Controlled Shear Stress Research Articles

Synthesis of silica bearing sulfobetaine and sulfonic groups and their electrorheological response

Organically modified silica bearing amino groups (SiO2-NH2) was prepared by the simple sol-gel procedure followed by treatment with butanesultone to produce zwitterionic silica bearing sulfobetaine groups (SiO2-SB). This particle was then treated with sulfuric acid to prepared particles carrying both sulfonic acid and ammonium salt (SiO2-SO3H). These particles were characterized by different methods and dispersed in silicone oil (15 wt%) to evaluate the electrorheological (ER) performance. Thermogravimetric (TG) analysis, zeta potential and Fourier transform infrared (FTIR) spectroscopy confirmed the structure of the modified silica. The ER response was evaluated using controlled shear stress (CSR) and oscillatory mode. The SiO2-NH2 and SiO2-SB based fluids displayed the highest shear stress at low shear rate even without an applied electric field. However the higher ER efficiency and lower leakage current was observed for the fluid containing SiO2-SO3H. From dielectric analysis, it was demonstrated that the zwitterionic SiO2-SB particle provided faster relaxation time and larger permittivity difference. Thus, it is possible to conclude that the lower viscosity of the SiO2-SO3H based fluid without electric field also plays an important role for a good ER efficiency. Both SiO2-SB and SiO2-SO3H particles are suitable for producing ER fluids due to their better dielectric properties and relaxation time. The former also presented better sedimentation stability.

High-throughput quantification of red blood cell deformability and oxygen saturation to probe mechanisms of sickle cell disease.

The complex, systemic pathology of sickle cell disease is driven by multiple mechanisms including red blood cells (RBCs) stiffened by polymerized fibers of deoxygenated sickle hemoglobin. A critical step toward understanding the pathologic role of polymer-containing RBCs is quantifying the biophysical changes in these cells in physiologically relevant oxygen environments. We have developed a microfluidic platform capable of simultaneously measuring single RBC deformability and oxygen saturation under controlled oxygen and shear stress. We found that RBCs with detectable amounts of polymer have decreased oxygen affinity and decreased deformability. Surprisingly, the deformability of the polymer-containing cells is oxygen-independent, while the fraction of these cells increases as oxygen decreases. We also find that some fraction of these cells is present at most physiologic oxygen tensions, suggesting a role for these cells in the systemic pathologies. Additionally, the ability to measure these pathological cells should provide clearer targets for evaluating therapies.

A Millifluidic Chamber for Controlled Shear Stress Testing: Application to Microbial Cultures

In vitro platforms such as bioreactors and microfluidic devices are commonly designed to engineer tissue models as well as to replicate the crosstalk between cells and microorganisms hosted in the human body. These systems promote nutrient supply and waste removal through culture medium recirculation; consequently, they intrinsically expose cellular structures to shear stress, be it a desired mechanical stimulus to drive the cell fate or a potential inhibitor for the model maturation. Assessing the impact of shear stress on cellular or microbial cultures thus represents a crucial step to define proper environmental conditions for in vitro models. In this light, the aim of this study was to develop a millifluidic device enabling to generate fully controlled shear stress profiles for quantitatively probing its influence on tissue or bacterial models, overcoming the limitations of previous reports proposing similar devices. Relying on this millifluidic tool, we present a systematic methodology to test how adherent cellular structures react to shear forces, which was applied to the case of microbial biofilms as a proof of concept. The results obtained suggest our approach as a suitable testbench to evaluate culture conditions in terms of shear stress faced by cells or microorganisms.Graphical

A standard 96-well based high throughput microfluidic perfusion biofilm reactor for in situ optical analysis.

Biofilm infections represent a major public health threat due to their high tolerance to antimicrobials and the lack of specific anti-biofilm drugs. To develop such drugs, it is crucial to have high-throughput biofilm growth systems that can emulate in vivo conditions without the cost and complexity of animal models. However, no current biofilm reactor can provide in vivo-like conditions in a high throughput standard microtiter format. This paper demonstrates a novel high-throughput (HT) microfluidic perfusion biofilm reactor (HT-μPBR) compatible with a standard 96-well microtiter plate for in situ optical analysis. A snap-on liquid-tight cover for standard microtiter plates was designed and fabricated with fluidic channels to provide closed-loop recirculating perfusion. Our system takes steps toward providing in vivo-like conditions with controlled shear stress and nutrient delivery. We describe the system fabrication and usage in optical analysis of biomass and viability of Escherichia coli (E. coli) biofilms. The HT-μPBR was set to perfuse at 1mL/min corresponding to an average shear rate of approximately [Formula: see text] on the bottom surface of a single well. Biofilms were detected on well plate bottoms and measured using a fluorescence microscope and plate reader to determine biomass and viability. Samples cultured in the HT-μPBR showed increased biomass while maintaining viability after 24h. The HT-μPBR can further be combined with HT antibiotic susceptibility testing and additional optical techniques such as time-lapse imaging to improve understanding of the drug reaction mechanism as well as the optimization of drug combinations and delivery profiles.

Hydrodynamics vs. membrane drag determines the mobility of bioengineered proteins during flow.

Biological membranes and the lipid-anchored proteins embedded in them experience shear forces, particularly in an environment such as the cardiovascular system. For example, Glypican-1, a GPI-anchored protein involved in flow sensing by cells, moves in the flow and direction to create a concentration gradient. The mobility of proteins and hence such formed concentration gradient profile can be affected by several factors such as protein size, shape, the viscosity of the surrounding media, protein-membrane anchor, and the composition of the membrane itself. To decouple the factors contributing to protein mobility, we developed a method to measure the flow mobility of proteins on a model system composed of lipid anchored proteins on solid-supported lipid bilayers (SSLBs). We combine microfluidics and confocal microscopy to monitor the protein gradients formed under controlled shear stress and hence measure the mobility of the protein. The protein mobility is determined by the balance of two forces experienced by the protein: the viscous drag force exerted by the membrane in which proteins are embedded and the hydrodynamic shear force exerted by the flow. The hydrodynamic shear force experienced by the protein under given stress is altered by protein size and shape whereas the viscous drag force exerted by the membranes depends on membrane composition and protein-membrane anchor. Here we independently vary these forces by creating a series of monomeric proteins and lipid mixtures. We successfully purified single and double-GFP-tagged monomeric Streptavidin protein and measured their mobilities in membranes with different lipid compositions. We obtain the parameters we can use to predict flow responses of protein in general.

Passive and reversible area regulation of supported lipid bilayers in response to fluid flow

Biological and model membranes are frequently subjected to fluid shear stress. However, membrane mechanical responses to flow remain incompletely described. This is particularly true of membranes supported on a solid substrate, and the influences of membrane composition and substrate roughness on membrane flow responses remain poorly understood. Here, we combine microfluidics, fluorescence microscopy, and neutron reflectivity to explore how supported lipid bilayer patches respond to controlled shear stress. We demonstrate that lipid membranes undergo a significant, passive, and partially reversible increase in membrane area due to flow. We show that these fluctuations in membrane area can be constrained, but not prevented, by increasing substrate roughness. Similar flow-induced changes to membrane structure may contribute to the ability of living cells to sense and respond to flow.

Lab-scale autothermal thermophilic aerobic digestion can maintain and remove nitrogen by controlling shear stress and oxygen supply system

Lab-scale autothermal thermophilic aerobic digestion can maintain and remove nitrogen by controlling shear stress and oxygen supply system

Extracellular Vesicles from Sickle Red Blood Cells Activate Endothelial Cells and Trigger Von Willebrand Factor-Mediated Sickle Red Cell Adhesion

Introduction: The sickle mutation of hemoglobin (HbS) afflicts millions of people worldwide and is characterized by hemolytic anemia, inflammation, painful vaso-occlusive crises, significant morbidity, and early mortality. In sickle cell disease (SCD), HbS polymerization under deoxygenation increases red blood cell (RBC) rigidity, adhesivity and susceptibility to lysis. Products of intravascular hemolysis including heme and RBC-released extracellular vesicles (REVs) promote acute and chronic inflammation triggering endothelial activation and abnormal RBC adhesion. Extracellular vesicles (EVs) are nano- or micro-particles composed of a lipid bilayer, comprised of transmembrane proteins, and enclosing intracellular remnants, including cytosolic proteins and miRNAs. EVs are known to exchange biomaterial between cells, and may serve as surrogate markers for the activated state of the parent cell thus are of high clinical significance. Quantitatively, REVs are more abundant from sickle RBCs (SS RBCs) compared with normal HbA-containing RBCs (AA RBCs). SS REVs are known to promote endothelial cell (EC) activation through cell signaling and transcriptional regulation at longer terms. However, the SS REV-mediated short term non transcriptional response of EC is unclear. Methods: Here, we have developed the SCD-EV-BioChip using microfluidic technology. SCD-EV-BioChip assesses RBC adhesion as a biomarker for REV-mediated human pulmonary microvascular endothelial cells (HPMECs) dysfunction using functional biomarker of RBC adhesion. Utilizing SCD-EV-BioChip, Here, we examined the impact of SS REVs on acute microvascular EC activation and RBC adhesion at 2 hours. For in vitro studies, SS REVs and AA REVs were collected from pooled human SS RBCs and AA RBCs activated using calcium ionophore. The generated REVs were characterized using scanning electron microscopy (SEM) and nanoparticle tracking analyzer (NTA). HPMECs were cultured in microfluidic channels under controlled shear stress for more than 72 hours then treated with REVs at 37 ºC for 2 hours. Von Willebrand factor (vWF) expression on REVs-treated HPMECs were quantified. RBC adhesion tests were conducted with and without vWF protease ADAMTS13 and heme-binding protein hemopexin under shear stress at 1 dyne/cm2 followed by a rinse step and quantification of adhered RBCs. For in vivo study, HbSS-Townes mice and a dorsal skin-fold chamber model was used to determine if ADAMTS13 would reduce microvascular stasis in response to hemin. Results: Within 2 hours, SS REVs, but not AA REVs, promoted increased levels of vWF expression on HPMECs, indicating HPMEC activation (Fig. 1A-C). VWF is known to trigger SRBC adhesion and vaso-occlusion. Using SCD-EV-BioChip, we found significantly increased SS RBC adhesion to HPMECs exposed to SREVs, compared to SRBC adhesion to HPMECs exposed to AA REVs, and AA RBC adhesion to HPMECs exposed to SS REVs (Fig. 1D-G). SS RBC adhesion was significantly reduced on HPMECs treated with SS REVs pre-incubated with hemopexin. ADAMTS13 is a regulator which is responsible for cleaving ultra large vWF. In this study, SS RBC adhesion was significantly reduced by vWF cleaving protease ADAMTS13 to a level similar to HPMECs treated with AA REVs (Fig. 1G). Consistent with these observations, studies in SS mice with implanted dorsal skin-fold chambers found hemin-induced stasis was inhibited by ADAMTS13 (Fig. 1F). SRBC adhesion was variable within a total of 15 test subjects with SCD, and was higher with SRBCs from patients with increased markers of hemolysis (LDH and reticulocyte count) or a concomitant clinical diagnosis of deep vein thrombosis. Conclusions: This work demonstrated the acute, non-transcriptional contribution made by REVs to the microvascular EC activation and vWF-mediated SRBC adhesion. Results from SCD-EV-BioChip indicated the effect of hemopexin in mitigating SREV-mediated HPMEC activation. Additionally, results from in vitro SCD-EV BioChip tests agreed with in vivo stasis tests using SS mice, both of which indicated the effect of ADAMTS13 in mitigating SS RBC adhesion and vaso-occlusion. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Different methods for determining the yield stress of ferrofluids

The yield stress of ferrofluids has been a hot topic in their rheological studies, and it is still controversial which method could obtain the more accurate yield stress value. In this work, we used varieties of methods to obtain the yield stress of the ferrofluid, including steady shear and oscillatory shear. We obtained the static yield stress and dynamic yield stress of the ferrofluid by Herschel–Bulkley fitting of the flow curves measured by the controlled shear rate mode and the controlled shear stress mode, and found that at any magnetic field strength, the static yield stress was always significantly greater than the dynamic yield stress. We then performed oscillatory shear of the ferrofluid and determined the yield stress using three methods, where the yield stress value corresponding to the intersection of the storage modulus G′ and the loss modulus G″ is similar to the static yield stress value fitted by H-B at low magnetic field strength. The power law function and shear stress as a function of shear strain consistently gave the maximum value of the yield stress. Ultimately, we believe that which method is ultimately chosen depends on the practical application conditions of interest.

Rheological characteristics of marine sediments from the Ulleung Basin, East Sea to estimate the mobility of submarine landslides

In estimating the geohazards posed by submarine landslides, the rheological properties of marine sediments are of significant importance for their postfailure dynamics. We report an experimental study of the rheological behavior of marine sediments taken from the Ulleung Basin, East Sea and their influence on numerical simulations of debris flow runout. Marine sediments exhibit a typical yield stress behavior, such as that of low-activity clays. For the materials examined, different yield stresses are observed depending on the shearing methods. Steady-state and oscillatory shear tests were conducted for different volumetric concentrations of sediment. According to the test results, the Bingham yield stresses under controlled shear stress and shear rate range from approximately 100 Pa to 1500 Pa, but the yield stresses under oscillatory shear loads range from approximately 25 Pa to 3500 Pa for a given sediment concentration. In the latter cases, the value obtained in the elastic region is approximately doubled. Experiments under steady-state and oscillatory shear loads can be helpful in determining the yield points in the elastic and viscous regions and in explaining changes in the structure of the soil sample due to shear. We apply the range of measured yield strength values to numerical simulations of debris flow runout using a Herschel-Bulkley model and find that only the lowest values of yield strength, despite the low sediment concentrations, could account for the observed runout and thickness distribution. We infer that significant wetting must occur during debris flow motion to attain the observed runout.

Thermal capability and entropy optimization for Prandtl-Eyring hybrid nanofluid flow in solar aircraft implementation

In addition to photovoltaic cells, solar power plates, photovoltaic lights, and solar pumping water, solar energy is the primary source of heat from the sun. At the moment, researchers are looking at the use of nanotechnological and solar radiation to increase aeronautical efficiency. In this study, hybrid nanofluid flow linearly passes through a parabolic trough solor collector (PTSC) on the interior of solar aircraft wings to study heat transmission. Solar radiative flow was the term used to describe the heat source. The heat transfer efficiency of the wings is evaluated for several effects, such as a slanted magnetic field, viscous dissipation, play heating, and thermal radiative flow. Entropy generation study was performed on the Prandtl-Eyring hybrid nanofluid (P-EHNF). The Keller box technique was used to solve the predicted energy and momentum equations. As a typical fluid, EG (ethylene glycol) is used to disperse the nanosolid particles, which consist of copper (Cu) and cobalt ferrite (CoFe2O4). A variety of control factors, including velocity, shear stress, and temperature outlines as well as a frictional factor and Nusselt number, are addressed in detail. Thermal radiation amplification and variable thermal conduction parameters appear to increase the efficiency of aircraft wings in terms of thermal transfer. Hybrid nanofluid is superior to conventional nanofluid in terms of heat transmission. Cu-EG has a low thermal efficiency between 3.8% and 4.8% than CoFe2O4-Cu/EG nanofluid.

Lab-scale autothermal thermophilic aerobic digestion can maintain and remove nitrogen by controlling shear stress and oxygen supply system

Autothermal thermophilic aerobic digestion (ATAD) is used to treat human excreta hygienically. We previously reported a unique full-scale ATAD, showing distinctive bacterial community transitions and producing high-nitrogen-content liquid fertilizer; nevertheless, the mechanism remains unclear. One hypothesis involves using a gas-inducing (GI) agitator. We designed a lab-scale GI system and compared it with a disk-turbine (DT) agitator system by mimicking the temperature shift of full-scale ATAD. The agitation system and its agitation speed greatly affected physicochemical properties and bacterial community structure. GI system at 1000rpm (GI1000; high total carbon removal efficiency, 88.3%), with few nitrifying and denitrifying bacteria, maintained a high ammoniacal nitrogen concentration and had more shared operational taxonomic units related to Acinetobacter sp., Arcobacter sp., and Longimicrobium sp. with the full-scale ATAD compared with the GI system at 490rpm and DT system at 1000rpm (DT1000). Furthermore, DT1000, with a high abundance of nitrifying and denitrifying bacteria such as Alcaligenes aquatilis and Pseudomonas caeni, removed 94.7% total nitrogen with 71.9% total carbon removal efficiency. These results suggested that shear stress and oxygen supply system would change the bacterial community structure, thus affected ATAD performances. Consequently, it is possible that ATAD can be applied for not only production of highly nitrogen-containing liquid fertilizer but also extremely nitrogen removal of wastewater.

Discovery of Targeted Material Binding Microorganisms Using a Centrifugal Microfluidic Platform

AbstractDiscovery of unique peptides that specifically bind to target materials of interest is commonly achieved through biopanning‐based screening of cell libraries having high diversity. However, conventional methods have limitations in the generation of controllable shear stress applied in order to effectively remove weak and unbound cells from a target material. Here, a centrifugal force‐based microfluidic biopanning platform is presented. Using this microfluidic platform, a wide range of shear stress conditions can be generated by simply adjusting the rotation speed of the platform, which provides a precisely controllable wash step. The enhanced circularly permuted outer membrane protein X (eCPX) 3.0 bacterial peptide display library (≈1011 number of cells) is screened, and many isolates that show strong affinity towards gold only, ITO only, or both are successfully obtained through a multiround iterative sorting process. Amino acid contents of the resulting isolates are analyzed to provide a better understanding of the distinctive attributes of these peptides and their specific material‐binding capabilities. This platform is simple and easy to use and can be readily applied to screen microbial libraries against virtually any material surface of interest, which can greatly accelerate the discovery of peptide‐driven biomaterials and the development of hybrid organic–inorganic materials.

A bioprinted composite hydrogel with controlled shear stress on cells.

In recent decades, three dimensional (3D) bio-printing technology has found widespread use in tissue engineering applications. The aim of this study is to scrutinize different parameters of the bioprinter - with the help of simulation software - to print a hydrogel so much so that avoid high amounts of shear stress which is detrimental for cell viability and cell proliferation. Rheology analysis was done on several hydrogels composed of different percentages of components: alginate, collagen, and gelatin. The results have led to the combination of percentages collagen:alginate:gelatin (1:4:8)% as the best condition which makes sol-gel transition at room temperature possible. The results have shown the highest diffusion rate and cell viability for the cross-linked sample with 1.5% CaCl2 for the duration of 1 h. Finally, we have succeeded in printing the hydrogel that is mechanically strong with suitable degradation rate and cell viability.

Pumpless microfluidic device with open top cell culture under oscillatory shear stress.

Here we developed a 96-well plate-based pumpless microfluidic device to mimic bidirectional oscillatory shear stress experienced by osteoblasts at the endosteal niche located at the interface between bone and bone marrow. The culture device was designed to be high-throughput with 32 open top culture chambers for convenient cell seeding and staining. Mathematical modeling was used to simulate the control of oscillatory shear stress with the peak stress in the range of 0.3 to 50mPa. Osteoblasts, cultured under oscillatory shear stress, were found to be highly viable and significantly aligned along the direction of flow. The modeling and experimental results demonstrate for the first time that cells can be cultured under controllable oscillatory shear stress in the open top culture chamber and pumpless configurations.

Computational Characterization of The Dish-In-A-Dish, A High Yield Culture Platform for Endothelial Shear Stress Studies on the Orbital Shaker.

Endothelial cells sense and respond to shear stress. Different in vitro model systems have been used to study the cellular responses to shear stress, but these platforms do not allow studies on high numbers of cells under uniform and controllable shear stress. The annular dish, or dish-in-a-dish (DiaD), on the orbital shaker has been proposed as an accessible system to overcome these challenges. However, the influence of the DiaD design and the experimental parameters on the shear stress patterns is not known. In this study, we characterize different designs and experimental parameters (orbit size, speed and fluid height) using computational fluid dynamics. We optimize the DiaD for an atheroprotective flow, combining high shear stress levels with a low oscillatory shear index (OSI). We find that orbit size determines the DiaD design and parameters. The shear stress levels increase with increasing rotational speed and fluid height. Based on our optimization, we experimentally compare the 134/56 DiaD with regular dishes for cellular alignment and KLF2, eNOS, CDH2 and MCP1 expression. The calculated OSI has a strong impact on alignment and gene expression, emphasizing the importance of characterizing shear profiles in orbital setups.

Unlocking the Potential of Organ-on-Chip Models through Pumpless and Tubeless Microfluidics.

Microfluidic organs-on-chips are rapidly being developed toward eliminating the shortcomings of static in vitro models and better addressing basic and translational research questions. A critical aspect is the dynamic culture environment they provide. However, the associated inherent requirement for controlled fluid shear stress (FSS) and therefore the need for precise pumps limits their implementation. To address this issue, here a novel approach to manufacture pumpless and tubeless organs-on-chips is reported. It relies on the use of a hydrophilic thread to provide a driving force for the perfusion of the cell culture medium through constant evaporation in the controlled conditions of a cell incubator. Well-defined and tuneable flow rates can be applied by adjusting the length and/or diameter of the thread. This approach for the preparation of an intestine-on-chip model based on the Caco-2 cell line is validated. Five days culture under 0.02dyn·cm-2 shear conditions yield monolayers similar to those prepared using a high-precision peristaltic pump. A pumpless device can also be used to delineate the effect of FSS on the phenotype of adenocarcinomic human alveolar basal epithelial A549 cells. It is anticipated that the pumpless approach will facilitate and herefore increase the use of organs-on-chips models in the future.

Effects of in‐vitro exercise‐induced endothelial shear stress on adhesion molecule gene expression

BackgroundExercise‐Induced Shear Stress (ESS) is characterized as a mechanical stimulus effecting cellular morphology and physiology. Varying ESS intensity elicit different response mechanisms through cellular signaling pathways. Higher intensity ESS enhances the expression of genes involved in protection against atherosclerosis. Adhesion molecules expression is common in atherosclerosis. Therefore, the purpose of this study was to determine the effects of different intensities of pulsatile ESS on vascular cell adhesion molecule‐1 (VCAM1) and intercellular adhesion molecule (ICAM1) gene expression.MethodsCommercially available human carotid artery endothelial cells (Sigma Aldrich) were cultured until 95–100% confluence and then exposed to pulsatile resting ESS (18 dynes/cm2) for 5 hours, followed by 1 hour low‐intensity ESS (35 dynes/cm2), or high‐intensity ESS (80 dynes/cm2) on parallel fluidic units (Ibidi, USA). Ibidi Pump Control Software (version 1.5.4, Ibidi, USA) was used to control shear stress intensity. mRNA was extracted and expression of VCAM1 and ICAM1 was assessed using qRT‐PCR. Samples were run in Changes in gene expression were calculated using the ΔΔ‐CT method, using GAPDH as the normalizing control gene. One‐way ANOVA was used to asses statistically significant differences (p < 0.05) using Prism version 8 (Graphpad).ResultsThe mRNA expression of VCAM1 and ICAM1 significantly increased (p <0.01). 6 and 8 folds respectively after exposure to low‐intensity ESS. Furthermore, high‐intensity ESS did not significantly increased the expression of VCAM1 and ICAM1.ConclusionLow‐intensity pulsatile exercise‐induced shear stress improves endothelial function in‐vitro through the increase in adhesion molecule’s gene expression.

Effects of in Vitro Exercise‐Induced Endothelial Shear Stress on Oxidative Stress and Vasoconstriction Gene Expression

BackgroundSedentary lifestyle contributes to endothelial dysfunction through increasing oxidative stress and endothelin‐1, a potent vasoconstrictor that contributes to the pathogenesis of vascular disease. Exercise‐induced endothelial shear stress (ESS) elicits a mechanical stimulus leading to intracellular signaling transduction regulating cellular function that might protect against endothelial dysfunction through promotion of the expression of anti‐oxidative and pro‐vasodilatory genes. Although it has been reported that increments on steady ESS has led to improvements in endothelial function in vivo, the role of pulsatile exercise induced ESS and varying exercise intensities in vitro has not been explored yet. Therefore, the purpose of this study was to determine the effects of pulsatile exercise‐induced ESS based on in vivo exercise intensity on anti‐oxidative (superoxide dismutase, SOD2) and vasoconstrictive (endothelin 1, EDN‐1) gene expression.MethodsCommercially available human carotid artery endothelial cells (Sigma‐Aldrich Comp.) were cultured until 95–100% confluence and exposed to pulsatile resting ESS (18 dynes/cm2) for 5 hours, followed by 1 hour at resting ESS, low‐intensity exercise‐induced ESS (35 dynes/cm2), or high‐intensity exercise‐induced ESS (80 dynes/cm2) on parallel fluidic units (Ibidi USA, Inc.). Ibidi pump software (PumpControl Software 1.5.4) was used to control shear stress intensity. Total RNA was extracted and reverse transcribed followed by measurement of EDN‐1 and SOD2 mRNA expression via qRT‐PCR. qRT‐PCRs were performed in duplicates and changes in gene expression were calculated using the ΔΔ‐CT method with GAPDH used as the normalizing control gene. Statistical analysis was performed using graphpad prism 8 software (Graphpad Software.). Significance was considered at p<0.05.ResultsmRNA expression of SOD2 increased 2.5‐fold after exposure to low‐intensity exercise‐induced ESS (p<0.05). EDN‐1 showed a 5‐fold increase following exposure to low‐intensity exercise‐induced ESS (p<0.05) in comparison to resting conditions. High‐intensity pulsatile exercise‐induced ESS decreased the expression of EDN‐1 in comparison to resting and low‐intensity conditions (p<0.05).ConclusionPulsatile exercise‐induced ESS improved anti‐oxidative properties in human carotid artery endothelial cells. It seems that higher exercise intensities are required to downregulate the expression of vasoconstrictive genes.

Hydrodynamic characterization within a spinner flask and a rotary wall vessel for stem cell culture

Stirred suspension culture is becoming a popular method for expanding human pluripotent stem cells (hPSCs). While stirring generates adequate fluid motions to lift the cells and facilitates mass transfers (of nutrients, dissolved gases, and metabolic wastes), excessive stirring could impose hydrodynamic forces deleterious for the growth of the cells. In this study, computational fluid dynamics (CFD) simulations were performed to first investigate hydrodynamic characteristics of fluid flows in a spinner flask, a common stirred suspension culture vessel used in laboratories. Flow patterns and distributions of shear stresses and the Kolmogorov length scales at varying impeller speeds were obtained. Comparison of the Kolmogorov length scales and sizes of hPSC aggregates, measured in the authors’ previous experimental study, showed a strong correlation between the two. In addition to the spinner flask which generated complex and transient turbulent flows, this study investigated a newly developed rotary wall vessel that had been designed to produce laminar, circular Couette flows in order to control shear stress. CFD simulations revealed significantly more uniform and homogeneous flows compared to those in the spinner flask, suggesting that the rotary wall vessel is a suitable culture vessel to investigate roles of shear stress on hPSCs in suspension.