Estimation of turbulent shear stresses in pulsatile flow immediately downstream of two artificial aortic valves in vitro

In this work, estimates of turbulence were made from pulsatile flow laser Doppler velocimetry measurements using traditional phase averaging and averaging after the removal of cyclic variation. These estimates were compared with estimates obtained from steady leakage flow LDV measurements and an analytical method. The results of these studies indicate that leakage jets which are free and planar in shape may be more unstable than other leakage jets, and that cyclic variation does not cause a gross overestimation of the Reynolds stresses at large distances from the leakage jet orifice.

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Two-Component Laser Velocimeter Measurements Downstream of Heart Valve Prostheses in Pulsatile Flow

Journal of Biomechanical Engineering ◽

10.1115/1.3138581 ◽

1986 ◽

Vol 108 (1) ◽

pp. 59-64 ◽

Cited By ~ 23

Author(s):

W. G. Tiederman ◽

M. J. Steinle ◽

W. M. Phillips

Keyword(s):

Shear Stress ◽

Pulsatile Flow ◽

Turbulent Shear ◽

Prosthetic Heart Valves ◽

Shear Stresses ◽

Axial Distance ◽

Prosthetic Valves ◽

Disk Valve ◽

Two Component ◽

Stress Levels

Elevated turbulent shear stresses resulting from disturbed blood flow through prosthetic heart valves can cause damage to red blood cells and platelets. The purpose of this study was to measure the turbulent shear stresses occurring downstream of aortic prosthetic valves during in-vitro pulsatile flow. By matching the indices of refraction of the blood analog fluid and model aorta, correlated, simultaneous two-component laser velocimeter measurements of the axial and radial velocity components were made immediately downstream of two aortic prosthetic valves. Velocity data were ensemble averaged over 200 or more cycles for a 15-ms window opened at peak systolic flow. The systolic duration for cardiac flows of 8.4 L/min was 200 ms. Ensemble-averaged total shear stress levels of 2820 dynes/cm2 and 2070 dynes/cm2 were found downstream of a trileaflet valve and a tilting disk valve, respectively. These shear stress levels decreased with axial distance downstream much faster for the tilting disk valve than for the trileaflet valve.

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In-Vitro Fluid Dynamic Characteristics of the Abiomed Trileaflet Heart Valve Prosthesis

Journal of Biomechanical Engineering ◽

10.1115/1.3138430 ◽

1983 ◽

Vol 105 (4) ◽

pp. 338-345 ◽

Cited By ~ 14

Author(s):

Yi-Ren Woo ◽

F. P. Williams ◽

A. P. Yoganathan

Keyword(s):

Fluid Dynamic ◽

Dynamic Performance ◽

Turbulent Shear ◽

Shear Stresses ◽

Valve Prosthesis ◽

Performance Indices ◽

Velocity Measurements ◽

And Performance ◽

Maximum Opening

The need for better and longer lasting trileaflet valves has led to the design and development of the Abiomed polymeric trileaflet valve prosthesis. In-vitro fluid dynamic studies on sizes 25 and 21 mm valves in the aortic position indicate an overall improvement in performance compared to the Carpentier-Edwards and Ionescu-Shiley tissue valves in current clinical use. The pressure drop studies yielded effective orifice areas of 1.99 and 1.54 cm2, and performance indices of 0.41 and 0.45 for the Nos. 25 and 21 valves, respectively. Leaflet photography studies indicated that the two valve sizes had maximum opening areas of 225 and 145 mm2, respectively, at a normal resting cardiac output. Steady and pulsatile flow velocity measurements with a laser-Doppler anemometer (LDA) system indicate that the flow field downstream of the Abiomed valve is jetlike and turbulent. Maximum mean square axial velocity fluctuations of 55 and 83 cm/s, and turbulent shear stresses of 220 and 450 N/m2 were measured in the immediate vicinity of the nos. 25 and 21 valves, respectively. The Abiomed valves studied had been originally configured for use in valved conduits, and it is therefore our opinion that further improvements can be made to the valve and stent design, which would enhance its fluid dynamic performance.

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Turbulent Stresses in the Region of Aortic and Pulmonary Valves

Journal of Biomechanical Engineering ◽

10.1115/1.3138355 ◽

1982 ◽

Vol 104 (3) ◽

pp. 238-244 ◽

Cited By ~ 27

Author(s):

P. D. Stein ◽

F. J. Walburn ◽

H. N. Sabbah

Keyword(s):

Shear Stress ◽

Normal Stress ◽

Blood Cells ◽

Reynolds Shear Stress ◽

Shear Stresses ◽

Normal Stresses ◽

Reynolds Stresses ◽

Aortic Valves ◽

Hot Film

The specific features of turbulent flow that are likely to be damaging to the blood cells and platelets are the stresses which are intrinsic to turbulence, known as Reynolds stresses. These include normal stresses as well as shear stresses. The purpose of this study is to determine the magnitude of the turbulent stresses that may occur during ejection in the vicinity of normal and diseased aortic valves near normal pulmonary valves. Both Reynolds normal stresses and Reynolds shear stresses were calculated from velocities obtained in vitro with a laser Doppler anemometer in the region of two severely stenotic and regurgitant human aortic valves. Reynolds normal stresses were also calculated from velocities obtained with a hot-film anemometer in 21 patients in the region of normal and diseased aortic valves. In seven of these patients, it was calculated in the region of the normal pulmonary valve. The Reynolds normal stress in patients with combined aortic stenosis and insufficiency was prominently higher than in patients with normal valves. In the former, the Reynolds normal stress during ejection transiently reached 18,000 dynes/cm2. This was in the range of the Reynolds normal stress observed in vitro. The Reynolds shear stress measured in vitro transiently reached 11,900 dynes/cm2 during ejection. Because the Reynolds normal stresses in the presence of the severely stenotic and regurgitant valves were comparable in vitro and in patients, it is likely that the Reynolds shear stress in patients is also comparable to values measured in vitro. These values were well above the stresses which, when sustained, have been shown to have a damaging effect upon blood cells and platelets.

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Pulsatile Flow-Induced Fatigue-Resistant Photopolymerizable Hydrogels for the Treatment of Intracranial Aneurysms

Frontiers in Bioengineering and Biotechnology ◽

10.3389/fbioe.2020.619858 ◽

2021 ◽

Vol 8 ◽

Author(s):

Oriane Poupart ◽

Riccardo Conti ◽

Andreas Schmocker ◽

Lucio Pancaldi ◽

Christophe Moser ◽

...

Keyword(s):

Pulsatile Flow ◽

Physical And Mechanical Properties ◽

Water Soluble ◽

Embolic Agent ◽

Parent Artery ◽

Surface Erosion ◽

Shear Stresses ◽

Poly Ethylene

An alternative intracranial aneurysm embolic agent is emerging in the form of hydrogels due to their ability to be injected in liquid phase and solidify in situ. Hydrogels have the ability to fill an aneurysm sac more completely compared to solid implants such as those used in coil embolization. Recently, the feasibility to implement photopolymerizable poly(ethylene glycol) dimethacrylate (PEGDMA) hydrogels in vitro has been demonstrated for aneurysm application. Nonetheless, the physical and mechanical properties of such hydrogels require further characterization to evaluate their long-term integrity and stability to avoid implant compaction and aneurysm recurrence over time. To that end, molecular weight and polymer content of the hydrogels were tuned to match the elastic modulus and compliance of aneurysmal tissue while minimizing the swelling volume and pressure. The hydrogel precursor was injected and photopolymerized in an in vitro aneurysm model, designed by casting polydimethylsiloxane (PDMS) around 3D printed water-soluble sacrificial molds. The hydrogels were then exposed to a fatigue test under physiological pulsatile flow, inducing a combination of circumferential and shear stresses. The hydrogels withstood 5.5 million cycles and no significant weight loss of the implant was observed nor did the polymerized hydrogel protrude or migrate into the parent artery. Slight surface erosion defects of 2–10 μm in depth were observed after loading compared to 2 μm maximum for non-loaded hydrogels. These results show that our fine-tuned photopolymerized hydrogel is expected to withstand the physiological conditions of an in vivo implant study.

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Platelet membrane-coated nanoparticles target sclerotic aortic valves in ApoE−/− mice by multiple binding mechanisms under pathological shear stress

European Heart Journal ◽

10.1093/ehjci/ehaa946.1863 ◽

2020 ◽

Vol 41 (Supplement_2) ◽

Author(s):

H Yang ◽

Y Song ◽

Z Huang ◽

J Qian ◽

Z Pang ◽

...

Keyword(s):

Shear Stress ◽

Aortic Valve ◽

Aortic Valve Disease ◽

Binding Capacity ◽

Platelet Membrane ◽

Valve Disease ◽

Funding Source ◽

Aortic Valves ◽

Coated Nanoparticles

Abstract Background Aortic valve disease is the most common valvular heart disease leading to valve replacement. The efficacy of pharmacological therapy for aortic valve disease is limited by the high mechanical stress at the aortic valves impairing the binding rate. We aimed to identify nanoparticle coating with entire platelet membranes to fully mimic their inherent multiple adhesion mechanisms and target the sclerotic aortic valve of apolipoprotein E-deficient (ApoE−/−) mice based on their multiple sites binding capacity under high shear stress. Methods Considering the potent interaction of platelet membrane glycoproteins with components present in sclerotic aortic valves, platelet membrane-coated nanoparticles (PNPs) were synthetized and the binding capacity under high shear stress was evaluated in vitro and in vivo. Results Compared with PNPs bound intensity in the static station, 161%, 59%, and 39% of attached PNPs remained adherent on VWF-, collagen-, and fibrin-coated surfaces under shear stress of 25dyn/cm2 respectively. PNPs demonstrated effectively adhering to von Willebrand factor, collagen and fibrin under shear stresses in vitro. In an aortic valve disease model established in ApoE−/− mice, PNPs group exhibited significant increase of accumulation in the aortic valves compared with PBS and control NP group. PNPs displayed high degrees of proximity or co-localization with vWF, collagen and fibrin, which exhibited good targeting to sclerotic aortic valves by mimicking platelet multiple adhesive mechanisms. Conclusion PNPs could provide a promising platform for the molecular diagnosis and targeting treatment of aortic valve disease. Targeting combination Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): National Natural Science Foundation of China

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Transcriptome comparisons of in vitro intestinal epithelia grown under static and microfluidic gut-on-chip conditions with in vivo human epithelia

Scientific Reports ◽

10.1038/s41598-021-82853-6 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Kornphimol Kulthong ◽

Guido J. E. J. Hooiveld ◽

Loes Duivenvoorde ◽

Ignacio Miro Estruch ◽

Victor Marin ◽

...

Keyword(s):

Gene Expression ◽

Culture Conditions ◽

Gene Set Enrichment Analysis ◽

Shear Stresses ◽

Static Culture ◽

Dynamic Culture ◽

Intestinal Segments ◽

On Chip

AbstractGut-on-chip devices enable exposure of cells to a continuous flow of culture medium, inducing shear stresses and could thus better recapitulate the in vivo human intestinal environment in an in vitro epithelial model compared to static culture methods. We aimed to study if dynamic culture conditions affect the gene expression of Caco-2 cells cultured statically or dynamically in a gut-on-chip device and how these gene expression patterns compared to that of intestinal segments in vivo. For this we applied whole genome transcriptomics. Dynamic culture conditions led to a total of 5927 differentially expressed genes (3280 upregulated and 2647 downregulated genes) compared to static culture conditions. Gene set enrichment analysis revealed upregulated pathways associated with the immune system, signal transduction and cell growth and death, and downregulated pathways associated with drug metabolism, compound digestion and absorption under dynamic culture conditions. Comparison of the in vitro gene expression data with transcriptome profiles of human in vivo duodenum, jejunum, ileum and colon tissue samples showed similarities in gene expression profiles with intestinal segments. It is concluded that both the static and the dynamic gut-on-chip model are suitable to study human intestinal epithelial responses as an alternative for animal models.

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Attenuation of Flow Disturbances in Tapered Arterial Grafts

Journal of Biomechanical Engineering ◽

10.1115/1.3168383 ◽

1989 ◽

Vol 111 (4) ◽

pp. 303-310 ◽

Cited By ~ 15

Author(s):

R. A. Black ◽

T. V. How

Keyword(s):

Pulsatile Flow ◽

Reynolds Numbers ◽

Axial Distance ◽

Pulsed Ultrasound ◽

Arterial Grafts ◽

Vascular Prostheses ◽

Disturbance Intensity ◽

Flow Disturbances ◽

Percent Area

Flow disturbances in tapered arterial grafts of angles of taper between 0.5 and 1.0 deg were measured in vitro using a pulsed ultrasound Doppler velocimeter. The increase in transition Reynolds numbers with angle of taper and axial distance was determined for steady flow. The instantaneous centerline velocities were measured distal to a 50 percent area stenosis (as a model of a proximal anastomosis), in steady and pulsatile flow, from which the disturbance intensities were calculated. A significant reduction in post-stenotic disturbance intensity was recorded in the tapered grafts, relative to a conventional cylindrical graft. In pulsatile flow with a large backflow component, however, there was an increase in disturbance intensity due to diverging flow during flow reversal. This was observed only in the 1.0 deg tapered graft. These findings indicate that taper is an important consideration in the design of vascular prostheses.

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