Shear Stress Forces Research Articles

Engineering anisotropic tissue analogues: harnessing synergistic potential of extrusion-based bioprinting and extracellular matrix-based bioink

In the realm of tissue engineering, replicating the intricate alignment of cells and the extracellular matrix (ECM) found in native tissue has long been a challenge. Most recent studies have relied on complex multi-step processes to approximate native tissue alignment. To address this challenge, we introduce a novel, single-step method for constructing highly aligned fibrous structures within multi-modular three-dimensional conglomerates. Our approach harnesses the synergistic potential of extrusion-based bioprinting and the fibrillogenesis kinetics of collagen-rich decellularized ECM. We have identified three key parameters governing ECM microfiber alignment during extrusion-based bioprinting: applied shear stress, stretching or extensional force, and post-print deformation. By carefully manipulating these parameters, we have successfully created highly aligned fibrous structures within multi-modular three-dimensional conglomerates. Our technique offers an efficient solution and has been validated by computational modeling. Comprehensive analyses confirm the efficacy across various scenarios, including encapsulated, top-seeded, and migratory cells. Notably, we have demonstrated the versatility and effectiveness of our approach by bioprinting highly aligned cardiac tissue patches, which show further maturation evidenced by the expression of Troponin-T and Myo-D differentiation factor needed for contractility and myotube formation, respectively. In summary, our streamlined approach offers a robust solution for creating anisotropic tissue analogues with precise ECM organization.

Comparison of Biomechanical Properties of the iCover and VBX Stent Grafts When Used as Bridge Stents in Fenestrated Endografts: An In Vitro Study.

The objective of this study was to compare in vitro the different biomechanical properties of 2 balloon-expandable covered stents, VBX (Viabahn VBX, W.L. Gore & Associates, Flagstaff, AZ) and iCover (iVascular, Barcelona, Spain), as bridging stents in fenestrated aortic endoprostheses. Three biomechanical tests were performed to evaluate a total of 12 stents (6 VBX 6 × 59 mm and 6 iCover 6 × 57m). First, a 3-point bending test was performed with a calibrated dynamometer to evaluate the bending strength of the 40% and 150% deformation of the system in its crimped state and the force necessary to deform the expanded stent by 40% with respect to its initial diameter. Then the stents were expanded to their nominal diameter inside a 6-mm-diameter handmade fenestration and flared up to 8 and 10 mm. The whole set was fixed in the dynamometer to carry out the pullout-force (perpendicular dislocation) and shear-stress-force (axial dislocation) tests. The resulting forces were recorded via the force transducer. Load, deformation, and displacement data were recorded in newtons. The results of each stent test were examined under the microscope, and both stent types were compared. Higher forces were required to bend the crimped VBX (16.24 N [IQR, 13.87-17.47 N] for the iCover and 19.01 N [IQR, 16.01-19.50 N] for VBX; P < 0.001), but lower forces were necessary for the expanded VBX compared with the iCover (0.36 N [IQR, 0.1-0.49 N] and 1.01 N [IQR, 0.97-1.09 N], respectively; p = 0.004). Pullout forces were 3.56 N (IQR, 3-4.1 N) and 7.07 N (IQR, 6.86-7.28 N) for the 8-mm flare and 7.29 N (IQR, 6.13-8.45 N) and 14 N (IQR, 12.05-15.95 N) for the 10-mm flare for the iCover and VBX, respectively (P = 0.333 for both comparisons). The shear-stress forces needed to dislocate the 6-mm iCover and VBX axially with a 10-mm flare to 50%, 100%, and 200% were 0.88, 1.61, and 3.55 N for the iCover and 0.71, 1.43, and 2.51 N for the VBX (P = 0.343, P = 0.486, and P = 0.486, respectively). After evaluating the stents under in vitro conditions, the VBX and iCover stents showed similar results in terms of biomechanical properties, which demonstrates their competence in in vitro conditions. Further in vitro comparisons with other stent grafts are required. The BECS used in FEVAR / BEVAR must ensure some properties to avoid the most frequent complications derived from the failure of these bridging stents (stenosis, thrombosis, stent integrity, dislodgement or endoleaks) that represent the most common cause for reintervention. This paper adds to the limited data available, information to the clinician after comparing some properties of two BECS used in these techniques that demonstrate their competence in in-vitro conditions.

Numerical Flow Simulations of the Shear Stress Forces Arising in Filtration Slits during Glomerular Filtration in Rat Kidney.

The flow dynamic forces during glomerular filtration challenging the fixation of podocytes to the GBM are insufficiently understood. Numerical flow simulations were used to estimate these forces in the rat kidney. Simulations were run with a 3D model of the slit diaphragm as a zipper structure according to Rodewald and Karnovsky 1. The GBM was modeled as a porous medium. Filtrate flow exerted a mean wall shear stress of 39 Pa with a maximum of 152 Pa on the plasma membrane of foot processes and up to 250 Pa on internal surfaces of the slit diaphragm. The slit diaphragm accounted for 25% of the hydrodynamic resistance of the glomerular filtration barrier. Based on the results of the 3D model, we developed a 2D model that allowed us to perform extensive parameter variations. Reducing the filtration slit width from 40 to 30 nm almost doubled wall shear stress. Furthermore, increasing filtrate flow velocity by 50% increased wall shear stress by 47%. When increasing the viscous resistance of the slit diaphragm, the pressure drop across the slit diaphragm increased to intolerably high values. A lower viscous resistance of the slit diaphragm than that of the GBM accounted for a gradual pressure decline along the filtration barrier. The sub-podocyte space tempered these challenges in circumscribed areas of filtration surface but had only a marginal impact on overall forces. The filtration barrier experiences high levels of shear and pressure stress accounting for the detachment of injured but viable podocytes from the GBM--a hallmark in many glomerular diseases.

The Effect of Lower Limb Pressotherapy Treatment on Selected Rheological and Biochemical Indices of Blood in Young, Healthy Women.

Background: Intermittent pneumatic compression is a non-invasive therapeutic technique that has been gaining popularity in recent years due to its potential use in many areas of medicine. It can be successfully used alone or in combination with other therapeutic methods. The aim of this study was to investigate whether and how a series of pressotherapy treatments on the lower limbs affects the rheological properties of blood (blood count, red blood cell deformability and aggregation, and blood viscosity), lipid profile (total cholesterol, triglycerides, low-density lipoprotein, and high-density lipoprotein), and renal profile (urea, creatinine, and estimated glomerular filtration rate) in young, healthy women. Methods: The study group consisted of 15 healthy women aged 20-26 (22.5 ± 1.5), without chronic diseases and not practicing competitive sports. The participants underwent a series of 10 lower limb pressotherapy treatments. A single treatment lasted 30 min and each time the pressure used during the treatment was individually selected according to the participants' preference. The first blood test was performed a week before the treatments; the second on the day of the start of treatment, but before the pneumatic massage; the third after the completed series of pressotherapy treatments; and the fourth a week after the completed series of treatments. Results: In the conducted study, the analysis of the values of the complete blood count showed the following: a significant decrease in red blood cell count, hemoglobin, average hemoglobin concentration in erythrocytes, average red blood cell volume, average hemoglobin mass in red blood cells; a significant increase in average red blood cell volume; and an average hemoglobin mass in red blood cells. The analysis of the values of rheological parameters showed the following: a significant decrease in elongation indices 0.58, 1.13, 4.24, 15.95, 30.94, and 60.00; blood viscosity; the aggregation index; the degree of complete aggregation; and a significant increase in elongation indices 0.30, 1.13, 8.23, 30.94, 60.00; blood viscosity; the degree of complete aggregation; and the half-time of complete aggregation. A decrease in the concentration of low-density lipoprotein and high-density lipoprotein fractions was also noted. No significant changes were found in the values of total cholesterol and triglycerides, as well as in renal profile elements. Conclusions: The application of a series of 10 lower limb pressotherapy treatments has a beneficial effect, with a decrease in blood viscosity and the aggregation index, and an increase in the elongation index at shear stress from 0.30 [Pa] to 8.23 [Pa] in young, healthy women. A series of 10 lower limb pressotherapy treatments may affect the decrease in the values at high shear stress forces of 30.95 [Pa] and from 60.00 [Pa] in young, healthy women. The use of a series of 10 lower limb pressotherapy treatments increases the values of hemoglobin, the average red blood cell volume, and the average hemoglobin concentration in erythrocytes, and also reduces the values of red blood cell count, average hemoglobin mass in red blood cells and low-density lipoproteins and high-density lipoproteins in young, healthy women (it also does not cause any adverse changes). The use of pressotherapy on the lower limbs seems to be an effective element of the multi-component prevention of circulatory system diseases.

Grouting sleeve/bird’s nest anchor cable anchoring capacity characteristics and numerical simulation study

With the deepening of coal mining resources, the safety issues of broken soft coal seams become increasingly prominent, severely affecting the safety of deep mining operations and workers. Traditional anchoring methods alone are ineffective in achieving secure anchorage. Therefore, the grouting anchor cable composite structure is explored to address the safety of roadway excavation in deep broken soft coal seams. Indoor grouting anchorage tests and pull-out tests for grouted anchorages are conducted to study their bearing characteristics and failure mechanisms. Discrete element numerical simulation methods are employed to verify the findings from indoor tests. Research indicates that the ultimate pull-out forces at grouting pressures of 0.5, 1.0, 1.5, and 2.0 MPa are 87, 104, 118, and 131 kN, respectively. The pull-out force of the grouted anchorage is positively correlated with the grouting pressure. At the loading end, shear stress and axial force reach their maximum values of 1.8 MPa and 106 kN, respectively, under 2.0 MPa grouting pressure. The distribution patterns of shear stress and axial force decrease gradually with increasing anchoring depth. Microscopic analysis reveals that the failure of the anchor body model is primarily due to the tensile cracks formed by the particle flow code in two dimensions. This finding is consistent with the failure mode observed in indoor tests, which involves the slip and debonding failure of the anchor cable. Crack evolution is categorized into three stages: initiation, continuous propagation, and anchor failure. As the inter-particle contact forces within the anchor body model decrease, the region of chain fracture expands. These results provide technical support for understanding the bearing characteristics of grouting anchor cable composite structures.

Dynamic cellular responses to gravitational forces: Exploring the impact on white blood cell(s).

In recent years, the allure of space exploration and human spaceflight has surged, yet the effects of microgravity on the human body remain a significant concern. Immune and red blood cells rely on hematic or lymphatic streams as their primary means of transportation, posing notable challenges under microgravity conditions. This study sheds light on the intricate dynamics of cell behavior when suspended in bio-fluid under varying gravitational forces. Utilizing the dissipative particle dynamics approach, blood and white blood cells were modeled, with gravity applied as an external force along the vertical axis, ranging from 0 to 2 g in parameter sweeps. The results revealed discernible alterations in the cell shape and spatial alignment in response to gravity, quantified through metrics such as elongation and deformation indices, pitch angle, and normalized center of mass. Statistical analysis using the Mann-Whitney U test underscored clear distinctions between microgravity (<1 g) and hypergravity (>1 g) samples compared to normal gravity (1 g). Furthermore, the examination of forces exerted on the solid, including drag, shear stress, and solid forces, unveiled a reduction in the magnitude as the gravitational force increased. Additional analysis through dimensionless numbers unveiled the dominance of capillary and gravitational forces, which impacted cell velocity, leading to closer proximity to the wall and heightened viscous interaction with surrounding fluid particles. These interactions prompted shape alterations and reduced white blood cell area while increasing red blood cells. This study represents an effort in comprehending the effects of gravity on blood cells, offering insights into the intricate interplay between cellular dynamics and gravitational forces.

C-Src-induced vascular malformations require localised matrix degradation at focal adhesions.

Endothelial cells lining the blood vessel wall communicate intricately with the surrounding extracellular matrix, translating mechanical cues into biochemical signals. Moreover, vessels require the capability to enzymatically degrade the matrix surrounding them, to facilitate vascular expansion. c-Src plays a key role in blood vessel growth, with its loss in the endothelium reducing vessel sprouting and focal adhesion signalling. Here, we show that constitutive activation of c-Src in endothelial cells results in rapid vascular expansion, operating independently of growth factor stimulation or fluid shear stress forces. This is driven by an increase in focal adhesion signalling and size, with enhancement of localised secretion of matrix metalloproteinases responsible for extracellular matrix remodelling. Inhibition of matrix metalloproteinase activity results in a robust rescue of the vascular expansion elicited by heightened c-Src activity. This supports the premise that moderating focal adhesion-related events and matrix degradation can counteract abnormal vascular expansion, with implications for pathologies driven by unusual vascular morphologies.

Bearing Capacity Characteristic Analysis of Anti-floating Bolts in Unsaturated Soil Based on Mindlin Solution

AbstractBased on Mindlin solution and the theory of unsaturated soil mechanics, the theoretical solutions of shear stress and axial force distribution in the elastic stage of full-length binding-type anti-floating bolts were derived, and the bearing capacity characteristics of such bolts and the influencing factors were analyzed. In this paper, the design parameters of anti-floating anchor in a negative two-floor basement of a commercial square are substituted into the formula derived in this paper. The results show that, in unsaturated soil, the shear stress and axial force of the full-length bonded anti-floating anchor are distributed along the total length of the anchor, but neutral points appear in both of them, which is mainly due to the reduction of the axial force and shear stress of the anti-floating anchor caused by the matric suction. The formula derived in this paper is used to analyze the factors affecting the bearing capacity of anti-floating anchor bolt in unsaturated soil. The results show that: the greater the elastic modulus of soil mass, the greater the peak value of shear stress curve, the closer the peak value is to the head of anchor bolt, and the greater the axial force decline rate. With the increase of anchor solid diameter D, the peak value of shear stress decreases, the peak value moves backward, the neutral point moves forward, the negative shear stress value increases, the decline rate of axial force distribution curve decreases, but the negative axial force increases. With the increase of the additional shear stress τ0, the peak value of the shear stress curve decreases, the peak value moves to the hole of the anchor rod, the neutral point moves to the hole, the negative shear stress increases, the decline rate of the axial force distribution curve increases, and the negative axial force increases.

Epigenetic changes in shear-stressed endothelial cells.

Epigenetic changes, particularly histone compaction modifications, have emerged as critical regulators in the epigenetic pathway driving endothelial cell phenotype under constant exposure to laminar forces induced by blood flow. However, the underlying epigenetic mechanisms governing endothelial cell behavior in this context remain poorly understood. To address this knowledge gap, we conducted in vitro experiments using human umbilical vein endothelial cells subjected to various tensional forces simulating pathophysiological blood flow shear stress conditions, ranging from normotensive to hypertensive forces. Our study uncovers a noteworthy observation wherein endothelial cells exposed to high shear stress demonstrate a decrease in the epigenetic marks H3K4ac and H3K27ac, accompanied by significant alterations in the levels of HDAC (histone deacetylase) proteins. Moreover, we demonstrate a negative regulatory effect of increased shear stress on HOXA13 gene expression and a concomitant increase in the expression of the long noncoding RNA, HOTTIP, suggesting a direct association with the suppression of HOXA13. Collectively, these findings represent the first evidence of the role of histone-related epigenetic modifications in modulating chromatin compaction during mechanosignaling of endothelial cells in response to elevated shear stress forces. Additionally, our results highlight the importance of understanding the physiological role of HOXA13 in vascular biology and hypertensive patients, emphasizing the potential for developing small molecules to modulate its activity. These findings warrant further preclinical investigations and open new avenues for therapeutic interventions targeting epigenetic mechanisms in hypertensive conditions.

On the Extension-Torsion of Short Hyperelastic Tubes of Axially Functionally-Graded Materials

The mechanical behavior of thick-walled tubes made of axially functionally graded (FG) incompressible nonlinear elastic materials under combined extension-torsion loading is focused on in this study. To achieve more realistic modeling, a computation-efficient semi-analytical approach is proposed, which is subsequently validated through finite element simulations. Axially functional grading is addressed by considering finite length instead of the commonly assumed infinite length. Additionally, a comparative study is conducted to examine twelve different functional grading distributions based on silicon-rubber Neo-Hookean material constant. 3D numerical simulations are outperformed by our approach by up to 50 times in computational efficiency under identical hardware conditions. The results indicate the model's capability to evaluate the non-linear distribution of twisting along the length, also stress analysis suggests that decreased shear stress variation, reaction torque, and force can be achieved by increasing the material gradient in larger than one composition ratio. Overall, valuable insights for engineers are provided by our approach, ensuring structural integrity and safe operation of functionally graded cylindrical components in various engineering applications.

Anti-sedimentation mechanism of rotary magnetorheological brake integrating multi-helix microstructure

Solving the sedimentation problem of magnetorheological (MR) fluids is the key to promoting the application of MR actuators for long-term storage. Current strategies for mitigating MR fluid sedimentation focus on improving the material constitution of MR fluids. However, the sedimentation is bound to emerge over time as a result of the density mismatch between carbonyl iron particles and carrier liquids. Therefore, more robust approach to solve the particle sedimentation should be considered, such as improving the robustness of the MR actuator. This paper proposes a novel anti-sedimentation MR brake (AS-MRB) that integrates a multi-helix microstructure on the shaft surface. The protrusion-shaped multi-helix microstructure applied a combination of shear stress, pressure, friction, and centrifugal force to MR fluids. Therefore, the AS-MRB can autonomously alter the internal flow state, thus performing the self-homogenization of sedimented particles. Remarkably, vortexes with axis displacement were generated in the MR working gap during the self-homogenization process. This phenomenon facilitated the mass transfer between different fluid layers, as confirmed by the speed reduction and torque test. To accurately describe the real-time rotational speed of the AS-MRB, an impact-introduced dynamic model of the shaft was also proposed. An inductance sensor-based test system was developed to characterize the volume fraction of the particle instantaneously, which is directly pertinent to the evaluation of the anti-sedimentation performance. Severely sedimented MR fluids were introduced into the AS-MRB for the performance evaluation in harsh conditions. The results show that the maximum volume fraction difference Δφmax of the sedimented MR fluid was decreased from 54.02 % to 2.46 % after the homogenization. The maximum shear stress τmax of the sedimented MR fluid was increased from 11.78 % to 80.7 % of that of the initial MR fluid. These demonstrate the strong anti-sedimentation performance of the AS-MRB. Consequently, this study has developed a unique method for solving the sedimentation problem of MR fluids and creates avenues for promoting the application of MR actuators in long-term storage.

Blood Flow Directs Yap/Taz-Mediated Transcriptional Regulation of Self-Renewal Programs to Control Developmental HSPC Expansion By Mechanical Stimulation of Piezo1

Hematopoietic stem and progenitor cells (HSPCs) emerge from artery-derived hemogenic endothelium (HE) in the vertebrate embryo during development. This process entails a cellular reprogramming from endothelial to hematopoietic gene signatures driven by the Runx1 transcription factor (TF), which is referred to as the endothelial-to-hematopoietic transition (EHT). A major goal of cellular therapeutics is to derive patient-specific HSPCs from iPSCs for clinical use, yet current differentiation protocols largely fail to recapitulate EHT to produce or expand long-lived multi-potent HSPCs in vitro suggesting an incomplete understanding of the in vivo regulatory cues. Physical forces of wall shear stress (WSS) and cyclic stretch (CS) produced by hemodynamic blood flow in embryos are one such cue required during EHT to generate HSPCs from HE, however the mechanisms by which these forces are sensed and converted into a “stemness” regulatory module remain undefined. Our previous work implicated the Hippo pathway TF YAP as essential for the maintenance, but not initiation, of the hematopoietic program in newly specified HE. Here, using scRNA-sequencing of sorted zebrafish trunk endothelial cells to capture all stages of EHT progression, we find that overexpression of YAP drives lipid metabolism, cell cycling, and propagation of a hematopoietic gene regulatory network (GRN) in the earliest specified HE cells. By employing a heat shock-inducible dominant negative YAP zebrafish line, we unmask a latent role for the YAP paralogue TAZ in hematopoiesis, which can promote CD41 + and Flk +/Myb + HSPC production upon reduced YAP function. YAP and TAZ initiate transcriptional responses downstream of mechanical stimuli and require DNA binding cofactors to regulate target genes. Surprisingly, luciferase assays in HEK293 cells demonstrated a potent synergistic effect of TAZ/RUNX1, but not YAP/RUNX1, in transcriptional regulation at RUNX enhancers. Finally, by pharmacologic and genetic manipulation, we identify the stretch-gated membrane ion channel Piezo1 as a potent regulator of CS-induced YAP/TAZ mechanotransduction in HE. Stimulation of zebrafish embryos with the Piezo1 small molecule agonist Yoda1 significantly increases HSPC number and YAP target gene expression in a YAP-dependent fashion. A similar modulation of blood and YAP target genes in human iPSC-derived CD34+ HE cells is seen with Yoda1, suggesting that this stretch-Piezo1-YAP axis can be chemically tuned in vitro to enhance HSPC differentiation. These results illuminate molecular details of how YAP/TAZ directs the production of HSPCs from HE in response to mechanical cues, and have broader implications for alternate regulatory effects of mechanically-stimulated Hippo TFs depending on the transcriptional milieu in cell-type specific contexts.

Boundary shear stress and apparent shear forces in compound channels with different floodplain widths

ABSTRACT The present study has studied a model to predict depth-averaged velocity distribution and boundary shear stress in compound channels with different floodplain widths. The model was verified against three different data sets of the present experiments and two data used in the literature. The results indicate that the present model can predict the depth-averaged velocity and shear stress distributions, promising to simulate the flow field and related characteristics better. The results show that the non-dimensional coefficient plays a dominant role in portraying the variation of depth-averaged velocity and shear stress distributions in compound channels with different floodplain widths. In addition, the apparent shear forces were examined by dividing the channel cross-section into seven parts, and each element carried shear forces and acted on the horizontal and vertical interfaces for three different width-to-depth ratios were discussed and analyzed. In all configurations, the horizontal interface was negative, indicating that the upper region of flow accelerates the flow in the lower main channel. In contrast, the vertical interfaces were positive, suggesting that the slower floodplain flows retards the faster main channel flows.

Study on lubrication performance of engine piston skirt with bionic design

As the main friction pair of engine, the friction loss of piston-cylinder liner assembly in the working process has become the main reason of engine friction power consumption. Many species in the biological world have formed non-smooth forms of resistance reduction after thousands of years of survival and evolution. Many people have applied this non-smooth shape of drag reduction on organisms to the surface of friction pairs in construction machinery. Based on LX108 engine, the wear and erosion resistance of Scapharca subcrenata surface is applied to the piston skirt, which is the main friction pair in the engine. Nine test schemes were designed according to orthogonal test. This design selects three factors, namely, groove distribution type, groove depth and width, groove spacing, and each factor includes three levels. The macroscopic fluid lubrication state of the whole piston skirt with bionic shape is studied. Through the change of oil film thickness caused by thermal-mechanical coupling deformation of skirt, combined with the average Reynolds equation, the hydrodynamic pressure of lubricating oil, shear stress, and skirt friction force are obtained to verify the contribution of bionic shape to piston drag reduction, wear reduction, wetting increase, and friction power consumption. The simulation and test results show that the lubrication of all parts of the bionic groove piston skirt is better than that of the standard piston; When the depth and width of groove is 0.8 mm and the spacing is 10°, the thicker the oil film thickness of skirt is; The bionic piston whose oil film bearing area is 74%–87% of the standard piston has the smallest normal pressure and friction; When the upper end of the skirt is arranged with groove shape and the lower end is arranged with narrow groove shape between wide grooves, the lubrication effect is better.

Numerical investigation of heat and mass transfer of the Sisko fluid in a wire-coating process with variable fluid properties

The fundamental and essential objective of the wire coating process is to reduce the shear stress and extraction force exerted on the wire from the die in order to achieve practical benefits. Therefore, the purpose of the present work is to develop a mathematical model for the wire coating process withdrawal of the wire from the die. The Sisko fluid model and the temperature-dependent thermophysical properties are taken into consideration for modelling the constitutive equation. The basic equations governing the flow are solved with the aid of the numerical method. The impact of key factors is scrutinized. The influence of shear stress on the surface of the wire and fluid flow rate are delineated. The linear regression model is formulated to explore the significance of the relationship between the amount of force required to pull the wire and flow control variables. Moreover, the heat transfer rate and shear stress rate of molten polymer are modeled using quadratic correlation models obtained through the Central Composite Design (CCD) technique. To simultaneously achieve maximum heat transfer rate and minimum shear stress rate for the melt, the ideal values of the variable viscosity parameter, Sisko fluid parameter, and Brinkman number are determined. The study reveals that the required result occurs for a low level of the variable viscosity parameter, Sisko fluid parameter, and the Brinkman number. Additionally, a sensitivity analysis has been performed. The result reveals that the shear stress rate and heat transfer rate exhibit the highest sensitivity to variations in the viscosity parameter.

Visualization research of energy dissipation in a pump turbine unit during turbine mode's starting up

Identifying the precise location of flow energy dissipation (FED) in pump turbines is crucial for enhancing the stability of pumped storage power stations. In this study, the transient process of the turbine mode's starting up in the pump-turbine has been simulated to examine the FED locations by using the one-dimensional and three-dimensional (1D-3D) coupled computational fluid dynamics (CFD) method. This analysis pinpoints high FED locations in each component of the pump-turbine. The observations reveals that the trailing edge of the guide vane consistently demonstrates high FED values, while wall shear stress, axial and radial forces had a significant effect on flow characteristics. Moreover, high FED sites correspond to high turbulence kinetic energy locations. Continuous wavelet transform (CWT) has been applied to examine the time-frequency characteristics during this process. Low frequency (fc = 0.12) has been identified as the dominant frequency in the volute. In the draft tube, the wavelet magnitude of the double blade passing frequency (fc = 18) is 30.4% of that under the dominant frequency (fc = 9). Regional visualization of FED offers a valuable method for the in-depth understanding of energy dissipation in pump turbines and improving operational stability in pumped storage power stations.

Image-based flow simulation of platelet aggregates under different shear rates.

Hemodynamics is crucial for the activation and aggregation of platelets in response to flow-induced shear. In this paper, a novel image-based computational model simulating blood flow through and around platelet aggregates is presented. The microstructure of aggregates was captured by two different modalities of microscopy images of in vitro whole blood perfusion experiments in microfluidic chambers coated with collagen. One set of images captured the geometry of the aggregate outline, while the other employed platelet labelling to infer the internal density. The platelet aggregates were modelled as a porous medium, the permeability of which was calculated with the Kozeny-Carman equation. The computational model was subsequently applied to study hemodynamics inside and around the platelet aggregates. The blood flow velocity, shear stress and kinetic force exerted on the aggregates were investigated and compared under 800 s-1, 1600 s-1 and 4000 s-1 wall shear rates. The advection-diffusion balance of agonist transport inside the platelet aggregates was also evaluated by local Péclet number. The findings show that the transport of agonists is not only affected by the shear rate but also significantly influenced by the microstructure of the aggregates. Moreover, large kinetic forces were found at the transition zone from shell to core of the aggregates, which could contribute to identifying the boundary between the shell and the core. The shear rate and the rate of elongation flow were investigated as well. The results imply that the emerging shapes of aggregates are highly correlated to the shear rate and the rate of elongation. The framework provides a way to incorporate the internal microstructure of the aggregates into the computational model and yields a better understanding of the hemodynamics and physiology of platelet aggregates, hence laying the foundation for predicting aggregation and deformation under different flow conditions.

Extracellular ATP-induced calcium oscillations regulating the differentiation of osteoblasts through aerobic oxidation metabolism pathways.

The increase of ATP concentration in the extracellular space represents one of the effective signals that stimulate the physiological activities of cells when the bone is exposed to external mechanical stimulation such as stretching and shear stress force throughout life. However, the effects of ATP on osteoblast differentiation and related mechanisms are not well understood. In this study, the roles of extracellular ATP on osteoblast differentiation, intracellular calcium ([Ca2+]i) levels, metabolomics, and the expression of proteins related to energy metabolism were investigated. Our results showed that 100μM extracellular ATP initiated intracellular calcium ([Ca2+]i) oscillations via the calcium-sensing receptor (P2R) and promoted the differentiation of MC3T3-E1 cells. Metabolomics analysis showed that the differentiation of MC3T3-E1 cells depended on aerobic oxidation, but little glycolysis. Moreover, the differentiation of MC3T3-E1 cells and aerobic oxidation were suppressed with the inhibition of AMP-activated protein kinase (AMPK). These results indicate that calcium oscillations triggered by extracellular ATP can activate aerobic oxidation through AMPK-related signaling pathways and thus promote osteoblast differentiation.

Missing links in preeclampsia cell model systems of endothelial dysfunction

Preeclampsia, one of the main hypertensive disorders of pregnancy, is associated with circulating factors released by the ischemic placenta accompanied by systemic endothelial dysfunction. The etiology of preeclampsia remains poorly understood although it is associated with high maternal and fetal mortality and increased cardiovascular disease risk. Most cell model systems used for studying endothelial dysfunction have not taken into account hemodynamic physical factors such as shear-stress forces which may prevent extrapolation of cell data to in vivo settings. We overview the role of hemodynamic forces in modulating endothelial cell function and discuss strategies to reproduce this biological characteristic in vitro to improve our understanding of endothelial dysfunction associated with preeclampsia.

Computational fluid dynamics simulations of mitral paravalvular leaks in the human heart

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Warsaw University of Technology - BIOTECHMED-3 project under the program Excellence Initiative: Research University. Background Presence of paravalvular leaks (PVL) can lead to hemolysis and high shear stress that affects erythrocytes passing through PVL channels may be the main reason behind this pathology. In vitro, shear stress forces above 300 Pa cause erythrocyte destruction. Distribution of shear stress can currently be precisely determined with computational fluid dynamics (CFD). CFD is a numerical modelling method based on solving equations of differential balance of mass, momentum and energy for a small section of fluid known as a computational cell. Purpose To investigate the magnitude of shear stress forces that affect erythrocytes in PVL channels and define properties of PVL channels that increase the likelihood of hemolysis. Methods Models of left-sided heart chambers with artificial mitral valves and PVLs were created based on cardiac computed tomography data from subjects with PVLs. Computational fluid dynamics principles were applied to create patterns of blood flow through PVL channels. 4 channels with cross-sectional areas (CSA) of 26.2 mm2 (model I), 15.7 mm2 (model 2), 20.4 mm2 (model 3) and 32 mm2 (model 4) were examined. Length of PVL channels was 6.5, 9.5, 7.3 and 3.25 mm respectively. In models I,III and IV the PVL channel was located anteriorly around the mitral annulus, whereas in model II a posterior location was described. Blood flow was simulated using a commercial CFD software (ANSYS Fluent 2020R1). Simulations were performed for heart rate of 60 beats per minute. The following variables were examined regarding blood flow through PVL channels: wall shear stress, shear stress in fluid, volume of PVL channels in which shear stress exceeded 300 Pa and duration of exposure of red blood cells to shear stress above 300 Pa. Obtained values were compared with lactate dehydrogenase (LDH) activities in subjects whose cardiac CTs were used to create PVL models. One of the models of the left ventricle is presented in picture 1. Studied PVL channels are presented in picture 2. Results In all models shear stress value of 300 Pa was exceeded. Maximal wall shear stress and maximal shear stress in fluid values were not related to CSA of the PVL channel. Lowest values of all examined variables were obtained for model 2, which had the longest PVL channel and a posterior location. The lowest LDH activity was noted in model with the lowest volume of the PVL channel with shear stress above 300 Pa (model 2) and the highest LDH activity in model with both the highest volume of the PVL channel with shear stress above 300 Pa and longest exposure to shear stress exceeding 300 Pa (model III). Conclusions Presence of PVLs is always accompanied by some degree of hemolysis. Shear stress values in PVL channels are not related to CSA of these channels. Volume of PVL channels in which shear stress exceeds 300 Pa and duration of exposure of erythrocytes to shear stress above 300 Pa may influence the severity of hemolysis.