Gregory Chagnon

Université Grenoble Alpes

The mechanical characterization of the oesophagus is essential for applications such as medical device design, surgical simulations and tissue engineering, as well as for investigating the organ's pathophysiology. However, the material response of the oesophagus has not been established ex vivo in regard to the more complex aspects of its mechanica...

A personalized 3D breast model could present a real benefit for preoperative discussion with patients, surgical planning, and guidance. Breast tissue biomechanical properties have been poorly studied in vivo, although they are important for breast deformation simulation. The main objective of our study was to determine breast skin thickness and bre...

The gastrointestinal (GI) organs of the human body are responsible for transporting and extracting nutrients from food and drink, as well as excreting solid waste. Biomechanical experimentation of the GI organs provides insight into the mechanisms involved in their normal physiological functions, as well as understanding of how diseases can cause d...

Tissues' nearly incompressibility was well reported in the literature but little effort has been made to compare volume variations computed by simulations with in vivo measurements. In this study, volume changes of the fat pad during controlled indentations of the human heel region were estimated from segmented medical images using digital volume c...

The mechanical characterisation of the oesophagus is essential for applications such as medical device design, surgical simulations, tissue engineering, understanding organ's pathophysiology. However, the material response of the oesophagus has not been established ex vivo in regard to the more complex aspects of its mechanical behaviour using fres...

OBJECTIVE Pressure injuries (PIs) result in an extended duration of care and increased risks of complications for patients. When treating a PI, the aim is to hinder further PI development and speed up the healing time. Urgo RID recently developed a new bilayer dressing to improve the healing of stages 2 and 3 heel PIs. This study aims to numericall...

Recently, a new bi-layer dressing was proposed by Urgo RID to reduce the healing time of pressure ulcers (PU). This dressing was numerically evaluated in previously published work. In the current work, the influence on the maximal shear strains of modelling parameters such as the dressing local geometry, the pressure applied by the gauze inside the...

Recently, a new bi-layer dressing was proposed by Urgo RID to reduce the healing time of pressure ulcers (PU). This dressing was numerically evaluated in previously published work. In the current work, the influence on the maximal shear strains of modelling parameters such as the dressing local geometry, the pressure applied by the gauze inside the...

Ecoflex silicone rubbers, served as the polymeric components of flexible electronic devices, actuators, energy converters, etc., are subjected to repetitive loadings during their service lives. The resulting stress softening and stress recovery phenomena can impose complicated impacts on their actual performances. Therefore, the importance of a bet...

Tissue adhesives are interesting materials for wound treatment as they present numerous advantages compared to traditional methods of wound closure such as suturing and stapling. Nowadays, fibrin and cyanoacrylate glues are the most widespread commercial biomedical adhesives, but these systems display some drawbacks. In this study, degradable bioad...

Mechanical characterisation of the layer-specific, viscoelastic properties of the human oesophagus is crucial in furthering the development of devices emerging in the field, such as robotic endoscopic biopsy devices, as well as to enhance the realism, and therefore effectiveness, of surgical simulations. In this study, the viscoelastic and stress-s...

The oesophagus is a primarily mechanical organ whose material characterisation would aid in the investigation of its pathophysiology, help in the field of tissue engineering, and improve surgical simulations and the design of medical devices. However, the layer-dependent, anisotropic properties of the organ have not been investigated using human ti...

The aim of this study was to characterise the mechanical behaviour of Cooper’s ligaments. Such ligaments are collagenous breast tissue that create a three-dimensional structure over the entire breast volume. Ten ligaments were extracted from a human cadaver, from which 28 samples were cut and used to perform uniaxial tensile tests. Histological ana...

Background This paper addresses the question of the in vivo measurement of breast tissues stiffness, which has no response nowadays, apart from elastography imaging that is still difficult for clinicians to use on a day-to-day basis. Estimating subject-specific tissues stiffness is indeed highly demanded due to the development of a large number of...

Pressure Ulcers (PU) are real burdens for patients in healthcare systems, affecting their quality of life. External devices such as prophylactic dressings may be used to prevent the onset of PU. A new type of dressing was designed to alleviate soft tissue under pressure, with the objective to prevent PU and to improve the healing conditions of cate...

Little information is available on the forces that fingers can generate, and few devices exist to measure the forces they can create. The objective of this paper is to propose an experimental device to measure the moments generated by finger joints. The idea is to focus on a single joint and not on the effort generated by the whole finger. A system...

Technological advancements in the field of robotics have led to endoscopic biopsy devices able to extract diseased tissue from between the layers of the gastrointestinal tract. Despite this, the layer-dependent properties of these tissues have yet to be mechanically characterised using human tissue. In this study, the ex vivo mechanical properties...

Silicone rubbers are promising materials that have extensively been used in many areas, including wear-able electronic devices, actuator materials in soft robotics, and energy harvesters. Ecoflex, a commercially available polymer, is a group of silicone rubbers appearing with various Shore hardnesses that has become popular in recent years. While s...

Synthetic vascular grafting is necessarily when the autografting is not possible in some cases. Conventional polyethylene terephthalate and expanded polytetrafluoroethylene vascular grafts are found to be effective for diameter bigger than 6 mm but not for the diameter smaller than 4 mm due to the compliance mismatch and thrombogenicity. Endotheliz...

Internal biliary stenting during biliary reconstruction in liver transplantation decrease anastomotic biliary complications. Implantation of a resorbable internal biliary stent (RIBS) is interesting since it would avoid an ablation gesture. The objective of present work was to evaluate adequacy of selected PLA-b-PEG-b-PLA copolymers for RIBS aimed...

Inside the Clausius-Clapeyron regime, transformation stresses during superelastic tensile tests of polycrystalline shape memory alloys are linearly dependent on temperature, with coefficients being the slopes of the forward and reverse transformation lines. In this work, experiments are performed to investigate the anisotropy of the slopes of the f...

Silicone polymers have enormous applications, especially in the areas of biomedical engineering. Ecoflex, a commercially available room temperature cured silicone polymer, has attracted considerable attention due to its wide range of applications as medical-grade silicones and as matrix materials in producing nano-filled stretchable sensors and die...

The implantation of an internal biliary stent (IBS) during liver transplantation has recently been shown to reduce biliary complications. To avoid a potentially morbid ablation procedure, we developed a resorbable and radiopaque internal biliary stent (RIBS). We studied the mechanical and radiological properties of RIBS upon in vivo implantation in...

Cell migration is essential for many biological processes such as tissue morphogenesis, wound healing or metastatic invasion in cancer. It is a complex and highly regulated phenomena closely guided and fine-tuned by both chemical and mechanical cues. Whereas chemoattraction has been extensively studied, the mechanical influence remains to be fully...

This article presents a new method to monitor beam shapes from strain measures. The beam is instrumented with strain sensors placed on its surface with an angle of orientation. The method developed is a 3D large deflection beam shape reconstruction based on a beam model incorporating Poisson effect and is thus able to take into account bending, tor...

In this paper, superelastic behavior of nickel-titanium thin wires is characterized using the method of dynamic mechanical analysis. Nominal dynamic storage modulus \( E^{{\prime }} \) is measured as function of nominal strain and stress during isothermal superelastic tensile tests at three testing temperatures above the reverse martensitic transfo...

Biliary diseases are the third most common cause of surgical digestive disease. There is a close relationship between the mechanical performance of the bile duct and its physiological function. Data of biomechanical properties of human main bile duct are scarce in literature. Furthermore, mechanical properties of soft tissues are affected by these...

Needles are tools that are used daily during minimally invasive procedures. During the insertions, needles may be affected by deformations which may threaten the success of the procedure. To tackle this problem, needles with embedded strain sensors have been developed and associated with navigation systems. The localization of the needle in the tis...

Properties or characteristics of fibers are affected by their topology. In fact, these topologies are found to have significant impacts in the functionalities of many applications. Hence, in this study, the relations between the spinning techniques and the topology of the resulting fibers are studied with the aim to provide a guideline for future r...

This paper presents a new approach validated experimentally to reconstruct with strain gauges the deformed shape of a straight beam with circular cross section. It is based on a novel beam-specific strain gauge model that improves the strain measurement by taking into account the width of the gauges. These improved strain measurements are used by a...

Simulating the deformations of soft tissues has gained importance in recent years due to the development of 3D patient-specific biomechanical models in the context of Computer Assisted Medical Interventions. To design such models, the mechanical behavior of each soft tissue has to be characterized in-vivo. In this paper, a volume-based aspiration m...

The present study focuses on the fabrication and mechanical responses of highly aligned thermoplastic polyurethane microfibres. A facile dry spinning assisted by an electrical field technique was used to fabricate these microfibres. The surface morphology of the microfibres were inspected under a scanning electron microscope, while their mechanical...

Characterizing the effects of cross-linking level and kinetics on the mechanical properties of rubber, especially viscoelasticity, provides information of importance to better understand and predict final mechanical properties. Classically, the effects of cross-linking on the mechanical properties are investigated with a rheometer. Typical results...

This work aims at observing the mechanical behavior of the membranous and spongy portions of urethrae sampled on male cadavers in compliance with French regulations on postmortem testing, in accordance with the Scientific Council of body donation center of Grenoble. In this perspective, a thermostatic water tank was designed to conduct ex vivo plan...

The knowledge of needle location during insertions is essential for the success of interventional radiology procedures. As the needle is susceptible to undergo deformations during its insertion into tissues, several methods have been proposed to monitor the needle deformed shape. Thus, instrumented needles with U-shaped strain gauges are currently...

Soft tissues are mainly composed of organized biological media giving them an anisotropic mechanical behavior. Soft tissues also have the ability to undergo large elastic reversible deformations. Many constitutive models were developed to describe these phenomena. In this chapter, we discuss several varying models and their constitutive equations w...

Superelastic behaviour of NiTi shape memory alloys thin wires is characterized mechanically using the method of Dynamic Mechanical Analysis (DMA). The method uses a non-conventional device which allows to determine storage modulus at high level of stress. Dynamic elastic modulus is measured during isothermal tensile tests at three testing temperatu...

Due to the industrial elaboration process, membranes can have an in-plane anisotropic mechanical behaviour. In this paper, anisotropic membranes elaborated with two different materials were developed either by calendering or by inducing a force in one direction during the process. Experimental tests are developed to measure the differences of mecha...

This paper investigates the influence of three different processing parameters on the global mechanical behavior of PVA (Polyvinyl alcohol)/DMSO (Dimethylsulfoxide) hydrogels: the initial concentration of PVA, the DMSO:H2O ratio and the number of freeze/thaw cycle applied to the material. A specific thermo-regulated testing apparatus for hydrophili...

One major challenge of biomaterial engineering is to mimic the mechanical properties of anisotropic, multifunctional natural soft tissues. Existing solutions toward controlled anisotropy include the use of oriented reinforcing fillers, with complicated interface issues, or UV-curing processing through patterned masks, that makes use of harmful phot...

Needles are tools widely used in minimally invasive surgery. During such procedures the localization of the needle and its tip is a challenging situation because of the needle deformations due to its interactions with tissues. To tackle this problem, instrumented needles with sensors have been currently developed to allow needle reconstruction and...

The biodegradable triblock copolymer PLA-b-PEG-b-PLA presents, in its initial state, a non-linear viscoelastic behavior. Its mechanical properties evolves during the in vitro degradation process. Tensile and relaxation tests are performed at 2%, 4% and 6% of load strain for different degradation steps. In order to describe the behavior of the polym...

The Mullins effect refers to a stress-softening phenomenon of rubber-like materials during cyclic loading. Anisotropy of the material behaviour is generally observed after stretching. In this paper, a large set of original suitable experiments are reported to characterise this effect under several deformation conditions. Then, a phenomenological mo...

The aim of this paper is to provide an experimental and modeling study of an architectured photosensitive silicone membrane. Mechanical properties are dependent of UV doses used to alter the local cross-link density, resulting in a direct effect on the macroscopic mechanical behavior. A series of mechanical tests were carried out to characterize th...

PLA-b-PEG-b-PLA is a biodegradable triblock copolymer that presents both the mechanical properties of PLA and the hydrophilicity of PEG. In this paper, physical and mechanical properties of PLA-b-PEG-b-PLA are studied during in vitro degradation. The degradation process leads to a mass loss, a decrease of number average molecular weight and an incr...

Electropulse heat treatment is a technique developed to realise fast heat treatment of NiTi shape memory alloys. This study investigates mechanical behaviour of cold worked NiTi wires heat treated with such a technique. It is demonstrated that milliseconds electropulses allow to realise homogeneous heat treatments and to adapt the mechanical behavi...

In the present paper, experimental investigation and continuum mechanical modeling of Mullins effect in swollen elastomers, due to exposure to palm biodiesel, under cyclic loading conditions are addressed. To this end, the nature of Mullins effect in both dry and swollen elastomers is explored and compared. It is found that swelling reduces Mullins...

Implantable polymeric medical devices suffer from a lack of visibility under current clinical imaging techniques. To circumvent this problem, poly(ε-caprolactone-co-α-triiodobenzoate-ε-caprolactone)s (PCL-TIB) containing from 3.5% to 24% of triiodobenzoate-ε-caprolactone units were synthesized as new X-ray macromolecular contrast agents. Physico-ch...

The main objective of this study is to generate anisotropic membranes stretched in their plane able to endure large deformations. In this perspective, different crenellated membranes were designed with a filled silicone rubber. The aim of this work is to build a constitutive equation which describes the mechanical behavior of such architectured mem...

Many soft tissues are naturally made of a matrix and fibres that present some privileged directions. They are known to support large reversible deformations. The mechanical behaviour of these tissues highlights different phenomena as hysteresis, stress softening or relaxation. A hyperelastic constitutive equation is typically the basis of the model...

This paper deals with composite structures for biomedical applications. For this purpose, an architectured tubular structure composed of Nickel Titanium (NiTi) Shape Memory Alloy (SMA) and silicone rubber was fabricated. One of the main interest of such structures is to ensure a good adhesion between its two constitutive materials. A previous study...

The mechanical behavior of elastomers strongly depends on the macromolecular network and the compound formulation. This explains why elastomer properties significantly differ from one to another and why hysteresis upon cyclic load can be either rate-dependent or rate-independent. In the present paper, a microsphere model taking into account rate-in...

In this paper, an extension of two classical viscoelastic models adapted in large deformation for incompressible rubber like materials or soft tissues is proposed. These models are built by using a three dimensional homogeneization by means of a sphere unit approach. Thus several comparisons between classical formulations and homogeneization on a s...

Many rubber-like materials present a phenomenon known as Mullins effect. It is characterized by a difference of behavior between the first and second loadings and by a permanent set after a first loading. Moreover, this phenomenon induces anisotropy in an initially isotropic material. A new constitutive equation is proposed in this paper. It relies...

Rubber-like materials present a stress softening phenomenon after a first loading known as the Mullins effect. Some recent experimental data on filled silicone rubber are presented in the literature, using uniaxial and biaxial tests to precondition samples thus induce some primary stress softening. A generic modeling based on the polymer network de...

Cold tube drawing is a metal forming process which enables to produce tubes with high dimensional precision. It consists in reducing tube dimensions by pulling it through a die. Tube outer diameter is calibrated by a die and the tube inner diameter and thickness are calibrated by a mandrel. One of the major concern of metal forming industry is the...

The aim of this study is to determine a generic static loading basis applied on a medical needle inserted into human tissue during a percutaneous procedure. Such a basis can be worthwhile to highlight the forces effectively encountered in a medical act and may be useful to develop models of needle deflection or medium deformation.

In this paper, the static interaction forces between a medical needle and soft tissue during CT (Computerized Tomography) guided insertion are studied. More precisely a set of linearly independent elements describing the forces (a basis) is identified. This forms a generic basis from which any forces that act on a static needle (that is not fixed a...

Use of the force distribution along the needle to determine the optimized an instrumented needle

Needles used in medical percutaneous procedures are brought to deform because of its interactions with inhomogeneous and anisotropic tissues. In this paper, the first step of the development of a new generation of tools for assistance in the realization of gestures taking into account these deformations are presented. We provide a new approach for...

Architectured membranes can be developed in order to mimic living tissues. The main point is to generate anisotropic membranes that can endure large deformations. In this way, crenellated membranes are elaborated with a filled silicone rubber. The aim of this work is to develop a constitutive equation which describes the mechanical behavior of such...

Many rubber like materials present a stress-softening phenomenon known as Mullins effect. It is characterized by a difference of behavior between the first and second loading and by a residual strain after a first loading. Moreover according to the literature this stress softening is anisotropic. A new constitutive equation is proposed. It relies o...

Thermomechanical behaviour of NiTi SMA is due to the complex interaction between several deformation mechanisms including lattice elasticity, phase transformations between austenite (A), martensite (M) and the R-phase (R), reorientations of R and/or M variants, twinning and detwinning phenomena and the usual plasticity due to dislocation movement....

Over the past few years, textiles made from thin NiTi wires have received increasing attention as they are already used as stents in medical field and further applications are being envisaged. To prevent some apparent drawbacks of NiTi textiles such as friction between NiTi wires and low tensile/shear stiffness, NiTi elastomeric composites are bein...

Rubber like materials parts are designed using finite element code in which more and more precise and robust constitutive equations are implemented. In general, constitutive equations developed in literature to represent the anisotropy induced by the Mullins effect present analytical forms that are not adapted to finite element implementation. The...

Drawing process of thin walled tubes used to fabricate catheters and stents for medical applications was studied. Medical use needs accurate dimensions and a smooth finish of the inner and outer surfaces. This paper deals with 316L stainless steel tubes which are manufactured by means of cold drawing with or without inner plug (mandrel drawing and...

The bulge test is mostly used to analyze equibiaxial tensile stress state at the pole of inflated isotropic membranes. Three-dimensional digital image correlation (3D-DIC) technique allows the determination of three-dimensional surface displacements and strain fields. In this paper, a method is proposed to determine also the membrane stress tensor...