Miguel A Martínez

University of Zaragoza | UNIZAR · Department of Mechanical Engineering

In this work an Artificial Neural Network (ANN) was developed to help in the diagnosis of plaque vulnerability by predicting the Young modulus of the core (E core ) and the plaque (E plaque ) of atherosclerotic coronary arteries. A representative in silico database was constructed to train the ANN using Finite Element simulations covering the range...

Background Aortic stiffness independently predicts mayor adverse cardiovascular events and mortality in the general population. Cardiovascular magnetic resonance (CMR) permits the assessment of a number of parameters theoretically linked to aortic stiffness, such as distensibility (AD), pulse wave velocity (PWV) and proximal aorta longitudinal stra...

Proper characterisation of biological tissue is key to understanding the effect of the biomechanical environment in the physiology and pathology of the cardiovascular system. Aortic dissection in particular is a prevalent and sometimes fatal disease that still lacks a complete comprehension of its progression. Its development and outcome, however,...

The most common treatment for obstructive coronary artery disease (CAD) is the implantation of a permanent drug-eluting stent (DES). Not only has this permanency been associated with delayed healing of the artery, but it also poses challenges when treating subsequent re-narrowing due to in-stent restenosis (ISR). Drug-coated balloons (DCBs) provide...

We analyze the residual stresses and mechanical properties of layer-dissected infrarenal abdominal aorta (IAA). We measured the axial pre-stretch and opening angle and performed uniaxial tests to study and compare the mechanical behavior of both intact and layer-dissected porcine IAA samples under physiological loads. Finally, some of the most popu...

Con el objetivo de caracterizar mecánicamente el tejido cardiaco porcino, se han llevado a cabo diferentes ensayos mecánicos sobre siete animales. Se han realizado ensayos biaxiales y tangenciales, elásticos y viscoelásticos. El procedimiento utilizado permite caracterizar el comportamiento del tejido con cualquier modelo de material existente en l...

In this work, we propose a mechanobiological atheroma growth model modulated by a new haemodynamic stimulus. To test this model, we analyse the development of atheroma plaques in patient-specific bifurcations of carotid arteries for a total time of 30 years. In particular, eight geometries (left or right carotid arteries) were segmented from clinic...

Stents have become the most successful device to treat advanced atherosclerotic lesions. However, one of the main issues with these interventions is the development of restenosis. The coating of stents with antiproliferative substances to reduce this effect is now standard, although such drugs can also delay re-endothelialization of the intima. The...

Perturbed aorta hemodynamics, as for the carotid and the coronary artery, has been identified as potential predicting factor for cardiovascular diseases. In this study, we propose a parametric study based on the computational fluid dynamics with the aim of providing information regarding aortic disease. In particular, the blood flow inside a parame...

Cardiovascular diseases related to atherosclerosis are the first cause of death in the western world. This relevant fact has motivated the development of numerical models for arterial behavior in order to understand better cardiovascular pathologies. This chapter provides a parametric tool, using Machine Learning Techniques (MLTs), to assist the cl...

This chapter focuses on physiological intraparietal stress distribution in vulnerable atherosclerotic plaques (VPs) and its potential for identifying VPs at high risk of rupture. Although several clinical and biomechanical studies have identified plaque morphology as a key predictor of vulnerability to rupture, predicting rupture remains imprecise,...

We present a multiphysical model to understand atheromatous plaque growth. The model was based on the physics of blood flow in the arterial lumen (Navier–Stokes equations and Darcy's law) coupled to a convection-diffusion-reaction equation to model exchange between lumen and arterial wall. The Kedem-Katchalsky theory was used to model intercellular...

Despite increasing experimental and analytical efforts to investigate the irreversible effects of arterial tissue failure, the underlying mechanisms are still poorly understood. The goal of this study was to characterize the failure properties of the intact wall and each separated layer (intima, media, and adventitia) of the descending thoracic and...

The stenting procedure has evolved to become a highly successful technique for the clinical treatment of advanced atherosclerotic lesions in arteries. However, the development of in-stent restenosis remains a key problem. In this work, a novel two-dimensional continuum mathematical model is proposed to describe the complex restenosis process follow...

In this paper, we hypothesize that the biaxial mechanical properties of the aorta may be dependent on arterial location. To demonstrate any possible position-related difference, our study analyzed and compared the biaxial mechanical properties of the ascending thoracic aorta, descending thoracic aorta and infrarenal abdominal aorta stemming from th...

Anticoagulants are the treatment of choice for pulmonary embolism. When these fail or are contraindicated, vena cava filters are effective devices for preventing clots from the legs from migrating to the lung. Many uncertainties exist when a filter is inserted, especially during physiological activity such as normal breathing and the Valsalva manoe...

The goal of this work consists in a quantitative analysis and constitutive modelling of ageing processes associated to plaque formation in mice arteries. Reliable information on the characteristic evolution of pressure-stretch curves due to the ageing effects is extracted from previous inflation test experiments. Furthermore, characteristic age-dep...

Background: Mechanical characteristics of vascular tissue may play a role in different arterial pathologies, which, amongst others, requires robust constitutive descriptions to capture the vessel wall's anisotropic and non-linear properties. Specifically, the complex 3D network of collagen and its interaction with other structural elements has a d...

Stenting technique is employed worldwide for treating atherosclerotic vessel and tracheal stenosis. Both diseases can be treated by means of metallic stents which present advantages but are affected by the main problem of restenosis of the stented area. In this study we have built a rabbit trachea numerical model and we have analyzed it before and...

This work analyzes the progressive stiffening of the aorta due to atherosclerosis development of both ApoE(-/-) and C57BL/6J mice fed on a Western (n = 5) and a normal (n = 5) chow diet for the ApoE(-/-) group and on a normal chow diet (n = 5) for the C57BL/6J group. Sets of 5 animals from the three groups were killed after 10, 20, 30 and 40 weeks...

An inferior vena cava filter is a medical device that is implanted in the inferior vena cava and is in charge of capturing blood clots before they reach the lungs, preventing from pulmonary embolism. There are some clinical problems regarding the use of inferior vena cava filters. One of them is the difficulty when retrieving the device due to the...

There are many evidences that coronary plaque is not only dependent on the formation and progression of atherosclerosis, but also on the vascular remodelling response. If the local wall shear stress is low, a proliferative plaque may develop. Local inflammatory response will stimulate the formation of a plaque prone to rupture with superimposed thr...

A new device for local delivery of antibiotics is presented, with potential use as a drug-eluting fixation pin for orthopedic applications. The implant consists of a stainless steel hollow tubular reservoir packed with the desired antibiotic. Release takes place through several orifices previously drilled in the reservoir wall, a process that does...

In this paper we hypothesize that the layer-separated residual stresses and mechanical properties of layer-separated thoracic aorta arteries may be dependent on arterial location of the vessel. To demonstrate any possible position differences, we measured the axial pre-stretch and opening angle and performed uniaxial and biaxial tests under physiol...

Endothelial cells are key units in the regulatory biological process of blood vessels. They represent an interface to transmit variations on the fluid dynamic changes. They are able to adapt its cytoskeleton, by means of microtubules reorientation and F-actin reorganization, due to new mechanical environments. Moreover, they are responsible for ini...

We propose a mathematical model of atheroma plaque initiation and early development in coronary arteries using anisotropic transmural diffusion properties. Our current approach is on the process on plaque initiation and intimal thickening rather than in severe plaque progression and rupture phenomena. The effect of transport properties, in particul...

It is well known that biological tissue adapt its properties due to different mechanical and chemical stimuli. The goal of this work is the study of the collagen turnover in the arterial tissue of hypertensive patients through a coupled computational mechano-chemical model. Although it has been widely studied experimentally, computational models de...

The purpose of this paper is to verify a commercial software based fluid–structure interaction scheme for the inferior vena cava. Vena cava deep thrombosis (TVP) is a potentially deathly disease consequent to pulmonary thromboembolism (TEP). TEP consist in the obstruction of the pulmonary artery due to a blood clot traveling in the cardiovascular s...

In this study, the trapping ability of the Günther Tulip and Celect inferior vena cava filters was evaluated. Thrombus capture rates of the filters were tested in vitro in horizontal position with thrombus diameters of 3 and 6 mm and tube diameter of 19 mm. The filters were tested in centered and tilted positions. Sets of 30 clots were injected int...

The purpose of the present study was to determine whether in vivo bifurcation geometric factors would permit prediction of the risk of atherosclerosis. It is worldwide accepted that low or oscillatory wall shear stress (WSS) is a robust hemodynamic factor in the development of atherosclerotic plaque and has a strong correlation with the local site...

Endotracheal stenting is a controversial treatment for tracheal stenosis. Metallic stents have advantages but also show disadvantages such as restenosis due to epithelial hyperplasia and granuloma formation. In this work we analyze the response of a rabbit tracheal wall during normal breathing under implantation of a Zilver® Flex™ Stent. Trachea ge...

In this work the mechanical response of the carotid arterial wall is studied. Some limitations of previous models of the arterial wall are overcomed and variability of the fitting problem is reduced. We review some experimental data from the literature and provide a constitutive model to characterize such data. A strain energy function is introduce...

Although stenting is the most commonly performed procedure for the treatment of coronary atherosclerotic lesions, in-stent restenosis (ISR) remains one of the most serious clinical complications. An important stimulus to ISR is the altered hemodynamics with abnormal shear stresses on endothelial cells generated by the stent presence. Computational...

The aim of this work is to study the applicability of a numerical-experimental methodology for wear modelling to the design of a lift car installation by means of finite element simulations. The study focuses on the sliding of guide shoe inserts, made of thermoplastic polyurethane, TPU, over fixed lift car guides, made of steel. This component incl...

Atherosclerosis is a vascular disease caused by inflammation of the arterial wall, which results in the accumulation of low-density lipoprotein (LDL) cholesterol, monocytes, macrophages and fat-laden foam cells at the place of the inflammation. This process is commonly referred to as plaque formation. The evolution of the atherosclerosis disease, a...

The objective of this work is to develop a remodeling model for biological matter coupling two different processes in a 3D framework: reorientation of the preferential direction of a given fibered structure and reorientation of the fibrils or filaments that make up such a structure. This work uses the microsphere-based approach to take into account...

Arterial hypertension is a chronic medical condition associated with an elevated blood pressure. Chronic arterial hypertension initiates a series of events, which are known to collectively initiate arterial wall thickening. However, the correlation between macrostructural mechanical loading, microstructural cellular changes, and macrostructural ada...

Rupture of atherosclerotic plaque, which is related to maximal stress conditions in the plaque among others, is a major cause of mortality. More careful examination of stress distributions in atherosclerotic plaques reports that it could be due to local stress behaviors at critical sites caused by cap thinning, inflammation, macroscopic heterogenei...

As plaque develops in arteries two types of remodeling can occur; positive and negative remodeling. Positive remodeling is an outward compensatory remodeling in which the arterial wall grows outward in an attempt to maintain a constant lumen diameter, while negative remodeling is defined as a local shrinkage of vessel size. Sudden heart attacks rem...

The study of the mechanical properties of swine carotids has clinical relevance because it is important for the appropriate design of intravascular devices in the animal trial phases. The inelastic properties of porcine carotid tissue were investigated. Experimental uniaxial cyclic tests were performed along the longitudinal and circumferential dir...

In this study, we develop structured tree outflow boundary conditions for modelling the human carotid haemodynamics. The model geometry was reconstructed through computerised tomography scan. Unsteady-state computational fluid dynamic analyses were performed under different conditions using a commercial software package ADINA R&D, Inc., (Watertown,...

We present a theoretical and computational model for collagen turnover in soft biological tissues. Driven by alterations in the mechanical environment, collagen fiber bundles may undergo important chronic changes, characterized primarily by alterations in collagen synthesis and degradation rates. In particular, hypertension triggers an increase in...

The viscoelastic properties of porcine carotid tissue are investigated in this work. Experimental uniaxial stress relaxation tests along the longitudinal and circumferential directions of the vessel were performed for carotid strips extracted from 10 vessels. Directional and local differences--distal versus proximal position--in the tissue behavior...

In this study, a Fluid Solid Interaction analysis (FSI) of a computerized tomography (CT) scan reconstructed left coronary artery was performed. The arterial wall was modeled as an isotropic hyperelastic material. The arterial wall shear stress (WSS) was computed in order to investigate a correlation between flow-induced wall shear stress and geome...

The goal of this work is to study the influence of the main geometrical parameters on the radial force of a self-expanding stent, and using them to advance towards a new design of a variable radial force stent to improve the interaction vessel-device. Using finite element simulations, a parametric analysis of a commercial stent model (Acculink, Abb...

The objective of this work is to present an integral methodology to numerically model the wear phenomena by friction in a polymer–metal contact pair, showing the development of a numerical tool to implement a wear model in the commercial finite element code Abaqus. The contact pair in which this work is based corresponds to the contact between a gu...

Plaque rupture plays a role in the majority of acute coronary syndromes. Rupture has usually been associated with stress concentrations, which are mainly affected by the plaque geometry and the tissue properties. The aim of this study is to evaluate the influence of morphology on the risk of plaque rupture, including the main geometrical factors, a...

The aim of this paper is to provide a computational study of migration forces of a retrievable filter (Günther Tulip inferior vena cava filter). Using an experimental setup and finite element simulation, the migration forces and stress at the end of the anchored hooks in the struts were estimated. After that, the estimation value of migration stres...

Enormous progress has been made during recent years in the phenomenological modelling of soft tissue. In general, three important softening phenomena associated with biological tissues may be distinguished. First, there is the dependence of the mechanical response on the previously attained maximum load level. This is quite similar to the well-know...

An anisotropic damage model for soft fibered tissue is presented in this paper, using a multi-scale scheme and focusing on the directionally dependent behavior of these materials. For this purpose, a micro-structural or, more precisely, a microsphere-based approach is used to model the contribution of the fibers. The link between micro-structural c...

The present study focusses on the determination, comparison and constitutive modelling of the passive mechanical properties of the swine carotid artery over very long stretches in both proximal and distal regions. Special attention is paid to the histological and mechanical variations of these properties depending on the proximity to the heart. The...

Nearly all soft tissues, including the vascular tissue, present a certain degree of viscoelastic material response, which becomes apparent performing multiple relaxation tests over a wide range of strain levels and plotting the resulting stress relaxation curves, nonlinear viscoelasticity of the tissue. Changes in relaxation rate at each strain may...

Constitutive models for arterial tissue have been an active research field during the last years. The main micro-constituents of blood vessels are different types of cells and the extra-cellular matrix formed by an isotropic high water content ground substance and a network composed of elastin and collagen fibres. Usually the arterial tissue has be...

An anisotropic damage model for vascular tissue is presented here. The widely used strain energy function in the quasi incompressible framework is exploited on its decoupled form to, additively, take into account the volumetric and the deviatoric contributions. Since a well-established neo-Hooke law is used to model the deviatoric part of the isotr...

Accurate determination of the biomechanical implications of vascular surgeries or pathologies on patients requires developing patient-specific models of the organ or vessel under consideration. In this regard, combining the development of advanced constitutive laws that mimic the behaviour of the vascular tissue with advanced computer analysis and...

Nearly all soft tissues, among which the vascular tissue is included, present a certain degree of viscoelastic response. This behaviour may be attributed in part to fluid transport within the solid matrix, and to the friction between its fluid and solid constituents. After being preconditioned, the tissue displays highly repetitive behaviour, so th...

Microsphere-based constitutive models are a helpful tool in the modelling of materials with a micro-structure composed of contributing elements directionally arranged. This is the case, for instance, for fibred soft tissues. In these models, the macroscopic mechanical behaviour is obtained from the integration of the micro-structural contribution o...

In this paper, the viscoelastic mechanical properties of vaginal tissue are investigated. Using previous results of the authors on the mechanical properties of biological soft tissues and newly experimental data from uniaxial tension tests, a new model for the viscoelastic mechanical properties of the human vaginal tissue is proposed. The structura...

A fully three-dimensional anisotropic elastic model for vascular tissue modelling is presented here. The underlying strain energy density function is assumed to additively decouple into volumetric and deviatoric contributions. A straightforward isotropic neo-Hooke-type law is used to model the deviatoric response of the ground substance, whereas a...

The passive mechanical properties of the ovine infrarenal vena cava are analysed in this paper. In vivo stretch from 15 venae was measured in order to get data from the physiological situation before harvesting the vessel. Vena cava strips (n=64) both in longitudinal and circumferential directions were cut and subjected to simple tension tests. Res...

The aim of this paper is to introduce a fully three-dimensional finite-strain damage model for visco-hyperelastic fibrous soft tissue. The structural model is formulated using the concept of internal variables that provide a very general description of materials involving irreversible effects. Continuum damage mechanics is used to describe the soft...

In this paper, the application of the natural element method (NEM) to solve inelastic finite deformation problems in isotropic and fiber-reinforced materials is presented. As most meshless methods, the NEM does not require an explicit connectivity definition. Consequently, it is quite adequate to simulate large strain problems with important mesh d...

Understanding the functional performance of vascular tissue is taking a rising importance due to the increasing impact of cardiovascular diseases in developed countries. Currently available medical imaging acquisition techniques, combined with computer modelling allow patient-specific simulations of customized geometries that may help in medical di...

It is commonly accepted that total or partial meniscectomies cause wear of articular cartilages that leads to severe damage in a period of few years. This also produces alteration of the biomechanical environment and increases articular instability, with a progressive and degenerative arthrosic pathology. Due to these negative consequences, total m...

While finite elements has been considered during the last decades as the universal tool to perform simulations in biomechanics, a recently developed wide family of methods, globally coined as meshless methods, has emerged as an attractive choice for an increasing variety of engineering problems. They present some key advantages such as the absence...

Numerical and analytical studies on cylindrical geometries have shown the relevance of accounting for residual stresses in arterial modeling. However, multiple difficulties, both geometrical and numerical, arise when enforcing residual stresses in patient-specific arteries. This is the reason of the few simulations that have been developed on this...

Physiological studies have shown that focal articular surface defects in the human knee may progress to degenerative arthritis. Although the risk of this evolutive process is multifactorial, defect size is one of the most important factors. In order to determine the influence of osteochondral defect size and location on the stress and strain concen...

This paper provides a critical review of past and current techniques for the computational modelling of diarthrodial joints. The objective of the paper is to describe strategies for addressing the computational modelling of joint mechanics using the finite element (FE) method, differentiating between geometry, constitutive modelling of the componen...

In this paper we present a fully three-dimensional finite-strain damage model for fibrous soft tissue. Continuum damage mechanics is used to describe the softening behaviour of soft tissues under large deformation. The structural model is formulated using the concept of internal variables that provides a very general description of materials involv...

In this paper we present a fully three-dimensional finite strain anisotropic visco-hyperelastic model for ligaments and tendons. The structural model is formulated within the framework of non-linear continuum mechanics and is well-suited for its finite element implementation. This model is based on a local additive decomposition of the stress tenso...