Low Shear Rates Research Articles

Intermittent negative pressure influences popliteal artery shear rate during supine and sitting postures.

Background: Intermittent negative pressure is an emerging treatment for lower limb vascular disease but the specific physiological effects, particularly upon large artery haemodynamics are unclear. This study examined the influence of intermittent negative pressure upon popliteal artery shear rate during both supine and sitting postures. Participants and methods: Eleven healthy participants (5 female; age: 28.3 ± 5.8 y; weight: 69.6 ± 9.8 kg, height: 1.75 ± 0.07 m) received intermittent negative pressure (-37 mmHg; 9.5-sec on, 7.5-sec off), upon the lower leg during both supine and sitting postures. Popliteal artery blood flow and shear rate were recorded (duplex ultrasound), accompanied by heart rate (3-lead ECG) and blood pressure (volume clamp method). Results: Compared to sitting, a supine posture led to greater mean shear rate during baseline (supine: 21[9]; sitting: 17[13] sec-1; all median [IQR]) and negative pressure phases (supine: 24[15]; sitting: 17[14] sec-1; both p<0.05). While supine, negative pressure raised mean shear rate above baseline levels (p<0.05) and reduced it upon return to atmospheric pressure (p < 0.05). In sitting, mean shear rate only differed from baseline at the points of peak and minimum shear (peak:18[17]; minimum: 10[9] sec-1; both p<0.05). Shear pattern (oscillatory shear index) showed changes from baseline during both postures (p<0.05), but was not different between postures. Conclusions: Intermittent negative pressure influenced lower limb popliteal artery shear rate during both the supine and sitting postures, the effect was greater while supine. Fluctuation in shear pattern seen during both positions may account for positive clinical effects observed following intermittent negative pressure treatment. These findings are framed against previous work investigating clinical populations. Future work should investigate any differences in lower limb haemodynamics and markers of endothelial function among patients with vascular disease.

Nonspherical Particle Stabilized Emulsions Formed through Destabilization and Arrested Coalescence.

To form nonspherical emulsion droplets, the interfacial tension driving droplet sphericity must be overcome. This can be achieved through interfacial particle jamming; however, careful control of particle coverage is required. In this work, we present a scalable novel batch process to form nonspherical particle-stabilized emulsions. This is achieved by concurrently forming interfacially active particles and drastically accelerating emulsion destabilization through addition of electrolyte. To achieve this, surfactant-stabilized oil-in-water emulsions in the presence of dopamine were first produced. These emulsions were then treated with tris(hydroxymethyl)aminomethane hydrochloride buffer to both simultaneously initiate polymerization of dopamine in the emulsion continuous phase and reduce the Debye length of the system, thus accelerating droplet coalescence while forming surface-active particles. The concentration of buffer and imposed shear was then systematically varied, and the behavior at the interface was studied using pendent drop tensiometry and interfacial shear rheology. It was found that polydopamine nanoparticles formed in the emulsion continuous phase adsorbed to the reducing interface during coalescence, resulting in anisotropic droplets formed via arrested coalescence. Greater shear rates resulted in accelerated coalescence and formation of secondary droplets, whereas lower shear rates resulted in thicker interfacial films. The efficacy of this method was further demonstrated with a second system consisting of sodium dodecyl sulfate as the surfactant and polypyrrole particles, which also resulted in nonspherical droplets for optimized conditions.

Development of a Microfluidic Viscometer for Non-Newtonian Blood Analog Fluid Analysis.

The incidence of stroke is on the rise globally. This affects one in every four individuals each year, underscoring the urgent need for early warning and prevention systems. The existing research highlights the significance of monitoring blood viscosity in stroke risk evaluations. However, the current methods lack the precision to measure viscosity under low shear rate conditions (<100 s⁻¹), which are observed during pulsatility flow. This study addresses this gap by introducing a novel microfluidic platform designed to measure blood viscosity with high precision under pulsatility flow conditions. The systolic blood viscosity (SBV) and diastolic blood viscosity (DBV) can be differentiated and evaluated by using this system. The non-Newtonian behavior of blood is captured across specific shear rate conditions. The platform employs a meticulously designed microarray to simulate the variations in blood viscosity during pulsation within blood vessels.The results demonstrate an impressive accuracy of 95% and excellent reproducibility when compared to traditional viscometers and rheometers and are within the human blood viscosity range of 1-10 cP. This monitoring system holds promise as a valuable addition to stroke risk evaluation methods, with the potential to enhance prediction accuracy.

Enhancing stroke risk stratification in atrial fibrillation through non-Newtonian blood modelling and Gaussian process emulation.

Atrial fibrillation (AF) is the most common heart arrhythmia, linked to a five-fold increase in stroke risk. The left atrial appendage (LAA), prone to blood stasis, is a common thrombus formation site in AF patients. The LAA can be classified into four morphologies: broccoli, cactus, chicken wing and windsock. Stroke risk prediction in AF typically relies on demographic characteristics and comorbidities, often overlooking blood flow dynamics. We developed patient-specific non-Newtonian models of blood flow, dependent on fibrinogen and haematocrit, to predict changes in LAA viscosity, aiming to predict stroke in AF patients. We conducted 480 computational fluid dynamics (CFD) simulations using the non-Newtonian model across the four LAA morphologies for four virtual patient cohorts: AF + Covid-19, AF + pathological fibrinogen, AF + normal fibrinogen, and healthy controls. Gaussian process emulators (GPEs) were trained on this in silico cohort to predict average LAA viscosity at near-zero computational cost. GPEs demonstrated high accuracy in AF cohorts but lower accuracy when the chicken wing GPE was applied to other morphologies. Global sensitivity analysis showed fibrinogen significantly influenced blood viscosity in all AF cohorts. The chicken wing morphology exhibited the highest viscosity, while the AF + Covid-19 cohort had the highest viscosity. Our non-Newtonian model in CFD simulations confirmed fibrinogen's substantial impact on blood viscosity at low shear rates in the LAA, suggesting that combining blood values and geometric parameters of the LAA into GPE training could enhance stroke risk stratification accuracy. KEY POINTS: Fibrinogen has a significant effect on blood viscosity in the left atrial appendage (LAA) at low shear rates. Gaussian process emulators (GPEs) can predict the viscosity of blood in the LAA at near-zero computational cost. Out of all LAA morphologies, the chicken wing morphology exhibited the highest average blood viscosity. High average blood viscosity in the LAA of atrial fibrilation + Covid-19 patients was observed due to high fibrinogen levels in this cohort. Combining blood values and geometric parameters of the LAA into GPE training could enhance stroke risk stratification accuracy.

Rheological Properties and Physical Stability of Aqueous Dispersions of Flaxseed Fibers.

The main objective of this work is to investigate the influence of shear on the rheological properties and physical stability of aqueous dispersions of flaxseed fiber. The variable to consider will be the homogenization rate in two different rotor-stator homogenizers, Ultraturrax T50 or T25. In order to achieve the proposed objective, small amplitude oscillatory tests, flow curves, and multiple light scattering measurements were carried out. All samples exhibited a shear thinning behavior that was not influenced by the shear imposed, and a weak gel-like behavior. The latter, unlike the flow behavior, was sensitive to the homogenization rate. Thus, an increase in this variable caused a decrease in the viscoelastic moduli values. This result pointed out a weakening of the network formed by the flaxseed fiber in an aqueous medium. On the contrary, the physical stability improved. Nevertheless, all samples were highly stable. The homogenizer used was a significant variable. The shear negatively influenced the microstructure of the aqueous flaxseed fiber dispersions, although the obtained gels were highly stable. The gel-like behavior, the high viscosity at low shear rates, and the high physical stability of the samples studied make them interesting food stabilizers and thickeners.

Rheology of dilute and semi-dilute non-Brownian suspensions made of irregular porous particles in a Newtonian fluid.

The porosity affects the rheological response of porous particle suspensions. Non-Brownian suspensions of porous particles immersed in a Newtonian Polyisobutene are investigated. Three different particles, with different porosity, pore structure and similar size, and non-porous irregular particles are used. The steady state and dynamic response of the suspensions are analyzed at several volume fractions. The behavior of the three porous particle suspensions is unique if the particle effective volume fraction, accounting for the polymer adsorbed into the particles, is considered. These suspensions are Newtonian until a critical volume fraction, beyond which they are shear thinning and exhibit a yield stress. Their rheological response differs from that of suspensions made of non-porous irregular particles as: (a) their critical volume fraction is much smaller than that of the irregular particle suspensions; (b) their viscoelastic spectra are different suggesting a denser and stronger percolated microstructure after a slow preshear. These results can be understood by considering the reduction of lubrication force induced by the porosity via two mechanisms: Darcyan flow through the porosity and propagation of the interparticle shear flow within the porosity. The first dominates at low shear rates, when the percolated microstructure is generated, the second prevails at high shear rates, where the particle clusters are disaggregated.

Rheology of polyacrylamide-based fluids and its impact on proppant transport in hydraulic fractures

Rheological experiments and measurements of particle settling velocity under static conditions were conducted for two types of polyacrylamide (PAA-based) fluids. The flow behavior of the viscoelastic fluids is described by a simplified, three-parameter model that integrates a constant viscosity at low shear rates with a power-law viscosity dependency at higher shear rates. The estimated dependencies of the rheological parameters and particle settling velocity on PAA concentration align with the classical power-law scaling for semi-dilute polymer solutions. The identified scaling offers valuable insight for optimizing the chemical composition of fracturing fluids, thereby improving the efficiency of hydraulic fracturing technology. By applying the lubrication approximation to the Navier–Stokes equations, a set of equations for the suspension flow in a vertical plane channel, characterized by the three-parameter rheology model, was derived. In typical fracturing conditions, the conventional power-law viscosity model used in current fracturing simulators significantly overestimates the gap-averaged apparent fluid viscosity compared to the proposed model. The novel model of the suspension flow aims to enhance the accuracy of proppant transport models applied in hydraulic fracturing simulators. Based on the three-parameter rheology model, a new model of particle settling in the studied PAA-based fluids is developed. It is based on smart Stokes' law, where viscosity is calculated according to either the plateau or power-law region, depending on the self-induced shear rate. The new model more accurately approximates experimentally determined settling velocity of proppant under static conditions across a broad range of PAA concentrations than existing models.

Rheological characterization and modeling of ultra-high-velocity fluidized submarine landslides

Submarine landslides are critical phenomena due to their potential to reshape seabed topography, trigger tsunamis, and compromise offshore infrastructure. Understanding the rheological properties, particularly shear stress and viscosity under high shear rates, is essential for comprehending the dynamics of these landslides, a topic often underexplored in previous research. This study explores the rheological behavior of fluidized submarine landslides, with a focus on in-site sediments from the South China Sea and the Western Pacific Ocean. Samples prepared with varying densities were subjected to extensive rheological testing in the laboratory and analyzed under shear rates of up to 2000 s−1. Results indicated that all samples exhibited non-Newtonian fluid characteristics, showing shear-thinning behavior at low shear rates and shear-thickening behavior at higher shear rates. This transition is attributed to the breakdown of internal sediment structures, leading to changes in viscosity. This study also found that higher water content generally results in lower yield stress and consistency coefficients, while increasing the shear rate reduces the nonlinearity of the fluid's behavior. To model this complex behavior, a piecewise rheological model based on the Herschel-Bulkley framework was proposed. This model effectively captures the variations in rheological properties across different shear rate stages, with critical shear rates influenced by the sediment type and water content. These findings contribute to a deeper understanding of submarine landslides under extreme conditions, and the proposed model offers a more accurate tool for predicting the behavior of fluidized submarine landslides.

Investigating the effect of reagents used in the transportation of hydrocarbons

The use of chemical reagents, such as paraffin inhibitors, viscosity regulators, anti-turbulence, and depressant additives, has recently been shown to significantly impact the rheological properties of oil flow. These additives function by forming asphaltene colloids through adsorption on aggregates, thereby reducing the energy of their interactions. This article describes the development, laboratory testing, and potential application in pipeline transport of the ANA-10 complex-action reagent, which combines the effects of an inhibitor of asphaltene-resin-paraffin deposits and an oil viscosity regulator. One component of the developed reagent is a synthetic carboxylic acid ester, while another group of active components includes imides of synthetic fatty acids, used as anti-wear additives for oils. The cold rod method was used to study the ability of the developed reagents to inhibit paraffin precipitation in oil. Rheological properties were analyzed at a low shear rate of 3.75 s–1, corresponding to the starting loads at oil pumping stations, as well as across a range of shear rates and temperatures typical for oil collection, in-field, and main transportation processes. When the newly developed reagent was applied to a specific section of the oil pipeline without additional supply branches, it reduced pressure losses at the pump by an average of 7% and decreased the frequency of pipe cleaning operations by 2.5 times.

The Impact of Nanocarbon Powder on the Characteristics of a Gel Propellant System with a High Concentration of Aluminum.

The addition of aluminum particles to a gel propellant has garnered attention through its potential for enhancing fuel properties. In order to enhance the energy performance of gel propellants, it is imperative to prepare gel propellants with high concentrations of aluminum. However, high-concentration aluminum-containing gels encounter two challenges. First, the combustion process leads to the agglomeration of aluminum particles, resulting in incomplete combustion. Additionally, elevated concentrations of aluminum particles increase the viscosity of the gel, impeding its atomization process and, subsequently, affecting combustion efficiency. These aforementioned issues pose practical obstacles for the application of high-concentration aluminum-containing gel propellants. In this research, a high-concentration aluminum-containing gel formulation was supplemented with nanocarbon powder. By investigating the impact of nanocarbon on various properties of the gel, its potential for addressing the above issues was analyzed. The investigation into the combustion performance of aluminum-containing gel blended with carbon powder revealed that the addition of 10 wt % nanocarbon powder to the gel system leads to a significant increase in the volumetric calorific value of the gel propellant by 21.21%. This enhancement not only improves the energy performance but also addresses the issue of incomplete combustion associated with aluminum. The rheology experiments conducted on gels demonstrate that the addition of nanocarbon powder results in an increased viscosity of the gel at lower shear rates, thereby enhancing its ability to withstand external disturbances during storage. Furthermore, this incorporation also enhances the gel's shear thinning properties, leading to a significant reduction in viscosity at higher shear rates and facilitating easier atomization of the gel system. In summary, the incorporation of nanocarbon powder can optimize the storage, atomization, and combustion processes of the gel, offering a straightforward and efficient approach to enhance the practical performance of metallized gel propellants.

Dry polymer model for a string of pushers: Nontrivial scaling of tumbling time with shear rate

Understanding the dynamics of active polymers is an important component for modeling the dynamic response of biological cells and microorganisms when subjected to external forces. A minimal computational model of active filaments that captures all the essential features of activity-induced filament motion is required to study large systems of dense suspensions. In this paper we present a model of a dry active polymer, compare its steady-state static and dynamic properties with those of a polymer consisting of extensile stresslets, and show that the two models give very similar results. When subjected to shear flow, both models show two distinct regimes in the tumbling interval as a function of shear rate, with a diffuse crossover regime in between. At high shear rate, the active and passive polymers follow the same power law for the tumbling interval. However, the tumbling interval is smaller than that of the passive polymer for low shear rates and larger for the high shear rate. We show that activity-induced large bends increase the coupling of the polymer with the shear gradient in the low-shear-rate regime, leading to a decrease in the tumbling interval. However, in the high-shear-rate regime, the active forces on the folds at the end of the stretched polymer prevent it from tumbling, leading to a larger tumbling interval. We show that the critical shear rate, at which the tumbling interval versus the shear-rate curve of the active polymer crosses that of the passive polymer, is determined by the balance of bending and shear forces and increases with κ/N3, where κ is the bending coefficient and N is the length of the polymer. Published by the American Physical Society 2024

Evaluation of Mixing Temperature in the Preparation of Plant-Based Bigels.

Understanding gel structures and behavior is a prerequisite for attaining the desired food application characteristics. The mixing temperature is crucial when incorporating thermolabile active compounds into gels. This study evaluated the effect of mixing temperature on the physical and chemical properties of a bigel system prepared using a carnauba wax/canola oil oleogel and Arabic gum hydrogels. The results showed that bigels prepared at lower temperatures (30 and 40 °C) resulted in a solid-like state under crystallization temperature, resulting in matrices with larger hydrogel droplets, softer texture, and lower adhesiveness, spreadability, and solvent binding capacity. In contrast, bigels prepared at higher temperatures (50 and 60 °C), around crystallization temperature but with no solid state, resulted in matrices with smaller hydrogel droplets and higher firmness, adhesiveness, and spreadability. These bigels had a higher apparent viscosity, especially at lower shear rates, and solid-like behavior in the linear viscosity range. During the bigel preparation process, adjusting the mixture temperature had no effect on the samples' oxidative stability, FTIR spectra, or thermal properties. The results highlighted the importance of hydrogel droplet size on the microstructure of the formed bigels, and smaller droplets could act as effective fillers to reinforce the matrix without making chemical changes.

Abstract 420: The Correlation of Whole Blood Viscosity and Outcome in Mechanical Thrombectomy for Acute Ischemic Stroke

Introduction Whole blood viscosity (WBV), reflecting the intrinsic resistance of blood flow, is an established predictor of stroke events in individuals. This study aims to correlate the WBV at different shear rates with the outcome of endovascular thrombectomy, known to be an effective treatment for large vessel occlusion (LVO) stroke. Methods This is a single‐center retrospective study conducted at our comprehensive stroke center. The charts of 317 patients who underwent endovascular thrombectomy within 6 hours of LVO stroke were reviewed. The modified Rankin score (mRS) at discharge was used as the outcome measure, with individuals categorized as low (0‐2) or high (3‐6). WBV at different shear rates was calculated using De Simone's Formula, dependent on hematocrit and total protein levels. The T‐test and Chi‐square test were used to compare baseline quantitative and categorical data, respectively, amongst the mRS study groups. We elaborated multivariable logistic regression analyses to identify the independent risk factors associated with the outcome of interest following mechanical thrombectomy. Finally, Spearman rank order correlation was used to assess for r between mRS and WBV at different shear rates. Results Baseline group characteristics, constituted by variables pertaining to demographics and medical history, were similar across the two study groups. However, our study found no significant differences in clinical outcomes between the two groups with WBV at high shear rate (OR 0.969, 95% CI 0.77‐1.204, p = 0.780) and low shear rate (OR 0.998, 95% CI 0.988‐1.008, p = 0.779) following mechanical thrombectomy. Spearman rank order correlation between WBV at high shear rate (r=0.058, p=0.123) and low shear rate (r=0.048, p=0.128) was non‐significant. Conclusion This is one of the few studies to evaluate the effect of WBV at high and low shear rates on the clinical outcome of endovascular thrombectomy in patients with LVO. Our results revealed that WBV at high and low shear rates did not affect the outcome of endovascular thrombectomy, as measured by mRS at discharge. We propose that different components of blood viscosity may uniquely affect blood flow, and our study provides a path for future research to further study the correlation.

Hydroxypropyl β Cyclodextrins Effects on Self-Assembly of Cyclic Peptide, Lanreotide Acetate, in Water and Subsequent Release rate from an in vitro Emulator of Subcutaneous Delivery

Most of peptide drugs are often delivered subcutaneously. The significant barrier in this type of peptide administration is the high concentration of formulation, which can lead to self-assembly and aggregation. These phenomena can negatively impact the bioavailability, manufacturing, and injectability of the peptide drug. This study investigated the self-assembly behavior of Lanreotide acetate at high concentration in water using Hydroxypropyl β- Cyclodextrins (HPβCyD) to mitigate the self-assembly and enhance release rate during subcutaneous administration. Our finding demonstrated that the lanreotide/ HPβCyD inclusion complex effectively prevents aromatic-aromatic interactions of lanreotide, thereby controlling self-assembly. This complexation also alters the viscosity behavior of lanreotide from non-Newtonian under low shear rates to Newtonian solution. Furthermore, the lanreotide/ HPβCyD inclusion complex reduces interactions with hyaluronic acid in the subcutaneous environment, leading to significant improvement in the release rate of lanreotide acetate at high concentrations (above 3% w/w in water).

Difference in structural changes of surfactant aggregates near solid surface under shear flow versus those in the bulk.

In water, the nonionic surfactant pentaethylene glycol monododecyl ether (C12E5) forms multi-lamellar vesicles upon application of shear, attributed to buckling instability of the surfactant layers. In the standard setup for applying shear, a pair of solid substrates is moved in opposite directions, and a non-slip condition at the solid surface is assumed. Based on theoretical predictions, the effective viscosity of the fluid surrounding the membrane is modified in this process, and this confinement may affect membrane fluctuation. However, only a few studies have analyzed the structural changes near the substrate. From this viewpoint, the structural changes in surfactant aggregates near a solid substrate under the application of shear were investigated herein using neutron reflectometry (NR). By increasing the shear rate, shear thickening at a lower shear rate and shear thinning at a higher shear rate were observed, similar to that in the bulk. However, a discontinuous change in the lamellar structure accompanying the condensation of the surfactant was observed in the NR experiments. This study presents the first experimental evidence indicating that the ramping speed of shear rates governs the shear-induced structuring of surfactant aggregates near the surface.

Using Machine Learning Algorithms for the Analysis and Modeling of the Rheological Properties of Algerian Crude Oils

Our research described in this report investigated the rheological behavior of crude oils from the Tin Fouye Tabankort oil field in Southern Algeria, focusing on their viscosity under varying temperatures (10 °C–50 °C). The results show that the oils exhibited non-Newtonian shear-thinning behavior at low shear rates, with the viscosity decreasing as the temperature was increased. At higher shear rates, the Herschel–Bulkley model accurately described the oils’ transition to Newtonian behavior. Machine learning models, including CatBoost, LightGBM, and XGBoost, were trained on the experimental data to predict the viscosity, with CatBoost and XGBoost showing superior performance. We suggest these findings are valuable for improving the efficiency of oil transportation and processing.

The combined effects of electrolyte addition and mechanical shearing on cellulose nanocrystal alignment

AbstractThis research explored the impact of four different electrolytes on the orientation of cellulose nanocrystals (CNCs) in shear-cast films prepared from aqueous CNC gels. Changes in the aqueous CNC gels’ rheological properties with electrolyte addition were correlated to the orientation and optical properties of dried CNC films. Film alignment was qualitatively assessed using cross-polarized optical microscopy and quantified by order parameters computed by UV–Vis transmission spectroscopy. Electrolyte addition resulted in an increased alignment in dried CNC films. For pure CNCs, the film order parameters remained constant at approximately 0.3 for shear rates from 20 s−1 to 100 s−1. However, higher order parameters were achieved in the presence of electrolytes. Notably, an order parameter of 0.88 was achieved at a shear rate of only 20 s−1. In addition, films produced from dispersions containing electrolytes exhibited improved clarity and haze. The results of this work highlight that electrolyte addition can enable higher order parameters at lower shear rates and facilitate the development of aligned CNC films for applications such as polarizers, clear coatings, and piezoelectric materials. Graphical abstract

Global and Local Shear Behavior of the Frozen Soil–Concrete Interface: Effects of Temperature, Water Content, Normal Stress, and Shear Rate

The interface between soil and concrete in cold climates has a significant effect on the structural integrity of embedded structures, including piles, liners, and others. In this study, a novel temperature control system was employed to conduct direct shear tests on this interface. The test conditions included normal stress (25 to 100 kPa), temperature (ranging from 20 to −6 °C), water content (from 10 to 19%), and shear rates (0.1 to 1.2 mm/min). Simultaneously, the deformation process of the interface was continuously photographed using a modified visual shear box, and the non-uniform deformation mechanism of the interface was analyzed by combining digital image correlation (DIC) technology with the photographic data. The findings revealed that the shear stress–shear displacement curves did not exhibit a discernible peak strength at elevated temperatures, indicating deformation behavior characterized by strain hardening. In the frozen state, however, the deformation softened, and the interfacial ice bonding strength exhibited a positive correlation with decreasing temperature. When the initial water content was 16% and the normal stress was 100 kPa, the peak shear strength increased significantly from 99.9 kPa to 182.9 kPa as the test temperature dropped from 20 °C to −6 °C. Both shear rate and temperature were found to have a marked effect on the peak shear strength, with interface cohesion being the principal factor contributing to this phenomenon. At a shear rate of 0.1 mm/min, the curve showed hardening characteristics, but at other shear rates, the curves exhibited strain-softening behavior, with the softening becoming more pronounced as shear rates increased and temperatures decreased. Due to the refreezing of interfacial ice, the residual shear strength increased in proportion to the reduction in shear rate. On a mesoscopic level, it was evident that the displacement of soil particles near the interface exhibited more pronounced changes. At lower shear rates, the phenomenon of interfacial refreezing became apparent, as evidenced by the periodic changes in interfacial granular displacement at the interface.

Low shear-induced fibrillar fibronectin: comparative analyses of morphologies and cellular effects on bovine aortic endothelial cell adhesion and proliferation

Wall shear stress (WSS) is a critical factor in vascular biology, and both high and low WSS are implicated in atherosclerosis. Fibronectin (FN) is a key extracellular matrix protein that plays an important role in cell activities. Under high shear stress, plasma FN undergoes fibrillogenesis; however, its behavior under low shear stress remains unclear. This study aimed to investigate the formation ofin vitrocell-free fibrillar FN (FFN) under low shear rate conditions and its effect on bovine aortic endothelial cell behavior. FN (500µg ml-1) was perfused through slide chambers at three flow rates (0.16 ml h-1, 0.25 ml h-1, and 0.48 ml h-1), corresponding to low shear rates of 0.35 s-1, 0.55 s-1, and 1.05 s-1, respectively, for 4 h at room temperature. The formed FN matrices were observed using fluorescence microscopy and scanning electron microscopy. Under low shear rates, distinct FN matrix structures were observed. FFN0.48 formed immense fibrils with smooth surfaces, FFN0.25 formed a matrix with a rough surface, and FFN16 exhibited nodular structures. FFN0.25 supported cell activities to a greater extent than native FN and other FFN surfaces. Our study suggests that abnormally low shear conditions impact FN structure and function and enhance the understanding of FN fibrillogenesis in vascular biology, particularly in atherosclerosis.

Comparative analysis of non-standardised aging methods for asphalt binder against standard laboratory aging and natural field aging

ABSTRACT This research investigates non-standardised and natural field aging methods, in comparison with standardised ones. Aging in the Rotational Viscometer (RV) for 24 hours was studied. Pressure Aging Vessel (PAV) aging time and film thickness were changed and compared with standard rolling thin film oven (RTFO) and field-aged binders. Finally, a conventional binder preserved from external conditions was tested over 24 months. Results showed that PAV-aged binders may exhibit greater susceptibility to changes captured by RV. The study also noted a higher increase in viscosities at lower shear rates over time in the RV. However, rheological results did not align with RV findings across all binders. Altering asphalt film thickness in the PAV from 32.5 mm to 25 ± 1 mm has a comparable effect to standard RTFO when the original binder is aged directly in the PAV for the same period of time. The recovered asphalt binder from a 15-year-old pavement showed similarities to 25–30 hours for high-temperature measures, and 55 hours for fatigue parameters indicating inconsistency between laboratory and filed aging. Finally, chemical changes indicated by carbonyl index showed that after 24 months of controlled environmental conditions, a conventional binder exhibited only 44% increase in the index compared to RTFO.