Vortex evolution patterns for flow of dilute polymer solutions in confined microfluidic cavities.

Flow instability in confined cavities has attracted extensive interest due to its significance in many natural and engineering processes. It also has applications in microfluidic devices for biomedical applications including flow mixing, nanoparticle synthesis, and cell manipulation. The recirculating vortex that characterizes the flow instability is regulated by the fluid rheological properties, cavity geometrical characteristics, and flow conditions, but there is a lack of quantitative understanding of how the vortex evolves as these factors change. Herein, we experimentally study the flow of dilute polymer solutions in confined microfluidic cavities and focus on a quantitative characterization of the vortex evolution. Three typical patterns of vortex evolution are identified in the cavity flow of dilute polymer solutions over a wide range of flow conditions. The geometrical characteristics of the cavity are found to have little effect on the patterns of vortex evolution. The geometry-independent patterns of vortex evolution provide us an intuitive paradigm, from which the interaction and competition among inertial, elastic and shear-thinning effects in these cavity-induced flow instabilities are clarified. These results extend our understanding of the flow instability of complex fluids in confined cavities, and provide useful guidelines for the design of cavity-structured microfluidic devices and their applications.

Relationship Between Blood Flow and Collapse of Nontraumatic Osteonecrosis of the Femoral Head.

BACKGROUND: To investigate the collapse mechanism in osteonecrosis of the femoral head (ONFH), we studied the relationship between the femoral head (FH) blood circulation changes and the collapse area histomorphometry characteristics. METHODS: A technique involving microvascular perfusion of the FH in vitro to reconstruct the vessels in the FH at different stages of nontraumatic ONFH (40 cases). In addition, we also examined the histomorphometry characteristics in the collapse area during ONFH at different stages using the hard tissue section technique. To investigate the blood supply changes in the FH on pathological involved in the FH collapse process. RESULTS: The results showed that in all FHs, the collapse area always involved the margin of the necrotic lesion of the lateral column. Histologically, the fracture occurred between the thickened and necrotic trabeculae at the junction. We found that the collapse started at the lateral column of the FH in the necrotic lesion and that the lateral column was ischemic, which caused the FH to begin to collapse. CONCLUSIONS: Based on the above findings, the relationship between associations of the blood circulation to the collapse showed that if a portion of the blood supply of the lateral column (the superior retinacular artery) was preserved, the prognosis of the natural progression of the diseases was improved, the collapse rate was low and collapse occurred later. The blood circulation of artery in the lateral column was good, and the FH maintained an intact shape even if the internal region was ischemic. Therefore, we can predict the collapse of the FH by measuring the blood flow in the lateral area of the FH, thus providing guidance for the selection of FH-preserving clinical therapy in young and middle-aged patients. CLINICAL RELEVANCE: This work provides a proof of how to predict the collapse of the FH by measuring the blood flow, providing guidance for FH-preserving clinical therapy in young and middle-aged patients.

Properties of an alginate-degrading Flavobacterium sp. strain LXA isolated from rotting algae from coastal China.

A novel bacterium exhibiting alginolytic activity was isolated from rotten algae. The alginate-degrading activity was detected in the culture supernatant by measuring the decrease in alginate viscosity or the increase in reducing sugars. Basic characterization showed that it was gram negative, rod shaped, yellow pigmented, and positive for oxidase and catalase, with a DNA G+C content of 35.6 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that this strain is related to members of the genus Flavobacterium. Sequence similarity values with their nearest phylogenetic neighbours ranged from 95.9% to 96.7%. Genotypic results, together with phenotypic characteristics, differentiated this species from related Flavobacterium organisms with validly published names, which suggests that the organism should be a new species of the genus Flavobacterium tentatively named as Flavobacterium sp. strain LXA.