Multi-scale Extracellular Matrix Mechanics and Mechanobiology, 2019
Fibrous collagen networks are well known to play a central role in the passive biomechanical resp... more Fibrous collagen networks are well known to play a central role in the passive biomechanical response of soft connective tissues to applied loads. In the current chapter we focus on vascular tissues and share our extensive experience in coupling mechanical loading and multi-photon imaging to investigate, across arteries, species and testing conditions, how collagen fibers move in response to mechanical loading. More specifically, we assess the deformations of collagen networks in rabbit, porcine or human arteries under different loading scenarios: uniaxial tension on flat samples, tension-inflation on tubular samples, bulge inflation on flat samples. We always observe that collagen fibers exhibit a wavy or crimped shape in load-free conditions, and tend to uncrimp when loads are applied, engaging sequentially to become the main load-bearing component. This sequential engagement, which is responsible for the nonlinear mechanical behaviour, is essential for an artery to function normally and appears to be less pronounced for arteries in elderly and aneurysmal patients. Although uncrimping of collagen fibers is a universal mechanism, we also observe large fiber rotations specific to tensile loading, with significant realignment along the loading axis. A unified approach is proposed to compare observations and quantitative analyses as the type of image processing may affect significantly the estimation of collagen fiber deformations. In summary, this chapter makes an important review of the basic roles of arterial microstructure and its deformations on the global mechanical response. Eventually, directions for future studies combining mechanical loading and multi-photon imaging are suggested, with the aim of addressing open questions related to tissue adaptation and rupture.
A computational strategy based on the finite element method for simulating the mechanical respons... more A computational strategy based on the finite element method for simulating the mechanical response of arterial tissues is herein proposed. The adopted constitutive formulation accounts for rotations of the adventitial collagen fibers and introduces parameters which are directly measurable or well established. Moreover, the refined constitutive model is readily utilized in finite element analyses, enabling the simulation of mechanical tests to reveal the influence of microstructural and histological features on macroscopic material behavior. Employing constitutive parameters supported by histological examinations, the results herein validate the model’s ability to predict the micro- and macroscopic mechanical behavior, closely matching previously observed experimental findings. Finally, the capabilities of the adopted constitutive description are shown investigating the influence of some collagen disorders on the macroscopic mechanical response of the arterial tissues.
ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, 2018
There is growing experimental evidence for non‐affine deformations occurring in different types o... more There is growing experimental evidence for non‐affine deformations occurring in different types of fibrous soft tissues; meaning that the fiber orientations do not follow the macroscopic deformation gradient. Suitable mathematical modeling of this phenomenon is an open challenge, which we here tackle in the framework of continuum micromechanics. From a rate‐based analogon of Eshelby's inhomogeneity problem, we derive strain and spin concentration tensors relating macroscopic strain rate tensors applied to the boundaries of a Representative Volume Element (RVE), to strain rates and spins within the tissue microstructure, in particular those associated with fiber rotations due to external mechanical loading. After presenting suitable algorithms for integrating the resulting rate‐type governing equations, a first relevance check of the novel modeling approach is undertaken, by comparison of model results to recent experiments performed on the adventitia layer of rabbit carotid tissue.
Shape Memory Alloys (SMAs) display interesting and unique features: they undergo high reversible ... more Shape Memory Alloys (SMAs) display interesting and unique features: they undergo high reversible strains (up to 10 %) and permanent deformations that disappear by simple heating. These interesting properties promoted the use of SMA devices in a wide range of applications where they are often subject to cyclic loading (actuators, stents, artificial muscles, etc.). Such in-service conditions induce a risk of failure by fatigue of SMA components that must be accounted for in the design phase. This is a challenging task however, namely because of the lack of reliable fatigue criteria applicable to analyzing structures made from shape memory materials. In this paper, we try to fill this gap by presenting a comprehensive approach to designing SMA devices subject to cyclic loading and fatigue. First, to evaluate the thermomechanical state of a SMA structure subject to cyclic loading and, second, to use our knowledge of this state in order to predict the fatigue behaviour of the structure. ...
Multi-scale Extracellular Matrix Mechanics and Mechanobiology, 2019
Fibrous collagen networks are well known to play a central role in the passive biomechanical resp... more Fibrous collagen networks are well known to play a central role in the passive biomechanical response of soft connective tissues to applied loads. In the current chapter we focus on vascular tissues and share our extensive experience in coupling mechanical loading and multi-photon imaging to investigate, across arteries, species and testing conditions, how collagen fibers move in response to mechanical loading. More specifically, we assess the deformations of collagen networks in rabbit, porcine or human arteries under different loading scenarios: uniaxial tension on flat samples, tension-inflation on tubular samples, bulge inflation on flat samples. We always observe that collagen fibers exhibit a wavy or crimped shape in load-free conditions, and tend to uncrimp when loads are applied, engaging sequentially to become the main load-bearing component. This sequential engagement, which is responsible for the nonlinear mechanical behaviour, is essential for an artery to function normally and appears to be less pronounced for arteries in elderly and aneurysmal patients. Although uncrimping of collagen fibers is a universal mechanism, we also observe large fiber rotations specific to tensile loading, with significant realignment along the loading axis. A unified approach is proposed to compare observations and quantitative analyses as the type of image processing may affect significantly the estimation of collagen fiber deformations. In summary, this chapter makes an important review of the basic roles of arterial microstructure and its deformations on the global mechanical response. Eventually, directions for future studies combining mechanical loading and multi-photon imaging are suggested, with the aim of addressing open questions related to tissue adaptation and rupture.
A computational strategy based on the finite element method for simulating the mechanical respons... more A computational strategy based on the finite element method for simulating the mechanical response of arterial tissues is herein proposed. The adopted constitutive formulation accounts for rotations of the adventitial collagen fibers and introduces parameters which are directly measurable or well established. Moreover, the refined constitutive model is readily utilized in finite element analyses, enabling the simulation of mechanical tests to reveal the influence of microstructural and histological features on macroscopic material behavior. Employing constitutive parameters supported by histological examinations, the results herein validate the model’s ability to predict the micro- and macroscopic mechanical behavior, closely matching previously observed experimental findings. Finally, the capabilities of the adopted constitutive description are shown investigating the influence of some collagen disorders on the macroscopic mechanical response of the arterial tissues.
ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, 2018
There is growing experimental evidence for non‐affine deformations occurring in different types o... more There is growing experimental evidence for non‐affine deformations occurring in different types of fibrous soft tissues; meaning that the fiber orientations do not follow the macroscopic deformation gradient. Suitable mathematical modeling of this phenomenon is an open challenge, which we here tackle in the framework of continuum micromechanics. From a rate‐based analogon of Eshelby's inhomogeneity problem, we derive strain and spin concentration tensors relating macroscopic strain rate tensors applied to the boundaries of a Representative Volume Element (RVE), to strain rates and spins within the tissue microstructure, in particular those associated with fiber rotations due to external mechanical loading. After presenting suitable algorithms for integrating the resulting rate‐type governing equations, a first relevance check of the novel modeling approach is undertaken, by comparison of model results to recent experiments performed on the adventitia layer of rabbit carotid tissue.
Shape Memory Alloys (SMAs) display interesting and unique features: they undergo high reversible ... more Shape Memory Alloys (SMAs) display interesting and unique features: they undergo high reversible strains (up to 10 %) and permanent deformations that disappear by simple heating. These interesting properties promoted the use of SMA devices in a wide range of applications where they are often subject to cyclic loading (actuators, stents, artificial muscles, etc.). Such in-service conditions induce a risk of failure by fatigue of SMA components that must be accounted for in the design phase. This is a challenging task however, namely because of the lack of reliable fatigue criteria applicable to analyzing structures made from shape memory materials. In this paper, we try to fill this gap by presenting a comprehensive approach to designing SMA devices subject to cyclic loading and fatigue. First, to evaluate the thermomechanical state of a SMA structure subject to cyclic loading and, second, to use our knowledge of this state in order to predict the fatigue behaviour of the structure. ...
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Papers by Claire Morin