Objective—
Acquired von Willebrand syndrome is defined by excessive cleavage of the VWF (von Willebrand Factor) and is associated with impaired primary hemostasis and severe bleeding. It often develops when blood is exposed to nonphysiological flow such as in aortic stenosis or mechanical circulatory support. We evaluated the role of laminar, transitional, and turbulent flow on VWF cleavage and the effects on VWF function.
Approach and Results—
We used a vane rheometer to generate laminar, transitional, and turbulent flow and evaluate the effect of each on VWF cleavage in the presence of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type-1 motif, member 13). We performed functional assays to evaluate the effect of these flows on VWF structure and function. Computational fluid dynamics was used to estimate the flow fields and forces within the vane rheometer under each flow condition. Turbulent flow is required for excessive cleavage of VWF in an ADAMTS13-dependent manner. The assay was repeated with whole blood, and the turbulent flow had the same effect. Our computational fluid dynamics results show that under turbulent conditions, the Kolmogorov scale approaches the size of VWF. Finally, cleavage of VWF in this study has functional consequences under flow as the resulting VWF has decreased ability to bind platelets and collagen.
Conclusions—
Turbulent flow mediates VWF cleavage in the presence of ADAMTS13, decreasing the ability of VWF to sustain platelet adhesion. These findings impact the design of mechanical circulatory support devices and are relevant to pathological environments where turbulence is added to circulation.
Continuous and reliable feeding of biomass is essential for successful biofuel production. However, the challenges associated with biomass solids handling are commonly overlooked. In this study, we examine the effects of preprocessing (particle size reduction, moisture content, chemical additives, etc.) on the flow properties of corn stover. Compressibility, flow properties (interparticle friction, cohesion, unconfined yield stress, etc.), and wall friction were examined for five corn stover samples: ground, milled (dry and wet), acid impregnated, and deacetylated. The ground corn stover was found to be the least compressible and most flowable material. The water and acid impregnated stovers had similar compressibilities. Yet, the wet corn stover was less flowable than the acid impregnated sample, which displayed a flow index equivalent to the dry, milled corn stover. The deacetylated stover, on the other hand, was the most compressible and least flowable examined material. However, all of the tested stover samples had internal friction angles >30°, which could present additional feeding and handling challenges. All of the "wetted" materials (water, acid, and deacetylated) displayed reduced flowabilities (excluding the acid impregnated sample), and enhanced compressibilities and wall friction angles, indicating the potential for added handling issues; which was corroborated via theoretical hopper design calculations. All of the "wetted" corn stovers require larger theoretical hopper outlet diameters and steeper hopper walls than the examined "dry" stovers.
Due to its low density and poor flowability, raw biomass may not be an economically viable feedstock for the production of biofuels. However, mechanical densification can be employed to improve its viability. In this study, the flow properties (compressibility, shear, and wall friction) of "pure" feedstocks (corn stover, hybrid poplar, switchgrass and Miscanthus), and feedstock blends, are investigated and compared to measured pelleting energy consumption values. As anticipated, the more compressible materials required lower pelletization energies. Conversely, the less flowable feedstocks (i.e., the materials with higher cohesion and yield strength) were less energy intensive to pellet. In addition, the flowability parameters of the blended materials could be predicted by averaging the measured flow parameters of their pure feedstock constituents. Therefore, only the flow characteristics of the pure feedstocks need to be directly measured, while the flowability of a blended feedstock with a known blend ratio can be accurately inferred. A model was also developed to calculate the required pressure to pellet a particular feedstock, pure or blended, based on its flowability parameters (namely compressibility and wall friction). Strong correlation was observed between the measured pelleting energy consumption and the predicted pelleting pressure values. This newly developed model allows for a material's pelleting feasibility to be assessed without having to physically pelletize the material.Published by Elsevier B.V.
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