Elongational Stresses and Cells

Fluid forces and their effects on cells have been researched for quite some time, especially in the realm of biology and medicine. Shear forces have been the primary emphasis, often attributed as being the main source of cell deformation/damage in devices like prosthetic heart valves and artificial organs. Less well understood and studied are extensional stresses which are often found in such devices, in bioreactors, and in normal blood circulation. Several microfluidic channels utilizing hyperbolic, abrupt, or tapered constrictions and cross-flow geometries, have been used to isolate the effects of extensional flow. Under such flow cell deformations, erythrocytes, leukocytes, and a variety of other cell types have been examined. Results suggest that extensional stresses cause larger deformation than shear stresses of the same magnitude. This has further implications in assessing cell injury from mechanical forces in artificial organs and bioreactors. The cells’ greater sensitivity to extensional stress has found utility in mechanophenotyping devices, which have been successfully used to identify pathologies that affect cell deformability. Further application outside of biology includes disrupting cells for increased food product stability and harvesting macromolecules for biofuel. The effects of extensional stresses on cells remains an area meriting further study.

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Evaluation of Platelet Activation Models With Dynamic Shear Stress In Vitro Experiments

ASME 2012 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2012-80134 ◽

2012 ◽

Author(s):

Jawaad Sheriff ◽

Michalis Xenos ◽

João S. Soares ◽

Jolyon Jesty ◽

Danny Bluestein

Keyword(s):

Platelet Activation ◽

Heart Valves ◽

Ventricular Assist Devices ◽

Prosthetic Heart Valves ◽

Shear Stresses ◽

Ventricular Assist ◽

Relative Paucity ◽

Valvular Diseases ◽

End Stage

Blood recirculating devices, which include ventricular assist devices and prosthetic heart valves, are necessary for some patients suffering from end-stage heart failure and valvular diseases. However, disturbed flow patterns in these devices cause shear-induced platelet activation and aggregation. Thromboembolic complications resulting from this platelet behavior necessitates lifelong anticoagulant therapy for patients implanted with such devices. In addition, blood recirculating device manufacturers mostly test and optimize their products for hemolysis, which occurs at shear stresses ten-fold higher than required for platelet activation. The relative paucity of optimization for flow-induced thrombogenicity is further exacerbated by the fact that there are few predictive shear-induced platelet activation models.

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Laser Anemometry Measurements of Steady Flow Past Aortic Valve Prostheses

Journal of Biomechanical Engineering ◽

10.1115/1.2895489 ◽

1993 ◽

Vol 115 (3) ◽

pp. 290-298 ◽

Cited By ~ 9

Author(s):

Y. T. Chew ◽

H. T. Low ◽

C. N. Lee ◽

S. S. Kwa

Keyword(s):

Steady Flow ◽

Heart Valves ◽

Flow Region ◽

Ball Valve ◽

Prosthetic Heart Valves ◽

Shear Stresses ◽

Normal Stresses ◽

Reversed Flow ◽

Disk Valve ◽

Wall Shear

An experimental investigation was conducted in steady flow to examine the fluid dynamics performance of three prosthetic heart valves of 27 mm diameter: Starr-Edwards caged ball valve, Bjork-Shiley convexo-concave tilting disk valve, and St. Vincent tilting disk valve. It was found that the pressure loss across the St. Vincent valve is the least and is, in general, about 70 percent of that of the Starr-Edwards valve. The pressure recovery is completed about 4 diameters downstream. The velocity profiles for the ball valve reveal a large single reversed flow region behind the occluder while those for the tilting disks valves reveal two reversed flow regions immediately behind the occluders. Small regions of stasis are also found near the wall in the minor opening of Bjork-Shiley valve and in the major opening of St. Vincent valve. The maximum wall shear stresses of the three valves at a flow rate of 30 l/min are in the range 30–50 dyn/cm2 which can cause hemolysis of attached red blood cells. The corresponding maximum Reynolds normal stresses are in the range of 1600–3100 dyn/cm2. The Reynolds normal stresses decay quickly and return approximately to the upstream undisturbed level at about 4 diameters downstream while the wall shear stresses decay at a slower rate. The maximum Reynolds normal stresses occur at about 1 diameter downstream while the maximum wall shear stress is at about 2 diameters downstream. In general, the St. Vincent valve has better performance. A method to compensate for refractive index variations and curvature effect of the sinus region of the aorta root using laser doppler anemometer measurements is also proposed.

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Artificial organs and devices track: Prosthetic Heart Valves — New Directions

Annals of Biomedical Engineering ◽

10.1007/bf02649700 ◽

1996 ◽

Vol 24 (1) ◽

pp. S1-S9 ◽

Cited By ~ 28

Keyword(s):

Heart Valves ◽

Artificial Organs ◽

Prosthetic Heart Valves ◽

New Directions

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Analysis of leaflet flutter in biological prosthetic heart valves using PIV measurements

Acta Scientiarum Technology ◽

10.4025/actascitechnol.v42i1.41746 ◽

2019 ◽

Vol 42 ◽

pp. e41746

Author(s):

Artur Henrique de Freitas Avelar ◽

Mairon Assis Guimaris Eller Stófel ◽

Glenda Dias Vieira ◽

Jean Andrade Canestri ◽

Rudolf Huebner

Keyword(s):

High Speed ◽

Heart Valves ◽

Particle Image ◽

Prosthetic Heart Valves ◽

Shear Stresses ◽

Lower Velocity ◽

Piv Measurements ◽

Prosthetic Valves ◽

Image Velocimetry ◽

Experimental Bench

The use of biological prosthetic valves has increased considerably in recent decades since they have several advantages over mechanical ones, but they still possess the great disadvantage of having a relatively short lifetime. An understudied phenomenon is the flutter effect that causes oscillations in the cusps, which is associated with regurgitation, calcification and fatigue, which can reduce even more the lifetime of bioproteses. In an experimental bench that simulates the cardiac flow, the behavior of a porcine and a bovine pericardium valves was recorded by a high-speed camera to quantify the oscillations of the cusps and an experiment using particle image velocimetry was conducted to study the velocity profiles and shear stresses and their relations with flutter. Results showed that the pericardial valve has lower values of frequencies and amplitudes compared to the porcine valve. Lower velocity values were found in the cusps that did not have flutter, but no relationship was observed between shear stress values and leaflet vibrations. These results may assist in future projects of biological prosthetic valves that have less flutter and longer lifespan.

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On the Hemolytic and Thrombogenic Potential of Occluder Prosthetic Heart Valves From In-Vitro Measurements

Journal of Biomechanical Engineering ◽

10.1115/1.3138265 ◽

1981 ◽

Vol 103 (2) ◽

pp. 83-90 ◽

Cited By ~ 36

Author(s):

R. S. Figliola ◽

T. J. Mueller

Keyword(s):

Heart Valves ◽

Thrombus Formation ◽

Test Chamber ◽

Separated Flow ◽

Prosthetic Heart Valves ◽

Shear Stresses ◽

Flow Loop ◽

Mean Velocity ◽

Test Loop

An experimental investigation was conducted to determine the magnitude of shear stresses and areas of stasis of several types of prosthetic occluder heart valves. These experiments were performed in a steady-flow test loop using an axisymmetric aortic-shaped test chamber and an aqueous-glycerine solution. The flow loop produced a low-turbulence intensity and uniform mean velocity profile upstream of the test chamber. Tests were perfomed on a Kay-Shiley disk, a Bjork-Shiley tilting disk and Starr-Edwards Models 1260 and 2320 ball prostheses at Reynolds numbers between 2000 and 6200. Momentum transfer and turbulence data were obtained both around and distal to the valve occluders using laser Doppler and hot-film anemometry. The region directly surrounding the valve occluders contained the largest stresses measured. Aortic wall shear measurements revealed magnitudes potentially damaging to the vessel lining. Regions of slowly moving separated flow found to exist in these occluder valve flow fields correlated with clinical findings of thrombus formation.

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In vivo velocity profiles and turbulent shear stresses distal to prosthetic heart valves

The American Journal of Cardiology ◽

10.1016/s0002-9149(79)80140-x ◽

1979 ◽

Vol 43 (2) ◽

pp. 369

Keyword(s):

Heart Valves ◽

Velocity Profiles ◽

Turbulent Shear ◽

Prosthetic Heart Valves ◽

Shear Stresses

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The Effect of Dipyridamole and RA 233 on Human Platelet Function in Vitro

Thrombosis and Haemostasis ◽

10.1055/s-0038-1648112 ◽

1973 ◽

Vol 29 (03) ◽

pp. 694-700 ◽

Cited By ~ 4

Author(s):

Paul L. Rifkin ◽

Marjorie B. Zucker

Keyword(s):

Mechanism Of Action ◽

Human Blood ◽

Glass Bead ◽

Heart Valves ◽

Human Platelet ◽

Drug Effects ◽

Simple Relation ◽

Prosthetic Heart Valves ◽

Induced Aggregation

SummaryDipyridamole (Persantin) is reported to prolong platelet survival and inhibit embolism in patients with prosthetic heart valves, but its mechanism of action is unknown. Fifty jxM dipyridamole failed to reduce the high percentage of platelets retained when heparinized human blood was passed through a glass bead column, but prolonged the inhibition of retention caused by disturbing blood in vitro. Possibly the prostheses act like disturbance. Although RA 233 was as effective as dipyridamole in inhibiting the return of retention, it was less effective in preventing the uptake of adenosine into erythrocytes, and more active in inhibiting ADP-induced aggregation and release. Thus there is no simple relation between these drug effects.

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