Shear Stress Conditions Research Articles

Hydraulics, sedimentation, and nutrient deposition within the middle Mississippi River Batture, USA

The Mississippi River batture (the land between the channel's low-water elevation and the flood mitigation levee) is an important sink for fluvial sediments and nutrients. However, the batture's role in sediment and nutrient storage remains poorly understood. To gain a better understanding of sediment and nutrient deposition within the batture, a 2D hydrodynamic model for a 30 km segment of the middle Mississippi River (MMR; between the confluences of the Missouri and Ohio Rivers) was developed to quantify flood extent and shear stresses for batture inundating discharges. Comparing modeled water surface elevations and shear stress to sedimentation estimates revealed which discharge conditions were conducive for deposition. Batture areas that experienced sedimentation during the 2019 flood were sampled for analysis of total organic carbon (TOC) and total nitrogen (TN) to gain insights into where these nutrients were deposited.Hydraulic modeling revealed MMR batture inundation includes six phases across both the rising and falling limb of the flood hydrograph: (1) back flooding (i.e., downstream to upstream inundation), (2) mixed back and overbank flooding, (3) overbank flooding conducive for deposition on the rising limb, (4) overbank flooding conducive for erosion on both the rising and falling limbs, (5) overbank flooding conducive for deposition on the falling limb, and (6) a floodplain draining phase. Phases two, three, and five (discharge conditions >20 to 86 % annual exceedance probability [AEP]), are most suitable for fine-grained deposition because of direct transfer of sediment-laden water from the river to batture, and large areas of the batture experiencing shear stress below the critical threshold for deposition. During the transition from phases three to four, flood depths increase, and hydraulic conditions rapidly favor erosion over the entire batture suggesting the batture may transition from sink to source of sediment for discharges that are ≤20 % AEP.Flood sediment TOC and TN concentrations were more than three times greater in backswamp clay and silt deposits, than in levee and splay sand. Within the backswamp, the most favorable discharge conditions for fine-sediment deposition are >20 to ≤86 % AEP on the rising limb, and >20 to ≤90 % AEP on the falling limb of the hydrograph. However, up to 40 % of the backswamp does not experience shear stress conditions below the threshold for fine-grained deposition. These findings highlight the impact hydraulic conditions have on sediment and nutrient retention in this important river connected landscape.

The endothelium permeability after bioresorbable scaffolds implantation caused by the heterogeneous expression of tight junction proteins.

As one of the main functions of vascular endothelial cells, Vascular permeability is determined by four tight junction proteins (TJPs): Zonula Occludens-1 (ZO-1), Claudin-5, Occludin and Tricellulin. The barrier function of blood vessels will be reconstructed after they are damaged by endothelial mechanical injuries caused by vascular interventions. In this study, the effects of balloon expansion (transient mechanical injury) on four TJPs and vascular permeability were compared with those of poly-l-lactic acid bioresorbable scaffolds (BRSs) implantation (continuous mechanical stimulation). We found that BRSs do not affect vascular permeability, while the recovery of vascular barrier function was found to be only related to the mechanical injuries and repair of endothelium. Mechanical stimulation affects and accelerates the recovery process of vascular permeability with the heterogeneous expression levels of TJPs induced after BRSs implantation. Different TJPs have different sensitivity to different loyal mechanical stimuli. ZO-1 is more sensitive to shear stress and tension than to static pressure. Occludin is sensitive to static pressure and shear stress. Tricellulin is more sensitive to tension stretching. Compared with the other three TJPs, Claudin-5 can respond to mechanical stimulation, with relatively low sensitivity, though. This difference in sensitivity determines the heterogeneous expression of TJPs. Mechanical stimulation of different kinds and strengths can also cause different cell morphological changes and inflammatory reactions. As an important element affecting endothelial function, the mechanical factors emerging after BRSs implantation are worthy of more attention.

Coupling Supramolecular Assemblies and Reactive Oxygen Species (ROS) with Megasonic Action for Applications in Shallow Trench Isolation (STI) Post-Chemical Mechanical Planarization (p-CMP) Cleaning.

Due to the continued miniaturization of semiconductor devices, slurry formulations utilized in the chemical mechanical planarization (CMP) process have become increasingly complex to meet stringent manufacturing specifications. Traditionally, in shallow trench isolation (STI), CMP, a contact cleaning method involving a poly(vinyl alcohol) (PVA) brush, is used to effectively transfer cleaning chemistry to the oxide substrate. This PVA brush can cause nonuniform cleaning chemistry transport, increased interfacial shear force, and cleaning-induced defectivity from brush loading. Previous work with traditional cleaning processes has shown that using “soft” supramolecular cleaning chemistries has dramatically improved cleaning efficacy while also minimizing the number of induced p-CMP defects. To minimize these effects, noncontact cleaning via the implementation of megasonic action has gained attention. This work employs “soft” cleaning chemistries with Cu2+–amino acid complexes, which can catalyze the formation of critical reactive oxygen species (ROS), and evaluates the p-CMP performance under megasonic action. Results from a second-order kinetic model indicate that megasonic conditions (i.e., time and power), “soft” cleaning chemistry structure (i.e., shape and charge), and the generation of ROS all play a critical role in cleaning efficacy under low shear stress conditions.

Cyclic behaviour of stratified soil under liquefied states

A substantial amount of work on the cyclic behaviour of cohesionless soil has been performed after neglecting the reality of stratification existing nearby marine structures or alluvial plains. This complicated mechanism of stratified soil failure on earthquake-induced soil liquefaction is affected significantly by the presence of a less permeable soil layer. Several past studies investigated that under the action of dynamic loads, the presence of a silt layer in homogeneous sandy soil crucially modifies the pore pressure dissipation characteristics, axial strain rate and stress–strain behaviour of the whole stratified specimen. In the present study, cyclic behaviour of sand specimen interlayered with silt layer has been presented in respect of its pre-and post-liquefaction behaviour. Undrained stress-controlled cyclic triaxial tests have been performed on homogeneous sand specimens and on specimens interlayered with a silt layer, placed at H/4, H/2 and 3H/4 (where H is the height of the specimen from the top) to signify the role of placement depth. The instability and failure of such specimens have been compared using the failure line and phase transformation line. Few key observations suggested that the number of liquefaction failure cycles enhanced two times and secant modulus (under post liquefied state) improved by 4.8 times when the placement depth of the silt layer increased from H/4 to 3H/4 under similar loading conditions. Additionally, the role of initial static shear stress has been investigated at three different confining pressures in a few stratified specimens. It has been observed that failure of the stratified specimen is due to the obstruction of pore water movement caused by the presence of the silt layer. A comparison of the present work has been made with significant studies using liquefaction resistant curves to ensure the efficacy of this study.

Assessment of on-treatment platelet reactivity at high and low shear stress and platelet activation status after the addition of dipyridamole to aspirin in the early and late phases after TIA and ischaemic stroke

BackgroundData are limited on the ability of dipyridamole to additionally inhibit platelet function/reactivity in ischaemic cerebrovascular disease (CVD) patients on aspirin. AimsTo assess inhibition of platelet function/reactivity and platelet activation with dipyridamole in CVD. MethodsThis prospective, observational study assessed TIA/ischaemic stroke patients before (baseline; N = 60), at 14 ±7 days (14d, N = 39) and ≥ 90 days (90d, N = 31) after adding dipyridamole to aspirin. Platelet function/reactivity at high shear stress (PFA-100® C-ADP) and low shear stress (VerifyNow® P2Y12 and Multiplate® ADP assays), and platelet activation status (% expression of CD62P, CD63 and leucocyte-platelet complexes on whole blood flow cytometry) were quantified. ‘Dipyridamole-high on-treatment platelet reactivity (HTPR)’ was defined as failure to inhibit ADP-induced platelet aggregation +/- adhesion compared with the patient's baseline on aspirin monotherapy by more than twice the coefficient-of-variation of the assay after adding dipyridamole to aspirin. ResultsDipyridamole-HTPR was identified in 71.4–75% of patients on PFA-100 C-ADP, 83.9–86.8% of patients on VerifyNow P2Y12, and 81.5–83.3% of patients on Multiplate ADP assays. There were no changes in CD62P/CD63 expression (P ≥ 0.18), or consistent changes in leucocyte-platelet complexes in CVD patients overall at 14d or 90d vs. baseline after commencing dipyridamole. Monocyte-platelet complexes increased in the patient subgroup with dipyridamole-HTPR at 14d and 90d on PFA-100, and at 14d on VerifyNow (P ≤ 0.04), but not in those without dipyridamole-HTPR. DiscussionAdditional antiplatelet effects of dipyridamole are detectable under high and low shear stress conditions with user-friendly platelet function/reactivity tests ex vivo. Increasing circulating monocyte-platelet complexes over time are associated with dipyridamole-HTPR.

Comparative studies between Semi-analytical and shear deformation theories for functionally graded beam under bending

In this paper, the bending response of functionally graded (FG) beam using three different approaches. viz. semi-analytical, higher-order shear and normal deformation theory (HOSNT), and trigonometric shear deformation theory (TSDT) under transverse loading conditions has been investigated. The boundary value problem (BVP) of the HOSNT and TSDT is derived using principle of virtual work whereas semi-analytical approach consist of formation of two-point BVP along the beam depth. All three models satisfy zero shear stress conditions at the top and bottom surfaces of the beam. The material properties of the FG beam vary across the thickness direction according to the power-law distribution. Aluminium-zirconia and aluminium-alumina are two types of compositions used to create FG beams. For comparison purpose, the authors have generated results for semi-analytical and HOSNT, being not available in the published literature. The numerical results are compared with previously published solutions to assess the correctness and effectiveness of the three models.

Tuning of fed-batch cultivation of Streptomyces clavuligerus for enhanced Clavulanic Acid production based on genome-scale dynamic modeling

Streptomyces clavuligerus (S. clavuligerus) is a filamentous Gram-positive bacterial producer of the β-lactamase inhibitor clavulanic acid (CA). Antibiotics biosynthesis and secretion in the Streptomyces genus are closely related with nutritional and environmental perturbations. In this study, the low productivity of CA in wild-type S. clavuligerus was analyzed by implementing a dynamic flux balance approach (dFBA) coupled to a validated genome-scale metabolic network of the organism. The dynamic analysis of fluxes evidenced the key role of the central metabolism (glycolysis, TCA and urea cycles) in regulating the carbon fluxes of the CA biosynthesis. CA production was favored by the fed-batch operation under high shear stress conditions that stimulates the growth rate and the carbon fluxes along the central metabolism. Dynamic experiments in silico allowed to identify potential scenarios of enhanced CA production (up to 2.5-fold higher) by maintaining the conversion rates within the central and secondary metabolism through fed-batch operation. The experimental validation of the most feasible production scenario as identified in silico showed 2.2-fold increase of CA production (equivalent to 0.382 mmol gDCW−1) by using the feeding condition as a mechanism to stimulate the carbon fluxes along the central metabolism and CA biosynthesis.

Experimental study on bond performance at UHPC-UHPC cold joints

There has been a rapid increase in the use of ultra-high-performance concrete (UHPC) as a construction or repair material worldwide due to its superior mechanical and durability characteristics. However, the bond strength of UHPC cast at different times is inadequately understood. This study examined the bond performance at UHPC-UHPC interfaces using five different surface preparations with mean texture depths (MTDs) ranging from 0.43 mm to 6.38 mm. The effect of fiber exposure techniques such as pressure washing, sandblasting, and needle scaler treatment on the bond performance at UHPC-UHPC cold joints was considered. The study also included the effect of grooved and smooth surface preparations on bond strength. The bond strength was investigated under tensile, shear and compression-shear stress conditions. The influence of inclination angle of the interface with different shear to compression ratios was studied. The results indicate that the presence of steel fibers at the interface plays a significant role in bond capacity by enhancing the bond strength and providing more interlock that results in ductility. The majority of the failure modes were at the bond interface due to the superior mechanical properties of UHPC. The cohesion and friction coefficients were determined from the experimental data and compared with values from design codes. It was discovered that pressure washed and grooved surface preparations exhibited superior bond performance compared to the other surface preparations under the stress conditions considered in this study.

Numerical modeling of injection-induced earthquakes based on fully coupled thermo-poroelastic boundary element method

In recent years, there has been a substantial increase in the induced seismicity associated with geothermal systems. However, understanding and modeling of injection-induced seismicity have still remained as a challenge. This paper presents a two-dimensional fully thermo-hydro-mechanical (THM) coupled boundary element approach to characterize the fault response to forced fluid injection and assess the effect of different injection protocols on seismic risk mitigation as well as permeability enhancement. The laboratory-derived rate-and-state friction law was used to capture the frictional paradigm observed in mature faults produced in granite rocks. All phases of stick-slip cycles, including aseismic slip, propagation of dynamic rupture, and interseismic periods, were simulated. The modeling results showed that the residual values of effective normal stress and static shear stress after a particular event completely dominate the constitutive behavior of fault friction during the next seismic event. The seismic energy analyses indicated that there is a negative correlation between the seismic magnitude and the total injected volume, such that a prolonged monotonic injection eventually results in the steady slip, rather than the seismic slip. Several fluid injection protocols were designed based on a volume-controlled (VC) approach and traffic light systems (TLS) to explore their effectiveness on the seismic risk mitigation and permeability enhancement. The results showed that cyclic injection based on TLS is the most effective approach for irreversible permeability enhancement of faults through promoting slow and steady slips. Our numerical simulations also revealed that fluid extraction (backflow-fixing bottom hole pressure at atmospheric pressure), regardless of the injection style, can considerably reduce the seismicity-related risks by preventing the fast-accelerated fracture slip during the post-injection stage. This study presents novel insights into modeling the rate-and-state governed faults exposed to forced fluid injection, and provides useful approaches for shear stimulation of faults with reduced seismic risks.

Exposure of human cerebral microvascular endothelial cells hCMEC/D3 to laminar shear stress induces vascular protective responses

Endothelial cells (ECs) are constantly submitted in vivo to hemodynamical forces derived from the blood circulation, including shear stress (SS). ECs are able to detect SS and consequently adapt their phenotype, thus affecting many endothelial functions. If a plethora of shear stress-regulated molecular networks have been described in peripheral ECs, less is known about the molecular responses of microvascular brain ECs which constitute the blood–brain barrier (BBB). In this work, we investigated the response of human cerebral microvascular ECs to laminar physiological shear stress using the well characterized hCMEC/D3 cell line. Interestingly, we showed that hCMEC/D3 cells responded to shear stress by aligning perpendicularly to the flow direction, contrary to peripheral endothelial cells which aligned in the flow direction. Whole proteomic profiles were compared between hCMEC/D3 cells cultured either in static condition or under 5 or 10 dyn.cm−2 SS for 3 days. 3592 proteins were identified and expression levels were significantly affected for 3% of them upon both SS conditions. Pathway analyses were performed which revealed that most proteins overexpressed by SS refer to the antioxidant defense, probably mediated by activation of the NRF2 transcriptional factor. Regarding down-regulated proteins, most of them participate to the pro-inflammatory response, cell motility and proliferation. These findings confirm the induction of EC quiescence by laminar physiological SS and reveal a strong protective effect of SS on hCMEC/D3 cells, suggesting a similar effect on the BBB. Our results also showed that SS did not significantly increase expression levels nor did it affect the localization of junctional proteins and did not afect either the functional activity of several ABC transporters (P-glycoprotein and MRPs). This work provides new insights on the response of microvascular brain ECs to SS and on the importance of SS for optimizing in vitro BBB models.

P19: In vitro Evaluation of Platelet Damage of Turbulent and Laminar Flow at Same Wall Shear Stress Conditions

P19: In vitro Evaluation of Platelet Damage of Turbulent and Laminar Flow at Same Wall Shear Stress Conditions

Finite element analysis on temperature field and stress distribution of thermal barrier coatings by laser modification and CMAS corrosion

Laser glazing to produce a modified layer on the surface of thermal barrier coatings (TBCs) is a promising method to alleviate calcium-magnesium-alumina-silicate (CMAS) attacks to coatings. In this study, finite element analysis is carried out to investigate the temperature field and stress distribution of TBCs after the laser glazing process and the modified TBCs after CMAS corrosion. Results revealed that along the direction of laser scanning, the principal stress was in a tensile state, which increased along the direction of the laser spot movement; while perpendicular to the laser scanning direction, the maximum principal stress appeared at the interface between the glazed layer and the unmodified coating, where could be a potential danger zone for crack initiation and coating spallation. For the modified TBCs with CMAS attack, in regions that are located in the range of 0–6 mm along the radial direction, the radial stress and maximum principal stress were high (∼1094 MPa), and the coating edge had complex shear stress state; as a result, these areas were easy to crack.

Crack propagation mechanism of single- and double-flawed rock specimens under tension–shear stress condition

Crack propagation mechanism of single- and double-flawed rock specimens under tension–shear stress condition

Transverse stretching vibration analysis of cross-ply composite and sandwich beams by means of an equivalent single-layer theory

Due to largely different stiffness between the face sheets and the core, the vibration modes corresponding to the transverse stretching displacement will occur in the sandwich plates. The third-order models will encounter difficulty to reasonably produce these frequencies corresponding to transverse stretching displacement modes, which will influence engineering design. Therefore, a global-local higher-order theory including transverse stretching effect has been proposed to study transverse stretching vibration, which can meet in advance the continuity conditions and the free surface conditions of transverse shear stresses. In the light of Hamilton’s principle, the equation of motion is presented, and analytical solutions of the simply-supported beams can be acquired by using Navier’s technique. In order to verify the capability of the proposed model, free vibration of composite beams is firstly investigated and the results have been compared to two-dimensional elasticity solutions. After the proposed model is assessed by two-dimensional elasticity solutions, the proposed model is extended to study dynamic behaviors corresponding to the transverse stretching displacement vibration modes, which will be verified by utilizing the three-dimensional finite element (3 D-FEM). Furthermore, variation of natural frequencies of the sandwich beams is also investigated by altering the thickness of the face sheets, which can further illustrate the capability of the proposed model.

Human dermal microvascular endothelial cell morphological response to fluid shear stress

As the cells that line the vasculature, endothelial cells are continually exposed to fluid shear stress by blood flow. Recent studies suggest that the morphological response of endothelial cells to fluid shear stress depends on the endothelial cell type. Thus, the present study characterizes the morphological response of human dermal microvascular endothelial cells (HMEC-1) and nuclei to steady, laminar, and unidirectional fluid shear stress. Cultured HMEC-1 monolayers were exposed to shear stress of 0.3 dyn/cm2, 16 dyn/cm2, or 32 dyn/cm2 for 72 h with hourly live-cell imaging capturing both the nuclear and cellular morphology. Despite changes in elongation and alignment occurring with increasing fluid shear stress, there was a lack of elongation and alignment over time under each fluid shear stress condition. Conversely, changes in cellular and nuclear area exhibited dependence on both time and fluid shear stress magnitude. The trends in cellular morphology differed at shear stress levels above and below 16 dyn/cm2, whereas the nuclear orientation was independent of fluid shear stress magnitude. These findings show the complex morphological response of HMEC-1 to fluid shear stress.

New HSDT for free vibration analysis of elastically supported porous bidirectional functionally graded sandwich plate using collocation method

The present paper deals with the free vibration response of elastically supported porous bidirectional functionally graded soft-core sandwich rectangular plate with proposed new tangent shape function-based higher-order transverse shear deformation theory. The theory is accomplished to uphold the continuity of transverse shear stresses and zero shear stress conditions on both the extreme surfaces of a plate. The bidirectional gradation varies through the thickness ( z-axis) and length ( x-axis) directions. The effective material properties are calculated via the modified power-law. The governing differential equations (GDEs) of motion are acquired via the Hamilton principle. The inverse multi-quadric radial basis function-based Collocation method is implemented to discretize the GDEs obtained by strong form formulation. The current theory and method’s accuracy and efficacy are validated by comparing the present results with existing results in the literature. Studies show that the results of the proposed theory are in close agreement with 3D approach. Numerical results are obtained with a different scheme of sandwich layers for free vibration analysis. Effects of grading index, porosity fraction, two parameters foundation, different scheme, and the span to thickness ratio on free vibration response have been discussed. New results for free vibration response in porous media are presented with different skin materials.

Laminar Shear Stress Enhances Cytosolic PINK1 Expression: Increased Mitophagic Sensitivity Toward Mitochondrial Dysfunction

PURPOSEPhosphatase and tensin homolog (PTEN)‐induced putative kinase 1 (PINK1) is an essential molecule in mitophagy process and known to act as a cytoprotective protein in mammalian cells. Mutation or deficiency of PINK1 has been closely related to several disease conditions. The purpose of this study was to determine PINK1 expression levels and subcellular localization under exercise‐mimic laminar shear stress (LSS) condition in human aortic endothelial cells (HAECs) or in exercising mice, and its implication on endothelial homeostasis and cardiovascular disease (CVD) prevention.METHODS & RESULTSFirst, we measured full‐length PINK1 (FL‐PINK1) mRNA and protein expression levels in HAECs under unidirectional laminar shear stress (LSS) at 15 dyne/cm2 for 48h. LSS significantly elevated both FL‐PINK1 mRNA and protein expressions in HAECs compared to static control. Mitochondrial fractionation assays showed a decrease in FL‐PINK1 accumulation in the mitochondria with a compensatory increase in the cytosolic FL‐PINK1 level under LSS. Confocal microscopic analysis confirmed these subcellular localization patterns suggesting downregulation of mitophagy induction. Also, mitophagy flux was decreased under LSS, determined by a mtKeima probe. Mitochondrial morphometric analysis and mitochondrial membrane potential (JC‐1) showed mitochondrial elongation and increased mitochondrial membrane potential, respectively, suggesting that an elevation of cytosolic PINK1 is not related to an immediate induction of mitophagy. Based on this observation, we further hypothesized that the elevation of the cytosolic pool of FL‐PINK1 would increase the sensitivity to mitophagic signals in pathological conditions. Preconditioned HAECs with LSS showed lower mtDNA lesions under angiotensin II stimulation (100 nM, 6h). Moreover, LSS‐preconditioned ECs showed rapid Parkin recruitment and mitophagy induction in response to mitochondrial toxin (i.e. CCCP) treatment compared to the control. We measured PINK1 expression at ECs of the thoracic aorta in exercised mice, a physiological LSS‐enhanced model, which was significantly elevated compared to sedentary animals. In addition, exercise‐preconditioned mice were more protective to angiotensin II‐induced mtDNA lesion formation in the mouse abdominal aorta than sedentary mice, suggesting a potential protective mechanism of exercise in a PINK1‐dependent manner.CONCLUSIONLSS increases a cytosolic pool of FL‐PINK1, which may elevate the mitophagic sensitivity toward dysfunctional mitochondria or activate other cytoprotective mechanisms in endothelial cells. Our data suggest that exercise may support mitochondrial homeostasis in vascular endothelial cells by enhancing PINK1‐dependent cell protection mechanisms.

Three-Dimensional Kidney-on-a-Chip Assessment of Contrast-Induced Kidney Injury: Osmolality and Viscosity.

Increased viscosity of concentrated contrast media (CM) in the renal tubules can perturb renal hemodynamics and have a detrimental effect on tubular epithelial cells. However, the effects of viscosity on contrast-induced nephropathy (CIN) remain poorly understood. Conventional in vitro culture studies do not reflect the rheological properties of CM. Therefore, we investigated the effects of CM viscosity on renal tubules using a kidney-on-a-chip and two different types of CM. Renal proximal tubule epithelial cells (RPTEC) were cultured in a three-dimensional microfluidic culture platform under bidirectional fluid shear stress. We treated the RPTEC with two types of CM: low- (LOCM, iopromide) and iso-osmolar contrast media (IOCM, iodixanol). Renal tubular cell injury induced by LOCM and IOCM was examined under different iodine concentrations (50–250 mgI/mL) and shear-stress conditions. LOCM showed a significant dose-dependent cytotoxic effect, which was significantly higher than that of IOCM under static and low-to-moderate shear stress conditions. However, high shear-stress resulted in reduced cell viability in IOCM; no difference between IOCM and LOCM was found under high shear-stress conditions. The cytotoxic effects were pronounced at a mean shear stress of 1 dyn/cm2 or higher. The high viscosity of IOCM slowed the fluid flow rate and augmented fluid shear-stress. We suggest an alternative in vitro model of CIN using the three-dimensional kidney-on-a-chip. Our results indicate a vital role of viscosity-induced nephrotoxicity under high shear-stress conditions, contrary to the findings of conventional in vitro studies.

A Compressed Collagen Construct for Studying Endothelial-Smooth Muscle Cell Interaction Under High Shear Stress.

The coculture of vascular endothelial cells (ECs) on collagen gels containing smooth muscle cells (SMCs) has been carried out to investigate cellular interactions associated with blood vessel pathophysiology under wall shear stress (WSS) conditions. However, due to a lack of gel stiffness, the previous collagen gel coculture constructs are difficult to use for pathologic higher WSS conditions. Here, we newly constructed a coculture model with centrifugally compressed cell-collagen combined construct (C6), which withstands higher WSS conditions. The elastic modulus of C6 was approximately 6 times higher than that of the uncompressed collagen construct. The level of α-smooth muscle actin, a contractile SMC phenotype marker observed in healthy arteries, was elevated in C6 compared with that of the uncompressed construct, and further increased by exposure to a physiological level WSS of 2 Pa, but not by a pathological level of 20 Pa. WSS conditions of 2 and 20 Pa also induced different expression ratios of matrix metalloproteinases and their inhibitors in the C6 coculture model but did not in monocultured ECs and SMCs. The C6 coculture model will be a powerful tool to investigate interactions between ECs and SMCs under pathologically high WSS conditions.

Shear Stress Induces α-Synuclein Aggregation Due to a Less Strained Protein Backbone and Protein Tyrosyl Groups Do Not Intervene in the Aggregation

Parkinson’s disease (PD) is an increasingly prevalent and currently incurable neurodegenerative disorder. The aggregation of the amyloid disordered protein α-synuclein (Syn) has been implicated in the development of PD. In the literature, it has been suggested that tyrosine residues of Syn play an important role in the interactions established during the fibrillation process. Herein, the prevalence of the referred interactions under shear stress conditions of Nα-acetyl-L-tyrosinamide (NAYA) and of Syn solutions by using membrane centrifugal filters with different cut-off of 200 nm, 100 kDa, 50 kDa and 30 kDa, under centrifugation conditions, were investigated. In order to determine the nature of the interactions involving the protein tyrosine residues the NAYA compound, which mimics the peptide bonds in protein and also possesses a tyrosyl group similar to the tyrosyl groups found in the Syn protein molecular structure, was used. It is expected that for a small molecule, such as NAYA, no molecular association occurs, contrary to what exists in the Syn protein solutions, which can more adequately retrieve the type of interactions formed, involving the tyrosyl group. Therefore, sensing the tyrosyl group absorption, spectroscopic techniques, in particular, were used. For NAYA, an intramolecular interaction between the tyrosyl group and the peptide bond was evidenced. For NAYA and Syn, it was observed that decreasing the membrane centrifugal filters pore size, under centrifugation conditions, was concomitant with the minimization of the intramolecular interactions between the tyrosyl group and the peptide bond. With this, it is likely to assume that shear stress conditions in the Syn solutions propel protein aggregation by a less strained protein backbone. Contrary to the centrifugation of NAYA solutions, centrifuging Syn solutions revealed molecular association and a progressive exposure of protein tyrosyl groups to water. Thus, we can also infer that shear stress conditions in the Syn solutions cause the protein tyrosyl groups to not intervene in the protein aggregation.