thromboplastin times, and/or platelet counts. Furthermore, no attempt was made to correct these episodes of coagulopathy with medications or infusion of blood products. No serious bleeding complications occurred during the 259 catheterizations, which suggests that experienced clinicians using appropriate techniques may safely perform central venous catheterization in patients with abnormal prothrombin times, activated partial thromboplastin times, and platelet counts.

Co-culture of primary pulmonary cells to model alveolar injury and translocation of proteins

Primary rat alveolar type II cells and early passage rat lung fibroblasts were co-cultured on opposite sides of a collagen-coated polycarbonate filter. This is an approach to "model", in part, an alveolar wall to study mechanisms of cytotoxicity and translocation of bioactive materials from the alveolar space to the lung interstitium. Type II cells were recovered from adult rat (Fischer 344) lungs by enzyme digestion and "panning". Lung fibroblasts were separated from the same species, cultured initially in 10% fetal bovine serum and used in the co-culture system at early passage. The type II cells formed a monolayer of dedifferentiated epithelium which provided a barrier on the upper side of the collagen (human type IV)-coated filter. The fibroblasts on the bottom of the filter replicated logarithmically in the presence of serum, could be rendered quiescent in defined medium and then returned to rapid growth phase with the reintroduction of serum. The intact epithelial monolayer excluded trypan blue, albumin, platelet-derived growth factor, and alpha2-macroglobulin from the lower compartment of the culture chamber. Altering the integrity of the monolayer by a variety of means allowed translocation of these materials through the collagen-coated filters. Particularly interesting was the effect of taurine chloramine which caused subtle changes in the alveolar epithelium and allowed subsequent translocation of albumin. In addition, we showed that rat alveolar macrophages remain viable with some spreading on the surface of the epithelial monolayer. This co-culture system will have future application in the study of how reactive oxygen species might affect the epithelial barrier, and whether macrophage-derived growth factors can influence fibroblast proliferation if the monolayer is intact or injured.

Personal safety. It is a matter of awareness

The safety and security points discussed in this article are only a few of the awareness tips that can add to your personal safety. When reporting to work, especially during odd hours, be suspicious of all activities. Ask yourself, "What if?" Becoming a victim or not becoming a victim is easy.

Development of the rabbit model for studying the effects of propranolol on cardiac contractility: relationship of intravenous pharmacodynamics and pharmacokinetics

The New Zealand white rabbit (3-4 kg) was chosen as an experimental model to determine the effects of propranolol, by intravenous bolus administration, on cardiac contractility. The cardiovascular effects were measured by systolic time interval recordings for up to 8 h. The study was performed on two groups of animals with 5 rabbits receiving active drug and another 5 rabbits receiving saline placebo. All animals were anesthetized by parenteral administration of urethane/acepromazine. The results indicated that at 15 min after intravenous administration, propranolol caused a maximum decrease in heart rate (p less than 0.01), as well as a maximum increase in QS2 (p less than 0.01), LVET (p less than 0.01), PEP (p less than 0.01) and PEP/LVET (p less than 0.05). Approximately 90 min after drug administration, a significant (p less than 0.01) "rebound phenomenon" was observed in the active group which continued throughout the 8-h observation period. This preliminary study suggests that the rabbit is a useful animal model to study the effects of propranolol on cardiac contractility.

Urethane-acepromazine: a novel method of administering parenteral anesthesia in the rabbit

Stable long-term anesthesia in the rabbit (greater than 8 hr) has been achieved by the administration of urethane and acepromazine. Twenty-five healthy male New Zealand white rabbits weighing 2 to 4 kg were used for this study. Two groups of animals were studied. The first group of 11 rabbits received urethane (1.0 g/kg) and acepromazine (1 mg/0.46 kg). This resulted in stable light plane anesthesia for 13.5 +/- 4.5 hr (mean + S.D.). The second group of 14 rabbits received urethane (1.3 g/kg) and acepromazine (1 mg/0.46 kg) which resulted in deep plane anesthesia for 23.0 +/- 4 hr. Heart rate and respiratory rate remained stable throughout the entire period and all animals were alert and without any observable side effects by 48 +/- 3 hr. This study indicates that the combination of urethane-acepromazine is a safe and reproducible parenteral anesthetic that may be used in studies of long duration in rabbits.

Forensic psychology: an empirical review of experimental research

The present paper evaluated the first 11 years of experimental research (1973-1983) publications, with a focus on forensic psychology, that were cited in Psychological Abstracts. Articles were reviewed for type of methodology and statistical analyses employed as well as the relationship between the number of empirical and nonempirical articles. Trends in publications are presented, and the type of empirical research is evaluated. Results indicate: a paucity of experimental research; a significant difference between empirical and nonempirical publications; and a transition--albeit based on a limited number of research publications--from descriptive to correlational and experimental research over time.