Etude de la faisabilité d'un composite à matrice cimentaire renforcé de fibres de jute

Le domaine de la construction doit jouer un rôle important dans la résolution des problèmes environnementaux lies au recyclage et l'exploitation de la biomasse. Dans la catégorie des matériaux cimentaires, différents types de déchets et coproduits issus de l'agriculture ont déjà été utilises, soit sous forme de particules, en remplacement total ou partiel des granulats minéraux, soit sous forme de fibres pour renforcement. Dans cette, étude nous nous sommes intéresses au potentiel d'utilisation des fibres de jute comme éléments de renfort pour mortiers. La fibre de jute a été utilisée en substitution partielle du sable à différents taux, le mortier de référence étant sans fibres. Un protocole d'essais expérimentaux à été mène pour étudier les composites a l'état frais et a l'état durci. La compatibilité chimique des fibres de jute avec le ciment à été évaluée a l'aide des tests d'hydratation qui consistent a enregistrer l'élévation de température au cœur du composite lors des réactions exothermiques des composants du ciment avec l'eau de gâchage. Les résultats révèlent un faible indice d'inhibition confirmant la compatibilité de la fibre avec le ciment. Les essais mécaniques montrent une baisse des performances avec l'augmentation du taux de fibres, mais un gain substantiel en poids.Mots clés: Composite cimentaire - Mortier de fibres - Fibres de jute - Compatibilité chimique. Construction field has to play an important role in resolving environmental problems related to recycling and exploitation of the biomass. In the category of cementitious materials, various types of wastes and byproducts derived from agriculture have already been used, either as particles, in total or partial replacement of mineral aggregates, or as fibers for reinforcement. In this study we were interested at the potential use of jute fibers as reinforcing elements for mortars. The jute fiber was used in partial replacement of sand at different rates; the control mortar was without fibers. A Memorandum of experimental tests was conducted in order to study the composite in fresh and hardened state. The chemical compatibility of jute fibers with cement was evaluated using tests of hydration which consist in recording the temperature rise in the heart of the composite during the exothermic reactions between the components of the cement and the mix water. The results of these tests revealed very low index of inhibition confirming the compatibility of the jute fiber with cement. The mechanical tests showed a decrease in performances according to the increase of fiber and a substantial gain weight.Keywords: Cementitious composite - Fiber mortars - Jute fibers - Chemical compatibility

How simple can a model of an empty viral capsid be? Charge distributions in viral capsids

We investigate and quantify salient features of the charge distributions on viral capsids. Our analysis combines the experimentally determined capsid geometry with simple models for ionization of amino acids, thus yielding the detailed description of spatial distribution for positive and negative charge across the capsid wall. The obtained data is processed in order to extract the mean radii of distributions, surface charge densities and dipole moment densities. The results are evaluated and examined in light of previously proposed models of capsid charge distributions, which are shown to have to some extent limited value when applied to real viruses.Comment: 10 pages, 10 figures; accepted for publication in Journal of Biological Physic

Erythropoietin Receptor Signaling Is Membrane Raft Dependent

Upon erythropoietin (Epo) engagement, Epo-receptor (R) homodimerizes to activate JAK2 and Lyn, which phosphorylate STAT5. Although recent investigations have identified key negative regulators of Epo-R signaling, little is known about the role of membrane localization in controlling receptor signal fidelity. Here we show a critical role for membrane raft (MR) microdomains in creation of discrete signaling platforms essential for Epo-R signaling. Treatment of UT7 cells with Epo induced MR assembly and coalescence. Confocal microscopy showed that raft aggregates significantly increased after Epo stimulation (mean, 4.3±1.4(SE) vs. 25.6±3.2 aggregates/cell; p≤0.001), accompanied by a >3-fold increase in cluster size (p≤0.001). Raft fraction immunoblotting showed Epo-R translocation to MR after Epo stimulation and was confirmed by fluorescence microscopy in Epo stimulated UT7 cells and primary erythroid bursts. Receptor recruitment into MR was accompanied by incorporation of JAK2, Lyn, and STAT5 and their activated forms. Raft disruption by cholesterol depletion extinguished Epo induced Jak2, STAT5, Akt and MAPK phosphorylation in UT7 cells and erythroid progenitors. Furthermore, inhibition of the Rho GTPases Rac1 or RhoA blocked receptor recruitment into raft fractions, indicating a role for these GTPases in receptor trafficking. These data establish a critical role for MR in recruitment and assembly of Epo-R and signal intermediates into discrete membrane signaling units

Localization of uPAR and MMP-9 in lipid rafts is critical for migration, invasion and angiogenesis in human breast cancer cells

<p>Abstract</p> <p>Background</p> <p>uPAR and MMP-9, which play critical roles in tumor cell invasion, migration and angiogenesis, have been shown to be associated with lipid rafts.</p> <p>Methods</p> <p>To investigate whether cholesterol could regulate uPAR and MMP-9 in breast carcinoma, we used MβCD (methyl beta cyclodextrin, which extracts cholesterol from lipid rafts) to disrupt lipid rafts and studied its effect on breast cancer cell migration, invasion, angiogenesis and signaling.</p> <p>Results</p> <p>Morphological evidence showed the association of uPAR with lipid rafts in breast carcinoma cells. MβCD treatment significantly reduced the colocalization of uPAR and MMP-9 with lipid raft markers and also significantly reduced uPAR and MMP-9 at both the protein and mRNA levels. Spheroid migration and invasion assays showed inhibition of breast carcinoma cell migration and invasion after MβCD treatment. <it>In vitro </it>angiogenesis studies showed a significant decrease in the angiogenic potential of cells pretreated with MβCD. MβCD treatment significantly reduced the levels of MMP-9 and uPAR in raft fractions of MDA-MB-231 and ZR 751 cells. Phosphorylated forms of Src, FAK, Cav, Akt and ERK were significantly inhibited upon MβCD treatment. Increased levels of soluble uPAR were observed upon MβCD treatment. Cholesterol supplementation restored uPAR expression to basal levels in breast carcinoma cell lines. Increased colocalization of uPAR with the lysosomal marker LAMP1 was observed in MβCD-treated cells when compared with untreated cells.</p> <p>Conclusion</p> <p>Taken together, our results suggest that cholesterol levels in lipid rafts are critical for the migration, invasion, and angiogenesis of breast carcinoma cells and could be a critical regulatory factor in these cancer cell processes mediated by uPAR and MMP-9.</p

Combined use of bacteriophage K and a novel bacteriophage to reduce Staphylococcus aureus biofilm formation

Biofilms are major causes of impairment of wound healing and patient morbidity. One of the most common and aggressive wound pathogens is Staphylococcus aureus, displaying a large repertoire of virulence factors and commonly reduced susceptibility to antibiotics, such as the spread of methicillin-resistant S. aureus (MRSA). Bacteriophages are obligate parasites of bacteria. They multiply intracellularly and lyse their bacterial host, releasing their progeny. We isolated a novel phage, DRA88, which has a broad host range among S. aureus bacteria. Morphologically, the phage belongs to the Myoviridae family and comprises a large double-stranded DNA (dsDNA) genome of 141,907 bp. DRA88 was mixed with phage K to produce a high-titer mixture that showed strong lytic activity against a wide range of S. aureus isolates, including representatives of the major international MRSA clones and coagulase-negative Staphylococcus. Its efficacy was assessed both in planktonic cultures and when treating established biofilms produced by three different biofilm-producing S. aureus isolates. A significant reduction of biofilm biomass over 48 h of treatment was recorded in all cases. The phage mixture may form the basis of an effective treatment for infections caused by S. aureus biofilms