Blood Flow Shear Stress Research Articles

The Influence of Enhanced External Counterpulsation Intervention on the Biomechanical Stress Distribution of Advanced Plaque: A 3D FSI Study Based on in vivo Animal Experiment

Enhanced external counterpulsation (EECP) is an effective therapy to provide beneficial assistance for the failing heart by reducing cardiac afterload and increasing blood flow perfusion noninvasively. The technique of EECP involves the use of the EECP device to inflate and deflate a series of compression cuffs wrapped around the patient’s calves, lower thighs, and upper thighs. As the result, the enhanced flow perfusion is derived from the device’s propelling blood from veins of lower body to arteries of upper body and increases the blood supply for the important organs and brain. In the ACCF/AHA Guideline and ESC Guideline on the management of stable ischemic heart disease and coronary artery disease, EECP has been given a Class IIb and Class IIa recommendation respectively. In the ASA Guideline on the early management of Acute Ischemic stroke, EECP has been given a Class IIa recommendation. However, considering that EECP performance significantly elevates the acute blood pressure level as well as the perfusion level in systemic arterial tree and in diastolic, whether it will increase the risk of hypertension-related events such as atherosclerotic plaque rupture causes great concern in its clinical applications. But, the influence of EECP intervention on plaque progression remains elusive to this day and need to be assessed. It is generally agreed that biomechanical stresses play important roles in advanced atherosclerotic plaque progression and rupture. We hypothesized that EECP may intervene the advanced plaque progression via induced the variation of mechanical stresses in plaques. In this present paper, a pilot study containing animal experiment and numerical simulation was conducted to quantify the variations of biomechanical stresses of the plaque during EECP intervention. An experimentally induced hypercholesterolemic porcine model was developed and the basic hemodynamic measurements were performed in vivo before and during EECP intervention. Meanwhile, 3D multi-component idealized models with fluid-structure interactions (FSI) for carotid atherosclerotic plaques were introduced to solve the wall shear stress (WSS) and plaque structural stress (PWS) before and during intervention. Three cases of fibrous cap thickness (FC=600, 200 and 65μm) and three cases of material properties of the plaque components (normal, hard and soft) were involved in the current study. Numerical results showed that the max WSS level at the throat of the plaque, the 3D critical plaque wall stress (3D CPWS) level at the fibrous cap and the global max plaque wall stress (GMPWS) level at the shoulder of the plaque were all significantly augmented during EECP. When FC=65μm, EECP intervention augmented 118.1%±1.1% of the Max WSS level, 15.56%±1.68% of the 3D CPWS level and 14.78%±0.24% of the GMPWS level comparing to situations without EECP intervention. Considering that blood flow shear stress and structural stress are indexes that are presently thought might contribute to advanced plaque progression and its final rupture, our pilot study thus suggests that EECP treatment may intervene the plaque progression by elevating the levels of these indexes. But whether EECP treatment will increase the risk of plaque rupture and should be taken into account in its patient selection need a further detailed study and follow-up observation.

Syk/PECAM-1 Signaling Pathway Mediates Low Shear Stress-Induced Inflammatory in Atherosclerosis

Although blood flow shear stress has been demonstrated to alter the physiology of vascular endothelial cells, little is known about the role of Syk in PECAM-1 signaling pathway exposed to low shear stress (LSS). Methods: In vitro, primary human umbilical vein endothelial cells (HUVECs) were stimulated with parallel plate flow chamber system for 12h under normal shear stress (NSS, 15dyne/cm2), LSS (5dyne/cm2) and high shear stress (HSS, 25dyne/cm2), respectively, followed by inflammatory response analysis. In vivo, atherosclerotic animal models of rat and rabbit were created by feeding with high cholesterol diets. The animals were applied with LSS stimulation by constricting left carotid artery with a blunted needle (0.8mm in diameter). Small molecule R406, a well-demonstrated Syk inhibitor, was applied to the atherosclerotic animal models as well as HUVEC cells. Results: LSS influenced carotid atherosclerosis in the LSS model of rabbits; LSS promoted expression of PECAM-1 and Syk in LSS-treated atherosclerotic rat model; LSS influenced the morphology of abdominal aortic endothelial cells in rats; LSS increased the expression of pPECAM-1, Syk and NF-κB in HUVECs, and inhibition of Syk attenuated LSSinduced inflammatory response. Conclusion: Activation of spleen tyrosine kinase (Syk)/platelet endothelial cell adhesion molecule-1(PECAM-1) signaling pathway was accompanied with inflammatory response induced by LSS stimulation both in vitro and in vivo. This work demonstrated the important role Syk/PECAM1/NF-κB signaling pathway plays in LSS-induced inflammatory response. Funding Statement: This work was supported by Pudong New Area Health Bureau of Shanghai (grant no.PWZbr2017-09), and the National Natural Science Foundation of China (grant no.81401428, 81571693 and 81871361). Declaration of Interests: The authors have declared that no competing interest exists. Ethics Approval Statement: Human umbilical vein from normal full-term newborns was obtained with informed consent and approved in accordance with the procedures of the Medical Ethics Committee of Shanghai East Hospital Affiliated to Tongji University (China).

Nature-inspired extracellular matrix coating produced by micro-patterned smooth muscle and endothelial cells endows cardiovascular materials with better biocompatibility.

Functionalizing cardiovascular biomaterials with an extracellular matrix (ECM) via in vitro decellularization has been applied as an effective method to improve the biocompatibility of implants. However, the current ECM modified materials used for surface engineering implants have functional restrictions compared with the natural blood vessel due to distinguished cell phenotypes in vitro. Herein, we are inspired by the natural vascular basement membrane which is composed of an ECM secreted by physiological endothelial cells (EC) and smooth muscle cells (SMC), preparing a novel ECM coating by successive cell culture and decellularization: appropriately scaled hyaluronic acid (HA) micro-patterns are used to regulate the SMC phenotype to contraction and simulate the blood flow shear stress (BFSS) effect to control the EC physiological phenotype. The nature-inspired ECM coating significantly improves the material's hemocompatibility, cytocompatibility and tissue compatibility, and may be promising to break the function limitation of a single ECM and address more clinical complications.

Preface: The First International Symposium on Biomechanics and Mechanobiology in Cardiovascular System

Preface: The First International Symposium on Biomechanics and Mechanobiology in Cardiovascular System

Preparation of a biomimetic ECM surface on cardiovascular biomaterials via a novel layer-by-layer decellularization for better biocompatibility

Endothelial extracellular matrix (EC-ECM) modification by decellularization is generally recognized as an effective method for cardiovascular biomaterials to enhance their biocompatibility. However, the now available EC-ECM was mainly secreted by the in vitro cultured endothelial cells which lacked a physiological growth environment in vivo, such as blood flow shear stress (BFSS) acting, thus had a serious defect of biocompatibility. Our previous work markedly improved the biocompatibility of the EC-ECM modified materials by simulating the BFSS acting to control the endothelial cells with hyaluronic acid (HA) micro-pattern. In this contribution, the EC-ECM was further enriched onto the HA micro-pattern via a novel layer-by-layer decellularizatio method. In vitro platelets adhesion/activation, macrophages attachment test and ex vivo blood experiment of New Zealand White Rabbits suggested better blood compatibility and anti-inflammation property of this novel biomimetic ECM surface. The endothelial cells culture tests and in vivo rat subcutaneous implantation also proved its good pro-endothelialization function and tissue compatibility. In summary, the present study demonstrated better biocompatibility of the novel biomimetic ECM surface and its potential application for cardiovascular biomaterials modification.

C-Src kinase contributes on endothelial cells mechanotransduction in a heat shock protein 70-dependent turnover manner.

Shear stress changes are associated with a repertory of signaling cascade modulating vascular phenotype. As shear stress-related tensional forces might be associated with pathophysiological susceptibility, a more comprehensive molecular map needs to be addressed. Thus, we subjected human umbilical vein endothelial cells (HUVECs) to a circuit of different tensional forces in vitro considering the following three groups: (a) physiological blood flow shear stress condition (named Normo), (b) a hypertensive blood flow shear stress (named Hyper), and (c) these hyper-stressed cells were returned to Normo condition (named Return). The samples were properly collected to allow different methodologies analysis. Our data showed a pivotal involvement of c-Src on driving the mechanotransduction cascade by modulating signaling related with adhesion, survival (PI3K/Akt) and proliferative phenotype. Moreover, c-Src seems to develop important role during extracellular matrix remodeling. Additionally, proteomic analysis showed strong involvement of heat shock protein 70 (HSP70) in the hypertensive-stressed cells; it being significantly decreased in return phenotype. This result prompted us to investigate 20S proteasome as an intracellular proteolytic alternative route to promote the turnover of those proteins. Surprisingly, our data reveled significant overexpression of sets of proteasome subunit α-type (PSMA) and β-type (PSMB) genes. In conjunction, our data showed c-Src as a pivotal protein to drive mechanotransduction in endothelial cells in a HSP70-dependent turnover scenario. Because shear patterns is associated with pathophysiological changes, such as atherosclerosis and hypertension, these results paved new road to understand the molecular mechanism on driving mechanotransduction in endothelial cells and, if drugable, these targets must be considered within pharmacological treatment optimization.

Role of local coronary blood flow patterns and shear stress on the development of microvascular and epicardial endothelial dysfunction and coronary plaque.

The natural history of coronary atherosclerosis is complex and atherosclerotic plaques exhibit large morphologic and functional variability within the same individual as well as over time. The purpose of this article is to review the role of blood flow patterns and shear stress on the development of microvascular and epicardial endothelial dysfunction and atherosclerosis progression. Recent breakthroughs in cardiovascular imaging have facilitated in-vivo characterization of the anatomic and functional characteristics of atherosclerotic plaques and have highlighted the role of endothelial shear stress and epicardial and microvascular endothelial dysfunction in the natural history of coronary atherosclerosis. There is an important need to identify individual lesions which may progress to vulnerable plaque in order to provide early therapeutic management. Evaluation of endothelial shear stress, local blood flow patterns, epicardial and microvascular endothelial dysfunction, as well as their complex associations might indicate those patients who have microvascular endothelial dysfunction and increased risk for upstream epicardial endothelial dysfunction and plaque progression. Such high-risk patients could potentially be targeted for more intensive therapeutic strategies to prevent the progression of both microvascular and epicardial atherosclerotic manifestations.

Shape factor and sphericity features examination of Cu and Cu-Al2O3/blood through atherosclerotic artery under the impact of wall characteristic

In this investigation heat transfer characteristic of the catheter is considered to attenuate the hemodynamic impacts of the atherosclerotic lesion. A shape factor phenomenon of nanoparticles has been taken into account. Arterial configuration is considered to be fixed for overlapping shape of lesion. Wall properties impact on the atherosclerotic wall is assume for the permeable resemblance of arterial wall thickness. This examination is considered to discuss the atherosclerotic lesion such as resistance to blood flow and wall shear stress. To conduct these impacts, firstly mathematical model is formulated for velocity and temperature profile expressions with hybrid nanofluid phenomena in which nanoparticles properties are utilized as drug agents. Closed form solution of theoretical problem is obtained by the means of corresponding conditions and then formations of results are plotted. From graphical formations of formulated problem, it is observed that Cu-Al2O3/blood mediation in blood is helpful to minimize the hemodynamic impacts of the atherosclerotic artery.

Transcatheter aortic valve replacement alters ascending aortic blood flow and wall shear stress patterns: A 4D flow MRI comparison with age-matched, elderly controls

BackgroundWith the implementation of transcatheter aortic valve replacement (TAVR) in lower-risk patients, evaluation of blood flow characteristics and the effect of TAVR on aortic dilatation becomes of considerable interest. We employed 4D flow MRI in the ascending aorta of patients after TAVR to assess wall shear stress (WSS) and compare blood flow patterns with surgical aortic valve replacement (SAVR) and age- and gender-matched controls.MethodsFourteen post-TAVR patients and ten age- and gender-matched controls underwent kt-PCA accelerated 4D flow MRI of the thoracic aorta at 3.0 Tesla. Velocity and wall shear stress was compared between the two groups. In addition, aortic flow eccentricity and displacement was assessed and compared between TAVR patients, controls and 14 SAVR patients recruited as part of an earlier study.ResultsCompared to controls, abnormally elevated WSS was present in 30±10% of the ascending aortic wall in TAVR patients. Increased WSS was present along the posterior mid-ascending aorta and the anterior distal-ascending aorta in all TAVR patients. TAVR results in eccentric and displaced flow in the mid- and distal-ascending aorta, whereas blood flow displacement in SAVR patients occurs only in the distal-ascending aorta.ConclusionThis study shows that TAVR results in increased blood flow velocity and WSS in the ascending aorta compared to age- and gender-matched elderly controls. This finding warrants longitudinal assessment of aortic dilatation after TAVR in the era of potential TAVR in lower-risk patients. Additionally, TAVR results in altered blood flow eccentricity and displacement in the mid- and distal-ascending aorta, whereas SAVR only results in altered blood flow eccentricity and displacement in the distal-ascending aorta.Key Points• TAVR results in increased blood flow velocity and WSS in the ascending aorta.• Longitudinal assessment of aortic dilatation after TAVR is warranted in the era of potential TAVR in lower-risk patients.• Both TAVR and SAVR result in altered blood flow patterns in the ascending aorta when compared to age-matched controls.

Measurement of flow-mediated dilation of mouse femoral artery in vivo by optical coherence tomography.

Flow-mediated vasodilation (FMD) is used for assessment of vascular endothelial function in humans as a predictor of cardiovascular events. It has been challenging to carry it on preclinical murine models due to the diminutive size of the femoral artery. Here, we present a new approach to accurately measure the blood velocity and femoral artery diameters of mice by acquiring Doppler optical coherence tomography and optical coherence tomography angiography continuously within 1 single experimental scanning protocol. Using the 3-dimensional imaging and new velocity algorithm, the measurement precision of diameter, blood flow, velocity and wall shear stress are improved to 0.91%, 11.0%, 10.7% and 14.0%, respectively. FMD of healthy mouse femoral artery measured by this method was 11.96% ± 0.98%, which was blunted to 5.69% ± 0.4% by intravenous administration of endothelial nitric oxide synthase inhibitor (L-NG -Nitroarginine methyl ester), in agreement with that reported in the literature.

Sensing the stress

Vascular Biology When blood flow in arteries increases, surrounding smooth muscle relaxes to allow blood vessel dilation. Using a high-throughput screen for mechanoreceptors that are sensitive to blood flow (shear stress), Xu et al. identified a type of sensor expressed by vascular endothelial cells

Mechanical Property of TiO₂ Nano-Tubes Surface Based on the Investigation of Residual Stress, Tensile Force and Fluid Flow Shear Stress: For Potential Application of Cardiovascular Devices.

The TiO2 nanotube has been anticipated for potential application for cardiovascular implanted devices for its excellent drug loading/release function and biocompatibility. However, its mechanical behavior has rarely been studied as the cardiovascular devices. The tube length is a crucial factor which not only decides the drug loading ability but also influences the devices' mechanical behavior. Therefore, in this work, the TiO2 nanotubes with different tube length (NT2, NT4 and NT6) were fabricated, and their surface energy, residual stress, tensile tolerability and blood flow shear stress tolerability were determined, respectively. The results showed that there were no significant difference for each film samples on surface energy, tensile tolerability and blood flow shear stress tolerability, while NT6 obtained the smallest residual stress. These results indicated that longer TiO2 nanotubes not only meant loading more drugs but also better mechanical properties for surface modification of cardiovascular devices.

Identification of Basic Fibroblast Growth Factor as the Dominant Protector of Laminar Shear Medium from the Modified Shear Device in Tumor Necrosis Factor-α Induced Endothelial Dysfunction.

Background and Aims: Endothelial dysfunction is a hallmark of cardiovascular diseases. The straight region of an artery is protected from atherosclerosis via its laminar blood flow and high shear stress. This study investigated the cytoprotective effects of a new laminar shear medium (LSM) derived from a modified cone-and-plate shear device and identified basic fibroblast growth factor (bFGF) secreted by human aortic endothelial cells (HAECs) as the dominant protective factor in the LSM.Methods: Based on a modified cone-and-plate shear device system, HAECs were exposed to laminar shear (15 dynes/cm2) and static control for 24 h to produce a new supernatant LSM and static medium (SM). Evaluation of the protective effects of LSM and SM on endothelial dysfunction induced by tumor necrosis factor (TNF)-α (10 ng/mL), which leads to production of reactive oxygen species (ROS), inflammatory monocyte adhesion, and tissue factor activity. ROS induction-, inflammation-, and thrombosis-related genes and protein expression were evaluated by quantitative-PCR and western blotting. To identify the cytokines that played a key role in the cytoprotective action of the LSM, we used cytokine antibody arrays, selected an abundant marker cytokine, bFGF, and validated the different cytoprotective effects of recombinant bFGF (rbFGF) and neutralization by monoclonal antibody (rbFGF+Ab) co-treatment. Aortic and lung tissues from different groups of C57BL/6J mice were examined by immunohistochemistry. SB203580 (specific inhibitor of p38) and BIX02189 (specific inhibitor of MEK5) were used to identify bFGF as the main cytoprotective factor acting via p38/MAPK and MEK5-KLF2 pathways.Results: Compared with traditional LSM, the new LSM not only significantly decreased TNF-α-induced intracellular adhesion molecule 1 and plasminogen activator inhibitor type 1 gene expression, but also significantly increased heme oxygenase 1 gene expression. The new LSM and bFGF attenuated TNF-α-induced ROS induction, inflammation, and tissue factor activity and inhibited the inflammatory- and thrombosis-related gene/protein overexpression both in vitro and in vivo. Mechanistically, the cytoprotective action of bFGF was mediated via the p38/MAPK and MEK5-KLF2 pathways.Conclusion: bFGF was identified as the critical factor mediating the cytoprotective effects of LSM derived from the modified laminar shear system.

Histological verification of atherosclerosis due to bends and bifurcations in carotid arteries predicted by hemodynamic model.

Background Tortuosity and bifurcations in carotid arteries alter the blood flow, causing atherosclerosis. Objectives The aim of the present study is to analyze the effect of variant vascular anatomy in the cervical region on development of atherosclerosis by microanatomical examination. Methods The effect of blood flow at anomalous bends and bifurcations was observed in right carotid arteries of a seventy year old female cadaver. Fifteen histological slides were prepared from the carotid arteries and interpreted to verify predictions of atherosclerosis. Results The model predicts atherosclerosis at bends, bifurcations and large aperture arteries. Microanatomical examination revealed presence of atherosclerosis of varying thickness at the bends and bifurcation in the right carotid arteries, as predicted. Atherosclerosis was also detected in the straight part of the wider common carotid artery. No atherosclerosis was observed in the contralateral carotid arteries. The variant carotid vascular anatomy consisting of bends, bifurcations and wider arteries revealed that the shear stress and velocity of blood flow are reduced at these anomalous sites. Conclusions Anatomical anomalies such as bends and branching in the carotid arteries alter the irrigation pattern and generate biomechanical forces that cause turbulent flow and reduce shear stress/blood flow velocity. Decreased shear stress and velocity causes development of atherosclerosis. Histological slides established the presence of atherosclerosis at bends and bifurcations and in wider arteries.

Experimental investigation of the effect of non-Newtonian behavior of blood flow in the Fontan circulation

The Fontan procedure for univentricular heart defects creates a unique circulation where all pulmonary blood flow is passively supplied directly from systemic veins. Computational simulations, aimed at optimizing the surgery, have assumed blood to be a Newtonian fluid without evaluating the potential error introduced by this assumption. We compared flow behavior between a non-Newtonian blood analog (0.04% xanthan gum) and a control Newtonian fluid (45% glycerol) in a simplified model of the Fontan circulation. Particle image velocimetry was used to examine flow behavior at two different cardiac outputs and two caval blood flow distributions. Pressure and flow rates were measured at each inlet and outlet. Velocity, shear strain, and shear stress maps were derived from velocity data. Power loss was calculated from pressure, flow, and velocity data. Power loss was increased in all test conditions with xanthan gum vs. glycerol (mean 10 ± 2.9% vs. 5.6 ± 1.3%, p=0.032). Pulmonary blood flow distribution differed in all conditions, more so at low cardiac output. Caval blood flow mixing patterns and shear stress were also qualitatively different between the solutions in all conditions. We conclude that assuming blood to be a Newtonian fluid introduces considerable error into simulations of the Fontan circulation, where low-shear flow predominates.

Numerical simulation of low-density lipoprotein mass transport in human arterial stenosis - Calculation of the filtration velocity.

Accumulation of cholesterol and other atherogenic lipids such as low-density lipoprotein (LDL) in artery wall causes reduction of vessel diameter and artery stenosis. The study of the mass transfer of these large molecules in the wall with considering effective factors on lumen flow and different physiological factors is the subject considered nowadays. In this paper, results of two dimensional and axi-symmetric simulations of three different models of the artery with 60% stenosis under pulsatile blood flow are presented. Filtration velocity of LDL mass transport in the permeable artery wall and shear stress of blood flow are investigated using ADINA software Three different flow models are considered. In the first and second models, the filtration velocity considered as a given parameter and constant in arterial wall boundary, while in third model arterial wall considered as porous wall, the filtration velocity is calculated from pressure difference as an input parameter of the model. The results show that filtration velocity is strongly depend on geometry and it is not constant along the wall, contrary to simplified models. The results of concentration variations in lumen and wall illustrate the increase in near wall LDL concentration or concentration polarization.

Correlation between quantitative analysis of wall shear stress and intima-media thickness in atherosclerosis development in carotid arteries

BackgroundThis paper presents quantitative analysis of blood flow shear stress by measuring the carotid arterial wall shear stress (WSS) and the intima-media thickness (IMT) of experimental rabbits fed with high-fat feedstuff on a weekly basis in order to cause atherosclerosis.MethodsThis study is based on establishing an atherosclerosis model of high-fat rabbits, and measuring the rabbits’ common carotid arterial WSS of the experimental group and control group on a weekly basis. Detailed analysis was performed by using WSS quantification.ResultsWe have demonstrated small significant difference of rabbit carotid artery WSS between the experimental group and the control group (P<0.01) from the 1st week onwards, while the IMT of experimental group had larger differences from 5th week compared with the control group (P<0.05). Next, we have shown that with increasing blood lipids, the rabbit carotid artery shear stress decreases and the rabbit carotid artery IMT goes up. The decrease of shear stress appears before the start of IMT growth. Furthermore, our receiver operator characteristic (ROC) curve analysis showed that when the mean value of shear stress is 1.198 dyne/cm2, the rabbit common carotid atherosclerosis fatty streaks sensitivity is 89.8%, and the specificity is 81.3%. The area under the ROC curve is 0.9283.ConclusionsAll these data goes to show that WSS decreasing to 1.198 dyne/cm2 can be used as an indicator that rabbit common carotid artery comes into the period of fibrous plaques. In conclusion, our study is able to find and confirm that the decrease of the arterial WSS can predict the occurrence of atherosclerosis earlier, and offer help for positive clinical intervention.

Engineering Cardiovascular Implant Surfaces to Create a Vascular Endothelial Growth Microenvironment.

Cardiovascular disease (CVD) is generally accepted as the leading cause of morbidity and mortality worldwide, and an increasing number of patients suffer from atherosclerosis and thrombosis annually. To treat these disorders and prolong the sufferers' life, several cardiovascular implants have been developed and applied clinically. Nevertheless, thrombosis and hyperplasia at the site of cardiovascular implants are recognized as long-term problems in the practice of interventional cardiology. Here, we start this review from the clinical requirement of the implants, such as anti-hyperplasia, anti-thrombosis, and pro-endothelialization, wherein particularly focus on the natural factors which influence functional endothelialization in situ, including the healthy smooth muscle cells (SMCs) environment, blood flow shear stress (BFSS), and the extracellular matrix (ECM) microenvironment. Then, the currently available strategies on surface modification of cardiovascular biomaterials to create vascular endothelial growth microenvironment are introduced as the main topic, e.g., BFSS effect simulation by surface micro-patterning, ECM rational construction and SMCs phenotype maintain. Finally, the prospects for extending use of the in situ construction of endothelial cells growth microenvironment are discussed and summarized in designing the next generation of vascular implants.

Mechanical Property of TiO&lt;sub&gt;2&lt;/sub&gt; Micro/Nano Surface Based on the Investigation of Residual Stress, Tensile Force and Fluid Flow Shear Stress: For Potential Application of Cardiovascular Devices

The micro-patterned TiO2 nanotube has been anticipated for potential application for cardiovascular implanted devices for its excellent drug loading/ release function and biocompatibility. However, its mechanical behavior has rarely been studied as the cardiovascular devices. The tube length is a crucial factor which not only decides the drug loading ability but also influences the devices’ mechanical behavior. Therefore, in this work, the micro-patterned TiO2 nanotubes with different tube length (MNT2, MNT4 and MNT6) were fabricated, and their surface energy, residual stress, tensile tolerability and blood flow shear stress tolerability were determined, respectively. The results showed that the microstructure reduced the surface energy of the nanotubes surfaces, enhanced or reduced surface tensile tolerability when parallel or vertical to the strain orientation, and also increased the nanotubes surfaces residual stress; In addition, both micro/nano and single nano surfaces possessed good blood flow shear stress tolerability. These results indicated that the micro/nano surfaces possesses excellent mechanical properties for surface modification of cardiovascular devices.

Biological and Physical Factors Involved in the Maturation of Arteriovenous Fistula for Hemodialysis

One of the most important limitations of hemodialysis (HD) treatment is the vascular access (VA) that is used to connect the patient's blood vessels to the extracorporeal circulation. The arteriovenous fistula (AVF) obtained with native vessels is the VA of choice for the low incidence of infections and the long-term patency, but it is affected by high incidence of non-maturation or primary failure. Before use for cannulation, AVF must undergo vascular remodeling, with progressive increase in vessel diameter, to accommodate the increase in blood flow. A growing body of evidence indicates that AVF maturation is related to the response of endothelial cells to changes in blood flow and wall shear stress. In the present report we examine the experimental and clinical evidences on the mechanisms that play a role in vascular remodeling during AVF maturation. The physical and biological factors that develop upon arteriovenous surgical connection affect endothelial and smooth muscle cell function, as well as extracellular matrix remodeling. They can explain to a great extent the process of vascular remodeling and put more light on cellular mechanisms of vessel wall adaptation. The understanding of these phenomena, besides indicating the reasons for non-maturation and primary failure, may be fundamental in the future to ameliorate clinical outcomes of AVF creation, with a great impact on the clinical management of HD patients and their quality of life.