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International audience; Low back pain represents a major economic and societal challenge due to its high prevalence. Lumbar orthoses are one of the recommended treatments. Even if previous results showed their clinical effects, the detailed mode of action is still poorly known, making the device design difficult. A renewed instrumentation and experimental protocol should bring better insight into the lumbar brace–trunk mechanical interaction. This instrumentation should give detailed information on the basic physical or geometrical parameters: the pressure applied on the trunk, the body shape and the strain in the belt. The principal objective of this study was to propose and validate a new measurement protocol, based on pressure mapping systems and full-field shape and strain measurement. The feasibility of the protocol was tested along with its validity and repeatability. The influence of various parameters, which could cause changes in the measurements, was tested with six different belt configurations on one subject. Measurements were also performed to study the impact of posture on pressure and strain. Both pressure and strain appeared to be asymmetric from left to right. The pressure applied by the lumbar belt on the back varies with breathing and with posture. This study showed that full-field measurements were necessary to render the high variability of pressure or strain around the trunk, under recommendations of their use to guarantee a satisfying repeatability.

International audience; Interface pressure applied by compression bandages is the therapeutic action of the treatment of some venous or lymphatic pathologies. The so-called Static Stiffness Index, which quantifies the pressure increase from supine to standing position, is usually used to differentiate compression bandages. It was hypothesized that this pressure increase was the consequence of a change in leg geometry (blood and muscle falling down) and a change in calf soft tissue mechanical properties (muscles contraction). Calf soft tissue global stiffness of both legs of 25 patients was characterized in a sitting and standing position. This characterization was combined with interface pressure measurements applied by six different bandages. Though soft tissue mechanical properties significantly increased from sitting to standing position, no correlation was observed with the corresponding pressure increase. Thus, pressure increase is mainly attributed to a change in leg geometry.

International audience; Background: The present study aimed to classify the relative contributions of four biomechanical factors—the root-end filling material, the apical preparation, the root resection length, and the bone height—on the root stresses of the resected premolar. Methods: A design of experiments approach based on a defined subset of factor combinations was conducted to calculate the influence of each factor and their interactions. Sixteen finite element models were created and analyzed using the von Mises stress criterion. The robustness of the design of experiments was evaluated with nine supplementary models. Results: The current study showed that the factors preparation and bone height had a high influence on root stresses. However, it also revealed that nearly half of the biomechanical impact was missed without considering interactions between factors, particularly between resection and preparation. Conclusions: Design of experiments appears to be a valuable strategy to classify the contributions of biomechanical factors related to endodontics. Imagining all possible interactions and their clinical impact is difficult and can require relying on one’s own experience. This study proposed a statistical method to quantify the mechanical risk when planning apicoectomy. A perspective could be to integrate the equation defined herein in future software to support decision-making.

International audience; 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 and the skin. The aim of this work was to develop a new device to study both the shear strains in the layers of the skin, using Digital Image Correlation (DIC), and the friction behaviour of ex vivo skin interacting with objects. Pig skin samples with various surface preparations were tested in friction experiments involving different contacting materials encountered in the conception of medical devices. The measure of the static and dynamic coefficients of friction as well as the length of adhesion has highlighted the great influence of skin surface conditioning on friction properties. Strain maps obtained through DIC provided insights into the impact of friction and adhesion effects on shear strain distribution in the skin as a function of depth beneath its surface.

International audience; Low-back pain (LBP) is a widespread disease which can also be highly disabling, but physicians lack of basic understanding and diagnosis tools. During this study, we have designed and built a new wearable device capable of detecting features helpful in LBP follow-up while being non-invasive. The device has been carefully validated, and shows good metrological features, with small noise level (σ = 1°) and no observable drift. Two simple exercises were proposed to two young volunteers, one of them with LBP history. These exercises are designed to target two characteristics: the lumbar lordosis angle and the hip & shoulder dissociation. Even if no general rules can be extracted from this study, we have shown that Inertial Measurement Units (IMU) are able to pick up those characteristics and the obtained values are meaningful refereeing to LBP disease. Henceforth, we are confident in going to clinical studies to investigate the link between back related feature and LBP, in particular the hip & shoulder dissociation which is poorly documented.; La lombalgie est une maladie très répandue qui peut également être très invalidante, mais les médecins manquent de connaissances de base et d'outils de diagnostic. Au cours de cette étude, nous avons conçu et construit un nouveau dispositif portable non invasif capable de détecter des caractéristiques utiles au suivi de la lombalgie. Le dispositif a été validé, et présente de bonnes caractéristiques métrologiques, avec un faible niveau de bruit (σ = 1°) et aucune dérive observable. Deux exercices simples ont été proposés à deux jeunes volontaires, dont l'une avait des antécédents de lombalgie. Ces exercices sont conçus pour cibler deux caractéristiques : l'angle de lordose lombaire et la dissociation des ceintures hanche-épaule. Même si aucune règle générale ne peut être extraite de cette étude, nous avons montré que les capteurs inertiels (UMI) sont capables de mesurer ces caractéristiques et que les valeurs obtenues sont significatives de la lombalgie. Ce travail ouvre la possibilité d'études cliniques pour étudier le lien entre les caractéristiques du dos et la lombalgie, en particulier la dissociation des ceintures hanche/épaule qui est peu documentée.

Understanding stress-strain relationships in arteries is important for fundamental investigations in mechanobiology. Here we demonstrate the essential role of chemoelasticity in determining the mechanical properties of arterial tissues. Stepwise stress-relaxation uniaxial tensile tests were carried out on samples of porcine thoracic aortas immersed in a hyperosmotic solution. The tissue deformations were tracked using optical coherence tomography (OCT) during the tensile tests and digital volume correlation (DVC) was used to obtain measurements of depth-resolved strains across the whole thickness of the tested aortas. The hyperosmotic solution exacerbated chemoelastic effects, and we were able to measure different manifestations of these chemoelastic effects: swelling of the media inducing a modification of its optical properties, existence of a transverse tensile strain. For the first time ever to our best knowledge, 3D strains induced by chemoelastic effects in soft tissues were quantified thanks to the OCT-DVC method. Without doubt, chemoelasticity plays an essential role in arterial mechanobiology in vivo and future work should focus on characterizing chemoelastic effects in arterial walls under physiological and disease conditions. Statement of significance: Chemoelasticity, coupling osmotic phenomena and mechanical stresses, is essential in soft tissue mechanobiology. For the first time ever, we measure and analyze 3D strain fields induced by these chemoelastic effects thanks to the unique combination of OCT imaging and digital volume correlation., Comment: Acta Biomaterialia, Elsevier, 2019, in press

International audience; Elastic compression of the lower leg is the traditional preventive and curative treatment of venous insufficiency. After presenting the medical strategies related to compression therapies, this chapter develops current advances in clinics as well as in engineering and outline the more important knowledge arising from this review. Compression hosiery acts by providing pressure to the leg. Pressure generation using socks mainly depends on the stiffness and the size of the socks, the size of the leg, but also the leg morphology. In the case of bandages, the role of friction must be outlined, as the main factor in maintaining the bandage wrapped around the leg, but also as an influencing factor in pressure generation. Besides generated pressure, response of superficial veins to compression also depends on the vein size and the fat stiffness. But mechanical assessments should not mask the importance of other factors such as muscular contraction or nurse formation. An important impact of these results would be head towards an improved personalization of compression treatment.; La compression élastique de la partie inférieure de la jambe est le traitement préventif et curatif traditionnel de l'insuffisance veineuse. Après avoir présenté les stratégies médicales liées aux thérapies de compression, ce chapitre développe les avancées actuelles dans les approches cliniques ainsi que dans l'ingénierie et expose les connaissances les plus importantes découlant de cette revue. Les bas de compression agissent en exerçant une pression sur la jambe. La génération de pression à l'aide de chaussettes dépend principalement de la rigidité et de la taille des chaussettes, de la taille de la jambe, mais aussi de la morphologie de la jambe. Dans le cas des bandages, le rôle du frottement doit être souligné, en tant que facteur principal dans le maintien du bandage enroulé autour de la jambe, mais aussi en tant que facteur d'influence dans la génération de pression. Outre la pression générée, la réponse des veines superficielles à la compression dépend également de la taille de la veine et de la rigidité de la graisse. Mais les évaluations mécaniques ne doivent pas masquer l'importance d'autres facteurs tels que la contraction musculaire ou la formation des soignants. Un impact important de ces résultats serait de se diriger vers une meilleure personnalisation du traitement de la compression.Traduit avec www.DeepL.com/Translator (version gratuite)

International audience; Objective: To develop a new method for the prediction of interface pressure applied by medical compression bandages. Methods: A finite element simulation of bandage application was designed, based on patient-specific leg geometries. For personalized interface pressure prediction, a model reduction approach was proposed, which included the parametrization of the leg geometry. Pressure values computed with this reduced model were then confronted to experimental pressure values. Results: The most influencing parameters were found to be the bandage tension, the skin-to-bandage friction coefficient and the leg morphology. Thanks to the model reduction approach, it was possible to compute interface pressure as a linear combination of these parameters. The pressures computed with this reduced model were in agreement with experimental pressure values measured on 66 patients' legs. Conclusion: This methodology helps to predict patient-specific interface pressure applied by compression bandages within a few minutes whereas it would take a few days for the numerical simulation. The results of this method show less bias than Laplace's Law, which is for now the only other method for interface pressure computation.

The objective of this study was to investigate the pressure applied by superimposed bandages and to compare it with the pressure applied by single-component bandages.Six different bandages, composed of one elastic bandage, one nonelastic bandage, or both, were applied in a spiral pattern on both legs of 25 patients at risk of venous thrombosis as a consequence of central or peripheral motor deficiency. Pressure was measured at four measurement points on the leg (B1 and C on the medial and lateral sides of the leg) and in three positions: supine, sitting, and standing.The two single bandages applied similar pressure in the supine position. Their superimposition showed different pressure levels (P .05) but similar static stiffness index, depending on the order in which the bandage components were applied on the leg. The highest interface pressure was measured at point B1 on the medial side of the leg. This point also showed the highest pressure increase from supine to standing position. The pressure applied by the superimposition of two bandages was computed as a linear combination of the pressure applied by each single component (with a constant term set to 0). However, this linear combination did not properly fit the experimental pressure measurements.The order of bandage application showed a significant impact on interface pressure. However, the poor correlation between the pressure applied by each bandage component and the pressure resulting from their superimposition underlined the poor understanding of interface pressure generated by the superimposition of compression bandages and should lead to further investigations.

Fabric-to-fabric friction is involved in the action mechanism of medical compression devices such as compression bandages or lumbar belts. To better understand the action of such devices, it is essential to characterize, in their use conditions (mainly pressure and stretch), the frictional properties of the fabrics they are composed of. A characterization method of fabric-to-fabric friction was developed. This method was based on the customization of the fourth instrument of the Kawabata Evaluation System, initially designed for fabric roughness and friction characterization. A friction contactor was developed so that the stretch of the fabric and the applied load can vary to replicate the use conditions. This methodology was implemented to measure the friction coefficient of several medical compression bandages. In the ranges of pressure and bandage stretch investigated in the study, bandage-to-bandage friction coefficient showed very little variation. This simple and reliable method, which was tested for commercially available medical compression bandages, could be used for other medical compression fabrics.

International audience; Objective: A numerical 3D model of the human trunk was developed to study the biomechanical effects of lumbar belts used to treat low back pain. Methods: This model was taken from trunk radiographies of a person and simplified so as to make a parametric study by varying morphological parameters of the patient, characteristic parameters of the lumbar belt and mechanical parameters of body and finally to determine the parameters influencing the effects of low back pain when of wearing the lumbar belt. The loading of lumbar belt is modelled by Laplace's law. These results were compared with clinical study. Results: All the results of this parametric study showed that the choice of belt is very important depending on the patient's morphology. Surprisingly, the therapeutic treatment is not influenced by the mechanical characteristics of the body structures except the mechanical properties of intervertebral discs. Discussion: The numerical model can serve as a basis for more in-depth studies concerning the analysis of efficiency of lumbar belts in low back pain. In order to study the impact of the belt's architecture, the pressure applied to the trunk modelled by Laplace's law could be improved. This model could also be used as the basis for a study of the impact of the belt over a period of wearing time. Indeed, the clinical study shows that movement has an important impact on the distribution of pressure applied by the belt.; Objectif : Un modèle numérique 3D du tronc humain a été développé pour étudier les effets biomécaniques des ceintures lombaires utilisées pour traiter les lombalgies. Méthodes : Ce modèle a été pris à partir de radiographies du tronc d'une personne et simplifié de manière à faire une étude paramétrique en faisant varier les paramètres morphologiques du patient, les paramètres caractéristiques de la ceinture lombaire et les paramètres mécaniques du corps et enfin à déterminer les paramètres influençant les effets de la lombalgie lors du port de la ceinture lombaire. La charge de la ceinture lombaire est modélisée par la loi de Laplace. Ces résultats ont été comparés à ceux d'une étude clinique. Résultats : Tous les résultats de cette étude paramétrique ont montré que le choix de la ceinture est très important en fonction de la morphologie du patient. De façon surprenante, le traitement thérapeutique n'est pas influencé par les caractéristiques mécaniques des structures corporelles, à l'exception des propriétés mécaniques des disques intervertébraux. Discussion : Le modèle numérique peut servir de base à des études plus approfondies concernant l'analyse de l'efficacité des ceintures lombaires dans les lombalgies. Afin d'étudier l'impact de l'architecture de la ceinture, la pression appliquée sur le tronc modélisée par la loi de Laplace pourrait être améliorée. Ce modèle pourrait également servir de base à une étude de l'impact de la ceinture sur une période de port. En effet, l'étude clinique montre que le mouvement a un impact important sur la répartition de la pression appliquée par la ceinture.

Ascending thoracic aortic aneurysm (ATAA) ruptures are life threatening phenomena which occur in local weaker regions of the diseased aortic wall. As ATAAs are evolving pathologies, their growth represents a significant local remodeling and degradation of the microstructural architecture and thus their mechanical properties. To address the need for deeper study of ATAAs and their failure, it is required to analyze the mechanical behavior at the sub-millimeter scale by making use of accurate geometrical and kinematical measurements during their deformation. For this purpose, we propose a novel methodology that combined a very accurate tool for thickness distribution measurement of the arterial wall, digital image correlation to assess local strain fields and bulge inflation to characterize the physiological and failure response of flat unruptured human ATAA specimens. The analysis of the heterogeneity of the local thickness and local physiological stress and strain was carried out for each investigated subject. At the subject level, our results state the presence of a non-consistent relationship between the local wall thickness and the local physiological strain field and high heterogeneity of the variables. At the inter-subject level, thicknesses were studied in relation to physiological strain and stress and load at rupture. The rupture pressure was correlated with neither the average thickness nor the lowest thickness of the specimens. Our results confirm that intrinsic material strength (hence structure) differs a lot from a subject to another and even within the same subject.

International audience; Lower back pain is a major public health problem. Despite claims that lumbar belts change spinal posture due to applied pressure on the trunk, no mechanical model has yet been published to prove this treatment. This paper describes a first model for belt design, based on the one hand on the mechanical properties of the fabrics and the belt geometry, and on the other hand on the trunk geometrical and mechanical description. The model provides the estimation of the pressure applied to the trunk, and a unique indicator of the belt mechanical efficiency is proposed: pressure is integrated into a bending moment characterizing the belt delordosing action on the spine. A first in-silico clinical study of belt efficiency for 15 patients with 2 different belts was conducted. Results are very dependent on the body shape: in the case of high BMI patients, the belt effect is significantly decreased, and can be even inverted, increasing the lordosis. The belt stiffness proportionally increases the pressure applied to the trunk, but the influence of the design itself on the bending moment is clearly outlined. Moreover, the belt/trunk interaction, modeled as sticking contact and the specific way patients lock their belts, dramatically modifies the belt action. Finally, even if further developments and tests are still necessary, the model presented in this paper seems suitable for in-silico pre-clinical trials on real body shapes at a design stage.

Goal: A non-invasive method is proposed to identify in vivo the passive mechanical properties of deep soft tissues in the human leg. How: Force-displacement curves in response to a localized compression of the calf are measured with a custom made experimental setup. The material parameters of a finite element model are then calibrated against the experimental curves using a genetic algorithm. A thorough investigation of the efficacy of this method to identify such mechanical properties is conducted through a design of experiments analysis and mixed numerical - experimental validations. Results: It is the first time that a thorough analysis is conducted to really separate the contribution of deep and superficial tissues in the response to compression tests and this permits to estimate the parameters of deep soft tissues on four subjects independently of the response of their other tissues. Two strain energy density functions are compared. It is shown that a 2nd order reduced polynomial better describes the passive mechanical behavior of the deep soft tissues of the leg than the neo-Hookean model.

International audience; Tissue engineered skin usually consist of a multi-layered visco-elastic material composed of a fibrillar matrix and cells. The complete mechanical characterization of these tissues has not yet been accomplished. The purpose of this study was to develop a multiscale approach to perform this characterization in order to link the development process of a cultured skin to the mechanical properties. As a proof-of-concept, tissue engineered skin samples were characterized at different stages of manufacturing (acellular matrix, reconstructed dermis and reconstructed skin) for two different aging models (using cells from an 18- and a 61-year-old man). To assess structural variations, bi-photonic confocal microscopy was used. To characterize mechanical properties at a macroscopic scale, a light-load micro-mechanical device that performs indentation and relaxation tests was designed. Finally, images of the internal network of the samples under stretching were acquired by combining confocal microscopy with a tensile device. Mechanical properties at microscopic scale were assessed. Results revealed that adding cells during manufacturing induced structural changes, which provided higher elastic modulus and viscosity. Moreover, senescence models exhibited lower elastic modulus and viscosity. This multiscale approach was efficient to characterize and compare skin equivalent samples and permitted the first experimental assessment of the Poisson’s ratio for such tissues.

International audience; Optical coherence tomography (OCT) combined with digital volume correlation (DVC) is a suitable technique to investigate the biomechanical behavior of biological tissues at the microscale. However, to characterize the whole thickness of large human or porcine arteries, the use of osmotic tissue clearing agents, such as propylene glycol (PG), is unavoidable due to intrinsic tissue scattering of light. The mechanical response of biological tissues immersed in tissue clearing agents has been poorly investigated so far. Nevertheless, understanding the mechanisms of tissue clearing could be helpful for developing safe optical-clearing methods for possible in vivo applications. The goal of the present work is to combine OCT and DVC to measure displacement and strain fields in porcine aortic tissues immersed in PG and subjected to stress-relaxation uniaxial tension. Displacement and strain fields are measured across the whole thickness of the porcine aortic wall for the first time. Measurement uncertainties and optimal OCT-DVC parameters are determined to define useful technical recommendations for future similar analyses. It is known that the main effect of PG is a significant increase in collagen fibril packing density due to important loss of water (dehydration). It results in a pronounced stiffening of the aortic tensile response when compared to the response of the same tissue immersed in phosphate buffered saline (PBS). This effect is reversible when the aortic tissue is removed from PG polypropylene glycol and immersed again in PBS. Another effect is a dramatic reduction in the Poisson’s effect during tensile loading. But the OCT-DVC-measured strain fields also reveal heterogeneities of this effect among the different layers of the aorta. It appears that the reduced Poisson’s effect is concentrated in the media layer, whereas the adventitia and intima layer keep a usual Poisson’s effect of nearly incompressible tissues. It is concluded that further work should be conducted on how the smooth muscle cells highly present in the media layer are affected by PG polypropylene glycol immersion for a better understanding of these effects.

Whereas industrial elastohydrodynamic (EHD) contacts are generally noncircular, most experimental observations are made on sphere-on-plane conjunctions. The circular case is indeed a specific ellip...

International audience; Compression therapy with stockings or bandage is the most common treatment for venous or lymphatic disorders. The objective of this study was to investigate the influence of bandage mechanical properties, application technique and subject morphology on the interface pressure, which is the key of this treatment. Bandage stretch and interface pressure measurements (between the bandage and theleg) were performed on 30 healthy subjects (15 men and 15 women) at two different heights on the lower leg and in two positions (supine and standing). Two bandages were applied with two application techniques by a single operator. The statistical analysis of the results revealed: no significant difference in pressure between men and women, except for the pressure variation between supine and standing position; a very strong correlation between pressure and bandage mechanical properties (p

International audience; The knee is the largest joint in the body and supports high loads, up to several times the body weight. It is vulnerable to injury during sport or professional activities, potentially leading to chronic knee instability. This instability is a functional issue to the patient and is characterized by a “wobbly” feeling. Different internal structures take part in joint stabilization by passive (ligaments, capsule) or active (neuro-muscular system and proprioception) action. The most common injury involves the anterior cruciate ligament (ACL) complete or partial rupture: it is involved in 24% of all knee injuries and 59% of ligamentous injuries [1]. In the United States,the annual incidence in the general population is approximately 1 in 3500 with 100,000 ACL reconstructions performed each year [2, 3]. These conditions are a huge burden on individualsand healthcare systems. Diagnosis of knee instability involves a discussion with the patient and a clinical examination, usually the Lachman test. It consists in a manual anterior translation of the tibia aiming at putting the ACL in tension. By practice, the examiner is able to grade the laxity by severity [4]. However, its sensitivity and specificity to detect complete ACL ruptures depends on the experience of the examiner, the patient’s body type and the delay between the accident and examination [5]. In order to reduce this variability, arthrometers were developed.These devices apply an increasing force to induce a postero-anterior drawer and measure the corresponding translation. Displacement-load curves of the healthy and injured knees are compared; ACL rupture is ascertained when differential laxity is higher than a certain threshold. Well-known arthrometer devices are the KT-1000 developed by [6] and the GNRB® [7]. The former is very popular and has been widely studied; its sensitivity to detect complete ACL ruptures is 77% and its specificity 90% (threshold: differential laxity of 3 mm at 130 N). Thelatter was developed recently; two studies [5, 7] highlighted the superiority of this device compared to similar apparatus. A differential threshold of 3 mm at 134 N is used to determine complete rupture: its sensitivity is 70% and specificity 99%. This arthrometer device is also used to diagnose partial ruptures (threshold of 1.5 mm at 134 N) with a sensitivity of 80% and a specificity of 87%.Knee braces or orthoses are usually part of the standard therapy for knee instability and are commonly prescribed by physicians and medical practitioners. Their claimed mechanical effects are to support/align the joint and increase proprioceptive input [8]. However, very few studies actually show significant actions, from biomechanical studies to therapeutic trials [9, 10]. Mechanical/ physiological effects have been emphasized, but the mechanisms of action have been poorly characterized [8, 9, 10, 11, 12, 13]. What is more, subjective evaluations of patients highlight a large demand for these products; therefore, their efficiency is still widely discussed among medical experts. In particular, therelative importance of the two principal stabilizing mechanisms is not known:- joint stiffening by adding supporting structures, e.g. hinged bars secured to the joint by straps and fabric (passive mechanism)- neuromuscular control enhancement by proprioceptive effect (active mechanism)As a consequence of these uncertainties, medical practitioners and manufacturers still lack a simple evaluation tool for knee orthoses. A French committee of experts highlighted this problem [14] and stated that orthoses must be evaluated by taking both the mechanisms of action and the desired therapeutic effects into account.Although the passive action of knee braces to prevent a drawer motion has already been characterized on surrogate limbs [15, 16, 17], only one attempt has been made to link these measures to corresponding expected in-vivo actions through numerical modelling [18, 19], highlighting a passive stiffening much lower than what is brought by intact ligaments. However, a real clinical study is still needed to validate the numerical results and investigate the influence of patient-specific factors such as morphology, injury severity, neuromuscular adaptation and instability feeling control.This study is aimed at objectively quantifying the joint stiffening action of various commercial braces in-vivo using a GNRB® arthrometer on a number of pathological patients.

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International audience

International audience; This chapter presents a quick and efficient approach to perform patient-specific Finite-Element (FE) predictions of the human calf response under elastic compression. The reconstruction of patient-specific material properties of soft tissues is based on two methodologies described extensively in two previous papers [1, 2]. After a detailed description of the implementation of this model, results obtained on four volunteers are presented. The deformed geometry predicted by the FE model is in very good agreement with the MRI scan of the same leg under elastic compression. Eventually , it is shown that elastic compression always induces a partial vein closure but the magnitude of vein closure depends strongly on the position of the vein, on the shape of the leg and on the material properties of surrounding soft tissues.

Objectifs Les dispositifs medicaux de compression (DMC) constituent le traitement de reference de l’insuffisance veineuse. Ces dispositifs sont bases sur des textiles tisses ou tricotes, chaussettes, bas ou bandes, et agissent sur les jambes par compression ou contention. Leur action mecanique doit etre controlee, cependant aucune norme europeenne ne fait actuellement consensus. En France, la norme preconise un essai de traction et relie la pression a la tension par la loi de Laplace ; en Allemagne, le dispositif Hosy permet de mieux prendre en compte la forme du DMC en effectuant simultanement une traction a differents niveaux ; enfin, en Angleterre et aux Etats-Unis, le systeme HATRA reproduit une jambe en bois permettant d’appliquer une tension. Les differents systemes proposes sont eloignes de la realite et ne permettent pas de comprendre comment les DMC agissent sur les jambes. L’objectif de ce travail est de presenter des methodes modernes d’etudes des DMC ; il s’articulera autour de travaux numeriques existants et proposera des pistes de travail pour le futur. Materiel et methodes Notre equipe a developpe des modeles numeriques pour comprendre l’action des DMC sur les jambes. Dans un premier temps, les modeles ont ete developpes pour une section de jambe, et la pression exercee a ete calculee a partir de la loi de Laplace, puis les modeles se sont complexifies, integrant le DMC en tant que tel sur une jambe decrite comme un volume. Les modeles ont cherche a integrer progressivement les caracteristiques de chaque patient, obtenues a partir d’IRM ou d’elastographie : la forme de la jambe, ses proprietes mecaniques globales puis locales, la position et la forme des veines. Resultats Ces travaux ont permis de mettre en evidence l’heterogeneite de la pression exercee par le DMC sur la jambe. L’efficacite sur la fermeture des veines a pu etre evaluee ; elle depend fortement de la forme de la jambe ainsi que de la position des veines. Les proprietes mecaniques de la jambe, et donc la nature des tissus et leur etat (masse graisseuse, muscles contractes ou relâches etc.) ont peu d’influence sur la generation de pression, mais interviennent dans sa transmission jusqu’aux veines. Conclusion et perspectives Ces resultats permettent une comprehension en profondeur des mecanismes d’action des DMC, mais ils restent limites a des etudes en statique, avec une description sommaire de la circulation du sang dans les veines. Une approche dynamique, incluant en particulier la pompe musculaire, mais aussi le flux sanguin devra etre proposee dans le futur. Par ailleurs, ces travaux numeriques doivent etre confrontes a l’experimentation clinique et mecanique. Il est urgent de progresser dans les modeles experimentaux et imaginer un ensemble de fantomes de jambes tri-dimensionnels, deformables, largement instrumentes, presentant quelques veines representatives.

Objective With cartilage physiopathology, knee stability and therefore the subsequent loadings on ligaments have a strong impact in the development of knee osteoarthritis. To understand this phenomenon, authors are proposing different knee models. Most of them are without any flexion, some have been introduced by controlling actively muscular groups. In this case, the forces used to achieve the flexion may not be physiological, and the pressure on the articulation can be questioned. We propose a mixed approach, both using medical imaging (MRI, EOS X-ray system) and force platform in conjunction with a finite element model. Material and methods One healthy volunteer underwent a MRI and an EOS imaging of the knee. EOS images gave the exact position of the bones for five flexion angles, the force platform ensuring consistent boundary conditions. A 3D geometrical model of the bones and cartilages was segmented from the MRI stacks; this model was meshed and smoothed for finite element analysis (FEA). The bones of the model were fitted to those of the EOS images to have the physiological positions of the knee. The FEA was carried out with the EOS imaging experimental boundary conditions, ensuring the global knee mechanical equilibrium. Results To validate this patient-specific model, its bony structure was confronted with the EOS images once the mechanical equilibrium reached. The difference of position was within the error range of the image registration, showing a satisfying equilibrium state. Last, this model gave us an estimation of the tension in the ligaments for every flexion as well as a pressure map on the cartilages. Discussion/Conclusion The FEA model main assumption lies on the absence of menisci and muscular active control. Nevertheless, the model is suitable to achieve a reasonable equilibrium. It has been used successfully in the study of ligament tension during the flexion cycle. It will then be used as a reference in studying arthritic knee joints for clinical cases.

International audience; Compression bandages are commonly used in the treatment of some venous or lymphatic pathologies. The success of the treatment relies on the applied pressure, which depends on several parameters related to the bandage but also to patients’ morphology. A previous experimental study showed that patient’s morphology and bandage elastic properties were not sufficient to explain interface pressure distribution [1]. However, these two parameters are the only one taken into account in Laplace’s Law, actual reference method to explain interface pressure distribution.

Objective Compression bandages are commonly used in the treatment of some venous or lymphatic pathologies. The success of the treatment relies on the applied pressure, which depends on several parameters, especially the bandage properties but also patients’ morphology. A previous experimental study showed that considering only patient's morphology and bandage elastic properties were not sufficient to explain interface pressure distribution. However, these two parameters are the only one taken into account in Laplace's Law, current standard method to explain interface pressure distribution. The objective of the study is to characterize and model compression bandages pressure generation mechanisms. Material and methods A patient-specific numerical simulation of 4 bandages application [Biflex ® 16 and Biflex ® 17 (Thuasne) applied with 2 and 3 layers on the leg] was developed for 5 subjects. The inputs of this simulation are the subjects’ morphology, the bandage's and soft tissues’ elastic properties and the application technique. The results of this simulation were then confronted to the experimental results and pressure values computed with Laplace's Law: P = nT/r, with P the pressure [N/mm 2 ], n the number of layers, T the bandage tension [N/mm] and r the local radius of curvature [mm]. Results The numerical simulation provides the complete pressure distribution over the leg but also considers the deformations of the leg, induced by bandage application. The comparison with the results given by Laplace's law highlighted the influence of these leg geometry changes on the applied pressure. However, the 4 parameters considered in this simulation (leg morphology and deformations, bandage elastic properties and application technique) are not sufficient to completely explain pressure generation, and differences with the experiments still persist. Discussion/Conclusion Numerical simulation still needs to be enriched to consider other parameters which may impact interface pressure such as bandage to bandage interaction for example.

International audience; Compression bandages are a common treatment for some lymphatics or venous pathologies. The treatment success directly depends on the pressure which is applied on the external surface of the leg and which is then transmitted to the internal tissues. This interface pressure (between the limb and the bandage) depends mainly on the following parameters:- the bandage components (padding layers, …)- their mechanical properties- the bandage stretch- the application technique (spiral, …) and number of layers (overlap)- patient’s leg morphology- other parameters such as friction between the different bandage layers.Though the efficacy of this treatment is admitted [1], its action mechanism and the pressure it applies on the leg remain poorly understood [2].For now, the reference method for the computation of interface pressure applied by compression bandage is Laplace’s Law:P = n T / r (1)with P the local pressure, n the number of layers of the bandage, T the bandage tension (i.e. force to stretch the bandage), r the local radius of curvature of the limb. However, this law, which only considers the non-deformed state of the limb, is unable to accurately predict interface pressures [3].The aim of this communication is to present a combined experimental and numerical approach for the assessment of interface pressure applied by compression bandages.

International audience; Low back pain is a pain felt in the lumbar region of the spine. Among a large series of care strategies, lumbar belt might be used to treat this pathology. Several clinical trials have shown the efficiency of lumbar belts [1]. Despite the high quantity of affected patients each year (about 80 % of the French population have /will suffer back pain in their life), few authors investigated the mechanism of action of belts. It is usually reported that the main mechanical effect of a lumbar belt is the pressure applied on the trunk. This pressure on the abdominal skin and muscles induce an increase of intra-abdominal pressure, a decrease of intra-discal pressure, and a proprioceptive reaction of the posture. Unfortunately, the link between the textile characteristics, the belt design and the pressure applied on the trunk has been poorly studied.Recently, Bonnaire [2] proposed a clinical study using optical methods and pressure map sensors; Munoz [3] proposed a detailed finite element model, closely linked to medical imaging showing the load release in the intervertebral disc, but resorting to a clinical study is a tedious task, and some early stage information should be of great help when designing new belts.The purpose of this communication is an assessment of the applied pressure by a lumbar belt onto the trunk from the mechanical properties of fabrics and the trunk shape. It gives a way to estimate the mechanical efficiency of belts at the design stage.

International audience; Compression of the lower leg by bandages is a common treatment for the advanced stages of some venous or lymphatic pathologies. The outcomes of this treatment directly result from the pressure generated onto the limb. Various bandage configurations are proposed by manufacturers: the study of these configurations requires the development of reliable methods to predict pressure distribution applied by compression bandages. Currently, clinicians and manufacturers have no dedicated tools to predict bandage pressure generation. A numerical simulation approach is presented in this work, which includes patient-specific leg geometry and bandage. This model provides the complete pressure distribution over the leg. The results were compared to experimental pressure measurements and pressure values computed with Laplace’s law. Using an appropriate surrogate model, this study demonstrated that such simulation is appropriate to account for phenomena which are neglected in Laplace’s law, like geometry changes due to bandage application.

International audience; Knee degradation and pain when developing osteoarthritis are strongly related not only to the pressure on the cartilage, but also to the knee stability and to the subsequent loadings on the ligaments. Authors proposed the knee models without any flexion. Knee flexion had been introduced by controlling actively muscular groups or by using a full displacement-controlled model. But in both cases, the pressure applied on the articulation has been questioned, the forces used to achieve the flexion being far from the physiology in the former and the bone positioning uncertainties leading to high variations in the cartilage pressure and ligament loads in the latter. Here, we propose a mixed approach, both using medical imaging (MRI, EOS X-ray system) and force platform in conjunction with a finite element model. A healthy volunteer underwent a MRI and an EOS imaging of the knee. EOS images gave the exact position of the bones for five flex-ion angles of the knee, ranging from 0° to 85°. The subject's knee was loaded with a specific force on his foot during all acquisitions to keep consistent boundary conditions on the knee. A 3D geometrical model of the bones and cartilages was segmented from the MRI stacks; this model was meshed and smoothed for Finite Element

International audience; Compression of the lower leg using medical compression stockings or bandages is a widely used treatment. We submit that the mechanical properties of soft tissues in the lower limb play a major role during compressive treatments of venous deficiency [1] and that predictive biomechanical models could help to better adapt the treatment to the specificity of each patient. A challenging step of the development of such models is to identify the mechanical properties of soft tissues for each patient [2]-[4].We recently developed a non-invasive and fast inverse approach to address this challenge. In this communication, the approach is described and assessed on several volunteers, showing promising results for an extension to large-size cohort of patients.

A novel direct approach to detect the resin flow front during the Liquid Resin Infusion process under industrial environment is proposed. To detect the resin front accurately and verify the results, which are deduced from indirect micro-thermocouples measurements, optical fiber sensors based on Fresnel reflection are utilized. It is expected that the results derived from both techniques will lead to an improvement of our understanding of the resin flow and in particular prove that micro-thermocouples can be used as sensors as routine technique under our experimental conditions. Moreover, comparisons with numerical simulations are carried out and experimental and simulated mold filling times are successfully compared., Comment: JM-JCM-46.pdf