Antibacterial polymeric coatings grown by matrix assisted pulsed laser evaporation

We report on a simple and environmental friendly method to produce composite biocompatible antibacterial coatings consisting of silver nanoparticles (AgNPs, size 40 nm) combined with polymer blends (polyethylene glycol/poly(lactide-co-glycolide), PEG/PLGA blends). The PEG/PLGA&AgNPs coatings were produced by Matrix Assisted Pulsed Laser Evaporation, using a Nd:YAG laser with λ=266 nm. The AgNPs were deposited either on top of a PEG/PLGA layer (i.e., bilayered coating), or simultaneously with the polymers (i.e., blended coating). In both cases, chemical analysis indicated that the polymers preserved their integrity, with no evidence of chemical interaction with the AgNPs. Morphological investigations evidenced homogenous distribution of individual AgNPs on the surface of the coatings, with no signs of aggregation. The size of the AgNPs was ～40 nm, consistent with size of the as-received ones. The presence of AgNPs in the coatings was confirmed by the absorption band at ～420 nm and their stability was checked by monitoring this absorption versus time. After exposure to air, the AgNPs from the bilayered coating showed signs of oxidation. In the blended coating, the oxidation of the AgNPs was prevented by the neighboring polymer molecules. Finally, preliminary investigations confirmed the bacterial killing activity of the coatings against Escherichia coli.     

Spectral Analysis of Methylene Blue–Mediated Photodynamic Inactivation of Bacteria Using a 635-nm Diode Laser System

In this paper we assess the efficacy of a laser system, emitting at 635 nm, in methylene blue–mediated photodynamic inactivation of Pseudomonas aeruginosa that contaminates wounds, using diffuse reflectance spectrometry. The spectral plots of the contaminated wounds were recorded before and after laser irradiation, and the refractive index and extinction coefficient were determined by Kramers-Kronig analysis of reflectance spectra. The changes in optical parameter values after the treatment were corroborated with bacterial counts determined by bacteriological examination. The results revealed that the combined treatment 635-nm laser–methylene blue is an efficient way to destroy the bacteria that contaminate the wounds.     

Multi-Wavelength-Switchable Double Clad Yb3+-Doped Fiber Laser Based on Reflectivity Control of Fiber Bragg Gratings by Induced Bend Loss

We propose and demonstrate an all-fiber multi-wavelength switchable double-clad Yb³⁺-doped fiber laser based on the reflectivity cavity control by induced bend loss. The wavelength switching is realized by a variable reflecting mirror that employs a cascaded array of three high reflection (>99%) fiber Bragg gratings at 1064, 1080 and 1096 nm, with a bending controller inserted between each grating. The order of the Bragg gratings is decided according to the gain profile of the Yb³⁺-doped fiber and the induced bending loss allows us to select the Bragg-wavelength laser operation. The laser is capable of switching continuously from one wavelength to another, and slope efficiencies over 50% are obtained at each wavelength.     

Broad distribution effects in sums of lognormal random variables

The lognormal distribution describing, e.g., exponentials of Gaussian random variables is one of the most common statistical distributions in physics. It can exhibit features of broad distributions that imply qualitative departure from the usual statistical scaling associated to narrow distributions. Approximate formulae are derived for the typical sums of lognormal random variables. The validity of these formulae is numerically checked and the physical consequences, e.g., for the current flowing through small tunnel junctions, are pointed out. Received 8 November 2002 / Received in final form 17 March 2003 Published online 7 May 2003     

Space charge limited avalanche growth in multigap resistive plate chambers

The European Physical Journal C - The ALICE TOF array will be built using the Multigap Resistive Plate Chamber(MRPC) configured as a double stack. Each stack contains 5 gas gaps with width of...     

Polyconvexity equals rank-one convexity for connected isotropic sets in M2×2

We give a short, self-contained argument showing that, for compact connected sets in $\text{M}{}^{\mathrm{2\times 2}}$ which are invariant under the left and right action of SO(2), polyconvexity is equivalent to rank-one convexity (and even to lamination convexity). As a corollary, the same holds for O(2)-invariant compact sets. These results were first proved by Cardaliaguet and Tahraoui. We also give an example showing that the assumption of connectedness is necessary in the SO(2) case. To cite this article: S. Conti et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Post-buckling behaviour of graphite/epoxy stiffened panels with initial imperfections subjected to eccentric biaxial compression loading

The post-buckling behaviour of anisotropic stiffened panels with initial imperfections is investigated. Since buckling of the skin between the stiffeners often occurs first, a non-linear analysis is developed for symmetric panels under biaxial compression in order to obtain the out-of-plane panel deflection in the post-buckling range. The non-linear differential equations are expressed in terms of the out-of-plane displacement and the Airy function. They are solved with the Galerkin method for various boundary conditions by imposing an edge displacement control. The theoretical and experimental results obtained by the present analysis show that the transverse load can greatly influence the buckling loads and halfwave number. Since no experimental results have been found in the literature, several tests have been carried out on graphite/epoxy blade stiffened panels 900 mm long and 620 mm wide applying simultaneously biaxial compression loads with several combined ratios. An eccentricity results between longitudinal and transverse load, because the longitudinal compression is applied along the centroidal axes of the stiffened section while the transverse compression is applied to the skin panel. The correlation between the experimental and analytical results has been quite good; the experimental results demonstrate the influence of eccentricity of the transverse load on panel deflection in the pre- and post-buckling range.     

Synthesis and Immunostimulating Activity of A Thioglycolipopeptide Glycomimetic As A Potential Anticancer Vaccine Derived From Tn Antigen

ABSTRACT

The Tn epitope is one of the tumor associated O-linked cell surface glycopeptides. It is expressed in over 70% of human epithelial cancers such as lung, colon, stomach and breast carcinomas. The glycosidic linkage of the Tn antigen, between N-acetylgalactosamine and serine or threonine, can be cleaved either chemically or enzymatically in the presence of glycosidases. The latter case is particularly a problem in vivo. Therefore, it would be of great interest to obtain a metabolically stable analogue of the Tn antigen that maintains or improves the immunogenic activity of the latter. The purpose of this work was to synthesize a totally synthetic vaccine using a chemically and metabolically stable glycomimetic of the Tn antigen in which the interglycosidic oxygen was replaced by a sulphur atom (S-Tn). The S-Tn thioglycopeptide was linked to the P₃CS immunoadjuvant to obtain the potential S-Tn vaccine. Moreover, we synthesized the natural Tn antigen and derivatized it similarly to obtain the Tn vaccine. Last, we evaluated the immunostimulating activity of the two synthetic potential vaccines in vitro using cultured mouse splenocytes. The S-Tn construct showed immunostimulating activity comparable, in terms of maximal response, to the Tn analogue. Moreover, due to its higher stability the S-Tn construct reached its maximal effect at lower doses compared to the Tn analogue.