Thermosensitive PNIPAM grafted alginate/chitosan PEC

Smart biomaterial functionality such as controlled adhesion properties is crucial to limit strip-off injuries. Among functional polymers, poly-N(isopropylacrylamide) (PNIPAM) allows surface properties to be changed depending on the temperature, with a transition of its properties that occurs around 32 °C, called the lower critical solution temperature (LCST). This transition is expected to modify surface interactions. Alginate and chitosan are biocompatible polymers commonly combined as polyelectrolyte complex (PEC) and are suitable for wound dressing applications. As a complex system, however, it is not so trivial to achieve an efficient functionalization. Herein, we elaborated a procedure to functionalize the surface of alginate/chitosan PECs without altering their intrinsic properties. FTIR revealed that acidic treatment led to a partial decomplexation of the PECs. Therefore, while the N-Hydroxysuccinimide/N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide (NHS/EDC) coupling usually requires an intermediate pH, we showed that a preliminary acidification seemed to increase the surface grafting efficiency. Water contact angle increased from 51° to 72°, showing that PNIPAM enhanced the surface hydrophobicity. The LCST transition modified the interaction forces between PNIPAM and model surfaces: it revealed an unexpected thermosensitive behaviour as hydrophobic transition favoured interactions with hydrophilic surfaces. It was presumably due to PNIPAM/PEC substrate interactions. Finally, the surface modification did not affect the release properties of the PEC biomaterial

Elaboration of a thermosensitive smart biomaterial: From synthesis to the ex vivo bioadhesion evaluation

Alginate and chitosan are polysaccharides that are widely used in the biomedical field, especially as wound dressings. Controlled bioadhesion is an advanced functionality that offers the potential to reduce injuries due to the stripping-off of the biomaterial. Herein, we report the efficient grafting of poly-N(isopropylacryamide) (PNIPAM), a thermosensitive polymer that exhibits a lower critical solution temperature (LCST) at 32 °C on the alginate/chitosan polyelectrolyte complex (PEC) surface. In vitro studies did not exhibit a cytotoxic effect, and cells adhered preferentially on the LCST on PNIPAM grafted surfaces, as reported in the literature. Ex vivo investigations revealed that the adhesive behavior of the biomaterials was not the same on the liver and pancreas. The effect of the temperature on the bioadhesion to organs was unexpected, as PNIPAM surfaces exhibited higher adhesion at low temperature. The PNIPAM was therefore able to confer PEC matrix thermosensitivity, but due to the application force, interactions between PNIPAM chains and their substrate could influence bioadhesion on tissues

Analysis of the mechanical behaviour of composites and their bonded assemblies under out-of-plane loads using a modified Arcan apparatus

International audienceAdhesively bonded assemblies, unlike riveted or bolted joints, do not require holes, which can lead to large stress concentrations in composites. For this reason adhesive bonding is attracting attention particularly when weight is critical. But failure in adhesively bonded assemblies involving composites is often associated with crack initiation in the adhesive or delamination of the composite plies close to the adhesive joint caused by interlaminar or through-thickness stresses. Such assemblies are often characterized by large stress concentrations, which make the analysis of their behaviour for industrial applications difficult. As the mechanical behaviour of adhesives and of composites are quite complex, a large database of experimental results under various loading conditions is necessary to develop accurate numerical models. Unfortunately, few experimental devices allow out-of-plane loading to be studied, except for specific loadings or by using thick composite specimens which are not always representative of industrial applications. This paper presents the possibilities of an experimental device, using a modified Arcan test, and optimized hybrid bonded assemblies, which limit the influence of edge effects. Some test results, showing the potential of the approach, are presented in the form of failure envelope curves for proportional monotonic out-of-plane loadings. Moreover, some aspects of the influence of low temperature on the mechanical behaviour of hybrid bonded assemblies with composites are analyzed

Modélisation du comportement de composite à matrice céramique sous sollicitation de fatigue

International audienceLe présent article propose une approche permettant de déterminer la durée de vie d'un composite à matrice céramique en fatigue. Cette approche est mise en place par un couplage entre un modèle d'endommagement purement mécanique et un modèle basé sur la physico-chimie du matériau. En effet, la physico-chimie du matériau joue un rôle très important sur la tenue à long terme du composite. Sous atmosphère oxydante, les composites à matrice céramique s'oxydent, ce qui entraîne une rupture prématurée du matériau. Cependant la création d'une matrice multiséquencée autocicatrisante permet, à partir d'une certaine température, la formation d'un bouchon de verre, limitant l'oxydation du composite. Le modèle mécanique permet de calculer la loi de comportement en statique, puis en fatigue par un accroissement de l'endommagement matriciel directement lié au cyclage. On constate que le cyclage influence l'endommagement du composite et donc l'oxydation du matériau. Le modèle physico-chimique permet, quant à lui, de prendre en compte les cinétiques d'endommagement des fibres liées à l'oxydation de l'interphase, mais aussi la création du bouchon de verre limitant cette oxydation. L'oxydation de l'interphase va fortement dépendre du temps d'ouverture des fissures. Le modèle physico-chimique est donc fonction du temps alors que le modèle mécanique dépend directement du nombre de cycles, avec de plus la nécessité de coupler ces deux modèles

T regulatory cells disrupt the CCL20-CCR6 axis driving Th17 homing to the gut

Background: During HIV-1 infection, the integrity of the intestinal immune barrier is disrupted due to a deep depletion of CD4 + T cells in the gut. The translocation of microbial products from the gut lumen into the bloodstream has been linked with systemic inflammation. Despite long-term effective cART, CD4 + T cells in the lamina propria are incompletely restored in most individuals. Aims: Among the chemotactic axes involved in CD4 + T cell homing to the gut, we focused on the CCR6-CCL20 axis as it governs Th17 cells homing, a T cell subset exerting a major role in antimicrobial immunity. We aimed to assess the factors regulating the expression of CCL20 by the enterocytes, and notably the role of the cytokines produced by Treg and Th17 cells. Methods: Small bowel biopsies were obtained by endoscopy in 20 HIV-1 + and 10 HIV-1-individuals. Intestinal lymphocytes phenotype was analyzed by flow cytometry. CCL20 mRNA was quantified by qRT-PCR. The effect of PRR ligands and cytokines on CCL20 expression was explored using an ex-vivosystem of human primary enterocytes. A coculture was done between the enterocytes and Th17/Treg cells. The expression of CCL20 by the enterocytes was evaluated by qRT-PCR and ELISA

Caractérisation de l'endommagement et de la rupture des composites à fibres longues et discontinues (DLF) sollicités en traction

L'une des barrières à l'usage des matériaux composites dans les nouvelles générations de moteurs pour l'aviation civile est la géométrie complexe des pièces à réaliser. Un matériau composite novateur (HexMC ®), composé de bandelettes (ou chips) unidirectionnelles de renforts fibreux longs discontinus et disposées aléatoirement, semble être un bon candidat. Cette étude s'intéresse à la caractérisation des premiers endommagements qui amorcent la rupture en traction dans le cas particulier du HexMC ®. Pour cela, différents types d'essais de traction multi-instrumentés (Corrélation d'images numériques (CIN), émission acoustique (EA), microscopie post-mortem/in-situ) ont été menés. Ainsi, les types d'endommagements présents (fissurations intra-chips, délaminage inter-chips, décohésions) ont été déterminés mais aussi leur séquencement d'apparition et leur méthode de propagation. Les chips orientées à 90° par rapport au chargement ont été directement incriminées comme étant les éléments déclencheurs des premiers endommagements. Ce sont dans ces chips en particulier qu'apparaissent les premières fissures intra-chips transversalement au chargement. Le niveau de charge d'apparition de ces premiers endommagements a également été déterminé. L'analyse combinée de l'ensemble de l'instrumentation mise en place a permis de proposer un scénario d'endommagement depuis le seuil d'endommagement jusqu'à la rupture fragile du matériau. Abstract Among the factors limiting the use of composite materials are the complex shapes to be found, for example, in aircraft engines. A new and innovative composite material (HexMC ®) unidirectional prepreg based, made of discontinuous and long strands (or "chips"), randomly oriented seems to match the demands. The goal of this study is to characterize the first damages that initiate the failure under tensile loading in the particular case of HexMC ®. For this purpose, various and multi-instrumented (Digital Image Correlation (DIC), Acoustic Emission (AE), post-mortem/ in-situ microscopy) tensile tests were conducted. Not only the types of damage were determined (intra-chips cracks, inter-chips delamination, debonding) but also the sequence in which they appear and the way they propagate. Cause of the first damages is attributed to chips oriented at 90° with respect to the loading direction. These particular chips are the ones in which appear the first intra-chips cracks transversely to the loading direction. The loading level at which occur the first damages is determined as well. Through this study and the multi-instrumented analyses, a damage scenario was created from the first damages until to catastrophic failure

From biological to numerical experiments in systemic neuroscience: a simulation platform

International audienceStudying and modeling the brain as a whole is a real challenge. For such systemic models (in contrast to models of one brain area or aspect), there is a real need for new tools designed to perform complex numerical experiments, beyond usual tools distributed in the computer science and neuroscience communities. Here, we describe an effective solution, freely available on line and already in use, to validate such models of the brain functions. We explain why this is the best choice, as a complement to robotic setup, and what are the general requirements for such a benchmarking platform. In this experimental setup, the brainy-bot implementing the model to study is embedded in a simplified but realistic controlled environment. From visual, tactile and olfactory input, to body, arm and eye motor command, in addition to vital interoceptive cues, complex survival behaviors can be experimented. We also discuss here algorithmic high-level cognitive modules, making the job of building biologically plausible bots easier. The key point is to possibly alternate the use of symbolic representation and of complementary and usual neural coding. As a consequence, algorithmic principles have to be considered at higher abstract level, beyond a given data representation, which is an interesting challenge

Stump closure reinforcement with absorbable fibrin collagen sealant sponge (TachoSil®) does not prevent pancreatic fistula after distal pancreatectomy: the FIABLE* multicenter controlled randomized study

International audienceBackground - The aim of this study is to evaluate the effectiveness of TachoSil sponge on distal pancreatectomy remnant stump in reducing the rate and severity of postoperative pancreatic fistula (POPF). Methods - All consecutive patients requiring distal pancreatectomy were randomized in 45 centers. The principal end point was onset of "clinically relevant" POPF. Univariate and multivariate analyses were searched for predictive factors. Results - Of the 270 patients randomized (134 with TachoSil; 136 without), 150 (55.6%) patients sustained a POPF [74 clinically relevant and 76 clinically silent (27.4% and 28.1%), respectively]: no statistically significant difference was found between patients sustaining clinically relevant POPF [41 (30.6%) with vs 33 (24.3%) without TachoSil (P = .276)], or overall POPF [73 (54.5%) with vs 77 (56.6%) without TachoSil, (P = .807)], but there were more clinically relevant POPF after hand-sewn (32.3%) versus mechanical closure (19.8%) (P = .025) and, in case of splenic preservation, after splenic vessel ligation (15/32, 46.9%) versus vascular preservation (17/72, 23.6%) (P = .024). Hand-sewn pancreatic remnant closure (P = .023) and splenic vessel ligation in splenic preservation (P = .035) were independent predictive factors for the onset of clinically relevant POPF. Conclusion - TachoSil sponge reinforcement of the proximal remnant after distal pancreatectomy reduced neither the rate nor the severity of POPF

Influence of Homogenization Technique and Blend Ratio on Chitosan/Alginate Polyelectrolyte Complex Properties

Polyelectrolyte complex (PEC) films were prepared from chitosan (CHI) and alginate (ALG) which are polymers of opposite charge. Two homogenization techniques and two ratios of ALG–CHI blends were compared: mechanical agitation under vacuum (ALG–CHI ST) or agitation by high turbulence (ALG–CHI UT) and 50/50 or 63/37 ratios. Surface and structure of PEC films are affected by the homogenization technique while the swelling percentage is only affected by polymer ratio. The homogenization ratio does not seem to influence in vitro cell proliferation. Results show that the UT homogenization technique with a 63/37 ratio, which gives films with a smooth, homogeneous surface and a higher rate of enzymatic resistance, is more efficient for cell proliferation and viability. These first results confirm the potential use of ALG–CHI films for surgery application