Une chaussure antique a inscription Grecque

On rencontre fréquemment dans les collections d'antiquités une sorte de petits vases fort curieux, qui reproduisent la forme d'un pied humain, non d'un pied nu, mais d'un pied chaussé. ..

Ultrasonication of spray- and freeze-dried cellulose nanocrystals in water

The structural and rheological properties of aqueous suspensions of spray-dried cellulose nanocrystals (CNCs) were investigated and compared to those of freeze-dried. The cellulose nanocrystals were obtained from sulfuric acid hydrolysis of wood pulp. Ultrasonication was used to disperse cellulose nanocrystals in Milli-Q water and the power applied during ultrasonication was shown to be the controlling parameter for their dispersion, more than total energy. Dynamic light scattering measurements showed a decrease of the average hydrodynamic diameter down to the same limiting value, i.e. ∼75 nm, for both spray and freeze-dried cellulose nanocrystals. Since the same maximum dispersion state was reached for both CNC types, it indicated that the spray drying process did not limit dispersion, provided that sufficient ultrasonication was provided. Moreover, no desulfation occurred during ultrasonication at ambient temperature. Strong ultrasonication also caused a decrease of intrinsic viscosity, along with an increase in maximum packing concentration. These properties were correlated to agglomerates break-up, which released both ions and water in suspension. The ionic strength increase may lead to a thinner electrostatic double layer surrounding the cellulose nanocrystals, reducing their apparent concentration

The structural amphiphilicity of cellulose nanocrystals characterized from their cohesion parameters

Cellulose nanocrystals (CNCs), usually considered as isotropically polar nanoparticles, are sheet-like crystalline assemblies of cellulose chains. Here, we link the anisotropy of the CNC structure to an amphiphilic behavior in suspension. The Hansen solubility parameters (HSP: δD; δP; δH) of woodbased H2SO4-hydrolyzed CNCs were measured from sedimentation tests in a wide set of 59 solvents and binary mixtures. Two sets of cohesion parameters corresponding to a polar surface (18.1; 20.4; 15.3) ± (0.5; 0.5; 0.4) MPa1/2 and to a mildly non-polar one (17.4; 4.8; 6.5) ± (0.3; 0.5; 0.6) MPa1/2 were determined, with respective solubility radii of 7.8 and 2.1MPa1/2. The polar sphere is thought to correspond to the (110)&(110) surfaces of cellulose Iβ nanocrystals, while the smaller non-polar sphere is coherent with the exposure of (200) surfaces. The HSP graph provides new insights on the amphiphilic nature of CNCs and a mapping of their chemical affnity for solvents and polymer matrices

The apparent structural hydrophobicity of cellulose nanocrystals

The Teas graph of wood-based sulfuric acid-hydrolyzed cellulose nanocrystals (CNCs) was plotted based on sedimentation tests in a set of 25 common solvents. Comparisons with those of sucrose and dextran, taken as equivalents for cellobiose (cellulose repeating unit) and amorphous cellulose, respectively, highlighted the amphiphilic nature of CNCs. In the absence of any chemical arguments, the hydrophobic behavior displayed is thought to be caused by the exposition of (200) lattice planes at the CNC surface. This apparent structural hydrophobicity may be exploited to achieve the dispersion of CNCs in some mildly-non polar matrices such as poly(ethylene glycol) and poly(lactic acid). The Teas graph is a useful tool to predict the dispersibility potential of CNCs and to select a proper solvent for nanocomposite preparatio

Tailoring cellulose nanocrystals rheological behavior in aqueous suspensions through surface functionalization with polyethyleneimine

The present paper reports the surface modification of commercially available cellulose nanocrystals (CNCs) using polyethyleneimine (PEI) by means of non-covalent electrostatic interaction between the negatively charged sulfate groups of CNCs and positively charged amine functionalities of PEI. The modification, carried out in an aqueous medium, results in a stable CNC-PEI suspension with no phase separation that exhibit interesting rheological behavior due to bridging-type inter-particle interactions. The Newtonian 3% (w/w) CNC suspension evolves into a non-Newtonian gel system after modification with PEI with a consequent increase of almost three decades in complex viscosity. Preshearing of the 3% (w/w) CNC-PEI suspension resulted in the loss of the linear viscoelastic properties with increasing shear rate, as would be expected from the breaking of the inter-particle network. However, the system gradually re-established the inter-particle network in less than an hour to give the original rheological parameters. The effect of PEI on the rheological properties was attributed to the physical adsorption of PEI chains on the CNC particles, examined by dynamic light scattering (DLS), zeta potential, X-ray photoelectron spectroscopy (XPS), elemental analyses, and isothermal adsorption studies. The modified CNC-PEI particles did not show any significant change in the particle morphology compared to the unmodified CNCs, as observed from transmission electron microscope (TEM) images

Early repolarization electrocardiography pattern with unexplained syncope during training in a young black African non-elite athlete: An accidental finding?

Until recently it was generally thought that early repolarization is benign. But a recent article in the NEJM (Haissaguerre et al.) suggests that some persons with early repolarization may be at risk of life-threatening ventricular tachyarrhythmia. Unexplained syncope or sudden death occurs mostly during sleep. However, some cases of cardiac arrest during exertion have been reported. We report the case of a 39 year-old black African male with early repolarization pattern on electrocardiogram who regularly experienced dizziness (and one episode of transient loss of consciousness) exclusively while exercising. Detailed examination was normal. Under quinidine therapy, he experienced no further episodes. Increasingly reported cases of cardiac arrest in Africans, and significant prevalence of early repolarization in this population, have to be taken into account since the Haissaguerre et al. report. Further evidence of the lethal consequences of this syndrome are needed, bearing in mind that diagnostic tools for life-threatening arrhythmias are often scarce in sub-Saharan Africa

Meta-analysis of the influence of chronic kidney disease on the risk of thromboembolism among patients with nonvalvular atrial fibrillation

Chronic kidney disease (CKD) and atrial fibrillation (AF) frequently coexist. However, the extent to which CKD increases the risk of thromboembolism in patients with nonvalvular AF and the benefits of anticoagulation in this group remain unclear. We addressed the role of CKD in the prediction of thromboembolic events and the impact of anticoagulation using a meta-analysis method. Data sources included MEDLINE, EMBASE, and Cochrane (from inception to January 2014). Three independent reviewers selected studies. Descriptive and quantitative information was extracted from each selected study and a random-effects meta-analysis was performed. After screening 962 search results, 19 studies were considered eligible. Among patients with AF, the presence of CKD resulted in an increased risk of thromboembolism (hazard ratio [HR] 1.46, 95% confidence interval [CI] 1.20 to 1.76, p = 0.0001), particularly in case of end-stage CKD (HR 1.83, 95% CI 1.56 to 2.14, p <0.00001). Warfarin decreased the incidence of thromboembolic events in patients with non-end-stage CKD (HR 0.39, 95% CI 0.18 to 0.86, p <0.00001). Recent data on novel oral anticoagulants suggested a higher efficacy of these agents compared with warfarin (HR 0.80, 95% CI 0.66 to 0.96, p = 0.02) and aspirin (HR 0.32, 95% CI 0.19 to 0.55, p <0.0001) in treating non-end-stage CKD. In conclusion, the presence of CKD in patients with AF is associated with an almost 50% increased thromboembolic risk, which can be effectively decreased with appropriate antithrombotic therapy. Further prospective studies are needed to better evaluate the interest of anticoagulation in patients with severe CKD

Non-covalent surface modification of cellulose nanocrystals by polyethyleneimine

Cellulose nanocrystals (CNCs) are bio-derived, natively hydrophilic nanomaterials that disperse well in water according to their surface chemistry upon extraction. However, to be suspended in non-polar, hydrophobic media such as most polymers [1], the CNCs are chemically modified by reactions that are environmentally unfriendly and not cost-effective for the industry. The present work reports the preliminary findings of the non-covalent surface modification of CNCs using polyethyleneimine (PEI), a common additive used in the paper industry [2], through a low-cost process and without any use of organic solvents. The successful surface modification was confirmed through different techniques, including Fourier transform infrared (FTIR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Dynamic Light Scattering (DLS) and Zeta Potential (ζ-potential) measurements. The CNC agglomerates formed in aqueous suspensions as a result of the modification showed improved dispersion in toluene and were found to precipitate in deionized water. The turbidity measurements of the water suspensions of pristine and modified CNCs (mCNCs) were performed using UV-Visible (UV-Vis) transmission spectroscopy

Properties of polylactide inks for solvent-cast printing of three-dimensional freeform microstructures

Solvent-cast printing is a highly versatile microfabrication technique that can be used to construct various geometries such as filaments, towers, scaffolds and freeform circular spirals by the robotic deposition of a polymer solution ink onto a moving stage. In this work, we have performed a comprehensive characterization of the solvent-cast printing process using polylactide (PLA) solutions by analyzing the flow behavior of the solutions, the solvent evaporation kinetics and the effect of process-related parameters on the crystallization of the extruded filaments. Rotational rheometry at low to moderate shear rates showed a nearly Newtonian behavior of the PLA solutions, while capillary flow analysis based on process-related data indicated shear-thinning at high shear rates. Solvent vaporization tests suggested that the internal diffusion of the solvent through the filaments controlled the solvent removal of the extrudates. Different kinds of three-dimensional (3D) structures including a layer-by-layer tower, 9-layer scaffold and freeform spiral were fabricated, and a processing map was given to show the proper ranges of process-related parameters (i.e., polymer content, applied pressure, nozzle diameter and robot velocity) for the different geometries. The results of differential scanning calorimetry revealed that slow solvent evaporation could increase the ability of PLA to complete its crystallization process during the filament drying stage. The method developed here offers a new perspective for manufacturing complex structures from polymer solutions and provide guidelines to optimize the various parameters for 3D geometry fabrication