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Shear stress

José R Agudo, Jiwon Han, Jinyoung Park, Sinyoung Kwon, Soebiakto Loekman, Giovanni Luzi, Christoph Linderberger, Antonio Delgado, Andreas Wierschem
Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to turbulent flow conditions are presented. For that purpose, the incipient motion of a single bead is studied on regular substrates that consist of a monolayer of fixed spheres of uniform size that are regularly arranged in triangular and quadratic symmetries. The threshold is characterized by the critical Shields number. The criterion for the onset of motion is defined as the displacement from the original equilibrium position to the neighboring one...
February 22, 2018: Journal of Visualized Experiments: JoVE
Joo Myung Lee, Gilwoo Choi, Bon-Kwon Koo, Doyeon Hwang, Jonghanne Park, Jinlong Zhang, Kyung-Jin Kim, Yaliang Tong, Hyun Jin Kim, Leo Grady, Joon-Hyung Doh, Chang-Wook Nam, Eun-Seok Shin, Young-Seok Cho, Su-Yeon Choi, Eun Ju Chun, Jin-Ho Choi, Bjarne L Nørgaard, Evald Christiansen, Koen Niemen, Hiromasa Otake, Martin Penicka, Bernard de Bruyne, Takashi Kubo, Takashi Akasaka, Jagat Narula, Pamela S Douglas, Charles A Taylor, Hyo-Soo Kim
OBJECTIVES: We investigated the utility of noninvasive hemodynamic assessment in the identification of high-risk plaques that caused subsequent acute coronary syndrome (ACS). BACKGROUND: ACS is a critical event that impacts the prognosis of patients with coronary artery disease. However, the role of hemodynamic factors in the development of ACS is not well-known. METHODS: Seventy-two patients with clearly documented ACS and available coronary computed tomographic angiography (CTA) acquired between 1 month and 2 years before the development of ACS were included...
March 9, 2018: JACC. Cardiovascular Imaging
Kai Yu, Paula Andruschak, Han Hung Yeh, Dana Grecov, Jayachandran N Kizhakkedathu
The information regarding the nature of protein corona (and its changes) and cell binding on biomaterial surface under dynamic conditions is critical to dissect the mechanism of surface-induced thrombosis. In this manuscript, we investigated the nature of protein corona and blood cell binding in heparinized recalcified human plasma, platelet rich plasma and whole blood on three highly hydrophilic antifouling polymer brushes, (poly(N, N-dimethylacrylamide) (PDMA), poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly[N-(2-hydroxypropyl) methacrylamide] (PHPMA) using an in vitro blood loop model at comparable arterial and venous flow, and static conditions...
March 8, 2018: Biomaterials
Anton G Kutikhin, Maxim Yu Sinitsky, Arseniy E Yuzhalin, Elena A Velikanova
The blood flow through vessels produces a tangential, or shear, stress sensed by their innermost layer (i.e., endothelium) and representing a major hemodynamic force. In humans, endothelial repair and blood vessel formation are mainly performed by circulating endothelial progenitor cells (EPCs) characterized by a considerable expression of vascular endothelial growth factor receptor 2 (VEGFR2), CD34, and CD133, pronounced tube formation activity in vitro, and strong reendothelialization or neovascularization capacity in vivo...
March 13, 2018: Journal of Molecular and Cellular Cardiology
Zhibing Yang, Ruben Juanes
Pore fluid pressure in a fault zone can be altered by natural processes (e.g., mineral dehydration and thermal pressurization) and industrial operations involving subsurface fluid injection and extraction for the development of energy and water resources. However, the effect of pore pressure change on the stability and slip motion of a preexisting geologic fault remains poorly understood; yet, it is critical for the assessment of seismic hazard. Here, we develop a micromechanical model to investigate the effect of pore pressure on fault slip behavior...
February 2018: Physical Review. E
Julia J Mack, M Luisa Iruela-Arispe
PURPOSE OF REVIEW: The formation of a hierarchical vascular network is a complex process that requires precise temporal and spatial integration of several signaling pathways. Amongst those, Notch has emerged as a key regulator of multiple steps that expand from endothelial sprouting to arterial specification and remains relevant in the adult. This review aims to summarize major concepts and rising hypotheses on the role of Notch signaling in the endothelium. RECENT FINDINGS: A wealth of new information has helped to clarify how Notch signaling cooperates with other pathways to orchestrate vascular morphogenesis, branching, and function...
March 14, 2018: Current Opinion in Hematology
Ran Chen, Ying Lu, Zhiyong Jiang, Yongfeng Men
The poly(4-methyl-1-pentene) sample was used to investigate the cavitation induced stress-whitening phenomenon during stretching at different temperatures via the ultra-small-angle X-ray scattering technique. Two modes of cavitation were found that mode I cavitation activated around yield point followed by mode II cavitation generated in highly oriented state. The critical strain for initiating the mode II cavitation increases with the increase of stretching temperature whereas the critical stress grew steadily in the lower temperature regime (30~60oC) and reached a plateau at 70oC...
March 16, 2018: Journal of Physical Chemistry. B
Andrea J Santamaría, Juan P Solano, Francisco D Benavides, James D Guest
Cell transplant-mediated tissue repair of the damaged spinal cord is being tested in several clinical trials. The current candidates are neural stem cells, stromal cells, and autologous Schwann cells (aSC). Due to their peripheral origin and limited penetration of astrocytic regions, aSC are transplanted intralesionally as compared to neural stem cells that are transplanted into intact spinal cord. Injections into either location can cause iatrogenic injury, and thus technical precision is important in the therapeutic risk-benefit equation...
2018: Methods in Molecular Biology
Mohamed A Mohamed, Rohit Abraham, Tareq I Maraqa, Samir Elian
Aortic dissection is a rare and fatal complication of cocaine-induced hypertension. The injury mechanism is through shear stress that penetrates the intimal vessel layer, allowing blood flow to separate intimal and medial layers. Due to its scarcity and the paucity of related literature, our knowledge of this condition is limited. We present a rare case of a cocaine-induced aortic dissection, which extended continuously from the aortic root to the common iliacs, along with a literature review of similar cases...
January 12, 2018: Curēus
Jiangwei Wang, Yanming Wang, Wei Cai, Jixue Li, Ze Zhang, Scott X Mao
Shear band in metallic crystals is localized deformation with high dislocation density, which is often observed in nanopillar deformation experiments. The shear band dynamics coupled with dislocation activities, however, remains unclear. Here, we investigate the dynamic processes of dislocation and shear band in body-centered cubic (BCC) tungsten nanowires via an integrated approach of in situ nanomechanical testing and atomistic simulation. We find a strong effect of surface orientation on dislocation nucleation in tungsten nanowires, in which {111} surfaces act as favorite sites under high strain...
March 15, 2018: Scientific Reports
H C Sun, Z L Ning, G Wang, W Z Liang, S Pauly, Y J Huang, S Guo, X Xue, J F Sun
ZrCu-based bulk metallic glass composites (BMGCs) are well known for their plastic deformability, superior to traditional metallic glasses (MGs), which is attributed to a unique dual-phases structure, namely, the glassy matrix and unstable B2 phase. In the present study, in-situ tensile testing is used to trace the deformation process of a ZrCu-based BMGC. Three deformation stages of the BMGC, i.e., the elastic-elastic stage, the elastic-plastic stage, and the plastic-plastic stage are identified. In the elastic-elastic and elastic-plastic stages, the yield strength and elastic limit are major influenced by the volume fraction of the B2 crystals...
March 15, 2018: Scientific Reports
Burak Kurşun, Levent Uğur, Gökhan Keskin
BACKGROUND AND OBJECTIVE: Hemodynamic analyzes are used in the clinical investigation and treatment of cardiovascular diseases. In the present study, the effect of bypass geometry on intracranial aneurysm hemodynamics was investigated numerically. Pressure, wall shear stress (WSS) and velocity distribution causing the aneurysm to grow and rupture were investigated and the best conditions were tried to be determined in case of bypassing between basilar (BA) and left/right posterior arteries (LPCA/RPCA) for different values of parameters...
May 2018: Computer Methods and Programs in Biomedicine
Josette M Northcott, Ivory S Dean, Janna K Mouw, Valerie M Weaver
The tumor microenvironment is a dynamic landscape in which the physical and mechanical properties evolve dramatically throughout cancer progression. These changes are driven by enhanced tumor cell contractility and expansion of the growing tumor mass, as well as through alterations to the material properties of the surrounding extracellular matrix (ECM). Consequently, tumor cells are exposed to a number of different mechanical inputs including cell-cell and cell-ECM tension, compression stress, interstitial fluid pressure and shear stress...
2018: Frontiers in Cell and Developmental Biology
M P A van den Ende, G Marketos, A R Niemeijer, C J Spiers
Intergranular pressure solution creep is an important deformation mechanism in the Earth's crust. The phenomenon has been frequently studied and several analytical models have been proposed that describe its constitutive behavior. These models require assumptions regarding the geometry of the aggregate and the grain size distribution in order to solve for the contact stresses and often neglect shear tractions. Furthermore, analytical models tend to overestimate experimental compaction rates at low porosities, an observation for which the underlying mechanisms remain to be elucidated...
January 2018: Journal of Geophysical Research. Solid Earth
Hua Zhang, Hongxia Liu, Yuanli Dong, Juan Wang, Yingxin Zhao, Yi Cui, Qiang Chai, Zhendong Liu
The association of hemodynamics with cognitive impairment and white matter lesions (WMLs) has come to the foreground in recent years. Six hundred eighty-nine elderly participants aged ≥60 years were eligible enrolled. After an average of 5.4 years follow-up, there was a significant decline in Mini-Mental State Examination (MMSE) scores and increases in total white matter hyperintensities (WMH), periventricular (P)WMH, and deep (D)WMH ( P < 0.001). The participants were grouped by the tertiles of carotid mean wall shear stress (WSS)...
February 16, 2018: Oncotarget
James Patrick Ewen, Sridhar Kumar Kannam, Billy D Todd, Daniele Dini
The slip and friction behaviour of n-hexadecane, confined between organic friction modifier (OFM) surfactant films adsorbed on hematite surfaces, have been studied using nonequilibrium molecular dynamics (NEMD) simulations. The influence of OFM type and coverage, as well as the applied shear rate and pressure have been investigated. A measurable slip length is only observed for OFM films with a high surface coverage, which provide smooth interfaces between well-defined OFM and hexadecane layers. Slip commences above a critical shear rate, beyond which the slip length first increases with increasing shear rate and then asymptotes towards a constant value...
March 14, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
Joyjyoti Das, Somnath Maji, Tarun Agarwal, Suman Chakraborty, Tapas K Maiti
During metastatic dissemination, cancer cells experience shear stresses in narrow confinements of in vivo vasculature. Such stresses are currently known to influence a gamut of cellular processes. While a host of cells emanating from a primary tumor perish in circulation due to shear, some cells manage to migrate to distant niches and form secondary tumors. Current research focuses on how cancer cells avert such mechanical stresses and adapt themselves in order to survive. This study deals with the autophagic response of cervical cancer cells HeLa and its subline HeLa 229, exposed to physiological shear stresses in vitro, and evaluates its role as a pro-survival mechanism...
March 13, 2018: Clinical & Experimental Metastasis
Nicole Varble, Vincent M Tutino, Jihnhee Yu, Ashish Sonig, Adnan H Siddiqui, Jason M Davies, Hui Meng
BACKGROUND AND PURPOSE: Many ruptured intracranial aneurysms (IAs) are small. Clinical presentations suggest that small and large IAs could have different phenotypes. It is unknown if small and large IAs have different characteristics that discriminate rupture. METHODS: We analyzed morphological, hemodynamic, and clinical parameters of 413 retrospectively collected IAs (training cohort; 102 ruptured IAs). Hierarchal cluster analysis was performed to determine a size cutoff to dichotomize the IA population into small and large IAs...
March 13, 2018: Stroke; a Journal of Cerebral Circulation
Aditi Chakrabarti, Amir Porat, Elie Raphael, Thomas Salez, Manoj K Chaudhury
When a soft hydrogel sphere is placed on a rigid hydrophilic substrate, it undergoes arrested spreading by forming an axisymmetric foot near the contact line, while conserving its global spherical shape. In contrast, liquid water (that constitutes greater than 90% of the hydrogel's volume) spreads into a thin film on the same surface. We study systematically this elastowetting of gel spheres on substrates of different surface energies, and find that their contact angle increases as the work of adhesion between the gel and the substrate decreases, as one would observe for drops of pure water - albeit being larger than in the latter case...
March 13, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
Vrishank Raghav, Sudeep Sastry, Neelakantan Saikrishnan
Experimental flow field characterization is a critical component of the assessment of the hemolytic and thrombogenic potential of heart valve substitutes, thus it is important to identify best practices for these experimental techniques. This paper presents a brief review of commonly used flow assessment techniques such as Particle image velocimetry (PIV), Laser doppler velocimetry, and Phase contrast magnetic resonance imaging and a comparison of these methodologies. In particular, recommendations for setting up planar PIV experiments such as recommended imaging instrumentation, acquisition and data processing are discussed in the context of heart valve flows...
March 12, 2018: Cardiovascular Engineering and Technology
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