In-vitro wall shear measurements at aortic valve prostheses

Tillmann, Wolfgang; Reul, H.; Herold, M.; Bruss, K.-H.; Gilse, J. van

doi:10.1016/0021-9290(84)90137-4

Cited by 69 publications

(28 citation statements)

References 30 publications

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“…4d) reporting the duration T * that a given flow requires to erode a certain root structure, which can be associated to a certain vegetation maturity stage (curves A-C, A representing the least, C the most mature vegetation). A similar plot is known in biomechanics as Leverett-Tillmann diagram (Leverett et al, 1972;Tillmann et al, 1984;Suresh, 1998), whose original formulation was meant to describe the mechanical fatigue induced by a continuously applied (flow) shear stress on red cells until the rupture of their external membrane.…”

Section: Mechanism Of Roots Erosion Type IImentioning

confidence: 99%

Mechanisms of vegetation uprooting by flow in alluvial non-cohesive sediment

Edmaier

Burlando

Perona

2011

Hydrol. Earth Syst. Sci.

100

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Abstract. The establishment of riparian pioneer vegetation is of crucial importance within river restoration projects. After germination or vegetative reproduction on river bars juvenile plants are often exposed to mortality by uprooting caused by floods. At later stages of root development vegetation uprooting by flow is seen to occur as a consequence of a marked erosion gradually exposing the root system and accordingly reducing the mechanical anchoring. How time scales of flow-induced uprooting do depend on vegetation stages growing in alluvial non-cohesive sediment is currently an open question that we conceptually address in this work. After reviewing vegetation root issues in relation to morphodynamic processes, we then propose two modelling mechanisms (Type I and Type II), respectively concerning the uprooting time scales of early germinated and of mature vegetation. Type I is a purely flow-induced drag mechanism, which causes alone a nearly instantaneous uprooting when exceeding root resistance. Type II arises as a combination of substantial sediment erosion exposing the root system and resulting in a decreased anchoring resistance, eventually degenerating into a Type I mechanism. We support our conceptual models with some preliminary experimental data and discuss the importance of better understanding such mechanisms in order to formulate sounding mathematical models that are suitable to plan and to manage river restoration projects.

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Section: Mechanism Of Roots Erosion Type IImentioning

confidence: 99%

Mechanisms of vegetation uprooting by flow in alluvial non-cohesive sediment

Edmaier

Burlando

Perona

2011

Hydrol. Earth Syst. Sci.

100

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“…It has been shown that platelets when exposed to high shear stress become activated with lower exposure time while those exposed to low shear stress can also get activated with longer exposure time. 5,31,57,70 Hence the time of exposure of platelets to shear stress must also be considered to be a major factor in the mechanism of platelet aggregation under shear. Though the shear stress is not the only activating agonist in vivo, the history of shear stress exposure changes the threshold of platelet activation by chemical agonists.…”

Section: Introductionmentioning

confidence: 99%

Two-Dimensional Dynamic Simulation of Platelet Activation During Mechanical Heart Valve Closure

et al. 2006

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A major drawback in the operation of mechanical heart valve prostheses is thrombus formation in the near valve region. Detailed flow analysis in this region during the valve closure phase is of interest in understanding the relationship between shear stress and platelet activation. A fixed-grid Cartesian mesh flow solver is used to simulate the blood flow through a bi-leaflet mechanical valve employing a two-dimensional geometry of the leaflet with a pivot point representing the hinge region. A local mesh refinement algorithm allows efficient and fast flow computations with mesh adaptation based on the gradients of the flow field in the leaflet-housing gap at the instant of valve closure. Leaflet motion is calculated dynamically based on the fluid forces acting on it employing a fluid-structure interaction algorithm. Platelets are modeled and tracked as point particles by a Lagrangian particle tracking method which incorporates the hemodynamic forces on the particles. A platelet activation model is included to predict regions which are prone to platelet activation. Closure time of the leaflet is validated against experimental studies. Results show that the orientation of the jet flow through the gap between the housing and the leaflet causes the boundary layer from the valve housing to be drawn in by the shear layer separating from the leaflet. The interaction between the separating shear layers is seen to cause a region of intensely rotating flow with high shear stress and high residence time of particles leading to high likelihood of platelet activation in that region.

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“…Based on the rationale that subhemolytic shear stresses applied on the erythrocyte membrane can induce membrane pore opening, the Tillman diagram (35) was used to determine the correct shear stress intensity (τ) and exposure time (t).…”

Section: Choice Of the Test Conditionsmentioning

confidence: 99%

Application of Controlled Shear Stresses on the Erythrocyte Membrane as a New Approach to Promote Molecule Encapsulation

et al. 2016

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Human red blood cells (RBCs) have a remarkable capacity to undergo reversible membrane swelling. Resealed erythrocytes have been proposed as carriers and bioreactors to be used in the treatment of various diseases. This work is aimed at developing a setup allowing the encapsulation of test molecules into erythrocytes by inducing reversible pore formation on the RBC membrane through the application of controlled mechanical shear stresses. The designed setup consists of two reservoirs connected by a glass capillary. Each reservoir is connected to a compressor; during the tests, the reservoirs were in turn pressurized to promote erythrocyte flow through the capillary. The setup was filled with a suspension of erythrocytes, phosphate buffer, and FITC-dextran. Dextran was chosen as the diffusive molecule to check membrane pore dimensions. Samples of the suspension were withdrawn at scheduled times while the setup was operating. Flow cytometry and stereo-optical microscopy analyses were used to evaluate the erythrocyte dextran uptake. The setup was shown to be safe, well controlled, and adjustable. The outcomes of the experimental tests showed significant dextran uptake by RBCs up to 8%. Microscopy observations highlighted the formation of echinocytes in the analyzed samples. Erythrocytes from different donors showed different reactions to mechanical stresses. The experimental outcomes proved the possibility to encapsulate test molecules into erythrocytes by applying controlled mechanical shear stresses on the RBC membrane, encouraging further studies.

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In-vitro wall shear measurements at aortic valve prostheses

Cited by 69 publications

References 30 publications

Mechanisms of vegetation uprooting by flow in alluvial non-cohesive sediment

Mechanisms of vegetation uprooting by flow in alluvial non-cohesive sediment

Two-Dimensional Dynamic Simulation of Platelet Activation During Mechanical Heart Valve Closure

Application of Controlled Shear Stresses on the Erythrocyte Membrane as a New Approach to Promote Molecule Encapsulation

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