Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 181-188).

No description available.

Microvascular transport is strongly influenced by the nonuniform partitioning of red blood cells at diverging microvessel bifurcations, where blood flows from one mother vessel into two daughter vessels. In such bifurcations, the volume fractions of red blood cells in the blood entering each daughter vessel typically differ significantly from the volume fraction in the mother vessel. This phenomenon is caused, to a first approximation, by nonuniform distribution of red blood cells in the cross-section of the mother vessel and the tendency of red blood cells to follow background fluid streamlines. In smaller vessels, however, red blood cell trajectories can deviate significantly from fluid streamlines. In this dissertation, the mechanical reasons for these deviations and their contributions to nonuniform partitioning are analyzed.A two-dimensional model is used to simulate the motion and deformation of flexible particles as they travel alone through a diverging microvessel bifurcation. Deviations of particle trajectories from background fluid streamlines result from migration towards the mother vessel centerline upstream of the bifurcation and flow perturbations caused by cell obstruction in the bifurcation region. Cell migration, which arises because of flexibility, causes more nonuniform partitioning while cell obstruction causes more uniform partitioning. Bifurcations with differently sized daughter vessels experience, on average, a higher red blood cell flux into the smaller branch. Partitioning is unaffected by daughter branching angles.The motion of two interacting cells is also considered. In diverging bifurcations several types of interactions were found, in which the presence of a nearby cell causes a cell to enter a different branch than it would have otherwise. The net effect of these interactions is to cause more uniform partitioning. In wall-bounded linear shear flow, a two-dimensional swapping interaction was identified, in which two cells on different background fluid streamlines approach each other, slowly move onto their partner's streamline, and then move away from each other.The simulations produced by this two-dimensional model provide insight into the effects of red blood cell deformability, bifurcation geometry and volume fraction of red blood cells on red blood cell partitioning and on the resultant distribution and transport of materials in the microvasculature.

Thesis (MAppSc) -- University of South Australia, 1999

Thesis (M.Sc.)--Memorial University of Newfoundland. / Typescript. Bibliography : leaves 128-148. Also available online.

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Margination is the migration of particles in a channel towards the outer walls of the channel. In blood microcirculation, studying the margination of microparticles is important to understand platelet migration and the kinetics of drug delivery. Many new topics in drug delivery research examine the slow release of drugs through micro particles, such as micelles. The margination of such drug carriers is related to tissue absorption and, consequently, to the efficiency of drug delivery. We hypothesized that the intensity of red blood cell (RBC) aggregation will change the level of margination in a cylindrical channel. RBC aggregation is the reversible process of RBCs clumping together over time, under low fluid shear rate. A higher level of aggregation means that this clumping occurs more quickly. The goal of this thesis is to design an experiment that measures the level margination of microparticles and the effect that RBC aggregation has on margination, in a controlled in vitro environment. Fluorescent microparticles were added to human blood preparations. The aggregation properties of the blood preparation were modulated by the addition of a macromolecule (Dextran 500). The blood preparations were injected into PDMS microfluidic devices that were modified to have circular channels in order to better mimic the geometry of physiological microcirculation. We designed a circular microchannel that worked to capture the marginating microparticles and it was found that the level of margination of the microparticles increased with an increase in aggregation of the RBCs. This increase in margination was especially sensitive to aggregation levels in the range of physiological aggregation levels of whole blood, suggesting that aggregation plays an important role in margination in vivo.

A computer visual-input system was built for the purpose of studying the classification of leukocytes. It consisted of an image dissector camera interfaced directly to a D.E.C. PDP-9 computer; a display of the image field was also provided, using a monitoring scope. The design and hardware arrangement of the system is briefly described, while detailed diagrams of the logic networks are shown in Appendix II. Photomicrographs of neutrophils were used as a pattern set, in a study of the computer classification of cell age and lobularity. Clustering of feature vectors was noted in a two-dimensional measurement space showing that metamyelocyte, banded and segmented cells can be distinguished. A square contour-trace of the neutrophil nuclei was performed and an area operator pre-processed the shape of a nucleus into a curvature function. Peaks in this curvature function, a measure of lobularity, as well as the ratio of the perimeter to square root of nuclear area, a measure of the irregularity in the nuclear boundary, were used as orientation and size-independent features. The area operator was found to be unsuitable for extracting curvature from leukocyte images. In cases of extreme nuclear curvature and nuclear filamentation, the basic formulations of the operator were violated giving an erroneous measure of curvature. The general form of the frequency spectrum of the video signal from the image dissector camera was derived. The signal bandwidth requirements and the camera resolution were found experimentally. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Although the key role played by stem cells in maintaining hemopoiesis is well recognized, mechanisms that determine stem cell behaviour (e.g. self-renewal) have remained poorly defined. Historical precedent has illustrated the usefulness of in viitro colony assays in facilitating the investigation of various primitive hemopoietic progenitor classes with restricted differentiation and proliferative potential. In particular, such assays have made possible the definition of the sequential nature of a series of events that early erythropoietic cells undergo and suggested properties that might be anticipated to characterize colonies derived from stem cells proliferating and differentiating in vitro. The present studies were undertaken to test the hypothesis that very large, late maturing erythroid colonies previously noted on occasion in routine erythroid colony assays were, in fact, derived from progenitors with the self-renewal and multiple myeloid differentiation properties associated with stem cells. Initial experiments showed that cells capable of yielding macroscopic sized erythroid colonies were present at low frequency in normal marrow but became the predominant erythropoietic cell type after 2 to 3 weeks in flask culture. Macroscopic erythroid colony formation in assays of cells from either source were shown to have: 1) identical very late maturation kinetics (onset of hemoglobinization after 1 week of initial colony growth), 2) the same high erythropoietin requirements, and 3) similar responsiveness to factors present in media conditioned by mitogen stimulated spleen cells. Optimization of these 2 classes of stimulant yielded an assay that was linear down to very low cell concentrations (less than 5 x 103 cells/ml). This made possible the cytological analysis of macroscopic erythroid colonies under conditions where overlap with other colony types was minimal. Such studies revealed that macroscopic colonies contained, in addition to erythroid cells, megakaryocytes ( > 90% of colonies) and granulocyte cells (30% of colonies) including cells of the eosinophil lineage. Such colonies were also found to contain cells capable of macroscopic spleen colony formation in irradiated mice, the conventional assay for mouse hemopoietic stem cells (on average 1 CFU-S per colony of flask culture origin, and 0.3 CFU-S per colony in assays of fresh marrow). Direct evidence for self-renewal was obtained from replating experiments using irradiated feeders to optimize plating efficiency. Mixed colonies of macroscopic size were regularly demonstrable in replating assays after 1, and even 2, generations of mixed colony formation indicating up to 6 self-renewal divisions during colony formation. By comparison to flask culture cells, the extent of self-renewal exhibited by cells in fresh marrow yielding macroscopic erythroid colonies was found to be 5-fold lower. Finally, the in vitro expression of stem cell self-renewal behaviour was investigated in individual colonies. The number of stem cells generated, when assessed either by CFU-S or replating assays was found to vary markedly. This variation was not accounted for by errors of detection or by variations in colony size. Such findings are similar to previous data on the CFU-S content of individual spleen colonies and provide the first evidence that the type of variation in stem cell self-renewal observed in vivo also occurs in vitro where microenvironmental factors are unlikely to be contributing factors. These results are consistent with a model of stem cell self-renewal in which intrinsic cellular factors play the key role in influencing the decision of individual cells to self-renew. / Medicine, Faculty of / Medical Genetics, Department of / Graduate

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