About
160
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Introduction
After 25 years as Faculty in France, I am now settling at California State University at Los Angeles at the Department of Mechanical Engineering.
My research interests are in Biomedical Engineering and Mechanics of soft materials.
Additional affiliations
January 2020 - present
September 1999 - August 2005
September 2004 - January 2019
Publications
Publications (160)
This study presents an experimental protocol for the characterization of the strain rate effects on the nonlinear behavior of an organic matrix composite. This protocol is based on the development of a displacement interrupted tensile test device adapted to servo-hydraulic jacks. The protocol allows for the performance of incremental cyclic tests f...
There is a significant need for tools to detect damage in composite materials, whether for the development of models, the characterization of materials or the validation of structures. However, many different methods are available, each with its own advantages and drawbacks, making the choice difficult when setting up tests. This paper will present...
The characterization of CFRP mechanical behavior under dynamic loading is an important topic for research laboratories. Literature reveals disparities in the evolution of shear behavior of CFRP materials under dynamic loading. Due to the lack of normative protocol for dynamic loading, these disparities can come from the geometry of the specimens us...
This article presents an open-source Integrated Digital Image Correlation (I-DIC) software written in Python using CUDA-enabled GPUs designed to run at high (1–100 Hz) frequency. The field computation is performed using a global approach and the result is a projection of the real field in a user-defined base of fields. This software can be used in...
The mobility of pelvic organs is the result of an equilibrium called Pelvic Static characterizing the balance between the properties and geometries of organs, suspensions and support system. Any imbalance in this complex system can cause of pelvic static disorder. Genital prolapse is a common hypermobility pathology which is complex, multi factoria...
Implants for the cure of female genital prolapse still show numerous complications cases that sometimes have dramatic consequences. These implants must be improved to provide physiological support and restore the normal functionalities of the pelvic area. Besides the trend towards lighter meshes, a better understanding of the in vivo role and impac...
The impact of the loading history on the resistance to break of a carbon-black filled styrene butadiene rubber is explored experimentally. Carbon-black filled rubberlike materials soften significantly upon the first loading due to the well known Mullins effect. The impact of this effect on the critical energy release rate at break, Gc, of the consi...
Architectured materials can now be easily produced thanks to recent developments in additive manufacturing processes. Such mesostructures have great potential to supplement the classical materials used for shock absorption in multiple protective applications (with expanded polystyrene (EPS) or ethylene-vinyl acetate (EVA) components), conferring se...
The characterization of soft tissue raises several difficulties. Indeed, soft biological tissues usually shrink when dissected from their in vivo location. This shrinkage is characteristic of the release of residual stresses, since soft tissues are indeed often pre-stressed in their physiological configuration.
During experimental loading, large ex...
This paper introduces a method for dynamic 3D registration of female pelvic organs using 2D dynamic magnetic‐resonance images (MRIs). The aim is to provide a better knowledge and understanding of pathologies such as prolapsus or abnormal mobility of tissues. 2D dynamic MRI sequences are commonly used in nowadays clinical routines in order to evalua...
Introduction and hypothesisPelvic organ mobility is defined as the displacement of pelvic organs between rest and maximal straining. We hypothesized that pelvic organ mobility after vaginal sacrospinous hysteropexy (SSHP) might be increased compared with other surgeries for uterine descent, which may contribute to the high occurrence of postoperati...
Numerical simulation is useful to help understand the behavior of pelvic system, and eventually to assist the diagnostic and surgery. Patient-specific simulation is expected to optimize the treatment of patients. Despite the requirement of mechanical properties and loading, patient-specific simulation requires first 3D geometry adapted to patient....
Introduction:
The women pelvic floor is a complex system, which seems to endure several modifications during pregnancy and childbirth. Our primary purpose was to build an extensive 3 dimensional (3D) numerical anatomical model of the women pelvic floor.
Methods:
First, the role and the location of each organ, muscle, or ligament, were identified...
Background:
Our study aimed at understanding the influence of healing time on the mechanical properties of meshes used in pelvic organ prolapse, once implanted in an animal model using the rat.
Methods:
A standard polypropylene mesh was implanted in 42 rats in order to evaluate the mechanical properties of the implanted mesh. Explantation occurr...
The aim of this paper is to propose a multi-scale anisotropic constitutive model based on a microscopic description of a soft fibrous tissue. The proposed model is based on directional (or micro-sphere) strain energy density, linking the contribution of fibers to macroscopic elasticity. The link between the microscopic fiber and the macroscopic res...
The effect of strain-softening due to Mullins effect on the propagation of a crack is experimen- tally investigated by applying various pre-stretches to a non-crystallizing carbon-black filled elastomer, followed by crack propagation tests. Pure shear tests carried at constant crosshead speed on notched samples, are chosen to characterize crack gro...
In order to estimate mode I fracture strain energy release rate of a rubber upon monotonic loadings, the material is submitted to pure shear and single edge notch tension tests. Catastrophic failure happens suddenly for both tests, revealing mirror-like crack surfaces, assessing the fragile fracture. Nonetheless, Griffith failure analysis could be...
Knitted fabrics are used to manufacture soft implants for medical applications. Once integrated in the body, the fabric forms a new composite material with the native and scar tissues. The mechanical behavior of the composite is assumed to be hyperelastic to match with the physiological behavior of the native tissues and thus to improve the fabric...
Numerical simulation of pelvic system could lead to a better understanding of common pathology through objective and reliable analyses of pelvic mobility according to mechanical principles. In clinical context, patient-specific simulation has the potential for a proper patient-personalised cure. For this purpose, a simulable 3D geometrical model, w...
This work presents a non-destructive method to assess mechanical properties of the patient-specific soft tissues of a multi-organ system under large strain. The presented application is focusing on the female pelvic cavity. Based on an experimental data bank of mechanical properties, dynamic MRI’s displacement field analysis, MRI’s geometrical reco...
The organic matrix composites (OMC) are widely used in aeronautical industry. The mechanical behaviour of these materials is known to be strain rate and temperature dependent. Therefore it is necessary to take the influence of temperature and strain rate into account in the behaviour models. The mechanical behaviour of OMC can be split into two dif...
Abdominal wall sheathing tissues are commonly involved in hernia formation. However, there is very limited work studying mechanics of all tissues from the same donor which prevents a complete understanding of the abdominal wall behavior and the differences in these tissues. The aim of this study was to investigate the differences between the mechan...
The resistance to mode I failure of rubbers is studied by submitting single edge notch samples to uniaxial tension. Reproducing the seminal work of Rivlin and Thomas (J Polym Sci 10:291–318, 1953), single edge notch tension specimens, presenting notches of various lengths, are stretched until break. A styrene butadiene rubber, unfilled and filled w...
Introduction and hypothesis:
We studied the geometry of and changes in structures that play an important role in stabilizing the pelvic system during pregnancy using a numerical system at different gestational ages and postpartum.
Methods:
We developed a parturient numerical model to assess pelvic structures at different gestational stages (16,...
New composite materials are increasingly used in aviation to reduce the mass of structures. Aeronautic structures have to be designed with respect to a broad range of mechanical loadings during their operational life. These loadings are considered in the design by numerous cases, from low up to high speeds. The motivation of the presented work is t...
The mechanical behaviour of organic matrix composite materials such as T700GC/M21 carbon fibre reinforced polymer (CFRP) is generally considered by the industry as being orthotropic elastic for the sizing of aeronautical structures under normal isothermal “static” flight loads. During the aircraft lifetime, it may be exposed to severe loading condi...
All civil engineering structures include seals to ensure water tightness. Seals have to be waterproof and seismic resistant since they are located between two concrete structures. Seals are usually rubbers as neoprene, polyurethane, or polydimethylsiloxane (Silicone). In order to guarantee the longevity of civil engineering structure, studies devot...
Since childbirth presents a significant risk factor for pathology occurrence of the pelvic floor, analysis of the phenomena involved during a vaginal delivery is a major issue in obstetrics and gynecology researches. Computational biomechanics tool dedicated to the delivery could help to understand the causes of injuries and predict the perineal le...
Objectives:
It has been demonstrated that both heterotopic and orthotopic transplants of epithelium-denuded cryopreserved tracheal allografts are feasible in immunosuppressant-free rabbits. Validation of these results in large animals is required before considering clinical applications. We evaluated the viability, immune tolerance and strain prop...
Due to their high deformability, the elastomers are widely used in various fields of applications. Their hyper-elastic behavior requires means of characterization adapted to contactless, high strain as well as heterogeneous strain field. Digital Image Correlation (DIC) have been used to characterize such material. In case of large strain it might b...
Female pelvic disorders have a large social impact; the diagnosis of which relies on a key indication: pelvic mobility. The normal mobility is present in a healthy patient, meanwhile the hypermobility can be a sign of female pelvic prolapse and the hypomobility for endometriosis. The evaluation of pelvic mobility is based on medical image analysis....
Purposes
The objective of this study is to design a 3D biomechanical model of the female pelvic system to assess pelvic organ suspension theories and understand cystocele mechanisms.
Methods
A finite elements (FE) model was constructed to calculate the impact of suspension structure geometry on cystocele. The sample was a geometric model of a contr...
To better understand the in vivo mechanical behavior of synthetic mesh implants, we designed a specific experimental protocol for the mechanical characterization of explanted mesh under uniaxial tension. The implantation of a mesh leads to the development of scar tissue and the formation of a new composite made of native tissue, a mesh implant and...
New composite materials are increasingly used in aviation to reduce the mass of structures. Aeronautic
structures have to be designed so as to be able to sustain a broad range of mechanical loadings during
their operational life. These loading cases need also to account for low to high loading rates. The
main objective of the present work is to est...
Introduction and hypothesis:
We aim to analyze the combined influence of the size of the mesh, the number of sutures, the combined use of an anterior and posterior mesh, and the tension applied to the promontory, on the mobility of the pelvic organs and on the sutures, using a Finite Element (FE) model of the female pelvic system during abdominal...
Introduction and hypothesis:
The aim of the study was to correlate histological and biomechanical characteristics of the vaginal wall in women with pelvic organ prolapse (POP).
Methods:
Tissue samples were collected from the anterior [point Ba; POP Questionnaire (POP-Q)] and/or posterior (point Bp; POP-Q) vaginal wall of 15 women who underwent v...
Simulation training is an appealing and useful addition to health facilities. Simulation centers are organized to maximize network resources. Simulation training is used for certification or recertification of health professionals and is now an integral part of the methods used in continuing professional development. Simulation has played a unique...
To understand the mechanical behavior of soft tissues, two fields of science are essential: biomechanics and histology. Nonetheless, those two fields have not yet been studied together often enough to be unified by a comprehensive model. This study attempts to produce such model. Biomechanical uniaxial tension tests were performed on vaginal tissue...
The woman pelvic system involves multiple organs, muscles, ligaments, and fasciae where different pathologies may occur. Here we are most interested in abnormal mobility, often caused by complex and not fully understood mechanisms. Computer simulation and modeling using the finite element (FE) method are the tools helping to better understand the p...
The effect of the Mullins softening on mode I fracture of carbon-black filled rubbers was investigated experimentally. Large specimen of NR and SBR filled with the same amount and nature of carbon-black were submitted to uniaxial tension. Then, single edge notch tension samples were cut along various directions with respect to the direction of prec...
Pelvic mobility is essential for good pelvic organ function. Any modification may be a sign of pathology. The objective of this study was to define a methodology to quantify pelvic mobility. An analysis protocol based on an image registration technique performed on dynamic magnetic resonance imaging sequences is presented. A methodology is proposed...
In the context of the female pelvic medicine, non-invasive magnetic resonance imaging is widely used for the diagnosis of pelvic floor disorders. Nowadays, in the clinical routine, diagnoses rely largely on human interpretation of medical images, on the experience of physicians, with sometimes subjective interpretations. Hence, image correlation me...
The lack of normalized protocols to perform dynamic material tests could lead to inconsistent results compared to normalized static tests ones, or between different dynamic test campaigns. Such inconsistencies may be problematic when an accurate identification of strain rate dependent material models is needed, from creep to fast dynamics loadings....
The purpose of this study is to propose a thermo-viscoelastic model able to describe the strain rate dependency, from creep to dynamic tests, and temperature dependency, from -100°C to room temperature, of organic matrix composite materials. A bi-spectral viscoelastic model, proved to be representative of the T700GC/M21 behaviour on a large range o...
Female pelvic organ prolapse is a complex mechanism combining the mechanical behavior of the tissues involved and their geometry defects. The developed approach consists in generating a parametric FE model of the whole pelvic system to analyze the influence of this material and geometric combination on median cystocele prolapse occurrence. In accor...
Anatomically detailed modeling of soft tissue structures such as the forehead plays an important role in physics based simulations of facial expressions, for surgery planning, and implant design. We present ultrasound measurements of through-layer tissue deformation in different regions of the forehead. These data were used to determine the local d...
In this study, strain rate and low temperature dependencies of the viscoelastic behaviour of the T700GC/M21 composite material are characterised and analysed. Dynamic tests for various environmental temperatures are performed on hydraulic jack equipped with an environmental chamber. Three speeds, between 8.33 · 10−4 m s−1 and 0.5 m s−1, at three te...
Introduction and hypothesis:
We created a pregnant woman pelvic model to perform a simulation of delivery to understand the pathophysiology of urogenital prolapse by studying the constraints on the pelvic components (muscles, ligaments, pelvic organs) during childbirth. These simulations will also provide valuable tools to understand and teach obs...
Introduction and hypothesis:
The female pelvic floor is a complex network of ligaments and muscles whose mechanical properties have not been completely understood. The goal of this study is to understand the biomechanical properties of the pelvic floor tissues of young women and the impact of aging.
Methods:
Biomechanical uniaxial tension tests...
The objective of this study is to propose a thermo-mechanical model of the organic matrix composite materials behaviour representative on large range of strain rates and temperatures. First, a full characterization of the strain rate and temperature dependencies of the viscoelastic behaviour of the T700GC/M21 is required to propose a physically bas...
Laminate composite materials are widely used for many industrial applications because of their high specific mechanical properties as well as the possibility to adapt the structure properties to its application and loading conditions by optimization of the stacking sequence. It is now well known that the mechanical properties mismatch of adjacent l...
The authors compared the mechanical behavior and, more precisely, the Mullins and the cyclic (post-Mullins) softenings of two filled rubbers. A crystallizing natural rubber and a noncrystallizing styrene-butadiene rubber of similar compositions resulting in similar cross-link densities and filled with 40 phr of N347 carbon-black fillers were tested...
Particulate
composite materials (PCM) consisting of a matrix reinforced by micro to nano-sized dispersed phase are receiving the attention of designers as a promising futuristic materials. This study unearths the thermal and mechanical behavior of maleic anhydride grafted polypropylene/silica (MA-g-PP/silica) composites for reinforcement ranging f...
Genital prolapse is a prevalent pelvic disorder inducing hypermobility of organs. Its physiopathology is not well understood as highlighted by the high rate of failure of the surgical treatments. A better definition of the pelvic tissues properties is needed to design more functional prostheses. Image registration is first used to describe the stru...
Le comportement sous sollicitations cycliques des matériaux élastomères induit un adoucissement, une déformation rémanente et une anisotropie. Le travail présenté portera sur la caractérisation de ces phénomènes d'endommagements afin d'établir des liens avec les propriétés matériaux. The behavior of rubber-like materials under cyclic loading induce...
The elastic property mismatch between plies with different orientations induces stress concentrations near free edges. This free edge effect can cause early delamination of composite structures. Laminates with 15 degrees and -15 degrees plies are studied experimentally to highlight the free-edge effect and the induced micromechanism damage. Full fi...
Genital prolapse is a pathologic hyper-mobility of the organs that forms the pelvic system. Although this is common condition, the pathophysiology of this disorder is not well known. In order to improve the understanding of its origins, we recreate--virtually--this biomechanical pathology using numerical simulation. The approach builds on a finite...
Genital prolapse remains a complex pathological condition. Physiopathology remains poorly understood, aetiology is multi-factorial, surgery is not always satisfying, as the rate of relapse cannot be overlooked. More over a good anatomical result will not always guarantee functional satisfaction. The aim of our study is to have a better understandin...