Baptiste Pierrat

• MS, PhD
• Researcher at Mines Saint-Étienne

The loss of elasticity is a hallmark of systemic aging or genetic syndromes (e.g. cutis laxa, Williams-Beuren and supravalvular aortic stenosis) with direct consequences on tissue functions, and particularly deleterious when associated to the cardiovascular system. Tissue elasticity is mainly provided by large elastic fibers composed of supramolecu...

This study aims to improve the reproducibility of sample dimension measurements from pictures, as plan during the C4bio challenge, and to estimate the effect of their uncertainty on the stress-strain curves through uncertainty propagation.

This study aims to improve the reproducibility of sample dimension measurements from pictures, as plan during the C4bio challenge, and to estimate the effect of their uncertainty on the stress-strain curves through uncertainty propagation.

So far, the prevalent rupture risk quantification of aortic aneurysms does not consider information of the underlying microscopic mechanisms. Uniaxial tension tests were performed on imaged aorta samples oriented in circumferential and longitudinal directions. To account for local heterogeneity in collagen fiber architecture, SHG imaging was perfor...

In the current study, we developed a new computational methodology to simulate wound healing in soft tissues. We assumed that the injured tissue recovers partially its mechanical strength and stiffness by gradually increasing the volume fraction of collagen fibers. Following the principles of the constrained mixture theory, we assumed that new coll...

Endoluminal reconstruction using flow diverters represents a novel paradigm for the minimally invasive treatment of intracranial aneurysms. The configuration assumed by these very dense braided stents once deployed within the parent vessel is not easily predictable and medical volumetric images alone may be insufficient to plan the treatment satisf...

Aortic aneurysm rupture is a sudden local event with high mortality. It is generally accepted that the adventitia acts as the final barrier protecting the aorta from over-expansion. Currently, the knowledge of microscopic structural determinants of the tissue's mechanical response and failure is very limited. The purpose of this study is to provide...

Endoluminal reconstruction using flow diverters represents a novel paradigm for the minimally invasive treatment of intracranial aneurysms. The configuration assumed by these very dense braided stents once deployed within the parent vessel is not easily predictable and medical volumetric images alone may be insufficient to plan the treatment satisf...

High-fidelity biomechanical models usually involve the mechanical characterization of biological tissues using experimental methods based on optical measurements. In most experiments, strains are evaluated based on displacements of a few markers and represents an average within the region of interest (ROI). Full-field measurements may improve descr...

Aortic dissection is a complex, intramural, and dynamic condition involving multiple mechanisms, hence, difficult to observe. In the present study, a controlled in vitro aortic dissection was performed using tension-inflation tests on notched rabbit aortic segments. The mechanical test was combined with conventional (cCT) and synchrotron (sCT) comp...

A comparative study of eight different lumbar belts, which are representative of the French market, was carried out on four typical morphologies of patients to assess their therapeutic effects and identify the correlation between the therapeutic parameters and mechanical ones. Four typical morphologies were chosen among 15 patients that had been ch...

The increasing use of mini-invasive and endovascular surgical techniques is at the origin of the pressing need for computational models to support planning and training. Several implantable devices have a wire-like structure, which can be modelled using beam elements. Our objective is to create an efficient Finite Element (FE) modelling framework f...

Constitutive models have been developed to describe damage behavior of materials, including soft tissues. However, most of them do not include crack opening and progression, which can be overcome using phase field damage method. Unfortunately, due to the complex behavior of soft tissues, damage parameters identification from experiments is very cha...

The decision of surgical intervention for an aortic aneurysm is usually associated with an assessment of risk of its rupture. Global rupture risk assessment parameters like wall diameter and growth of the aneurysm over time often fail at predicting the risk of rupture with accuracy. This paper will investigate the hypothesis that the tissue’s micro...

Predicting the damage in soft tissues remains a major challenge because of its computational difficulty and the need to involve inverse methods for parameter identification. One of the main limitations is the transition from damage to fracture which can be overcome using the diffuse phase field method [1]. Due to the unstable propagation of the cra...

High‐fidelity biomechanical models usually involve the mechanical characterisation of biological tissues using experimental methods based on optical measurements. In most experiments, strains are evaluated based on displacements of a few markers and represents an average within the region of interest (ROI). Full‐field measurements may improve descr...

The most common method to study the mechanical behavior of soft tissue is to test animal specimens, which should be prepared as soon as possible after the death to avoid biological deterioration effects such as rigor mortis. Freezing and cryo-preservation could allow extending the time between procurement and implantation. From a mechanical perspec...

Skin irritation is a common phenomenon that becomes a real concern when caused by the use of medical devices. Because the materials used for the design of these devices are usually carefully selected for chemical compatibility with the skin, it is reasonable to assume that the irritations result from the mechanical interaction between the devices a...

https://doi.org/10.1080/10255842.2021.1978758 Page S316-S318

Background Digital image correlation (DIC) methods are increasingly used for non-contact optical assessment of geometry and deformation in soft tissue biomechanics, thus providing the full-field strain estimates needed for robust inverse material characterization. Despite the well-known flexibility and ease of use of DIC, issues related to spatial...

The skin is subject to daily mechanical stress when in contact with objects. Being able to make predictions about the skin's ability to withstand interactions with every day used products is therefore of great interest. Skin mechanical behaviour has already been widely studied. However, the current understanding of the through layer behaviour of s...

Fenestrated Endovascular Aortic Repair, also known as FEVAR, is a minimally invasive procedure that allows surgeons to repair the aorta while still preserving blood flow to kidneys and other critical organs. Given the high complexity of FEVAR, there is a pressing need to develop numerical tools that can assist practitioners at the preoperative plan...

In this paper we introduce a new method simulating stent graft deployment for assisting endovascular repair of abdominal aortic aneurysms. The method relies on intraoperative images coupled with mechanical models. A multi-step algorithm has been developed to increase the reliability of simulations. The first step predicts the position of the stent...

Textile-based implant (mesh) treatment is considered as a standard of care for abdominal wall hernia repair. Computational models and simulations have appeared as one of the most promising approach to investigate biomechanics related to hernia repair and to improve clinical outcomes. This paper presents a novel anisotropic hypo-elastoplastic consti...

Objective: Aortic dissection is a life-threatening event which starts most of the time with an intimal tear propagating along the aortic wall, while blood enters the medial layer and delaminates the medial lamellar units. Studies investigating the mechanisms underlying the initiation sequence of aortic dissection are rare in the literature, the ma...

Lesions of the Musculotendinous Unit (MTU, i.e. tendon, myotendinous junction, muscle, aponeurosis and myoaponeurotic junction) are a common injury and a leading cause of functional impairment, long-term pain, and/or physical disability worldwide. Though a large effort has been devoted to macroscopic failure evaluation, these injuries suffer from a...

In order to study Musculo-Tendinous Unit (MTU) failure mechanisms and locations, rupture tests in mode I were performed through tensile tests (in the fibre and transverse directions) as well as peeling tests (to better investigate the transverse cohesion between muscle fibres), and mode II through shear lap tests (either at the muscle/muscle or mus...

The cerebral meninges, made up of the dura, arachnoid, and pia mater, is a tri-layer membrane that surrounds the brain and the spinal cord and has an important function in protecting the brain from injury. Understanding its mechanical behavior is important to ensure the accuracy of finite element (FE) head model simulations which are commonly used...

Background It is commonly admitted that a dissection initiates with an intimal tear or at least a defect inside the arterial wall. Nevertheless, few studies investigated the initiation sequence due to the difficulty to monitor this process. Objective The objective of this work was to observe and investigate the mechanisms leading an intimal tear t...

In this paper we introduce a new method simulating stent graft deployment for assisting endovascular repair of abdominal aortic aneurysms. The method relies on intraoperative images coupled with mechanical models. A multi-step algorithm has been developed to increase the reliability of simulations. The first step predicts the position of the stent...

In this paper we introduce a new method for the registration between preoperative and intraoperative computerized tomography (CT) images used in endovascular interventions for aortic aneurysm repair. The method relies on a 3D finite-element model (FEM) of the aortic centerline reconstructed from preoperative CT scans. Intraoperative 2D fluoroscopic...

The mechanical behavior of the foot is often studied through the movement of the segments composing it and not through the movement of each individual bone, preventing an accurate and unambiguous study of soft tissue strains and foot posture. In order to describe the internal behavior of the foot under static load, we present here an original metho...

Aortic dissection is a life-threatening event associated with a very poor outcome. A number of complex phenomena are involved in the initiation and propagation of the disease. Advances in the comprehension of the mechanisms leading to dissection have been made these last decades thanks to improvements in imaging and experimental techniques. However...

file:///home/jerome/T%C3%A9l%C3%A9chargements/Biomechanical%20consequences%20of%20lumbar%20belt%20design%20for%20the%20therapeutic%20treatment%20of%20low%20back%20pain.pdf

Abdominal aortic aneurysm is a prevalent cardiovascular disease with high mortality rates. The mechanical response of the arterial wall relies on the organizational and structural behavior of its microstructural components, and thus, a detailed understanding of the microscopic mechanical response of the arterial wall layers at loads ranging up to r...

The liver is the most commonly injured abdominal organ following either blunt or penetrating impact. Current mechanical properties available in the literature are typically only measured at low strain rates, low strains, or use linear viscoelastic models. There is also a dearth of high-rate, large strain, viscoelastic data available for liver tissu...

Aortic dissection represents a serious cardio-vascular disease and life-threatening event. Dissection is a sudden delamination event of the wall, possibly leading to rupture within a few hours. Current knowledge and practical criteria to understand and predict this phenomenon lack reliable models and experimental observations of rupture at the lame...

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Traumatic brain injuries, the leading cause of death and disability in children and young adults, are the result of a rapid acceleration or impact of the head. In recent years, a global effort to better understand the biomechanics of TBI has been undertaken, with many laboratories creating detailed computational models of the head and brain. For th...

Statement of significance: We present the first mechanical analysis of the protective capacity of the cranial meninges using in situ micro-indentation techniques. Force-relaxation tests are performed on in situ meninges and cortex tissue, under large strain dynamic micro-indentation. A quasi-linear viscoelastic model is used subsequently, providin...

In the domain of soft tissue biomechanics, the development of numerical simulations has raised the experimental challenge of identifying local internal mechanical constitutive data of heterogeneous organs (e.g. brain tissue). In this context, this paper presents an ex-vivo alternative characterization method to full-field imaging techniques. It is...

Many models of the mechanical response of arteries assume a reinforcement with two families of helically wound fibres of collagen of opposite pitch. Motivated by experimental observations, the consequences for the internal pressurisation of arteries of a slight asymmetry in the winding angles is investigated here. It is shown that a torsional shear...

In order to avoid the numerical difficulties in locally enforcing the incompressibility constraint using the displacement formulation of the Finite Element Method, slight compressibility is typically assumed when simulating the mechanical response of arterial tissue. The current standard method of accounting for slight compressibility of hyperelast...

Statement of significance: We present the first mechanical characterization of the viscoelastic response for different regions of mouse brain. Force-relaxation tests are performed under large strain dynamic micro-indentation, and viscoelastic models are used subsequently, providing time-dependent mechanical properties of brain tissue under loading...

The brain is a complex organ made up of many different functional and structural regions consisting of different types of cells such as neurons and glia, as well as complex anatomical geometries. It is hypothesized that the different regions of the brain exhibit significantly different mechanical properties, which may be attributed to the diversity...

Modelling transversely isotropic materials in finite strain problems is a complex task in biomechanics, and is usually addressed by using finite element (FE) simulations. The standard method developed to account for the quasi-incompressible nature of soft tissues is to decompose the strain energy function (SEF) into volumetric and deviatoric parts....

In the past 50 years significant advances have been made in determining the macro-scale properties of brain tissue in compression, tension, shear and indentation. There has also been significant work done at the nanoscale using the AFM method to characterise the properties of individual neurons. However, there has been little published work on the...

Background: The knee joint is vulnerable to various injuries and degenerative conditions, potentially leading to functional instability. Usual treatments involve knee orthoses to support the joint. However, the level of mechanical action of these devices remains controversial despite high prescription and demand. Methods: The mechanical ability...

In order to avoid the numerical difficulties in locally enforcing the incompressibility constraint using the displacement formulation of the Finite Element Method, slight compressibility is typically assumed when simulating transversely isotropic, soft tissue. The current standard method of accounting for slight compressibility of hyperelastic soft...

Knee orthotic devices are widely proposed by physicians and medical practitioners for preventive or therapeutic objectives in relation with their effects, usually known as to stabilize joint or restrict ranges of motion. This study focuses on the understanding of force transfer mechanisms from the brace to the joint thanks to a Finite Element Model...

Knee orthotic devices are commonly prescribed by physicians and medical practitioners for preventive or therapeutic purposes with the aim of supporting, aligning or immobilising the joint. However, the evaluation of these devices relies on few biomechanical studies or therapeutic trials and the level of their mechanical actions remain unclear. The...

Fabric-based knee braces are widely used as orthotic devices to support and align the joint. Despite significant prescription, compliance with the treatment is often negatively affected by discomfort issues, in particular brace slippage and migration. Full-field measurements associated with digital image correlation were performed on 11 subjects to...

Knee orthotic devices are commonly prescribed by physicians and medical practitioners for preventive or therapeutic purposes on account of their claimed effect: joint stabilisation and proprioceptive input. However, the force transfer mechanisms of these devices and their level of action remain controversial. The objectives of this work are to char...

Knee orthotic devices are widely proposed by physicians and medical practitioners for preventive or therapeutic objectives in relation with their effects, usually known as to stabilize joint or restrict ranges of motion. The objectives of this work are to characterize the mechanical performance of knee orthoses using a Finite Element Model of a bra...

This article reports on the study of the oxidation of ZrC–20 vol% MoSi2 in the temperature range 1800–2400 K in air, in order to partially reproduce the operating conditions of a high-temperature receiver for concentrated solar radiation. Such receivers are used in solar tower power plants, this technology being likely to grow in scale in the futur...

In this paper, the concentrated solar energy is used as a source of high temperatures to study the physical and chemical behaviors and intrinsic properties of refractory materials. The atmospheres surrounding the materials have to be simulated in experimental reactors to characterize the materials in real environments. Several application fields ar...