Design of an innovative exoskeletal forearm-wrist mechanism

International audienceThis paper presents an innovative 3-joints structure designed as the forearm-wrist of a force controlled exoskeleton. It is composed of an open parallel mechanism both fitting the human forearm and able to rotate on its longitudinal joint (prono-supination), in a similar manner of the ulna-radius movement. This structure advantageously replaces circular guidings in terms of mass, volume and friction and can be freely scaled. A lightweight 3 dof forearm-wrist mechanism is proposed as an integral rotation module for the general-purpose arm exoskeleton ABLE 7 D

Durabilité de composites bois - polymers biodégradables Durability of Wood - biodegradable Polymer Composites.

International audienceCette étude porte sur la photodurabilité de matériaux entièrement biodégradables : des composites bois - polymères biodégradables. Les matrices polymères sont le poly(acide lactique), l'Ecoflex® et l'Ecovio®. Les charges sont différentes farines de peuplier dont certaines ont subi un traitement thermique appelé rétification, visant à diminuer leur hygroscopie et ainsi leur biodégradabilité. Ces mélanges (50/50) sont analysés par rhéométrie à l'état fondu et par analyse enthalpique différentielle (DSC) afin de caractériser leurs propriétés initiales. Ils sont ensuite soumis à un photovieillissement naturel et accéléré en enceinte et analysés de la même façon afin d'évaluer leur durabilité face à la lumière solaire. En effet, des mesures rhéologiques et thermiques vont nous permettre d'observer les changements intervenant au niveau moléculaire au cours de la dégradation et ainsi de proposer des mécanismes de photodégradation. // The topic of the study is the photoageing of completely biodegradable composites: Wood-biodegradable Polymer Composites. The polymer matrices are poly (lactic acid), Ecoflex®_and Ecovio®. The fillers are different poplar flours. Some of them have undergone a retification process: a thermal treatment. This process leads to chemical modification of wood which results in higher hydrophoby and thus to greater resistance against biodegradation. These blends (50/50) were analysed by melt rheological measurements and by Differential Scanning Calorimetry (DSC) to characterize their initial properties. In a second time, natural and artificial photoageing of these blends were carried out. Rheological and DSC measurements permit to find out their durability under UV-visible light. Indeed, these analyses allows us to observe molecular changes during degradation and therefore to determine photodegradationmechanism at work

Durabilité de composites bois – polymères biodégradables

Etant données les préoccupations environnementales actuelles, il est important de s'intéresser dés à présent aux matériaux entièrement biodégradables. C'est pourquoi nous étudions des mélanges composites polymères biodégradables – charges d'origine naturelle. Le projet est de découpler l'aspect photodégradation de l'aspect biodégradation afin d'obtenir à terme une durabilité contrôlée. Ce contrôle permettrait d'associer un matériau à une durée d'application et donc d'éliminer l'étape de recyclage

Etude rhéologique de nouveaux biocomposites bois - polymères biodégradables

L'étude porte sur la photodurabilité de composites entièrement biodégradables. Ils sont constitués de trois matrices polymère biodégradables (PLA, Ecoflex® et Ecovio®) mélangées avec différentes farines de bois dont certaines ont subi un traitement thermique visant à renforcer leurs propriétés hydrophobes. La rhéologie dynamique à l'état fondu a permis de caractériser initialement le comportement viscoélastique de ces matériaux mais également d'observer les coupures ou recombinaisons éventuelles des chaînes macromoléculaires intervenant lors de la dégradation photochimique

What is the influence of using generic material properties on the estimation of the pelvis sagging when sitting from a Finite Element model of the buttock region?

Ischial pressure sores are painful, slow healing wounds that develop during prolonged sitting. Its formation is associated with the high internal strains induced by the compression of the soft tissues under the ischium [1]. 3D Finite Element (FE) models have been developed to estimate internal strains in the subdermal soft tissues. Some authors have also investigated the influence of the material properties of the soft tissues [2]. However, the interval of variation of the parameters in these sensitivity studies are not necessarily representative of the variability of subgroups of population. In this contribution, we investigate the influence of using the material properties of one given individual (generic material properties) as representative of a population. The generic material properties were obtained by Finite Element Updating to fit the experimental sagging of the pelvis of one subject when sitting. The 3D subject-specific FE model was generated from the combination of bi-planar Radiography, ultrasound imaging and optical scanner and is composed of the pelvis (rigid body) and 3 homogeneous layers representing the muscle tissue, fat and skin. The adipose tissue and the muscle layer were modelled as an Ogden quasi-incompressible hyperelastic material. The same material parameters were used to estimate the pelvis sagging of 7 healthy subjects. The estimated sagging was compared to the experimental one measured by computing the vertical displacements of both ischial tuberosities visible on the radiographs before and after sitting (Figure 1). For 5 subjects, the differences between both were below 1mm. For the two other subjects, the differences were 4 and 6 mm. These findings suggest that using generic material properties allow to reproduce the biomechanical response of the buttock when sitting for healthy subjects. The same approach could be applied to spinal cord injury population, which will allow to clarify the necessity of personalizing the material properties in models developed for this population

Development and validation of a new methodology for the fast generation of patient-specific FE models of the buttock for pressure ulcer prevention.

Ischial pressure sores are painful, slow healing wounds that develop during prolonged sitting. Its formation is associated with the high internal strains induced by the compression of the soft tissues under the ischium [1]. Although, many 3D Finite Element (FE) models have been developed to predict the mechanical response of the subdermal soft tissues, they are always constructed from segmentation of MRI or CT-Scan acquisitions limiting the studies to only one individual and overlooking the inter-individual variability. In this contribution, we present a new methodology for a fast 3D FE model generation of the buttock for PU prevention. The 3D subject-specific FE model was generated from the combination of bi-planar Radiography, ultrasound imaging and optical scanner and is composed of the pelvis (rigid body) and 3 homogeneous layers representing the muscle tissue, fat and skin. The adipose tissue and the muscle layer were modelled as an Ogden quasi-incompressible hyperelastic material and the material properties were calibrated to fit the experimental data. The validation of the model was performed from external pressure measurement on a population of 6 healthy subjects. The mean difference of the median pressure was 0.32kPa (std 0.8kPa), showing good agreement between the experiments and FE models and representing 2% of the mean value. The low generation time of this model compared to existing methodologies will allow to investigate the influence of pelvis and buttock geometry on the biomechanical response of the subdermal soft tissues under the ischium during sitting

Is a simplified Finite Element model of the gluteus region able to capture the mechanical response of the internal soft tissues under compression?

Internal soft tissue strains have been shown to be one of the main factors responsible for the onset of Pressure Ulcers and to be representative of its risk of development. However, the estimation of this parameter using Finite Element (FE) analysis in clinical setups is currently hindered by costly acquisition, reconstruction and computation times. Ultrasound (US) imaging is a promising candidate for the clinical assessment of both morphological and material parameters. Method: The aim of this study was to investigate the ability of a local FE model of the region beneath the ischium with a limited number of parameters to capture the internal response of the gluteus region predicted by a complete 3D FE model. 26 local FE models were developed, and their predictions were compared to those of the patient-specific reference FE models in sitting position. Findings: A high correlation was observed (R = 0.90, p-value < 0.01). A sensitivity analysis showed that the most influent parameters were the mechanical behaviour of the muscle tissues, the ischium morphology and the external mechanical loading. Interpretation: Given the progress of US for capturing both morphological and material parameters, these results are promising because they open up the possibility to use personalised simplified FE models for risk estimation in daily clinical routine.This work was supported by the Fondation de l'Avenir (grant number AP-RM-2016-030), by la Fondation des Arts et Métiers and the Fonds de dotation Clinatec. The authors are also grateful to the ParisTech BiomecAM chair program on subject-specific musculoskeletal modelling

Cultural Heritage and Climate Change: New challenges and perspectives for research

JPI Cultural Heritage & JPI ClimateCollaboration between the two Joint Programming Initiatives “Cultural Heritage and Global Change” (JPI CH), and “Connecting Climate Knowledge for Europe” (JPI Climate) began in 2019 and led to the organisation of a joint workshop a year later. Following the recommendations in the workshop report, an expert working group was set up to scope research gaps and opportunities at the interface of cultural heritage and climate change, culminating in the publication of this White Paper. This strategic document is expected to support the two JPIs to generate policy-relevant research outcomes.Peer reviewe

Development and evaluation of a new methodology for the fast generation of patient-specific Finite Element models of the buttock for sitting-acquired deep tissue injury prevention

International audienceThe occurrence and management of Pressure Ulcers remain a major issue for patients with reduced mobility and neurosensory loss despite significant improvement in the prevention methods. These injuries are caused by biological cascades leading from a given mechanical loading state in tissues to irreversible tissue damage. Estimating the internal mechanical conditions within loaded soft tissues has the potential of improving the management and prevention of PU. Several Finite Element models of the buttock have therefore been proposed based on either MRI or CT-Scan data. However, because of the limited availability of MRI or CT-Scan systems and of the long segmentation time, all studies in the literature include the data of only one individual. Yet the inter-individual variability can’t be overlooked when dealing with patient specific estimation of internal tissue loading. As an alternative, this contribution focuses on the combined use of low-dose biplanar X-ray images, B-mode ultrasound images and optical scanner acquisitions in a non-weight-bearing sitting posture for the fast generation of patient-specific FE models of the buttock. Model calibration was performed based on Ischial Tuberosity sagging. Model evaluation was performed by comparing the simulated contact pressure with experimental observations on a population of 6 healthy subjects. Analysis of the models confirmed the high inter-individual variability of soft tissue response (maximum Green Lagrange shear strains of 213 ± 101% in the muscle). This methodology opens the way for investigating inter-individual factors influencing the soft tissue response during sitting and for providing tools to assess PU risk

Lifetime durability of bio-based composites

International audienceThe markets for applications of biocomposites are expanding internationally. A biocomposite is a material made from a mixture of natural fibers and a thermoplastic polymer to obtain a product having some characteristics of both resources: (a) filler reinforcement (plus wood-like appearance of wood plastics) and (b) plastic performance in wet conditions. Wood–polymer composites (WPCs) are used mainly in four different sectors of materials applications: building, construction, automotive, and marine infrastructures. Current major scientific and technological efforts are focused on increasing the bio-based carbon content and minimizing environmental impacts associated with the use of polymeric materials. However, bio-based composites can create problems at the end of their lives. The current recycling streams are not suited to such materials. That is why the focus is increasingly on “eco-friendly” materials such as composites based on natural or synthetic biodegradable polymers and fillers such as starch, vegetable fiber, or wood flour. The most studied WPC-based biodegradable matrix systems are composites based on polylactic acid (PLA). Many studies deal with the mechanical properties and the inclusions of additives to improve the effects of reinforcing fillers. However, very few studies are devoted to the durability of these new biocomposites during their service life