Natural polymers are often used to functionalize the surface of synthetic polymer scaffolds to improve their cytocompatibility for their use as biomaterial for tissue engineering. Here we used hyaluronan (HA), a glycosaminoglycan providing essential functions in human tissues, to functionalize the surface of poly(lactic acid) (PLA) films. PLA was first aminolyzed using hexane-1,6-diamine (HDA) to bring positive charges to the scaffold surface, then allowing HA immobilization by electrostatic interactions. Since HA interact specifically with various proteins, it should be considered as a bioactive species. Thus, we investigated the influence of both aminolysis and HA immobilization conditions on HA immobilization and on mesenchymal stem cells (MSC) proliferation. Results show that (i) there is an optimum in the number of HDA molecules grafted per surface unit to reach the highest surface concentration of hydrated HA, (ii) MSC proliferation is maximal for a low surface concentration of hydrated HA (20-100 ng.cm(-2)), and (iii) whatever the surface concentration of hydrated HA, the MSC proliferation level depends on aminolysis conditions. We conclude that conditions used for PLA aminolysis and HA immobilization influence MSC proliferation by affecting the organization of HA molecules on scaffold surface and consequently their ability to interact with MSC membrane receptors.

One major factor inhibiting natural wound-healing processes is infection through bacterial biofilms, particularly in the case of chronic wounds. In this study, the micro/nanostructure of a wound dressing was optimized in order to obtain a more efficient antibiofilm protein-release profile for biofilm inhibition and/or detachment. A 3D substrate was developed with asymmetric polyhydroxyalkanoate (PHA) membranes to entrap Dispersin B (DB), the antibiofilm protein. The membranes were prepared using wet-induced phase separation (WIPS). By modulating the concentration and the molecular weight of the porogen polymer, polyvinylpyrrolidone (PVP), asymmetric membranes with controlled porosity were obtained. PVP was added at 10, 30, and 50% w/w, relative to the total polymer concentration. The physical and kinetic properties of the quaternary nonsolvent/solvent/PHA/PVP systems were studied and correlated with the membrane structures obtained. The results show that at high molecular weight (M-w = 360 kDa) and high PVP content (above 30%), pore size decreased and the membrane became extremely brittle with serious loss of physical integrity. This brittle effect was not observed for low molecular weight PVP (M-w = 40 kDa) at comparable contents. Whatever the molecular weight, porogen content up to 30% increased membrane surface porosity and consequently protein uptake. Above 30% porogen content, the pore size and the physical integrity/mechanical robustness both decreased. The PHA membranes were loaded with DB and their antibiofilm activity was evaluated against Staphylococcus epidermidis biofilms. When the bacterial biofilms were exposed to the DB-loaded PHA membrane, up to 33% of the S. epidermidis biofilm formation was inhibited, while 26% of the biofilm already formed was destroyed. These promising results validate our approach based on the development of bioactive-protein-loaded asymmetric membranes for antibiofilm strategies in situations where traditional antibiotic therapies are ineffective.

Surface functionalization of polyimide films was carried out by cold plasma treatment using a radio frequency discharge and the optimum plasma conditions were evaluated by water contact angle measurements. The relationship between gas permeation behaviour and surface modification of the films was discussed.

Competitive adsorption is a general problem both in polymer and in biological systems. The equilibrium composition at a surface in contact either with polymer solutions or biological fluids depends on the competition between all the surface active material present in the medium. Such competition is particularly important in cell membranes where membrane proteins generated on ribosomes have to incorporate in the cell. Here we use fluovideo microscopy to study the competition for adsorption at the air/water interface between the enzyme glucose oxidase (GOx) and fluid monolayers of pentadecanoic acid (PDA). Although water soluble, GOx has a strong affinity for the air/water interface. We show that under certain conditions it inserts in the monolayer and causes a contraction of the Langmuir film and the formation of condensed domains. When exposed to a heterogeneous surface it is inserted in the less dense regions. Its crystallization leads to the deformation of the condensed domains followed by the destruction of their initial shape. By compressing the layer the protein is not removed from the interface where it eventually forms three-dimensional structures.

Poly(ethylene-co-vinyl alcohol) (EVOH) films with two different ethylene contents (29 and 44 mol %) have been treated by hydrophobic plasma (CF4, tetramethylsilane (TMS), CF4/H-2, and CF4/C2H2). Conditions of the cold plasma treatment were optimized by the water contact angle measurements as a function of the different plasma parameters (plasma power, gas flow, and treatment time). Chemical changes of the film surface were characterized by X-ray photoelectron spectroscopy. The obtained results revealed the presence of fluorine containing functional groups such as CF, CF2, and CF3 in the case of CF4, CF4/H-2, and CF4/C2H2 plasma treatment and the presence of SiOxCy compounds after TMS treatment. The morphology of the plasma treated EVOH films was examined by atomic force microscopy, which indicated an increase of the film roughness after treatment. Negligible changes of thermal properties of the modified EVOH films were observed by means of the temperature modulated differential scanning calorimetry. The barrier properties of films were characterized by water permeability measurements. It was found that the hydrophobicity was significantly improved after plasma treatment and for some treated films the water permeability was decreased up to 28%.

Composite polymer membranes were prepared by incorporation of modified layered inorganic clay (Laponite) into Nafion® membranes. The modification of Laponite particles was performed by the plasma activation process and the chemical grafting of sulfonic groups as well as by the direct plasma sulfonation. The modified Laponite particles incorporated into a polymer film contribute to an increase of the proton conductivity of composite membranes at high temperatures (85°C). For the first time the water vapor sorption properties of the modified clay and the composite membranes were investigated varying water activity conditions (from 0.1 to 0.95) by means of microgravimetry. The BET adsorption model as well as models of Park and Feng were applied to the experimental data. The parameter values (concentration of the adsorbed water, specific capacity and different aggregation constants) were found to agree well with the measured ones.

Two methods are developed for the determination of the diffusion parameters of a penetrant inside polymer membranes whose diffusivity varies exponentially with its concentration. Two cases are considered in this report depending on the sign of the plasticization coefficient parameter.The method using differential permeation data is based on the correlations between the slope of the reduced permeation flux versus time plot at the inflexion point, and the two key parameters of the concentration-dependent diffusivity laws.For the transient sorption/desorption method, the slope of the penetrant mass uptake versus square-root of time curve leads to the same parameters of the diffusion law via similar correlations. No specific computer software is required for the use of these methods and they are user friendly. (C) 2009 Elsevier B.V. All rights reserved.

In prokaryotic cells, the hypothesis of the existence of lipid domains was considered. In order to test this hypothesis and study the organization of lipids in the inner membrane of Escherichia coli, we elaborated Langmuir films mimicking the inner leaflet of this membrane by considering lipids extracted from the inner membrane of E coli by Folch protocol. Lipid monolayers were elaborated by using these extracts (Langmuir technique); the organization of the resulting films was studied at the air-water interface by Brewster angle microscopy and after transfer onto muscovite by atomic force microscopy. The existence of domains was demonstrated for different interfacial pressures of biological interest, and their stability was studied.

Assembly of the tubulin-like protein FtsZ at or near the cytoplasmic membrane is one of the earliest steps in division of bacteria such as Escherichia coli. Exactly what constitutes the site at which FtsZ acts is less clear. To investigate the influence of the membrane phospholipids on FtsZ localization and assembly, we have elaborated with the Langmuir technique a two-lipid monolayer made of dilauryl-phosphatidylethanolamine (DLPE) and dipalmitoyl-phosphatidylglycerol (DPPG). This monolayer comprised stable condensed domains in an expanded continuous phase. In the presence of GTP, FtsZ assembly disrupts the condensed domains within 5 min. After several hours, with or without GTP, FtsZ assembled into large aggregates at the domain interface. We suggest that the GTP-induced polymerization of FtsZ is coupled to the association of FtsZ protofilaments with domain interfaces.

Dipalmitoylphosphatidylethanolamine (DDPE) Langmuir films at the air/water interface have been studied. These films exhibit high stability. The resulting films transferred on muscovite have been studied by scanning force microscopy with the contact mode. At the microscopic scale, DDPE Langmuir-Blodgett films appear densely packed with few defects. At molecular resolution the films appear well ordered; the double tail of the lipids has been observed.d Copyright 2000 Academic Press.

Dipalmitoylphosphatidylethanolamine (DDPE) Langmuir films at the air/water interface have been studied. These films exhibit high stability. The resulting films transferred on muscovite have been studied by scanning force microscopy with the contact mode. At the microscopic scale, DDPE Langmuir–Blodgett films appear densely packed with few defects. At molecular resolution the films appear well ordered; the double tail of the lipids has been observed.d

Les prions sont responsables d'encéphalopathies subaiguës spongiformes transmissibles telles que la tremblante du mouton ou l'encéphalopathie spongiforme bovine. Il est à l'heure actuelle généralement admis que le mécanisme pathogène résulte de la conversion de la protéine cellulaire native, PrPC, en une forme pathologique, PrPSc, et que cette isoforme est infectieuse. Dans le cas de la tremblante, quinze formes différentes de la maladie ont été décrites et certains de ces phéno-types peuvent être induits par des prions infectieux qui sont eux-mêmes codés par des gènes cellulaires normaux. Nous proposons dans cet article que la forme altérée de la protéine prion ait de façon corrélative une affinité modifiée pour les lipides ; cette affinité modifiée entraînerait la structuration de domaines protéolipidiques contenant différents lipides et autres facteurs tels que des protéines chaperons ou des enzymes responsables de modifications post-traductionnelles. La protéine prion native, associée à ce domaine anormal, adopterait la conformation imposée par la composition lipidique environnante (et par les autres facteurs présents) et acquerrait ainsi l'affinité lipidique de l'isoforme pathologique initiatrice. Ces isoformes néo-engendrées créeraient à leur tour de nouveaux domaines protéolipidiques. Ce processus pourrait être assimilé à une réplication semi-conservative dans laquelle la protéine et les lipides seraient analogues aux brins complémentaires de l'ADN, et le domaine protéolipidique analogue à la double hélice elle-même.

A mixed Langmuir-Blodgett film constituted of behenic acid and glucose oxidase transferred on HOPG has been studied by scanning force microscopy at microscopic and nanoscopic scales; the results concerning the structures observed at the atomic scale are discussed in reference with a model. At the molecular level, it was possible to observe the arrangement of enzyme molecules and their individual structure revealing their two subunits.

Volume changes of polymer networks composed of ionizable functions depend on the nature of the solvent, the pH and the ionic strength. We have studied the dependence of volume changes (swelling ratio) of partially hydrolyzed polyacrylamide (PHPA) gels as a function of pH and ionic strength. The swelling force (the force exerted by the polymer network when it is confined in a cell of constant volume) of a gel composed of ionizable functions depends on pH and ionic strength. The variation of gel volume or swelling force involves a chemo-mechanical energy conversion. This aspect is briefly discussed. In addition, the variation of swelling properties of these polyelectrolytic gels has been compared with the variation of rheological properties of a solution of the same polyelectrolyte.