Comportement viscoélastique linéaire et faiblement non-linéaire de suspensions concentrées de plaquettes d'argile colloïdales

Le comportement viscoélastique des suspensions très concentrées (f > 0,4) a été étudié en régime linéaire et faiblement non-linéaire, en fonction de la fraction volumique, de la force ionique et en présence d'un polymère à différentes concentrations. Les grandeurs matérielles telles que les modules viscoélastiques en régime linéaire et l'énergie de cohésion sont fortement augmentées à la fois par l'augmentation de la fraction volumique et par la diminution de la force ionique. Notre attention a porté sur l'étude du comportement des suspensions de plaquettes d'argiles soumises à des cisaillements oscillatoires à forte amplitude (LOSE). La réponse viscoélastique présente en particulier un pic du module G" caractéristique d'un effet extra dissipatif. L'étude rhéologique montre que l'intensité de cet effet extra dissipatif est fortement influencée par les interactions de volume exclu, électrostatiques et stériques. Les interprétations proposées sont basées sur le couplage entre les interactions inter-particulaires et les interactions hydrodynamiques

Biopharmaceutical Assessment of Dexamethasone Acetate-Based Hydrogels Combining Hydroxypropyl Cyclodextrins and Polysaccharides for Ocular Delivery

We previously developed two optimized formulations of dexamethasone acetate (DXMa) hydrogels by means of special cubic mixture designs for topical ocular administration. These gels were elaborated with hydroxypropyl-β-CD (HPβCD) and hydroxypropyl-γ-CD (HPγCD) and commercial hydrogels in order to enhance DXMa water solubility and finally DXMa’s ocular bioavailability and transcorneal penetration. The main objective of this study was to characterize them and to evaluate in vitro, ex vivo, and in vivo their safety, biopermanence, and transcorneal permeation. Gels A and B are Newtonian fluids and display a viscosity of 13.2 mPa.s and 18.6 mPa.s, respectively, which increases their ocular retention, according to the in vivo biopermanence study by PET/CT. These hydrogels could act as corneal absorption promoters as they allow a higher transcorneal permeation of DXMa through porcine excised cornea, compared to DEXAFREE® and MAXIDEX®. Cytotoxicity assays showed no cytotoxic effects on human primary corneal epithelial cells (HCE). Furthermore, Gel B is clearly safe for the eye, but the effect of Gel A on the human eye cannot be predicted. Both gels were also stable 12 months at 25 °C after sterilization by filtration. These results demonstrate that the developed formulations present a high potential for the topical ocular administration of dexamethasone acetateThis work was supported by Labex ARCANE (ANR-11-LABX-0003-01) and Institut de Chimie Moléculaire de Grenoble (FR 2607) and the Glyco@Alps program (ANR-15-IDEX-02). A.F.-F. acknowledges the support obtained from the Instituto de Salud Carlos III (ISCIII) through its research grants (JR18/00014). X.G.-O. acknowledges the financial support of the IDIS (Health Research Institute of Santiago de Compostela) (predoctoral research fellowships)S

Relating Habitat and Climatic Niches in Birds

Predicting species' responses to the combined effects of habitat and climate changes has become a major challenge in ecology and conservation biology. However, the effects of climatic and habitat gradients on species distributions have generally been considered separately. Here, we explore the relationships between the habitat and thermal dimensions of the ecological niche in European common birds. Using data from the French Breeding Bird Survey, a large-scale bird monitoring program, we correlated the habitat and thermal positions and breadths of 74 bird species, controlling for life history traits and phylogeny. We found that cold climate species tend to have niche positions in closed habitats, as expected by the conjunction of the biogeographic history of birds' habitats, and their current continent-scale gradients. We also report a positive correlation between thermal and habitat niche breadths, a pattern consistent with macroecological predictions concerning the processes shaping species' distributions. Our results suggest that the relationships between the climatic and habitat components of the niche have to be taken into account to understand and predict changes in species' distributions

CD4CD8αα Lymphocytes, A Novel Human Regulatory T Cell Subset Induced by Colonic Bacteria and Deficient in Patients with Inflammatory Bowel Disease

It has become evident that bacteria in our gut affect health and disease, but less is known about how they do this. Recent studies in mice showed that gut Clostridium bacteria and their metabolites can activate regulatory T cells (Treg) that in turn mediate tolerance to signals that would ordinarily cause inflammation. In this study we identify a subset of human T lymphocytes, designated CD4CD8αα T cells that are present in the surface lining of the colon and in the blood. We demonstrate Treg activity and show these cells to be activated by microbiota; we identify F. prausnitzii, a core Clostridium strain of the human gut microbiota, as a major inducer of these Treg cells. Interestingly, there are fewer F. prausnitzii in individuals suffering from inflammatory bowel disease (IBD), and accordingly the CD4CD8αα T cells are decreased in the blood and gut of patients with IBD. We argue that CD4CD8αα colonic Treg probably help control or prevent IBD. These data open the road to new diagnostic and therapeutic strategies for the management of IBD and provide new tools to address the impact of the intestinal microbiota on the human immune system

Etude rhéologique de suspensions aqueuses diluées et concentrées de plaquettes d'argile colloidales (effets de l'adsorption de polymères associatifs)

BREST-BU Droit-Sciences-Sports (290192103) / SudocNANCY/VANDOEUVRE-INPL (545472102) / SudocSudocFranceF

Mise en forme et caractérisation de nano-fibres fonctionnalisées par chimie click pour l'ingénierie tissulaire

Le procédé d électro-filage est devenu une technique privilégiée pour la préparation des matériaux nano-fibreux, grâce à sa simplicité de mise en oeuvre, la polyvalence des matières premières utilisées, ainsi que la diversité des structures obtenues. Sa capacité à produire des réseaux fibrillaires, proches de ceux du vivant ont ouvert la voie à d importantes applications en ingénierie tissulaire. Cette étude a porté sur i) l'élaboration de nano-fibres à base de biopolymères commerciaux par un procédé d électro-filage, pour des applications en ingénierie tissulaire, ii) leur fonctionnalisation et, iii) l étude par SANS de la stabilité des chaînes de polymères constituant ces fibres. La stabilité d un polymère est un facteur important pour la dégradation contrôlée dans les systèmes biologiques. Des études de la stabilité de polystyrène, utilisé ici comme un modèle simple, dans le milieu confiné des nanofibres, ont été élaborés avec la technique de diffusion de neutrons aux petits angles. L investigation de la conformation des chaînes de polymère dans les nanofibres montre une anisotropie remarquable, en suggérant une forte déformation des chaînes dans la direction axiale des fibres d au cours de procédé d électro-filage. La dynamique de relaxation des chaînes a permis d évaluer leur stabilité et vieillissement dans le milieu confiné des nanofibres. Des fibres biocompatibles à base de poly( -caprolactone) (PCL) ont été électro-filées et optimisées pour obtenir des matériaux nano-structurés et fonctionnalisés en vue d applications biomédicales. L introduction par chimie click azide-alcyne de groupes saccharidiques dans le coeur ou en surface des fibres de PCL a été réalisée très efficacement selon deux approches distinctes avant ou après électro-filage. Les caractérisations physico-chimiques et biologiques réalisées sur les différents systèmes ont notamment permis de mettre en évidence la biodisponibilité des sucres à la surface des fibres ainsi que leur capacité à rendre la PCL hydrophile. Ces résultats attestent du potentiel de la chimie click à permettre la fonctionnalisation de fibres de polyesters sans altération de leur structure ouvrant ainsi d importantes perspectives dans le domaine de l ingénierie tissulaire.Electrospinning process has become a leading technique for producing nano-fibrous scaffolds that are highly porous, lighter, and with superior mechanical properties than their bulk equivalents. Structural properties of electrospun fibers closely resemble to the connective cell tissue, making these nonwovens readily employed in medicine and pharmacy. The research study of this thesis focused on bridging the commercially available biopolymers with the tissue engineering applications through multifunctional aspects of carbohydrates and click chemistry coupling. Biocompatible fibers were electrospun from poly( -caprolactone) and further optimized into clickable azido-PCL scaffolds. Their surface-activity was visualized after click coupling of a fluorescent dye onto PCL-based electrospun fibers, while hydrophilicity and bioactivity were achieved by covalent bonding of carbohydrates, enabling specific cell adhesion possibilities of these nonwovens. Selective lectin surface-immobilization revealed the potential of these scaffolds for specific protein adhesion and therefore controlled cell-material interactions. Polymer stability is an important factor for controlled degradation in tissue engineering applications. Small angle neutron scattering studies were carried out to estimate the stability of polystyrene as a model-polymer, its chain conformation in as-spun and thermally annealed electrospun fibers. Notable anisotropy of polymeric chains within the fibers was observed. The terminal relaxation time of the polystyrene was estimated and compared to the theoretical value.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Very Concentrated Plate-Like Kaolin Suspensions Under Large Amplitude Oscillatory Shear: a Microstructural Approach

International audienceKaolinite particles are plate-like natural clay particles. The behavior of very concentrated kaolinite suspensions {0> 0,4) atpH 7 is governed by both repulsive electrostatic interactions between negatively charged basal planes and excluded volume interactions [1]. The complex rheological behavior of kaolinite suspensions is closely related to the suspension microstructure at rest, resulting from inter-particle interactions, and its deformation under stress. Very concentrated kaolinite suspensions undergoing large amplitude oscillatory shear (LAOS) are known to exhibit a peculiar nonlinear viscoelastic behavior, characterized by a hump in G" modulus, whose microscopic origin is still a matter of debate. In this work, a microstructural interpretation of this nonlinear behavior is proposed. For this purpose, the viscoelastic behavior of suspensions has been investigated as a function of volume fraction, ionic strength and in the presence of polymer at various concentrations, in order to monitor the influence of both the nature and the intensity of interparticle interactions

Rheological study of compositional heterogeneity in an associative commercial polymer solution

International audienc