Variation Of Shear Stress Research Articles

Mechanical analysis of modified femoral neck system in the treatment of osteoporotic femoral neck fractures

BackgroundDespite the explicit biomechanical advantages associated with FNS, it is currently inconclusive, based on the existing literature, whether Femoral Neck System (FNS) outperforms Cannulated cancellous screws (CSS) in all aspects. Due to variances in bone morphology and bone density between the elderly and young cohorts, additional research is warranted to ascertain whether the benefits of FNS remain applicable to elderly osteoporosis patients. This study aimed to investigate the biomechanical properties of FNS in osteoporotic femoral neck fractures and propose optimization strategies including additional anti-rotation screw.MethodsThe Pauwels type III femoral neck fracture models were reconstructed using finite element numerical techniques. The CSS, FNS, and modified FNS (M-FNS) models were created based on features and parameterization. The various internal fixations were individually assembled with the assigned normal and osteoporotic models. In the static analysis mode, uniform stress loads were imposed on all models. The deformation and stress variations of the femur and internal fixation models were recorded. Simultaneously, descriptions of shear stress and strain energy were also incorporated into the figures.ResultsFollowing bone mass reduction, deformations in CSS, FNS, and M-FNS increased by 47%, 52%, and 40%, respectively. The equivalent stress increments for CSS, FNS, and M-FNS were 3%, 43%, 17%, respectively. Meanwhile, variations in strain energy and shear stress were observed. The strain energy increments for CSS, FNS, and M-FNS were 4%, 76%, and 5%, respectively. The shear stress increments for CSS, FNS, and M-FNS were 4%, 65% and 44%, respectively. Within the osteoporotic model, M-FNS demonstrated the lowest total displacement, shear stress, and strain energy.ConclusionModified FNS showed better stability in the osteoporotic model (OM). Using FNS alone may not exhibit immediate shear resistance advantages in OM. Concurrently, the addition of one anti-rotation screw can be regarded as a potential optimization choice, ensuring a harmonious alignment with the structural characteristics of FNS.

Research on heat transfer characteristics and prediction methods of supercritical liquified natural gas flowing horizontally under the influence of buoyancy

An exhaustive elucidation of the heat transfer performances and mechanisms of supercritical LNG under water-bath heating conditions is paramount for optimizing heat transfer and designing related heat exchangers. This study employs experiments and numerical simulations to explore the heat transfer mechanisms and prediction methods of supercritical LNG flowing horizontally under buoyancy. The experimental investigation was executed within a small SCV using the N2-Ar mixture as a substitute medium for safety considerations. Concurrently, the accuracy of the numerical model employed is rigorously authenticated through a comparative analysis with the empirical findings obtained from the experimental endeavor. The investigation delves into the impacts of operating conditions, structural parameters, and medium composition on heat transfer through numerical simulations. The influence mechanism of buoyancy on heat transfer is meticulously explicated by examining the distribution of flow fields and thermophysical properties within the boundary layer. The introduction of a novel criterion, Bufull, derived from the analysis of wall shear stress variation caused by buoyancy, facilitates a quantitative assessment of the impact of buoyancy on heat transfer. Additionally, a simplified buoyancy criterion, FBu, is introduced, dependent solely on fundamental operating parameters and tailored for engineering applications, with a determined critical value of 1/ FBu = 60.3. Based on the dramatically variable thermophysical and transport properties, that occurs near the critical point, as well as buoyancy correction, a correlation is formulated for predicting mixed convection heat transfer, exhibiting an MAE of merely 3.04% and accurately predicting 81.28% of the data within a ± 5% margin of error, surpassing existing correlations. Finally, the proposed heat transfer calculation method is validated using five groups of operational data from two in-service SCVs. The maximum absolute discrepancy between the computed outlet temperature and the monitored value is 1.95K. The findings of this paper can support practical applications.

Dynamic conformational response of von Willebrand factor to varying shear stress: A hybrid computational approach

This computational study examines the mechanobiological responses of von Willebrand Factor (vWF) to different shear stress levels, emphasizing the unique structural dynamics of its various domains. We introduce a novel coarse-grained model, representing each cluster of six amino acids as a bead, to synthesize the Lattice Boltzmann method with Brownian dynamics. This approach captures the vWF molecule’s conformational adaptability across a spectrum of shear rates, ranging from 5 to 5e + 7s−1, encompassing normal physiological flows to those resembling the high-shear environment of arterial stenosis.Our results reveal domain-specific responses of vWF, particularly in the A2 and A3 domains, which demonstrate significant elongation under elevated shear—reflecting their pivotal roles in clotting processes. Moreover, the study underscores the critical influence of random thermal forces on the molecule’s conformation, with simulations including these forces showing substantially greater conformational variability compared to those without.As shear rates increase, we observe a notable reorganization in the spatial arrangement of vWF domains. This reconfiguration is most evident in the increased separation between the A1 and D’D3 domains under high shear conditions, potentially enhancing the accessibility of platelets to key binding sites on vWF. These findings are paramount for a deeper understanding of vWF’s mechanical behavior in blood clotting and thrombosis, particularly the delicate balance between facilitating platelet adhesion and avoiding excessive stretching that could lead to thrombosis.Our work provides a foundation for future studies investigating vWF behavior in complex flow geometries and its interactions with other blood components. Such insights pave the way for more informed therapeutic strategies targeting vWF function in vascular health and disease, potentially leading to improved treatments for thrombotic disorders.

Numerical study of Casson dusty hybrid nanofluid flow with volume fraction over a Darcy–Forchheimer porous medium

AbstractThis study develops a mathematical model for dusty Casson hybrid nanofluid flow over a vertical stretching sheet, considering the influence of volume fractions for the dust particles and nanoparticles, magnetic field and Darcy–Forchheimer penetrating medium. The nanoparticles used are TC4 (Ti‐6Al‐4V) and Nichrome (80% Ni and 20% Cr), suspended in unused engine oil (EO). The governing partial differential equations are transformed into ordinary ones using suitable transforms. Solutions are obtained numerically via the Matlab built‐in program Bvp4c technique and represent graphically the velocity, temperature, and concentration profiles for both the fluid and dust phases. Additionally, tabular forms present wall shear stress and heat transfer rate variations under different parameter values. It is found that the enhancing volume fraction parameter helps to boost the magnitude of shear stress, heat, and mass diffusivity.

Relative Residence Time Can Account for Half of the Anatomical Variation in Fatty Streak Prevalence Within the Right Coronary Artery.

The patchy anatomical distribution of atherosclerosis has been attributed to variation in haemodynamic wall shear stress (WSS). The consensus is that low WSS and a high Oscillatory Shear Index (OSI) trigger the disease. We found that atherosclerosis at aortic branch sites correlates threefold better with transverse WSS (transWSS), a metric which quantifies multidirectional near-wall flow. Coronary artery disease has greater clinical significance than aortic disease but computation of WSS metrics is complicated by the substantial vessel motion occurring during each cardiac cycle. Here we present the first comparison of the distribution of atherosclerosis with WSS metrics computed for moving coronary arteries. Maps of WSS metrics were computed using dynamic geometries reconstructed from angiograms of ten non-stenosed human right coronary arteries (RCAs). They were compared with maps of fatty streak prevalence derived from a previous study of 1852 RCAs. Time average WSS (TAWSS), OSI, transWSS and the cross-flow index (CFI), a non-dimensional form of the transWSS, gave non-significant or significant but low spatial correlations with lesion prevalence. The highest correlation coefficient (0.71) was for the relative residence time (RRT), a metric that decreases with TAWSS and increases with OSI. The coefficient was not changed if RRT was calculated using CFI, which captures multidirectional WSS only, rather than OSI, which encompasses both multidirectional and oscillatory WSS. Contrary to our earlier findings in the aorta, low WSS in combination with highly multidirectional flow correlates best with lesion location in the RCA, explaining approximately half of its anatomical variation.

Design and comprehensive characterization of dry powder inhalation aerosols of simvastatin DPPC/DPPG lung surfactant-mimic nanoparticles/microparticles for pulmonary nanomedicine.

The Rho Kinase (ROCK) pathway is recognized to be involved in changes that lead to remodeling in pulmonary hypertension (PH), particularly cellular processes including signaling, contraction, migration, proliferation, differentiation, and apoptosis. Simvastatin (Sim) has a potent anti-proliferative and pro-apoptotic effect on vasculature smooth muscle cells through the inhibition of the synthesis of isoprenoids intermediates which are essential for the post-translational isoprenylation of Rho, Rac, and Ras family GTPases. Sim targets the underlying mechanism in vascular remodeling. Using bionanomaterials and particle engineering design, this innovative study reports on the advanced inhalable dry powders composed of sim with synthetic phospholipid bionanomaterials, DPPC/DPPG, as a lung surfactant-mimic. These were successfully designed and produced as co-spray dried (Co-SD) nanoparticles and microparticles for nanomedicine delivery as dry powder inhalers (DPIs). Different techniques were used to comprehensively characterize the physicochemical properties of the resulting Co-SD particles. The Next Generation ImpactorTM (NGI™) was used with three different FDA-approved human DPI devices with varying shear stress which were the HandiHaler®, Neohaler®, Aerolizer® DPI devices for aerosol dispersion performance. The formulation-device interactions were examined and correlated. Using human lung cells from different lung regions, in vitro cell viability and transepithelial electrical resistance (TEER) at the air-liquid interface showed biocompatibility of the formulations as a function of dose.

Numerical prediction of passive speed and performance for multistage pump without power drive in natural flow process

With the development of engineering applications and the increase in system complexity, some particular fields, such as liquid rocket engine turbopumps, aircraft engine fuel systems, and marine natural flow cooling systems, are increasingly focusing on the performance characteristics of pumps under natural flow conditions. The pump is in the form of resistance components under natural flow conditions without a power drive. The impeller undergoes passive rotation by the impact of inlet flow. Due to the specificity of its operating conditions and performance indicators, the pump's natural flow performance cannot be evaluated by regular methods. Therefore, this paper proposed a numerical prediction method for pump natural flow performance based on a coupled computational fluid dynamics coupled with six-degrees-of freedom model. The performance of a multistage pump with guide vanes was evaluated under different natural flow conditions, and the accuracy was verified by experimental measurements. The transient variation mode of pump performance parameters with time at the initial stage of natural flow impact was analyzed. The flow field's transient evolution characteristics and the wall shear stress variation during natural flow were investigated. It was found that the impeller's passive rotational speed increases linearly with the natural flow rate, while the hydraulic loss shows an exponentially increasing trend. Meanwhile, the natural flow loss coefficient shows an exponentially decreasing trend and gradually tends to a stable value. The high turbulent kinetic energy inside the impeller is mainly distributed in the flow separation region and large velocity gradients. The distribution of shear stresses is closely related to the flow behavior inside the pump and the geometrical features of the hydraulic components.

Cerebro-spinal flow pattern in the cervical subarachnoid space of healthy volunteers: Influence of the spinal cord morphology.

Toward further cerebro-spinal flow quantification in clinical practice, this study aims at assessing the variations in the cerebro spinal fluid flow pattern associated with change in the morphology of the subarachnoid space of the cervical canal of healthy humans by developing a computational fluid dynamics model. 3D T2-space MRI sequence images of the cervical spine were used to segment 11 cervical subarachnoid space. Model validation (time-step, mesh size, size and number of boundary layers, influences of parted inflow and inflow continuous velocity) was performed a 40-year-old patient-specific model. Simulations were performed using computational fluid dynamics approach simulating transient flow (Sparlart-Almaras turbulence model) with a mesh size of 0.6, 6 boundary layers of 0.05 mm, a time step of 20 ms simulated on 15 cycles. Distributions of components velocity and WSS were respectively analyzed within the subarachnoid space (intervertebral et intravertebral levels) and on dura and pia maters. Mean values cerebro spinal fluid velocity in specific local slices of the canal range between 0.07 and 0.17 m.s-1 and 0.1 and 0.3 m.s-1 for maximum values. Maximum wall shear stress values vary between 0.1 and 0.5 Pa with higher value at the middle of the cervical spine on pia mater and at the lower part of the cervical spine on dura mater. Intra and inter-individual variations of the wall shear stress were highlighted significant correlation gwith compression ratio (r = 0.76), occupation ratio and cross section area of the spinal cord. The inter-individual variability in term of subarachnoid canal morphology and spinal cord position influence the cerebro-spinal flow pattern, highlighting the significance of canal morphology investigation before surgery.

FSGe: A fast and strongly-coupled 3D fluid–solid-growth interaction method

Equilibrated fluid–solid-growth (FSGe) is a fast, open source, three-dimensional (3D) computational platform for simulating interactions between instantaneous hemodynamics and long-term vessel wall adaptation through mechanobiologically equilibrated growth and remodeling (G&R). Such models can capture evolving geometry, composition, and material properties in health and disease and following clinical interventions. In traditional G&R models, this feedback is modeled through highly simplified fluid solutions, neglecting local variations in blood pressure and wall shear stress (WSS). FSGe overcomes these inherent limitations by strongly coupling the 3D Navier–Stokes equations for blood flow with a 3D equilibrated constrained mixture model (CMMe) for vascular tissue G&R. CMMe allows one to predict long-term evolved mechanobiological equilibria from an original homeostatic state at a computational cost equivalent to that of a standard hyperelastic material model. In illustrative computational examples, we focus on the development of a stable aortic aneurysm in a mouse model to highlight key differences in growth patterns between FSGe and solid-only G&R models. We show that FSGe is especially important in blood vessels with asymmetric stimuli. Simulation results reveal greater local variation in fluid-derived WSS than in intramural stress (IMS). Thus, differences between FSGe and G&R models became more pronounced with the growing influence of WSS relative to pressure. Future applications in highly localized disease processes, such as for lesion formation in atherosclerosis, can now include spatial and temporal variations of WSS.

A Pseudo-Spectral Method for Wall Shear Stress Estimation from Doppler Ultrasound Imaging in Coronary Arteries.

The Wall Shear Stress (WSS) is the component tangential to the boundary of the normal stress tensor in an incompressible fluid, and it has been recognized as a quantity of primary importance in predicting possible adverse events in cardiovascular diseases, in general, and in coronary diseases, in particular. The quantification of the WSS in patient-specific settings can be achieved by performing a Computational Fluid Dynamics (CFD) analysis based on patient geometry, or it can be retrieved by a numerical approximation based on blood flow velocity data, e.g., ultrasound (US) Doppler measurements. This paper presents a novel method for WSS quantification from 2D vector Doppler measurements. Images were obtained through unfocused plane waves and transverse oscillation to acquire both in-plane velocity components. These velocity components were processed using pseudo-spectral differentiation techniques based on Fourier approximations of the derivatives to compute the WSS. Our Pseudo-Spectral Method (PSM) is tested in two vessel phantoms, straight and stenotic, where a steady flow of 15mL/min is applied. The method is successfully validated against CFD simulations and compared against current techniques based on the assumption of a parabolic velocity profile. The PSM accurately detected Wall Shear Stress (WSS) variations in geometries differing from straight cylinders, and is less sensitive to measurement noise. In particular, when using synthetic data (noise free, e.g., generated by CFD) on cylindrical geometries, the Poiseuille-based methods and PSM have comparable accuracy; on the contrary, when using the data retrieved from US measures, the average error of the WSS obtained with the PSM turned out to be 3 to 9 times smaller than that obtained by state-of-the-art methods. The pseudo-spectral approach allows controlling the approximation errors in the presence of noisy data. This gives a more accurate alternative to the present standard and a less computationally expensive choice compared to CFD, which also requires high-quality data to reconstruct the vessel geometry.

Numerical investigation on flow-induced wall shear stress variation of metastatic cancer cells in lymphatics with elastic valves

Hematogenous metastasis occurs when cancer cells detach from the extracellular matrix in the primary tumor into the bloodstream or lymphatic system. Elucidating the response of metastatic tumor cells in suspension to the flow conditions in lymphatics with valves from a mechanical/fluidic perspective is necessary. A physiologically relevant computational model of a lymphatic vessel with valves was constructed using fully coupled fluid–cell–vessel interactions to investigate the effects of lymphatic vessel contractility, valve properties, and cell size and stiffness on the variations in magnitude and gradient of the flow-induced wall shear stress (WSS) experienced by suspended tumor cells. Results indicated that the maximum WSSmax increased with the increments in cell diameter, vessel contraction amplitude, and valve stiffness. The decrease in vessel contraction period and valve aspect ratio also increased the maximum WSSmax. The influence of the properties of the valve on the WSS was more significant among the factors mentioned above. The maximum WSSmax acting on the cancer cell when the cell reversed the direction of its motion in the valve region increased by 0.5–1.4 times that before the cell entered the valve region. The maximum change in WSS was in the range of 0.004–0.028 Pa/µm depending on the factors studied. They slightly exceeded the values associated with breast cancer cell apoptosis. The results of this study provide biofluid mechanics-based support for mechanobiological research on the metastasis of metastatic cancer cells in suspension within the lymphatics.

Unsteady electroosmotic flow of Carreau–Newtonian fluids through a cylindrical tube

The present study aims to investigate the fully developed electroosmotic flow of Carreau–Newtonian fluids within a circular tube, considering two different boundary conditions of zeta potential. The unsteady behavior of Carreau–Newtonian fluids, is attributed to the pulsatile pressure-driven flow. Studying two distinct formulations, slip and no-slip zeta potentials, illustrates the relative movement of fluid particles and the charged surface. The proposed study’s framework is divided into two regions: a central region containing a non-Newtonian Carreau fluid exhibiting both shear-thinning and thickening behavior, and a peripheral region containing a Newtonian fluid with the effect of an electrical double layer at the solid wall of the cylindrical tube. The Poisson–Boltzmann equation under the assumption of Debye–Hückel approximation governs the potential distribution due to the electric double layer, facilitating the examination of electroosmotic flow through tube. Obtaining analytical solutions for the momentum equations in both regions becomes challenging due to the inclusion of pulsatile pressure-driven flow and a non-Newtonian Carreau fluid. Asymptotic series expansions are employed, utilizing small parameters such as the Weissenberg number (We≪1) and a pulsatile Reynolds number (α≪1), to derive velocity expressions for both regions. Wall shear stress fluctuations, as indicated by time-averaged wall shear stress and oscillatory shear index are assessed to gauge the temporal variation of wall shear stress from the dominant blood flow direction. By utilizing potential and hydrodynamic variables, an asymptotic formulation for the streaming potential is developed to ascertain the asymptotic expression of electrokinetic energy conversion efficiency and scrutinize the impacts of pertinent physical parameters on it. The proposed study prominently shows that the Debye–Hückel parameter, Weissenberg number, pulsatile Reynolds number, and time-dependent pressure gradient significantly influence the fluid velocity, flow rate, and flow resistance. The notable determination of the present study is that the velocity amplitude and electrokinetic energy conversion efficiency are enlarged in the slip-dependent case relative to the no-slip zeta potential. It is noteworthy that as inertial forces become more prominent compared to viscous forces, both time-average wall shear stress and oscillatory shear index experience a slight decrease, although the reduction in oscillatory shear index is minimal owing to the absence of obstruction within the tube wall. The NDSolve numerical scheme in Mathematica software is employed to calculate numerical solutions for the governing equations, which are subsequently verified against results obtained through asymptotic analysis. The findings of this study are expected to deepen our understanding of unsteady electroosmotic flows of Carreau fluid and contribute to the design and development of advanced microfluidic devices with enhanced performance for various applications.

Investigating Shear Stress of Ice Accumulated on Surfaces with Various Roughnesses: Effects of a Quasi-Water Layer.

The investigation of the anti-icing/deicing is essential because the icing phenomenon deteriorates the natural environment and various projects. By conducting molecular dynamics simulation, this work analyzes the effect of the quasi-water layer on the ice shear stress over smooth and rough surfaces, along with the underlying physics of the quasi-water layer. The results indicate that the thickness of the quasi-water layer monotonically increases with temperature, resulting in a monotonic decrease in the ice shear stress on the smooth surface. Due to the joint effects of the smooth surface wettability and the quasi-water layer, the ice shear stress increases and then decreases to almost a constant value when the surface changes from a hydrophobic to a hydrophilic one. For rough surfaces with stripe nanostructures, when the width of the bump for one case equals the depression for the other case, the variations of shear stress with height for these two cases are almost the same. The rough surface is effective in reducing the ice shear stress compared to the smooth surface due to the thickening of the quasi-water layer. Each molecule in the quasi-water layer and its four nearest neighboring molecules gradually form a tetrahedral ice-like structure along the direction away from the surface. The radial distribution function also shows that the quasi-water layer resembles the liquid water rather than the ice structure. These findings shed light on developing anti-icing and deicing techniques.

Mathematical modeling of creeping electromagnetohydrodynamic peristaltic propulsion in an annular gap between sinusoidally deforming permeable and impermeable curved tubes

The present work investigates the creeping peristaltic propulsion of viscid fluid in an annular gap between sinusoidally deforming permeable and impermeable curved tubes of similar shape under the influence of an externally imposed electric and magnetic field. In this model, the outer tube with a permeable wall surface is supposed to satisfy the Saffman slip condition. The flow equations are simplified by the estimation of a large wavelength in comparison with the radius of the external tube. An analytical solution for the axial velocity is obtained in the computational software MATHEMATICA. Graphical analyses are conducted to explore the variations in wall shear stress, velocity, pressure rise, frictional force, and stream function with respect to different emergent parameters, providing insight into the underlying physics of the flow phenomena. An investigation of the effects of the Hartmann number and electric field strength on the flow through a gap between deformable tubes with curved structures has important implications for a variety of engineering applications, including mechanical and biomedical engineering. The streamlines are plotted to discuss fluid trapping and visualize the flow pattern of the viscid fluid inside the curved annular domain. A comparative analysis of fluid transport induced by sinusoidal, triangular, trapezoidal, and square wave shapes is encountered with the help of streamlined contour diagrams. The comparison of pressure gradients in three different models is also discussed to gain insight due to fluid–structure interaction. A gap in the body of recently published literature is filled by the results discussed in this paper.

Spatial variation in stress orientation in and around Türkiye: rupture propagation across the stress regime transition in the 2023 Mw 7.8 Kahramanmaraş earthquake

SUMMARY On 6 February 2023, the Mw 7.8 Kahramanmaraş, Türkiye, earthquake occurred on the East Anatolian Fault Zone (EAFZ). This study examined the spatial variation of the stress field in and around Türkiye, particularly along the EAFZ, better to understand the rupture process of this event. We first combined focal mechanisms around Türkiye, created a data set consisting of 2984 focal mechanisms, and conducted stress tensor inversion. The results showed that the maximum compressional axis near the EAFZ was oriented north–south and slightly varied along the strike. Moreover, the relative magnitude of north–south compressional stress gradually increased from south to north, and the stress regime changes from a normal fault regime to a strike-slip fault regime. The static stress change caused by the 2023 Mw 7.8 and 7.7 events does not explain this lateral pattern, implying that this stress regime transition existed before the main shock. This suggests that shear stress on the EAFZ was low in this southern segment because it was unfavourably oriented to the regional stress field. Dynamic stress changes due to rupture propagation and dynamic weakening may have triggered the slip at the southern segment under low background shear stress. Previous studies have reported that the Mw 7.8 main shock rupture started at a splay fault, first propagated through the central and northern segments and then backpropagated with a time delay towards the southern segment, where it caused a significant but relatively small slip. The pre-existing along-strike shear stress variation on the fault may have contributed to the smaller and delayed coseismic slip in the southern segment than in the central and northern segments. The main shock rupture possibly caused stress rotation locally near the central segment where the magnitudes of the vertical and north–south compressional stresses were almost equal.

Exercise-Induced Laminar Blood Flow Maintains Vascular Function by Enhanced Endothelial Homeostasis

PURPOSE: Laminar blood flow is known to play a critical role in maintaining endothelial homeostasis in blood vessels. It exerts a shear stress on the endothelial cells (ECs), which is essential for the regulation of various vascular functions. In this study, the effects of laminar blood flow-induced enhanced endothelial homeostasis on the maintenance of vascular function were investigated.METHODS: Human umbilical vein endothelial cells (HUVECs) were employed to study gene expression associated with vessel dilation and angiogenesis in response to varying shear stress levels. To assess angiogenesis, experimental mice participated in voluntary wheel running for 16 weeks. To evaluate the vascular autophagic function, the six weeks old C57BL/6 mice underwent an hour of forced treadmill running for 10 weeks. The resulting gene expression was evaluated through western blotting and quantitative real-time polymerase chain reaction (qRT-PCR).RESULTS: Disturbed flow resulting from partial ligation surgery in the mice’s carotid artery led to a decrease in angiogenic capacity compared to the laminar flow observed in ex vivo sprouting assays. Cultured HUVECs exhibited a significant increase in VEGF expression when exposed to increased durations of 20 dyne/cm² laminar shear stress (LSS). Following a 10-week treadmill exercise regimen, ECs in the carotid arteries of mice showed a significant increase in the expression of autophagic genes, such as LC3II, Atg3, and Atg7, which was not observed in smooth muscle cells (SMCs). LSS was found to boost the expression of both total and phosphorylated eNOS, genes involved in vascular dilation regulation, specifically in ECs.CONCLUSIONS: These findings suggest that laminar blood flow sustains vascular function, such as angiogenic capacity, through the enhancement of endothelial homeostasis.

Numerical study on influence of protrusion heights on Reynolds stress and viscous stress variations in turbulent vortical structures

Analysing the influence mechanism of the riblet protrusion height on turbulent drag components is more beneficial in organising the vortical structure over the riblet surface. Therefore, the Large Eddy Simulation (LES) is used to investigate the vortex structure over the riblet surface with different protrusion heights. Then, the variations of Reynolds stress and viscous shear stress in a turbulent channel are analysed. As a result, the drag reduction rate increases from 3.4% when the riblets are completely submerged in the turbulent boundary layer to 7.9% when the protrusion height is 11.2. Further analysis shows that the protrusion height affects the streamwise vortices and the normal diffusivity of spanwise and normal vortices, thus driving the variation of Reynolds stress. Compared with the smooth surface, the vorticity strength and the number of streamwise vortices are weakened near the wall but increase in the logarithmic layer with increased protrusion height. Meanwhile, the normal diffusivity of spanwise vorticity decreases with the increase of protrusion height, and the normal diffusivity of normal vorticity is the smallest when the protrusion height is 11.2. Moreover, the protrusion height affects the velocity gradient of the riblet tip and riblet valley, thus driving the variation of viscous shear stress. With the increase of protrusion height, the velocity gradient of the riblet tip increases dramatically but decreases in the riblet valley.

A tempo-spatial controllable microfluidic shear-stress generator for in-vitro mimicking of the thrombus

Pathological conditions linked to shear stress have been identified in hematological diseases, cardiovascular diseases, and cancer. These conditions often exhibit significantly elevated shear stress levels, surpassing 1000 dyn/cm2 in severely stenotic arteries. Heightened shear stress can induce mechanical harm to endothelial cells, potentially leading to bleeding and fatal consequences. However, current technology still grapples with limitations, including inadequate flexibility in simulating bodily shear stress environments, limited range of shear stress generation, and spatial and temporal adaptability. Consequently, a comprehensive understanding of the mechanisms underlying the impact of shear stress on physiological and pathological conditions, like thrombosis, remains inadequate. To address these limitations, this study presents a microfluidic-based shear stress generation chip as a proposed solution. The chip achieves a substantial 929-fold variation in shear stress solely by adjusting the degree of constriction in branch channels after PDMS fabrication. Experiments demonstrated that a rapid increase in shear stress up to 1000 dyn/cm2 significantly detached 88.2% cells from the substrate. Long-term exposure (24 h) to shear stress levels below 8.3 dyn/cm2 did not significantly impact cell growth. Furthermore, cells exposed to shear stress levels equal to or greater than 8.3 dyn/cm2 exhibited significant alterations in aspect ratio and orientation, following a normal distribution. This microfluidic chip provides a reliable tool for investigating cellular responses to the wide-ranging shear stress existing in both physiological and pathological flow conditions.Graphical

Evaluation of the shrinkage process of a neck remnant after stent-coil treatment of a cerebral aneurysm using silent magnetic resonance angiography and computational fluid dynamics analysis: illustrative case.

Silent magnetic resonance angiography (MRA) mitigates metal artifacts, facilitating clear visualization of neck remnants after stent and coil embolization of cerebral aneurysms. This study aims to scrutinize hemodynamics at the neck remnant by employing silent MRA and computational fluid dynamics. The authors longitudinally tracked images of a partially thrombosed anterior communicating artery aneurysm's neck remnant, which had been treated with stent-assisted coil embolization, using silent MRA over a decade. Computational fluid dynamics delineated the neck remnant's reduction process, evaluating hemodynamic parameters such as flow rate, wall shear stress magnitude and vector, and streamlines. The neck remnant exhibited diminishing surface area, volume, neck size, dome depth, and aspect ratio. Its reduction correlated with a decline in the flow rate ratio of the remnant dome to the inflow parent artery. Analysis delineated regions within the contracting neck remnant characterized by consistently low average wall shear stress magnitude and variation, accompanied by notable variations in wall shear stress vector directionality. Evaluation of neck remnants after stent-coil embolization is possible through silent MRA and computational fluid dynamics. Predicting the neck remnant reduction may be achievable through hemodynamic parameter analysis.

Analyzing the effect of elliptical vibration assistance in machining of Zr-based BMG

Bulk metallic glasses (BMGs) are known as amorphous metal alloys that have a distinct advantage compared to crystalline metal alloys due to fewer microstructural defects. Elliptical vibration-assisted machining (EVAM) is a promising technique to improve the machining performance of high-strength materials. This paper addresses a knowledge gap by investigating the chip formation mechanism in EVAM of Zr-BMG considering the shear localization due to its amorphous structure. A coupled thermo-mechanical model including the effect of vibration kinematics on Zr-BMG deformation mechanics is proposed. The effects of tool-workpiece separation, speed ratio, and strain rate on shear stress, temperature, and free volume variations due to chip segmentation are predicted and analyzed. The predicted chip formation from the developed model is validated through the comparison of chip morphology with experimental results of EVAM of Zr-BMG. The model reveals the underlying mechanism of material deformation during EVAM of Zr-BMG. According to the simulations and experimental results, the shear localization phenomena in EVAM is delayed due to insignificant changes in free volume, and enhanced heat dissipation resulted in lower temperatures in the cutting zone caused by tool-workpiece separation. Compared to traditional machining, the disparity in temperature generation and free volume diffusion in EVAM reduces as the speed ratio increases. The suppressed accumulation of periodic shear and thermal stresses at the tool tip increases the tool life in EVAM compared to the fractured tool tip in traditional machining.