Shear Stress Values Research Articles

Жидкокристаллическая визуализация при изучении течения в мелкой каверне

Using the example of a flow around a shallow cavity, the possibilities of liquid-crystal visualization at subsonic and supersonic flow velocities are demonstrated. To determine the flow structure at the bottom of the cavity, a coating based on a composition of pure cholesteric liquid crystals (ChLC) was used. To determine the distribution of temperatures and heat fluxes, thermosensitive films formed by encapsulation of ChLC in a polymer matrix were used. Based on the experimental results, the influence of the Mach number on the spatial pattern of the flow inside the cavity and the temperature distribution at the bottom of the cavity was obtained. The pattern of surface streamlines obtained by the LC coating coincides with that obtained using the oil film visualization. In this case, the LC method makes it possible to compare the values of shear stresses in different parts of the surface also. It is found that the occurrence of resonance phenomena leads to restructuring of the flow inside the cavity and a change in the values of shear stresses. It is shown, that in subsonic flow around the zone of increased heat transfer is concentrated near the axis of symmetry of the cavity.

Resolution-based comparative analysis of 4D-phase-contrast magnetic resonance images and hemodynamic simulations of the aortic arch

Abstract Introduction: In this study, phase-contrast magnetic resonance imaging (PC-MRI) 4D flow data for patients with bicuspid aortic valve (BAV) were analyzed based on the spatial resolution of the images. BAV is a congenital heart defect characterized by the presence of two cusps in the aortic valve, leading to various complications. PC-MRI is a noninvasive imaging technique used to assess the hemodynamics in patients. However, interpretation of PC-MRI data can be challenging due to complex hemodynamics, which makes numerical simulations necessary to complement the results. Methods:Within this study PC-MRI 4D flow data in the aortic arch (AA) were compared with hemodynamic numerical simulations based on the MRI resolution for six patient-specific AAs with BAV. First, the segmentations were reconstructed and divided into three groups based on the resolution. Second, the numerical simulations were performed and resulting hemodynamics compared to PC-MRI results at three time points in the cardiac cycle using velocity and wall shear stress. Results: Results from group 1 (highest resolution) show an overestimation of wall shear stress (WSS) values during peaksystole in the three arteries and along the AA and descending aorta (DAo). Nevertheless, velocity mean values show an overall good agreement. Group 2 shows higher velocity magnitudes in the simulation than in PC-MRI. Within group 3, velocity values differ from the measurements. Conclusion: The study shows that with a low resolution, flow patterns can already be evaluated based on PC-MRI, but to get an insight into the flow quantitatively a higher resolution is necessary.

Evaluating uncertainties in CFD simulations of patient-specific aorta models using Grid Convergence Index method

Cardiovascular diseases are among the most important causes of global mortality. Computational Fluid Dynamics (CFD) is a powerful research tool that analyzes the hemodynamics of artery and blood flow patterns. In this study, CFD simulations are performed to assess the patient-specific healthy aorta, fusiform, and saccular aneurysm with various mesh types, including tetrahedral, polyhedral, and poly-hexacore. The aim of this study is to explore how different mesh types and grid densities impact the hemodynamic properties of physiological flows, with the goal of identifying the most cost-effective meshing approach. A mesh independence study is carried out to ensure the precision of the results, considering the wall shear stress distribution. For this, five different mesh resolutions are generated for each geometry. The uncertainties of the simulations associated with the discretization techniques and solutions are evaluated using the Grid Convergence Index (GCI) method. The findings showed that increasing the mesh density provides smaller uncertainty. GCI values for the wall shear stress are in the range of convergence, indicating that the results are reliable and accurate. Mesh type selection affects the accuracy and computational cost of our simulations. The polyhedral and poly-hexacore meshes lead to a good compromise between precision and computational cost, while the tetrahedral mesh style gives the most precise results with fluctuation. This work provides a systematic approach based on the Grid Convergence Index method in order to select the most appropriate mesh type for evaluating uncertainties in CFD simulations of patient-specific healthy aortas and aortas with abdominal aneurysms. According to the findings and GCI analysis, the polyhedral mesh type was chosen for all patient-specific aorta models. The study clearly demonstrated its superiority over other mesh types, considering uncertainties and computational costs associated with different mesh styles.

Highlighting Hemodynamic Risks for Bioresorbable Stents in Coronary Arteries

A three-dimensional, transient computational fluid dynamics analysis was conducted on an idealised geometry of a coronary artery fitted with representative geometries of an Absorb bioresorbable vascular scaffold (BVS) or a Xience drug-eluting stent (DES) in order to identify and compare areas of disturbed flow and potential risk sites. A non-Newtonian viscosity model was used with a transient velocity boundary condition programmed with user-defined functions. At-risk areas were quantified in terms of several parameters linked to restenosis: wall shear stress, time-averaged wall shear stress, oscillatory shear index, particle residence time, and shear rate. Results indicated that 71% of the BVS stented surface area had time-averaged wall shear stress values under 0.4 Pa compared to 45% of the DES area. Additionally, high particle residence times were present in 23% and 8% of the BVS and DES areas, respectively, with risk areas identified as being more prominent in close proximity to crowns and link struts. These results suggest an increased risk for thrombosis and neointimal hyperplasia for the BVS compared to the DES, which is in agreement with the outcomes of clinical trials. It is intended that the results of this study may be used as a pre-clinical tool to aid in the design of bioresorbable coronary stents.

READY-TO-EAT CHICKPEA PURÉE POWDER BY DRUM DRYING; PHYSICOCHEMICAL AND RHEOLOGICAL PROPERTIES OF POWDER PRODUCT

This study aims to convert raw chickpea (Cicer arietinum L.) into dried chickpea puree powder form using a drum dryer having a high rehydration ratio and for ready-to-use consumption form maintaining its healthy properties. The effects of the drying conditions on the physical, chemical, and rheological properties of chickpea puree powders were investigated. Before drying, raw chickpeas were soaked in water at 25°C for 12 hours and boiled at 100°C for 55 minutes. In the drying process, saturated steam pressures (2, 3, and 4 bar) and drum rotation speeds (2.0, 3.0, 4.0, and 5.0 rpm) were chosen as process variables. The most appropriate process conditions were determined as 3 bar of steam pressure and 2 rpm of drum rotation speed targeting the maximum protein content (30.35±0.18%), maximum rehydration ratio (515±0.01%), and as low as possible browning index (BI)(59.28±4.90) values. It was determined that chickpea puree had the appropriate rheological characteristics when the shear stress and shear rate values for chickpea puree powders with various dry matter contents (%25, %26, %27.5, %30) produced under suitable process parameters were examined.

Numerical Validation of Low Reynolds Number Airfoil for Uav

Low Reynolds flow continues to get researchers attention for its relevance in a number of areas including the flight regimes of Micro Air Vehicle (MAV). The Laminar Separation Bubble (LSB) which is largely responsible for the non-linear aerodynamic characteristics have been studied both numerically and experimentally. In this work, a high fidelity computation was carried out to study LSB as well as the dependence of aerodynamic characteristics on a symmetrical thick airfoil at low Reynolds numbers. Flow structure in the bubble is clearly brought out with the appropriate selection of turbulence model in the solver. Also, the extent of LSB was well predicted by transition SST turbulence model in the solver. A novel approach has been made to obtain the location and length of LSB using the values of wall shear stress and the results are encouraging. Also, a comparative analysis of flow transition and surface pressure distribution was made by four different turbulence models and the results are discussed.

Interface horizontal shear strength requirement in Ultra-thin whitetopping (UTW) pavement.

Ultra-thin whitetopping (UTW) is a thin (5-10 cm) layer of concrete overlaying over an existing asphalt pavement. This concrete layer is bonded on the asphalt surface. Although UTW has been successful in strengthening asphalt pavement, in some cases, the composite pavement may debond at the interface under the concrete slab due to high shear stress. This paper aims to determine the interface shear strength required for UTW pavement systems using theoretical methods and calibrated numerical models (FEMs). The study analysed 432 pavement scenarios with different slab sizes, thicknesses, and material properties. The results show that higher shear stress occurs when the asphalt modulus is stiffer. The size of the slab, the modulus of the supporting layer, and the asphalt thickness have only a minor effect on the shear stress value. However, the thickness of the concrete slab significantly affects the maximum shear stress in the UTW, with an increase of up to 36.6% when reducing the slab thickness from 100mm to 50 mm. The FEM calculations can be used to determine the required interface horizontal shear strength for UTW.

Rheological behavior of activated bentonite suspensions and estimation of flow models using least squares method

In this study, bentonite samples were obtained from Wyoming-USA (WB), Eldivan-Çankırı (EB), Reşadiye-Tokat (RB), Niksar-Tokat (NB) and Ünye-Ordu (UB) regions. Then, these were evaluated in two main sections as raw and activated. Raw samples were obtained by reducing the samples obtained from the quarry to less than 75 μm particle size as a result of grinding and sieving processes. On the other hand, activated bentonites were obtained as a result of the activation process with 2.5%wt Na2CO3 and 0.5%wt MgO by dry activation method. After the sample preparation procedures, for the characterization X-ray fluorescence spectroscopy (XRF), X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), brunauer-emmett-teller (BET) surface area and cation exchange capacity (CEC) analyzes were performed. With the suspensions prepared according to American Petroleum Institute (API) 13A standard with bentonite samples and shear stress measurements were performed at different shear rates. According to measured shear stress values, rheological evaluations with Bingham Plastic (BPM), Power Law (PLM), Casson (CM) and Robertson-Stiff (RSM) models were done by using least squared method (LSM) by MatLab. Also, results were validated statistically. When BPM was evaluated, it showed the R-EB coded suspension as the best with 0.9960 R2. R–NB for PLM was expressed as 0.9927 R2. For CM, the sample coded A-WB with 0.9975 R2 was best expressed. When the results were evaluated in general, it was determined that RSM expressed the shear stresses of the samples with higher accuracy compared to the others. Despite the high accuracy in all of the samples for RSM, the A-UB coded suspension stood out with 0.9987 R2.

Role of Crystal Orientation in the Dynamic Strength of Magnesium Alloy AZ31B

The effect of grain orientation distribution on the dynamic strength of highly textured magnesium alloy AZ31B has been studied in a series of plate-impact experiments. Specimens with thicknesses between 0.45 mm and 2 mm were cut parallel and perpendicular to the material extrusion direction and shock loaded to impact stresses between 1.4 GPa and 3.4 GPa. The dynamic strength is found to be highly dependent on the loading direction, with loading along the extrusion direction exhibiting significantly higher Hugoniot elastic limits than the transverse direction, including a much slower precursor decay rate. Application of an orientation-based analysis framework shows that the yield point of the polycrystalline material can be predicted reasonably well from its grain orientation distribution, predicated upon the use of dynamic critical resolved shear stress values from single-crystal data modified by a fitted strengthening factor. It is shown that the strong dependence on loading orientation in Mg AZ31 is caused by the relative differences in slip system activity and the slip anisotropies inherent to the hexagonal close packed crystal structure.

Feasibility study of combining wall shear stress and elastography to assess the vascular status of carotid artery.

At present, early detection of the potential risk of atherosclerosis and prevention is of great significance to reduce the occurrence of stroke. This study aims to explore the value of combining the wall shear stress measured by ultrasound vector flow imaging technique and sound touch elastography of common carotid artery in normal adults using the Mindray Resona 7 ultrasound system. Forty volunteers (mean age 39.5 y, 23 females, 17 males) were divided into four groups according to their age. All volunteers underwent ultrasound carotid artery examination, and the values of wall shear stress and elasticity on the posterior wall of the common carotid artery were measured using advanced imaging functions, vector flow imaging technique, and sound touch elastography. Different cut-off values of wall shear stress were used to investigate the significance between two groups with corresponding sound touch elastography values. It can be seen that the statistical difference could be found when the mean wall shear stress was larger than 1.5 Pa approximately (statistical significance was defined when P < 0.05), and the sound touch elastography value was positively correlated with the wall shear stress value. This study reveals that the combination of wall shear stress and sound touch elastography is an effective and feasible method for assessing carotid artery health. When the mean wall shear stress value is over 1.5 Pa, the corresponding sound touch elastography value increases significantly. The risk of atherosclerosis increases with the stiffness of blood vessel walls.

Pullout damage analysis of steel fibers under dynamic load based on numerical simulation

FRC is constantly subjected to dynamic loads during its service period, and dynamic pullout behavior of the fibers and the coupling effect between fibers can significantly affect the crack initiation and propagation of FRC. In this paper, based on the single fiber pullout behavior of experimental and numerical results, the failure process of the twin fibers dynamic pullout test was simulated by RFPA3D program with discontinuous and heterogeneous characteristics. The influence of fiber embedding length and fiber spacing on the interfacial bond behavior were analyzed in details. The internal damage degree, crack propagation, and interfacial shear stress of all test series were quantitatively characterized. The results indicate that the specimens with various fiber embedding lengths and fiber spacings present distinct damage evolution patterns. The decrease of the peak of AE events is followed by an increase, when the fiber embedding length is increased. In addition, the fiber spacing has a large influence on the distribution and transmission of interfacial shear stress. With the increase of fiber spacing, the peak of interfacial outside shear stress increases, while the peak value of interfacial inside shear stress gradually decreases. Meanwhile, the AE-accumulative energy presents a trend of decreasing first and then increasing.

Optimal additional support screw position for prevention of hinge fracture in biplanar closed wedge distal femoral osteotomy

BackgroundThe purpose of this study was to examine the biomechanical significance of supplemental fixation using a positional screw in prevention of the hinge fracture in lateral closed-wedge distal femoral osteotomy (LCW-DFO) by means of a three-dimensional finite element analysis. MethodsThe three-dimensional numerical knee models with LCW-DFO were developed. To assess the mechanical efficacy of the positional screw and determine its optimal position and orientation, in total, 13 screwing methods were analyzed. In the first four methods, the screw was supported by the cortical bone only on the medial surface (mono-cortical). In the other 9 models, the screw was supported by both medial and lateral cortical bones (bi-cortical). Under 1000 N of vertical force and 5 Nm of rotational torques, the highest shear stress value around the medial hinge area was adopted as an analytical parameter. ResultsIn mono-cortical methods, with the cancellous bone support, all methods were able to reduce the highest stress value compared to the value without the screw, while the efficacy was rather inferior when the screw was in horizontal direction. Without the cancellous bone support, however, all methods were not able to reduce the stress value. In bi-cortical methods, with the cancellous bone support, almost all screw augmentation methods were able to reduce the stress value. When screwing from the medial to the lateral, it only gets worse when going extremely posterior. Without the cancellous bone support, all methods were able to reduce the stress value. ConclusionThe mechanical efficacy of the bi-cortical method was proven regardless of the quality of the local cancellous bone.

Research on key influencing factors of scrap tire-soil retaining wall

The emergence of STSW can reduce the amount of materials such as sand and gravel and improve its performance compared to conventional retaining walls. In order to investigate the key influencing factors of STSW, the compression modulus of Scrap tire-soil module (STSM) was obtained by designing a full-scale compression strength test. The shear strength was obtained through a scale-test of shear strength. On this basis, the gravity STSW was established by the finite element numerical simulation software, and the bearing capacity of STSW was analyzed. Further, the key influencing factors of the bearing capacity of STSW were analyzed by designing orthogonal tests, and suggestions for parameter selection for designing STSW were given. The results show that: the friction angle of STSW increases and becomes larger with the increase of area ratio, and the cohesion decreases and decreases with the increase of area ratio; with the increase of compression modulus and internal friction angle, the maximum shear stress inside the retaining wall increases, while the cohesive force has almost no effect on the maximum value of shear stress inside the retaining wall; when constructing retaining walls, it is recommended to use Internal filling material with large compression modulus, small area ratio and its in the range of [0.3–0.5] of STSM.

INFLUENCE OF ELECTROCHEMICALLY ACTIVATED WATER ON THE FUNCTIONAL AND TECHNOLOGICAL PROPERTIES AND RHEOLOGICAL INDICATORS OF MEAT PATES

Preparation of water for food production, as components for increasing the biological integrity of food products by optimizing the content of macro- and microelements with biogenic properties in water, is an urgent issue in solving the problems of water preparation and determining the parameters of this process to ensure the structuring of food systems. The influence of activated water in the composition of starch suspensions on the functional and technological properties and rheological indicators of pates using them was determined. Activated water, and to a greater extent anolyte, significantly affects the moisture-binding capacity of pates. It was confirmed that samples of pates with a starch suspension with 2% starch on activated water demonstrate an increase in this indicator: on the anolyte and catholyte, the moisture-binding capacity of the pates in relation to the weight of the sample increased by 32.39% and 2.41% before pasteurization, compared to the control sample and by 33.05% and 1.71% after pasteurization. In the samples on the anolyte, the achievement of the maximum value of the indicator 100% is observed both before and after pasteurization. In the case of pates with 5% starch, the trend is similar. The indicator of the moisture-binding capacity of pates in relation to the mass of moisture in samples with a starch suspension with 2% starch on the anolyte increased by 3.71% before pasteurization, compared to the control sample, and on the catholyte it practically did not change. The values of this indicator in all samples after pasteurization were in the range of 90-100%. It was shown that the rheological parameters, namely the shear stress value of all pate samples regardless of the dosage of starch suspension in the range of shear rate - 0-8 s-1, increased sharply, after which the curves changed their character. In samples with a suspension of 2% starch, the indicator decreased linearly, while the catholyte has a smaller effect on the change in shear stress. When adding suspension with 2% starch at zero shear rate, the initial shear viscosity of pates was higher than in the sample with 5% and the control sample. So, activated water in the composition of corn starch suspensions helps to change the functional and technological properties and rheological indicators of pates with their content, which in turn will be reflected in the consistency of meat pates.

Hyperbaric oxygenation improve red blood cell deformability in patients with acute or chronic inflammation.

Red blood cells (RBC) are one of the key elements of the microcirculation. Their ability to pass through capillaries and to deliver oxygen to cells is due to their large degree of deformability linked to the characteristics of the RBC membrane. Alterations in RBC deformability as a result of membrane damage, linked in part to increased synthesis of reactive oxygen species (ROS), can be observed in several diseases, such as sepsis, and may contribute to the altered microcirculation observed in these pathologies. Hyperbaric oxygen therapy (HBOT), with inhalation of 100% oxygen, has been proposed in several acute or chronic pathologies, including carbon monoxide poisoning. We investigated the effects of HBOT on oxidative stress from ROS produced by myeloperoxidase (MPO) and on RBC deformability in patients with acute or chronic inflammation (n=10), in patients with acute carbon monoxide poisoning (n=10), and in healthy volunteers (n=10). RBC deformability was evaluated before and after HBOT in the various populations using the ektacytometry technique (Laser-assisted Optical Rotational Red Cell Analyzer - LORRCA). Deformability was determined by the elongation index (EI) in relation to the shear stress (SS) over a range of 0.3 to 50Pa. Oxidative stress was estimated through changes in proteins (chlorotyrosine and homocitrulline) induced by MPO activity measured by liquid chromatography-tandem mass spectrometry analysis. Before HBOT, EI was significantly lower in patients with acute or chronic inflammation than in healthy volunteers and patients with acute carbon monoxide poisoning for the majority of SS values studied. After one session of HBOT, the EI was significantly higher than before HBOT for SS values of 1.93Pa or higher in patients with acute or chronic inflammation. This effect remains constant after 10 sessions. There were no differences before and after HBOT in protein or amino acid oxidation due to ROS generation mediated by MPO in the three populations. Our results confirm altered RBC deformability in patients with acute and chronic conditions associated with an underlying inflammatory process. HBOT improves deformability only after one session and therefore may improve microcirculation in this population. According to our results, this improvement does not seem mediated by the ROS pathway via MPO. These results need to be confirmed in a larger population.

Assessment of unsteady-state thermal expansion in saccular aneurysms with Newtonian blood circulation including silver nanoparticles

The current study is based on an examination of the effect of Newtonian blood flow on the value of the wall shearing stress of an intracranial aneurysm using computational fluid dynamics. Blood is frequently thought to behave like a Newtonian fluid in cerebral arteries. It is fully described how a saccular aneurysm affects a model of blood-silver (Ag) nanofluid flow via an artery. Blood is regarded as a based fluid because of its rheology. The blood flow is Newtonian, laminar, incompressible, viscous, and unsteady, blood enters with a velocity of 0.08 ms−1 and the arterial wall should be flexible. The novelty of the research is to examine the impact of nanoparticles (Ag) on saccular aneurysm. To find the solution, a time-dependent direct solver was employed. To get the answer, the finite element discretization method (FDM) is applied. Coupled partial differential equations are used to mathematically describe the rheology of blood. In the current analysis, the solutions for velocity, temperature, and pressure distribution are found. Figures are used to illustrate and quickly discuss the effects of physical parameters on the characteristics of arterial blood flow for silver nanoparticles. These findings will be extremely beneficial in the treatment of arteries with aneurysms.

Three-dimensional bio-convection mechanism and heat transportation of nanofluid induced by magnetic field

There are several uses for bio-convection mechanisms, such as in sedimentary pools, fuel models, and microbially accelerated oil restoration. These are the basis of motile microorganisms which are applied to improve the mixability of fluid and tiny nanoparticles because they are accountable for biological transmission procedure. This work examines the bio-convective nanoparticles fluid flow and electrically conducting incompressible magneto-hydrodynamic flow of nanofluid towards a chemically reactive stretchable surface. Buongiorno model is considered here, which incorporates Brownian motion and thermophoretic diffusion, is employed in this study to explain how nanofluids improve heat transfer. The controlling boundary layer nonlinear PDEs are converted into ODEs by utilizing certain suitable similarity approaches. Numerical scheme is adopted to solve the transformed ordinary differential equations. The main findings of this research are that the magnetic field slows motion of the fluid when the thermal and mass buoyancy forces speed it up, and that thermophoretic diffusion increases the temperature and concentration of dimensionless fluids, resulting in stronger concentration and thermal boundary layers. The Brownian motion, concentration exponent, and chemical reaction parameters show an inverse relationship between temperature and concentration. Additionally, the first-order chemical reaction creates a lighter concentration boundary layer while the magnetic field’s presence due to impact of thermal and mass buoyancies helps to lower the heat transfer rate and shear stress. The findings show that while the Nusselt number and wall shear stress values are declining, the microorganism number is increasing.

Comparison of Welded Joint Stress with Experimental and Finite Element Method Using of Hotspot Method

The purpose of the welded structures is to combine the two different structures defined as the workpiece and the main material in order to ensure that they remain in the elastic deformation zone by meeting the loading conditions safely. Welding parameters such as preheating, welding speed, shielding gas selection, filler wire selection, voltage, current values affect the mechanical properties of the HAZ zone and the general structure, especially when welding fine-grained structural steels are performed. Strain gauge sensors can give normal stress and shear stress values for structures forced by static loadings depending on the stable x, y, z axes. The hotspot stress method used with the finite element method gives closer results to experimental studies. In this study, two different S960QL steels were combined with workpiece and main material using MAG welding. Data were taken from the strain gauge sensor connected to the samples prepared by the hotspot stress method. Using the finite element method, different types of models were analyzed and experimental data were compared with analysis outputs. As a result of the comparison, the most accurate welded joint analysis modeling with the hotspot method has been determined by the results of the experiment and analysis and has been proven with an accuracy rate of 89%.

Soft Perfusable Device to Culture Skeletal Muscle 3D Constructs in Air.

Devices for in vitro culture of three-dimensional (3D) skeletal muscle tissues have multiple applications, including tissue engineering and muscle-powered biorobotics. In both cases, it is crucial to recreate a biomimetic environment by using tailored scaffolds at multiple length scales and to administer prodifferentiative biophysical stimuli (e.g., mechanical loading). On the contrary, there is an increasing need to develop flexible biohybrid robotic devices capable of maintaining their functionality beyond laboratory settings. In this study, we describe a stretchable and perfusable device to sustain cell culture and maintenance in a 3D scaffold. The device mimics the structure of a muscle connected to two tendons: Tendon-Muscle-Tendon (TMT). The TMT device is composed of a soft (E ∼ 6 kPa) porous (pore diameter: ∼650 μm) polyurethane scaffold, encased within a compliant silicone membrane to prevent medium evaporation. Two tendon-like hollow channels interface the scaffold with a fluidic circuit and a stretching device. We report an optimized protocol to sustain C2C12 adhesion by coating the scaffold with polydopamine and fibronectin. Then, we show the procedure for the soft scaffold inclusion in the TMT device, demonstrating the device's ability to bear multiple cycles of elongations, simulating a protocol for cell mechanical stimulation. By using computational fluid dynamic simulations, we show that a flow rate of 0.62 mL/min ensures a wall shear stress value safe for cells (<2 Pa) and 50% of scaffold coverage by an optimal fluid velocity. Finally, we demonstrate the effectiveness of the TMT device to sustain cell viability under perfusion for 24 h outside of the CO2 incubator. We believe that the proposed TMT device can be considered an interesting platform to combine several biophysical stimuli, aimed at boosting skeletal muscle tissue differentiation in vitro, opening chances for the development of muscle-powered biohybrid soft robots with long-term operability in real-world environments.

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.