Search

International audience; The use of numerical simulation to investigate heart and valvular mechanics is becoming increasingly popular. In particular, finite element analysis is often used to support the operation planning procedure as well as the design of new prostheses with mechanical properties as close as possible to those of natural tissues and an even better biocompatibility. With one of the highest prevalence of cardiovascular degenerative diseases [1], aortic valves (AV) have been widely studied during the last decades.The elastic [2] and time-dependent [3] behaviors of the AV leaflets under physiological biaxial loading states have been previously investigated in the literature over a wide range of loading conditions.. As most soft tissues, AV has an oriented network of collagen fibers embedded in an elastin matrix, which is responsible for their hyperelastic and anisotropic behaviors. Accordingly, non-linear transverse isotropic constitutive equations are often used assuming a macroscopically-identifiable preferred fiber direction.In this study a new method is proposed in order to estimate relevant material and structural properties of AV while reducing at the same time the number of complex and time-consuming experiments. An inverse analysis procedure based on the finite element computation of planar biaxial tensile tests was used to set-up a reduced protocol. This protocol was then experimentally reproduced to identify real material parameters. The obtained material parameters will be later used to model heart valve tissues.

International audience; Constitutive modelling of soft biological tissues has been the topic of abundant literature. These biological tissues, made of variously oriented and crimped fibers embedded in a soft matrix, exhibit a highly nonlinear anisotropic behavior with the ability to sustain large reversible strains. The existing constitutive models are mainly phenomenological hyperelastic models developed at the macroscopic scale (Holzapfel & Gasser 2000). Experimental mechanical tests performed on soft tissues and coupled to confocal microscopic imaging (Schrauwen et al. 2012) reveal that this nonlinear behavior originates in geometrical changes in the microstructure, such as progressive decrimping and re-alignement of the fibers along the load direction. This confirms the growing need to understand the relationship between phenomena taking place in the microstructure and macroscopic mechanical response; subsequently driving forward multi-scale approaches (Morin & Hellmich 2014). We here propose to model the reorientation of the fibers within the matrix through extension of the framework of continuum micromechanics (Zaoui 2002) and Eshelby’s inclusion problems (Eshelby 1957). We investigate the ability of the proposed model to capture, through microstructure morphology changes, the non-linear mechanical response of soft tissues, the possible path dependence of their response to multiaxial loading, and a remaining frozen elastic energy after complete unloading of the tissue.

International audience; Compression therapy is traditionally employed to achieve a variety of therapeutic goals related to venous insufficiency but its mechanisms are neither clearly understood nor conclusively demonstrated. (Avril et al., 2010) have pointed out that the capacity of the treatment to achieve the desired medical goal is closely related to the question of transmission of pressure through the soft tissues, as a result of which biomechanical models have been developed (Dubuis et al., 2012). In these models, the prediction of pressure was made based on the rather strong assumption that the behaviour of soft tissues (muscles and adipose tissues) can be approximated as homogeneous materials. Recent developments in ultrasound imaging can be helpful to improve both our understanding of the effect of medical compression stockings (MCS) on the blood return and on the quality of our predictions. (Bercoff et al., 2004) introduced a new ultrasound based technology called Supersonic Shear Imaging (SSI), for real-time soft tissue elasticity mapping. This transient elastography technique remotely produces a low frequency shear wave inside soft tissue through a radiation force by focusing ultrasonic beams at a supersonic speed. The shear wave motion is captured at a frame rate of 5 MHz. The velocity field of the medium can be mapped an dassuming the medium to be elastic, Young's modulus can be estimated quantitatively. This non-invasive technique allows identifying the material property heterogeneities inside the different compartments of the human leg. Using this experimental technique combined with FE modeling, the present study aims at shedding a light on the influence of those heterogeneities of material properties on the pressure inside the leg under elastic compression.

International audience; Elastic compression bandage is a common treatment for venous or lymphatic disorders. Even though the efficacy of this treatment is admitted, its mechanism remains poorly understood. The success of the treatment depends on the applied pressure, which depends on the bandage tension and the curvature of the limb (Laplace’s Law), the number of layers of the bandage, its components (padding layer, crepe …) and elastic properties, and the interactions between bandages and leg. To better understand the action of compression bandage, many interface pressure measurements have been done, but those measurements only give local information and for now, the whole pressure distribution on the leg is not known. Also, due to complex leg curvature and to bandage-leg and bandage-bandage interactions, the Laplace’s law is not sufficient to give a fine description of the pressure fields. Some simulations of the leg compression exist. Most of them are modeling the action of a compression sock on a leg [1][2], whose mechanical properties are more or less complex [3]. As far as we know, the simulation of bandage application on the leg has never been done yet. The aim of this communication is to present a first numerical model of the action mechanisms of bandages onto the skin developed through an experimental-numerical approach. A subject-specific FE model of bandage application is developed and compared with experimental measurements on two subjects.