EFFECT OF STRESS INTENSITY FACTOR IN EVALUATION OF INSTABILITY OF ATHEROSCLEROTIC PLAQUE

2014 ◽  
Vol 14 (05) ◽  
pp. 1450072 ◽  
Author(s):  
HADI MOHAMMADI ◽  
KIBRET MEQUANINT

Understanding the relationship between coronary arterial blood pressure, plaque morphology and composition, and sites of fibrous cap (FC) bursting, has been the focus of many recent studies. Instability of atherosclerotic plaques, defined as the propensity for FCs to burst, has been thought to occur at places where FCs are thin and necrotic core (NC) areas are large and highly compliant. However, here we show quantitatively, using a fiber-reinforced, anisotropic and hyperelastic FE model, that FC thickness and NC size and compliance alone are limited in predicting vulnerable and high-risk plaques. We suggest that plaque instabilities primarily occur at sites of high and concentrated mechanical stresses irrespective of fibrous cap thickness or NC area and compliance. Also, limitations of imaging techniques, such as intravascular ultrasound and optical coherence tomography, for providing input into (FE) models of atherosclerosis are discussed. The proposed model can be used to predict vulnerable plaque sites and rupture risks in patients. The current study also provides a framework for future research in which three-dimensional platform and viscoelastic properties of plaque composition can be considered in time-dependent and fatigue studies.

Author(s):  
Hang Yao ◽  
Wei Tong

Knowledge of mechanical properties of bones is important for the designing of bone replacements and implants as well as the research of bone diseases such as osteoporosis. However, bone, especially trabecular bone, is a highly anisotropic and heterogeneous living tissue. Micro-computed-tomography (micro-CT) and three-dimensional ultrasound imaging techniques are valuable tools for nondestructive investigation of three-dimensional trabecular bone architecture. From a reconstruction of trabecular bone, a numerical model such as finite element (FE) model can be generated. Using this FE model to simulate compression test, and comparing the simulation results to the results from real mechanical test of the same specimen, the relationship between the observed mechanical behaviors and the microstructure can be established.


1987 ◽  
Vol 31 (02) ◽  
pp. 101-106
Author(s):  
Kyu Nam Cho ◽  
William S. Vorus

A new three-dimensional method is proposed for analyzing orthogonally stiffened grillage structures. The method is based on earlier work related to bridge decks. The relationship between system displacement and loads is described mathematically, and matrices are developed to examine the shear compatibility between plate and beam elements. The paper concludes with a comparison between deflections obtained by several different procedures and the proposed model.


2021 ◽  
Vol 18 (177) ◽  
Author(s):  
Weiwei Jin ◽  
Jordi Alastruey

One-dimensional (1-D) arterial blood flow modelling was tested in a series of idealized vascular geometries representing the abdominal aorta, common carotid and iliac arteries with different sizes of stenoses and/or aneurysms. Three-dimensional (3-D) modelling and in vitro measurements were used as ground truth to assess the accuracy of 1-D model pressure and flow waves. The 1-D and 3-D formulations shared identical boundary conditions and had equivalent vascular geometries and material properties. The parameters of an experimental set-up of the abdominal aorta for different aneurysm sizes were matched in corresponding 1-D models. Results show the ability of 1-D modelling to capture the main features of pressure and flow waves, pressure drop across the stenoses and energy dissipation across aneurysms observed in the 3-D and experimental models. Under physiological Reynolds numbers ( Re ), root mean square errors were smaller than 5.4% for pressure and 7.3% for the flow, for stenosis and aneurysm sizes of up to 85% and 400%, respectively. Relative errors increased with the increasing stenosis and aneurysm size, aneurysm length and Re , and decreasing stenosis length. All data generated in this study are freely available and provide a valuable resource for future research.


Micromachines ◽  
2018 ◽  
Vol 9 (12) ◽  
pp. 617 ◽  
Author(s):  
Ali Kafash Hoshiar ◽  
Sungwoong Jeon ◽  
Kangho Kim ◽  
Seungmin Lee ◽  
Jin-young Kim ◽  
...  

Magnetically driven microrobots have been widely studied for various biomedical applications in the past decade. An important application of these biomedical microrobots is heart disease treatment. In intravascular treatments, a particular challenge is the submillimeter-sized guidewire steering; this requires a new microrobotic approach. In this study, a flexible microrobot was fabricated by the replica molding method, which consists of three parts: (1) a flexible polydimethylsiloxane (PDMS) body, (2) two permanent magnets, and (3) a micro-spring connector. A mathematical model was developed to describe the relationship between the magnetic field and the deformation. A system identification approach and an algorithm were proposed for steering. The microrobot was fabricated, and the models for steering were experimentally validated under a magnetic field intensity of 15 mT. Limitations to control were identified, and the microrobot was steered in an arbitrary path using the proposed model. Furthermore, the flexible microrobot was steered using the guidewire within a three-dimensional (3D) transparent phantom of the right coronary artery filled with water, to show the potential application in a realistic environment. The flexible microrobot presented here showed promising results for enhancing guidewire steering in percutaneous coronary intervention (PCI).


Author(s):  
Ping Ren ◽  
Ya Wang ◽  
Dennis Hong

In this paper, the inverse and forward kinematics of a novel mobile robot that utilizes two actuated spoke wheels is presented. Intelligent Mobility Platform with Active Spoke System (IMPASS) is a wheel-leg hybrid robot that can walk in unstructured environments by stretching in or out three independently actuated spokes of each wheel. First, the unique locomotion scheme of IMPASS is introduced. Then the configuration of the robot when each of its two spoke wheels has one spoke in contact with the ground is modeled as a two-branch parallel mechanism with spherical and prismatic joints. An equivalent serial manipulator of the 2-SP mechanism with the same degrees of freedom is proposed to solve for the inverse and forward kinematic problems. The relationship between the physical limits of the stroke of the spokes (effective spoke length) and the limits of its equivalent degree of freedom is established. This approach can also be expanded to deal with the forward and inverse kinematics of other configurations which has more than two ground contact points. Several examples are used to illustrate the method. The results obtained will be used in the future research on the motion planning of IMPASS walking in unstructured environment.


2012 ◽  
Vol 433-440 ◽  
pp. 558-562
Author(s):  
Min Wang

How to effectively reduce spread is an important subject in the area of ring rolling. In the paper, a reliable coupled thermo-mechanical three-dimensional (3D) finite element (FE) model for hot rolling of large rings is developed. The relationship between spread and the equivalent shape parameters of the deformation zone is discussed. Variations of spread with relative reduction Rr during hot rolling of titanium alloy large rings with different sizes are analyzed and compared using FE simulation. The main results reveal that (1) the spread in a ring exhibits an axisymmetric distribution after the first revolution of the ring. (2) the peak spread appears in the inside or outside layer of a ring, and the minimum spread is found in the middle layer. (2) as Rr increases, the spread increases and the end-plane quality of the ring reduces.


2015 ◽  
Vol 3 (2) ◽  
pp. 157
Author(s):  
Kyriakos Charalampous ◽  
Constantinos M Kokkinos

The purpose of the present paper was to review the extant research on Classroom Psycho-Social Climate (CPSC), in order to underscore and resolve misconceptions, contradictions, and deficiencies, as well as to critically present two of its most important research accomplishments: (a) the construction of a plethora of valid and reliable research instruments to measure the construct of CPSC in various learning environments and at different educational levels, and (b) the association of CPSC with cognitive and affective learning outcomes. The definitions proposed for CPSC are generally characterized by ambiguity. Yet, most researchers agree that the CPSC represents a multidimensional construct, the defining indicators of which, tend to be statistically confirmed in most studies, while at the same time new ones are added, thus providing the construct with a dynamic status. Various theories have been proposed to conceptualize CPSC, the most acknowledged being that of Lewin’s (1936) Field Theory, Murray’s (1938) Needs-Press model, and Getzel and Thelen’s (1960) Socio-Psychological Theory. Two independent research programs and their enduring theoretical and empirical legacy signaled the new era in CPSC research. Rudolf Moos proposed a three-dimensional structure descriptive of all psycho-social climates regardless of the social context (school classrooms, correctional institutions, military facilities, etc.) (1974), and Herbert Walberg demonstrated that students’ were in position to make valid inferences regarding CPSC (1969). Contemporary CPSC research has revealed some methodological issues which need to be taken into consideration when designing CPSC studies. One of the most remarkable achievements of CPSC research is the development of many valid and widely used research instruments for measuring CPSC in various educational contexts and at different educational levels. These instruments reflect the expansion of CPSC research in terms of the integration of new conceptual dimensions, as well as the widening of the age level of students to whom they are addressed. However, despite the increased production of mixed-methods studies in contemporary CPSC research, the cross-cultural adaptation of CPSC instruments, especially those addressing elementary students, has resulted in ambiguous findings. Moreover, whereas most CPSC instruments are based on Moos’s three-dimensional proposal, empirical findings support different allocation of the subscales in these dimensions than the scale developers. Another significant outcome of CPSC research is the examination of the association of CPSC with students’ cognitive and affective learning outcomes. Indeed, empirical findings support the link between the CPSC and various learning outcomes, such as academic achievement, attitudes, self-efficacy, motivation, self-handicapping, and students’ emotional and cognitive involvement. In addition, contemporary CPSC research has examined different paths through which CPSC affects student outcomes. For example, researchers have shown that self-efficacy and achievement goals mediate the relationship between CPSC and student outcomes, such as academic achievement, emotional involvement, etc. Nonetheless, and despite the extended investigation of the relationship between CPSC and student outcomes, research has failed to present consistent evidence with regards to the effect of specific CPSC indicators on student outcomes. What’s more, in cases where CPSC indicators presented negative associations with student outcomes, the explanations provided were insufficient, whereas follow up investigations did not take place. Of course CPSC research has followed other fruitful directions which are also presented in this review. Practical implications of CPSC research findings and future research directions are also discussed.


2017 ◽  
Author(s):  
Saman Naghieh ◽  
Md Sarker ◽  
Mohammad Izadifar ◽  
Xiongbiao Chen

Over the past two decades, significant progress has been achieved in the field of tissue engineering (TE) to restore/repair damaged tissues or organs and, in this regard, scaffolds made from biomaterials have played a critical role. Notably, recent advances in biomaterials and three-dimensional (3D) printing have enabled the manipulation of two or more biomaterials of distinct, yet complementary, mechanical and/or biological properties to form so-called hybrid scaffolds mimicking native tissues. Among various biomaterials, hydrogels synthesized to incorporate living cells and/or biological molecules have dominated due to their hydrated tissue-like environment. Moreover, dispensing-based bioprinting has evolved to the point that it can now be used to create hybrid scaffolds with complex structures. However, the complexities associated with multi-material bioprinting and synthesis of hydrogels used for hybrid scaffolds pose many challenges for their fabrication. This paper presents a brief review of dispensing-based bioprinting of hybrid scaffolds for TE applications. The focus is on the design and fabrication of hybrid scaffolds, including imaging techniques, potential biomaterials, physical architecture, mechanical properties, cell viability, and the importance of vessel-like channels. The key issues and challenges for dispensing-based bioprinting of hybrid scaffolds are also identified and discussed along with recommendations for future research directions. Addressing these issues will significantly enhance the design and fabrication of hybrid scaffolds to and pave the way for translating them into clinical applications.


2008 ◽  
Vol 295 (2) ◽  
pp. H717-H727 ◽  
Author(s):  
Jacques Ohayon ◽  
Gérard Finet ◽  
Ahmed M. Gharib ◽  
Daniel A. Herzka ◽  
Philippe Tracqui ◽  
...  

Fibrous cap thickness is often considered as diagnostic of the degree of plaque instability. Necrotic core area (Corearea) and the arterial remodeling index (Remodindex), on the other hand, are difficult to use as clinical morphological indexes: literature data show a wide dispersion of Corearea thresholds above which plaque becomes unstable. Although histopathology shows a strong correlation between Corearea and Remodindex, it remains unclear how these interact and affect peak cap stress (Capstress), a known predictor of rupture. The aim of this study was to investigate the change in plaque vulnerability as a function of necrotic core size and plaque morphology. Capstress value was calculated on 5,500 idealized atherosclerotic vessel models that had the original feature of mimicking the positive arterial remodeling process described by Glagov. Twenty-four nonruptured plaques acquired by intravascular ultrasound on patients were used to test the performance of the associated idealized morphological models. Taking advantage of the extensive simulations, we investigated the effects of anatomical plaque features on Capstress. It was found that: 1) at the early stages of positive remodeling, lesions were more prone to rupture, which could explain the progression and growth of clinically silent plaques and 2) in addition to cap thickness, necrotic core thickness, rather than area, was critical in determining plaque stability. This study demonstrates that plaque instability is to be viewed not as a consequence of fibrous cap thickness alone but rather as a combination of cap thickness, necrotic core thickness, and the arterial remodeling index.


Author(s):  
Fan Yang ◽  
Yukui Gao

This paper is intended to quantify the relationship between the peen forming effectiveness and various involved parameters through a realistic numerical study. For this purpose, a new finite element (FE) model is proposed with full geometry representation, random shots generation, and rate-dependent material law of kinematic strain-hardening. The mesh sensitivity and effects of boundary conditions are carefully examined. The FE model is validated by comparing the results with the experimental measurements. The proposed model is then used to investigate the effects of the peening intensity (represented as the shot velocity) and the strip thickness on the peen-formed deflection and the residual stress distribution for strips made of Ti-6Al-4V. Our results indicate the existence of a maximum convex deflection for different strip thicknesses. In addition, a reversed deflection (i.e., concaved curvature) is observed for severe peening conditions (i.e., thin strip under high peening intensity). Our simulations verify the previous proposition that a concaved curvature can be generated only when the whole cross section is plastically deformed.


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