Study of cationic N-isopropylacrylamide-styrene copolymer latex particles using fluorescent probes

Monodisperse cationically charged core-shell poly[styrene/N-isopropylacrylamide] latexes, differing in their shell structure, were studied at temperatures around the lower critical solution temperature (LCST) of poly[N-isopropylacrylamide]. Near the LCST, a transition on the latex dimensions was observed by quasi-elastic light scattering measurements. The same transition could also be detected using the intensity ratio of the pyrene fluorescence vibronic bands, I1/I3, and the excimer to monomer fluorescence intensity ratio of 1,10-bis(1-pyrenyl)decane. The fluorescence spectra and decay curve measurements of 1,10-bis-(1-pyrenyl)decane provided a better understanding of both the hydrophilic-hydrophobic variation and the conformational changes occurring in the poly[N-isopropylacrylamide] shell of the latex particles upon temperature variation.J. M. G. Martinho is grateful for the support of this work from FCT. E. M. S. Castanheira acknowledges FCT for a grant (PRAXIS XXI/BPD/9968/96)

Poly(N-Isopropylacrylamide) surface-grafted ghitosan membranes as a new substrate for cell sheet engineering and manipulation

The immobilization of poly(N-isopropylacrylamide) (PNIPAAm) on chitosanmembranes was performed in order to render membranes with thermo-responsive surface properties. The aim was to create membranes suitable for cell culture and in which confluent cell sheets can be recovered by simply lowering the temperature. The chitosan membranes were immersed in a solution of the monomer that was polymerized via radical initiation. The composition of the polymerization reaction solvent, which was a mixture of a chitosan non-solvent (isopropanol) and a solvent (water), provided a tight control over the chitosan membranes swelling capability. The different swelling ratio, obtained at different solvent composition of the reaction mixture, drives simultaneously the monomer solubility and diffusion into the polymeric matrix, the polymerization reaction rate, as well as the eventual chain transfer to the side substituents of the pyranosyl groups of chitosan. A combined analysis of the modified membranes chemistry by proton nuclear magnetic resonance (1H-NMR), Fourier transform spectroscopy with attenuated total reflection (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS) showed that it was possible to control the chitosan modification yield and depth in the solvent composition range between 75% and 100% of isopropanol. Plasma treatment was also applied to the original chitosan membranes in order to improve cell adhesion and proliferation. Chitosan membranes, which had been previously subjected to oxygen plasma treatment, were then modified by means of the previously describedmethodology. A human fetal lung fibroblast cell line was cultured until confluence on the plasma-treated thermo-responsive chitosan membranes and cell sheets were harvested lowering the temperature.Contract grant sponsor: European NoE EXPERTISSUESContract grant number: NMP3-CT-2004-500283Contract grant sponsor: European UnionContract grant number: NMP3-CT-2003-50575

Coupling of Rotational Motion with Shape Fluctuations of Core-shell Microgels Having Tunable Softness

The influence of shape fluctuations on deformable thermosensitive microgels in aqueous solution is investigated by dynamic light scattering (DLS) and depolarized dynamic light scattering (DDLS). The systems under study consist of a solid core of polystyrene and a thermosensitive shell of cross-linked poly(N-isopropylacrylamide) (PNIPA) without and with embedded palladium nanoparticles. PNIPA is soluble in water, but has a lower critical solution temperature at 32 C (LCST). Below the LCST the PNIPA shell is swollen. Here we find that besides translational and rotational diffusion, the particles exhibit additional dynamics resulting from shape fluctuations. This leads to a pronounced apparent increase of the rotational diffusion coefficient. Above the transition temperature the shell collapses and provides a rather tight envelope of the core. In this state the dynamics of the shell is frozen and the core-shell particles behave like hard spheres. A simple physical model is presented to capture and explain the essentials of the coupling of rotational motion and shape fluctuations.Comment: 9 pages, 7 figure

Incidents critiques en anesthésie pédiatrique : bilan après 2 ans d'analyse

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocSudocFranceF

L' absorption cutanée (stratégies de formulation et influence de l'irradiation solaire)

L'épiderme humain est particulièrement bien adapté pour jouer une fonction essentielle de "barrière", il limite l'entrée des xénobiotiques et participe à l'homéostasie générale de l'organisme en régulant la perte en eau transépidermique. Cependant, cette "barrière protectrice" n'est pas absolue, elle est perméable à certaines substances, dont le degré de perméabilité varie en fonction de nombreux facteurs et notamment de la formulation. Le travail de thèse se base sur l étude de la compréhension de la pénétration cutanée et de la maîtrise de l absorption. Dans le sens de la promotion de l absorption par l utilisation de promoteurs d absorption qui additionnés dans la formulation augmentent la pénétration de la molécule modèle, la caféine. Le 1,2-pentanediol s avère être un nouvel agent promoteur très efficace à faible concentration par rapport à un mélange binaire éthanol/propylène glycol référent utilisé à forte concentration. Dans le cas de la benzophénone-3, un filtre UVA-B, la modulation de l absorption a été ciblée dans le sens de la rétention. Pour cela, deux stratégies d encapsulation ont été développées ; en premier la benzophénone-3 a été incorporée dans un système de type matriciel que sont les microsphères lipidiques solides, puis dans des microcapsules sous forme solubilisée dans un liquide. Ces deux formulations comparées à un véhicule liquide huileux ont montré une rétention significative du filtre solaire au niveau du stratum corneum alors que solubilisé dans la formulation huileuse il atteint le compartiment systémique. La dernière étape de ce travail a été de préciser l influence d une irradiation sur l absorption cutanée de molécules qui présentent un caractère lipophile différent dont la caféine, la benzophénone-3 et l octocrylène. Les niveaux de pénétration dans les différentes couches de la peau de ces substances ont été reliés à cette caractéristique physico-chimique et le flux à l équilibre a été d autant plus limité que la molécule était hydrophile.MONTPELLIER-BU Pharmacie (341722105) / SudocSudocFranceF