scholarly journals Computational Analysis of Fluid Flow Within a Device for Applying Biaxial Strain to Cultured Cells

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Jason Lee ◽  
Aaron B. Baker
Keyword(s):  
Shear Stress ◽  
Cultured Cells ◽  
Fluid Velocity ◽  
Mechanical Strain ◽  
Cell Types ◽  
Linear Increase ◽  
Shear Stresses ◽  
Biaxial Strain ◽  
Maximal Strain

In vitro systems for applying mechanical strain to cultured cells are commonly used to investigate cellular mechanotransduction pathways in a variety of cell types. These systems often apply mechanical forces to a flexible membrane on which cells are cultured. A consequence of the motion of the membrane in these systems is the generation of flow and the unintended application of shear stress to the cells. We recently described a flexible system for applying mechanical strain to cultured cells, which uses a linear motor to drive a piston array to create biaxial strain within multiwell culture plates. To better understand the fluidic stresses generated by this system and other systems of this type, we created a computational fluid dynamics model to simulate the flow during the mechanical loading cycle. Alterations in the frequency or maximal strain magnitude led to a linear increase in the average fluid velocity within the well and a nonlinear increase in the shear stress at the culture surface over the ranges tested (0.5–2.0 Hz and 1–10% maximal strain). For all cases, the applied shear stresses were relatively low and on the order of millipascal with a dynamic waveform having a primary and secondary peak in the shear stress over a single mechanical strain cycle. These findings should be considered when interpreting experimental results using these devices, particularly in the case when the cell type used is sensitive to low magnitude, oscillatory shear stresses.

scholarly journals Mechanical Strain-Enabled Reconstitution of Dynamic Environment in Organ-on-a-Chip Platforms: A Review

Micromachines ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 765
Author(s):  
Qianbin Zhao ◽  
Tim Cole ◽  
Yuxin Zhang ◽  
Shi-Yang Tang
Keyword(s):  
Cell Culture ◽  
Shear Stress ◽  
Cultured Cells ◽  
Mechanical Strain ◽  
3D Cell Culture ◽  
Small Scale ◽  
Mechanical Stimuli ◽  
Human Organ ◽  
Organ On A Chip

Organ-on-a-chip (OOC) uses the microfluidic 3D cell culture principle to reproduce organ- or tissue-level functionality at a small scale instead of replicating the entire human organ. This provides an alternative to animal models for drug development and environmental toxicology screening. In addition to the biomimetic 3D microarchitecture and cell–cell interactions, it has been demonstrated that mechanical stimuli such as shear stress and mechanical strain significantly influence cell behavior and their response to pharmaceuticals. Microfluidics is capable of precisely manipulating the fluid of a microenvironment within a 3D cell culture platform. As a result, many OOC prototypes leverage microfluidic technology to reproduce the mechanically dynamic microenvironment on-chip and achieve enhanced in vitro functional organ models. Unlike shear stress that can be readily generated and precisely controlled using commercial pumping systems, dynamic systems for generating proper levels of mechanical strains are more complicated, and often require miniaturization and specialized designs. As such, this review proposes to summarize innovative microfluidic OOC platforms utilizing mechanical actuators that induce deflection of cultured cells/tissues for replicating the dynamic microenvironment of human organs.

Microdevice for Delivering Homogeneous Equi-Biaxial Strain to Live Cells Without the Use of Platen Structures

2013 ◽  
Author(s):  
Qian Wang ◽  
Yi Zhao
Keyword(s):  
Cultured Cells ◽  
Flexible Substrate ◽  
Mechanical Strain ◽  
Live Cells ◽  
Biaxial Strain ◽  
Thin Membrane ◽  
Strain Homogeneity ◽  
Homogeneous Strain

Live cells from most of the membranous tissues such as alveoli are subjected to equi-biaxial strain originated from their extracellular environments. To understand the role of equi-biaxial strain in live cells, a number of engineered methods have been developed for applying such mechanical strain to in vitro cultured cells. Among these methods, deforming a flexible substrate on a circular platen has been widely used [1], and has been miniaturized into millimeter scale for parallel stretching assay (Figure 1a). Nonetheless, the strain homogeneity becomes increasingly challenging at smaller scale, since it requires an ultra-thin membrane, an indentation platen with well controlled dimension, and the highly precise alignment. This obviously increases the fabrication and operation complexities. Devices that deliver homogeneous strain with minimal fabrication and assembling complexities are needed.

Strain and Substrate Stiffness Affect Calcium Accumulation in Aortic Valve Interstitial Cells

2011 ◽  
Author(s):  
Joshua D. Hutcheson ◽  
M. K. Sewell-Loftin ◽  
W. David Merryman
Keyword(s):  
Aortic Valve ◽  
Molecular Mechanisms ◽  
Cultured Cells ◽  
Mechanical Strain ◽  
Cell Types ◽  
Interstitial Cells ◽  
Nodule Formation ◽  
Native Tissue

The progression of aortic valve (AV) disease is often characterized by the formation of calcific nodules on thickened AV leaflets, limiting the biomechanical function of the valve. Calcification is a major problem that often leads to the failure of bioprosthetic replacement valves [1]. In these cases, the association of extracellular Ca2+ with phosphates remaining in cellular debris within the decellularized scaffolds has been proposed to lead to the nucleation and growth of Ca3(PO4)2 nodules. In native tissue, calcification is thought to be a more active process involving AV interstitial cells (AVICs). The exact molecular mechanisms that lead to the formation of these calcific nodules in native tissue remain unclear; however, AVICs have been shown to form nodule-like structures in vitro through differentiation to a phenotype with osteogenic character [2]. Additionally, in vitro nodules are characterized by activated smooth muscle α-actin positive AVICs and high levels of apoptosis [2–3]. Mechanical strain has also been shown to influence nodule formation in excised AV leaflets [4]. Intracellular Ca2+ exhibits mechanodependency in cultured cells [5], and heightened levels of intracellular Ca2+ have been shown to be associated with apoptosis in many cell types [6] In this study, we assess the role of mechanically-induced changes in intracellular calcium and its function in modulating AVIC behavior. We hypothesized that intracellular Ca2+ will increase in strained AVICs and that over time, this will lead to apoptosis. We believe that the results from this study will help illustrate the mechanotransductive role of Ca2+ in AVICs and may elucidate early cellular changes that lead to AV calcification.

Cultured epithelial cells derived from human foetal pancreas as a model for the study of cystic fibrosis: further analyses on the origins and nature of the cell types

1988 ◽  
Vol 90 (1) ◽  
pp. 73-77
Author(s):  
A. Harris ◽  
L. Coleman
Keyword(s):  
Cystic Fibrosis ◽  
Tissue Culture ◽  
Epithelial Cells ◽  
Culture System ◽  
Cultured Cells ◽  
Cell Types ◽  
Cultured Epithelial Cells ◽  
Different Cell Types ◽  
Foetal Pancreas

The establishment of a tissue-culture system for epithelial cells derived from human foetal pancreas has recently been reported. Further analyses have now been made on these cells in vitro, together with parallel investigation of the distribution of different cell types within the intact foetal pancreas. Results support the view that the cultured cells are ductal in origin and nature. Pancreatic epithelial cell cultures have also been established from foetuses with cystic fibrosis.

Physiological fluid shear stress causes downregulation of endothelin-1 mRNA in bovine aortic endothelium

1992 ◽  
Vol 263 (2) ◽  
pp. C389-C396 ◽  
Author(s):  
A. Malek ◽  
S. Izumo
Keyword(s):  
Shear Stress ◽  
Fluid Shear Stress ◽  
Fluid Velocity ◽  
Low Frequency ◽  
Turbulent Shear ◽  
Specific Response ◽  
Dependent Manner ◽  
Fluid Shear ◽  
Endothelin 1

We report here that the level of endothelin-1 (ET-1) mRNA from bovine aortic endothelial cells grown in vitro is rapidly (within 1 h of exposure) and significantly (fivefold) decreased in response to fluid shear stress of physiological magnitude. The downregulation of ET-1 mRNA occurs in a dose-dependent manner that exhibits saturation above 15 dyn/cm2. The decrease is complete prior to detectable changes in endothelial cell shape and is maintained throughout and following alignment in the direction of blood flow. Peptide levels of ET-1 secreted into the media are also reduced in response to fluid shear stress. Cyclical stretch experiments demonstrated no changes in ET-1 mRNA, while increasing media viscosity with dextran showed that the downregulation is a specific response to shear stress and not to fluid velocity. Although both pulsatile and turbulent shear stress of equal time-average magnitude elicited the same decrease in ET-1 mRNA as steady laminar shear (15 dyn/cm2), low-frequency reversing shear stress did not result in any change. These results show that the magnitude as well as the dynamic character of fluid shear stress can modulate expression of ET-1 in vascular endothelium.

Hemodynamic Shear Stress And Endothelial Cell Function: In Vitro Studies

1981 ◽  
Author(s):  
M A Gimbrone ◽  
C F Dewey ◽  
P F Davies ◽  
S R Bussolari
Keyword(s):  
Shear Stress ◽  
Endothelial Cell ◽  
Fluid Shear Stress ◽  
Cell Structure ◽  
Structure And Function ◽  
Cellular Migration ◽  
Shear Stresses ◽  
Endothelial Cell Function ◽  
And Function

The vascular endothelial lining in vivo is constantly subjected to hemodynamic shear stresses resulting from normal and altered patterns of blood flow. To facilitate the study of effects of fluid shear stress on endothelial cell structure and function, we have developed an in vitro system, utilizing a cone-plate apparatus, to subject coverslip cultures of bovine aortic endothelial cells (BAEC) to controlled levels of shear (up to 102 dynes/cm2) in either laminar or turbulent flow. The magnitude and direction of shear stress within the system are accurately known from both theory and experimental measurements. The data reported here are for laminar flow. Subconfluent BAEC cultures continuously exposed to 1-5 dynes/cm2 shear proliferated at a rate comparable to that of static cultures, and postconfluent monolayers appeared unaltered morphologically for up to 1 week. In contrast, BAEC cultures (both postconfluent and subconfluent) exposed to 8 dynes/cm2 developed dramatic, time-dependent morphological changes. By 48 hrs, cells uniformly assumed an ellipsoidal configuration, with their major axes aligned in the direction of flow. Exposure to >10 dynes/cm2 caused variable cell detachment from plain glass substrates. Cellular migration into linear “wounds”, created in confluent areas, was influenced by both the direction and amplitude of applied shear. Exposure to 8 dynes/ cm2 induced functional alterations, including increased fluid (bulk phase) endocytosis, prostaglandin production and platelet reactivity. These observations indicate that fluid mechanical forces can directly influence endothelial cell structure and function. Hemodynamic modulation of endothelial cell behavior may be relevant to normal vessel wall physiology, as well as the pathogenesis of atherosclerosis and thrombosis.

Eulerian-Eulerian Multiphase Modeling of Blood Cells Segregation in Flow Through Microtubes

2017 ◽  
Author(s):  
Yertay Mendygarin ◽  
Luis R. Rojas-Solórzano ◽  
Nurassyl Kussaiyn ◽  
Rakhim Supiyev ◽  
Mansur Zhussupbekov
Keyword(s):  
Shear Stress ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Heart Diseases ◽  
Accurate Determination ◽  
Shear Stresses ◽  
High Shear ◽  
Blood Damage ◽  
Solid Phases

Cardiovascular Diseases, the common name for various Heart Diseases, are responsible for nearly 17.3 million deaths annually and remain the leading global cause of death in the world. It is estimated that this number will grow to more than 23.6 million by 2030, with almost 80% of all cases taking place in low and middle income countries. Surgical treatment of these diseases involves the use of blood-wetted devices, whose relatively recent development has given rise to numerous possibilities for design improvements. However, blood can be damaged when flowing through these devices due to the lack of biocompatibility of surrounding walls, thermal and osmotic effects and most prominently, due to the excessive exposure of blood cells to shear stress for prolonged periods of time. This extended exposure may lead to a rupture of membrane of red blood cells, resulting in a release of hemoglobin into the blood plasma, in a process called hemolysis. Moreover, exposure of platelets to high shear stresses can increase the likelihood of thrombosis. Therefore, regions of high shear stress and residence time of blood cells must be considered thoroughly during the design of blood-contacting devices. Though laboratory tests are vital for design improvements, in-vitro experiments have proven to be costly, time-intensive and ethically controversial. On the other hand, simulating blood behavior using Computational Fluid Dynamics (CFD) is considered to be an inexpensive and promising tool to help predicting blood damage in complex flows. Nevertheless, current state-of-the-art CFD models of blood flow to predict hemolysis are still far from being fully reliable and accurate for design purposes. Previous work have demonstrated that prediction of hemolysis can be dramatically improved when using a multiphase (i.e., phases are plasma, red blood cells and platelets) model of the blood instead of assuming the blood as a homogeneous mixture. Nonetheless, the accurate determination of how the cells segregate becomes the critical issue in reaching a truthful prediction of blood damage. Therefore, the attempt of this study is to develop and validate a numerical model based on Granular Kinetic Theory (GKT) for solid phases (i.e., cells treated as particles) that provides an improved prediction of blood cells segregation within the flow in a microtube. Simulations were based on finite volume method using Eulerian-Eulerian modeling for treatment of three-phase (liquid-red blood cells and platelets) flow including the GKT to deal with viscous properties of the solid phases. GKT proved to be a good model to predict particle concentration and pressure drop by taking into account the contribution of collisional, kinetic and frictional effects in the stress tensor of the segregated solid phases. Preliminary results show that the improved segregated model leads to a better prediction of spatial distribution of blood cells. Simulations were performed using ANSYS FLUENT platform.

scholarly journals The functional expression of tissue factor by fibroblasts and endothelial cells under flow conditions

Blood ◽  
1993 ◽  
Vol 81 (12) ◽  
pp. 3265-3270 ◽  
Author(s):  
EF Grabowski ◽  
DB Zuckerman ◽  
Y Nemerson
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Tissue Factor ◽  
Factor Viia ◽  
Factor Xa ◽  
Cell Types ◽  
Shear Stresses ◽  
Factor X ◽  
Flow Conditions ◽  
Production Values

Abstract The expression of tissue factor (TF) by a variety of vascular cell types under physiologic flow conditions is critical to factor X activation and in vivo clotting. Therefore, in a parallel-plate flow chamber (volume 40 microL) we mounted monolayers of human embryonic fibroblasts (FBs) or interleukin-1 alpha (IL-1 alpha) (5 U/mL x 4 hours)-stimulated human umbilical vein endothelial cells (ECs). Inflow buffer contained 10 nmol/L factor VIIa, 100 nmol/L factor X, and 2.0 mmol/L CaCl. With FBs, production of factor Xa (product of outflow concentration of factor Xa-and flow rate) increased 200-fold over the range of shear stress from 0 to 2.7 dynes/cm2. Production values (mean +/- SE (N)) were 7.93 +/- 0.024 (6), 312 +/- 7.3 (6), 688 +/- 33.1 (8), 1,033 +/- 119 (6), and 1,601 +/- 183 (7) fmol/cm2.minute at shear stresses of 0, 0.27, 0.68, 1.35, and 2.7 dynes/cm2, respectively. Further experiments at 0.68 dynes/cm2 indicated that factor Xa production increased with factor X concentration over the range from 3 to 100 nmol/L, but changed little from 300 to 1,000 nmol/L. With ECs, production was 0.13 +/- 0.86 (6), 8.17 +/- 1.65 (13), and 1.66 +/- 1.66 (5) fmol/cm2.minute at 0, 0.68, and 2.7 dynes/cm2, respectively. However, in the presence of an antibody directed against tissue factor pathway inhibitor (TFPI) production with ECs was augmented to 16.46 +/- 0.80 (8), 149.8 +/- 18.6 (8), and 48.9 +/- 10.3 (10), respectively, at these same shear stresses. Control experiments with factor VIIa, factor X, or both absent confirm for both cell types the specificity of the reaction for the TF pathway. Similarly, specificity for TF itself is shown by the virtual absence of factor Xa generation in the presence of the monoclonal antibody HTF1–7B8 directed against human TF. We conclude that ECs, even when activated, are normally unable to generate significant quantities of factor Xa in the presence of factors X and VIIa. However, significant quantities of factor Xa are possible in the presence of an inhibitor of TFPI. On the other hand, production of factor Xa by fibroblasts is markedly augmented by shear stress, yet independent of the availability of substrate factor X above an inflow concentration of 100 nmol/L. The latter suggests a direct effect of flow on the fibroblast monolayers, not substrate limitation by convective diffusion.

P0658MATRIX AND FLOW MODULATE GENE EXPRESSION IN A 3D VASCULARISED TUBULE MODEL

2020 ◽  
Vol 35 (Supplement_3) ◽  
Author(s):  
Julie Williams ◽  
Sanlin Robinson ◽  
Babak Alaei ◽  
Kimberly Homan ◽  
Maryam Clausen ◽  
...  
Keyword(s):  
Gene Expression ◽  
Extracellular Matrix ◽  
Impact Analysis ◽  
Cell Types ◽  
Drug Uptake ◽  
Shear Stresses ◽  
The Matrix ◽  
And Function

Abstract Background and Aims Questions abound regarding the translation of in vitro 2D cell culture systems to the human setting. This is especially true of the kidney in which there is a complex hierarchical structure and a multitude of cell types. While it is well accepted that extracellular matrix plays a large part in directing cellular physiology emerging research has highlighted the importance of shear stresses and flow rates too. To fully recapitulate the normal gene expression and function of a particular renal cell type how important is it to completely reconstitute their in vivo surroundings? Method To answer this question, we have cultured proximal tubular (PT) epithelial cells in a 3-dimensional channel embedded within an engineered extracellular matrix (ECM) under physiological flow that is colocalised with an adjacent channel lined with renal microvascular endothelial cells that mimic a peritubular capillary. Modifications to the system were made to allow up to 12 chips to be run in parallel in an easily handleable form. After a period of maturation under continuous flow, both cell types were harvested for RNAseq analyses. RNA expression data was compared with cells cultured under static 2-dimensional conditions on plastic or the engineered ECM. Additionally, the perfusion of glucose through this 3D vascularised PT model has been investigated in the presence and absence of known diabetes modulating agents. Results PCA of RNAseq data showed that a) static non-coated, b) static matrix-coated and c) flow matrix-coated conditions separated into 3 distinct groups, while cell co-culture had less impact. Analysis of transcriptomic signatures showed that many genes were modulated by the matrix with additional genes influenced under flow conditions. Several of these genes, classified as transporters, are of particular importance when using this model to assess drug uptake and safety implications. Co-culture regulated some interesting genes, but fewer than anticipated. Preliminary experiments are underway to monitor glucose uptake and transport between tubules under different conditions. Conclusion We have developed a medium throughput system in which matrix and flow modulate gene expression. This system can be used to study the physiology of molecular cross-talk between cells. Ongoing analysis will further consider relevance to human physiology.

Flow-induced dilation of rat soleus feed arteries

1997 ◽  
Vol 273 (5) ◽  
pp. H2423-H2427 ◽  
Author(s):  
Jeffrey L. Jasperse ◽  
M. Harold Laughlin
Keyword(s):  
Shear Stress ◽  
Maximum Flow ◽  
Intraluminal Pressure ◽  
Shear Stresses ◽  
Potential Contribution ◽  
Basal Diameter ◽  
Exercise Hyperemia ◽  
Feed Arteries

Flow-induced dilation is thought to contribute to dilation of skeletal muscle arteries and arterioles during exercise hyperemia. We sought to determine whether rat soleus feed arteries (SFA) exhibit flow-induced dilation and to evaluate the potential contribution of flow-induced dilation of SFA to exercise hyperemia. Rat SFA were isolated and cannulated to allow pressure and intraluminal flow to be independently controlled. Intraluminal pressure was maintained at 90 cmH2O throughout the experiment. All SFA ( n = 13) developed spontaneous tone and dilated in response to flow. Flow of 10 and 14 μl/min produced a 34 ± 14 and 56 ± 17 μm increase above basal diameter (135 ± 12 μm), respectively. Flows >14 μl/min produced little further dilation. Maximum flow-induced dilation was 86 ± 3% of passive diameter determined in calcium-free physiological saline solution. Calculated shear stress was maintained at 4–6 dyn/cm2 at flows of 10–20 μl/min but increased at greater flows because SFA did not dilate further. To determine whether dilation in response to flows in this range may contribute to exercise hyperemia, we estimated in vivo SFA blood flows from previously published soleus blood flow data. Anesthetized rats are estimated to have flows of 10 μl/min per SFA, and conscious rats are estimated to have flows of 95 (nonexercising), 153 (walking), and 225 (running) μl/min per SFA. Corresponding shear stresses were estimated to be 26 (anesthetized), 47 (conscious, nonexercising), 75 (walking), and 111 (running) dyn/cm2. Because estimated in vivo values for both flow and wall shear stress are far greater than the flow and/or shear stresses at which maximal flow-induced dilation occurs in vitro, we conclude that flow-induced dilation contributes little to dilation of SFA during locomotory exercise.

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