Pascal Thebault

The antibacterial activity of Magainin I immobilized onto mixed thiols Self-Assembled Monolayers

An antibacterial peptide, Magainin I, was covalently bound to a mixed 11-mercaptoundecanoïc acid (MUA) and 6-mercaptohexanol (C6OH) (ratio 1:3) Self-Assembled Monolayer (SAM) on gold surfaces. Each step of the surface functionalization was characterized by Polarization Modulation Reflection Absorption InfraRed Spectroscopy (PM-RAIRS) and X-ray Photoelectron Spectroscopy (XPS). The antibacterial activity of the anchored Magainin was tested against three Gram-positive bacteria (Listeria ivanovii, Enterococcus faecalis and Staphylococcus aureus), and the results revealed that the adsorbed Magainin I reduced by more than 50% the adhesion of bacteria at the surface, together with the killing of the bacteria that nonetheless adhered to the surface. No release of the peptide was observed upon contact with the bacterial suspension; the activity has proven to be persistent overtime, up to six months after the first use.

Polysaccharide-based antibiofilm surfaces.

UNLABELLED Surface treatment by natural or modified polysaccharide polymers is a promising means to fight against implant-associated biofilm infections. The present review focuses on polysaccharide-based coatings that have been proposed over the last ten years to impede biofilm formation on material surfaces exposed to bacterial contamination. Anti-adhesive and bactericidal coatings are considered. Besides classical hydrophilic coatings based on hyaluronic acid and heparin, the promising anti-adhesive properties of the algal polysaccharide ulvan are underlined. Surface functionalization by antimicrobial chitosan and derivatives is extensively surveyed, in particular chitosan association with other polysaccharides in layer-by-layer assemblies to form both anti-adhesive and bactericidal coatings. STATEMENT OF SIGNIFICANCE Bacterial contamination of surfaces, leading to biofilm formation, is a major problem in fields as diverse as medicine, first, but also food and cosmetics. Many prophylactic strategies have emerged to try to eliminate or reduce bacterial adhesion and biofilm formation on surfaces of materials exposed to bacterial contamination, in particular implant materials. Polysaccharides are widely distributed in nature. A number of these natural polymers display antibiofilm properties. Hence, surface treatment by natural or modified polysaccharides is a promising means to fight against implant-associated biofilm infections. The present manuscript is an in-depth look at polysaccharide-based antibiofilm surfaces that have been proposed over the last ten years. This review, which is a novelty compared to published literature, will bring well documented and updated information to readers of Acta Biomaterialia.

Antiadhesive activity of ulvan polysaccharides covalently immobilized onto titanium surface

Bacterial adhesion leading to biofilm formation on the surface of implants is responsible for pathogenesis infections. One promising strategy to reduce the risk of infection consists of modifying implant surfaces by antibacterial coating. In the present study, the ability of ulvan, a non biocidal algal polysaccharide, to limit bacterial adhesion on titanium was investigated. To this end, titanium surfaces were modified by two different ulvans. Polysaccharides were covalently immobilized on titanium surfaces which had been previously functionalized by self assembled monolayers of aminoundecyltrimethoxysilane (AUTMS). Each step in the modification process was characterized by contact angle, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Bacterial adhesion assays showed that immobilized ulvans on titanium surface strongly decreased by about 90% the adhesion of Pseudomonas aeruginosa. Moreover, AFM observations showed that the polysaccharide also inhibited the bacterial spreading on the surface but not cell-to-cell interaction. The permanence of the anti-adhesive effect of the surfaces was finally tested on a non-motile organism, i.e., Staphylococcus epidermidis. The results showed that the effect was maintained for at least 24h.

Tailoring nanostructures using copolymer nanoimprint lithography.

The generation of defect-free polymer nanostructures by nanoimprinting methods is described. Long-range nanorheology and shorter-range surface energy effects can be efficiently combined to provide alignment of copolymer lamellae over several micrometers. As an example, a perpendicular organization with respect to circular tracks is shown, demonstrating the possibility of writing ordered radial nanostructures over large distances.

Easy Orientation of Diblock Copolymers on Self-Assembled Monolayers Using UV Irradiation

A simple method based on UV/ozone treatment is proposed to control the surface energy of dense grafted silane layers for orientating block copolymer mesophases. Our method allows one to tune the surface energy down to a fraction of a mN/m. We show that related to the surface, perpendicular orientation of a lamellar phase of a PS-PMMA diblock copolymer (neutral surface) is obtained for a critical surface energy of 23.9-25.7 mN/m. Perpendicular cylinders are obtained for 24.6 mN/m and parallel cylinders for 26.8 mN/m.

Organization of Block Copolymers using NanoImprint Lithography: Comparison of Theory and Experiments

We present NanoImprint lithography experiments and modeling of thin films of block copolymers (BCP). The NanoImprint technique is found to be an efficient tool not only to align lamellar phases perpendicularly to the substrate but also to get rid of in-plane defects over distances much larger than the natural lamellar periodicity. The modeling relies on self-consistent field calculations done in two- and three-dimensions and is found to be in good agreement with the experiments. It also offers some insight on the NanoImprint lithography setup and on the conditions required to perfectly ordered BCP lamellae.

Role of molecular properties of ulvans on their ability to elaborate antiadhesive surfaces

Antiadhesive properties of polysaccharides (such ulvans) once immobilized on a surface are described in the literature but the parameters governing their antifouling properties are not yet well identified. In the present study, the relationship between molecular parameters of ulvans and the inhibition of bacterial adhesion was investigated. To this aim, various ulvans were grafted on silicon wafers under two different experimental immobilization conditions. Results showed that the experimental immobilization conditions and the polysaccharides molecular weight led to specific layer conformations which exhibited a key role in the surface antiadhesive properties.

Development of a novel functional core-shell-shell nanoparticles: From design to anti-bacterial applications

This article reports the synthesis and functionalization of a novel CuO@SiO2-APTES@Ag0 core-shell-shell material using a simple and low-cost process. The growth, design strategies and synthesis approach are the key factors for the development of CuO@SiO2-APTES@Ag0 as efficient material with enhanced antibacterial activity. We investigated the morphology, surface charge, structure and stability of our new core-shell-shell by atomic force microscopy, scanning electron microscopy, energy dispersive X-ray, Fourier transform infrared and UV-visible spectroscopies, zeta potential measurements, and differential scanning calorimetry. The covalent surface grafting of APTES (3-(aminopropyl)triethoxysilane) onto CuO@SiO2 involving electrostatic interactions was confirmed. Size measurements and Scanning electron images showed that both APTES grafting and SiO2/Ag shells dropped on the surface of CuO produced structural compaction. UV-Vis spectroscopy proved to be a fast and convenient way to optically detect SiO2 shell on the surface of colloids. Additionally, the Ag-decorated CuO@SiO2-APTES surfaces were found to possess antibacterial activity and thermally more stable than undecorated surfaces. CuO@SiO2-APTES@Ag0 core-shell had antibacterial properties against Gram-positive bacteria making it a promising candidate for antibacterial applications.

Elucidation of innovative antibiofilm materials

It is known for roughly a decade that bacterial communities (called biofilms) are responsible for significant enhanced antibiotherapy resistance. Biofilms are involved in tissue persistent infection, causing direct or collateral damage leading to chronic wounds development and impairing natural wound healing. In this study, we are interested in the development of supported protein materials which consist of asymmetric membranes as reservoir supports for the incorporation and controlled release of biomolecules capable of dissolving biofilms (or preventing their formation) and their use as wound dressing for chronic wound treatment. In a first step, polyhydroxyalkanoates (PHAs) asymmetric membranes were prepared using wet phase inversion technique. Scanning microscopy (SEM) analysis has showed the influence of different processing parameters. In a second step, the porous side of the membranes were functionalized with a surface treatment and then loaded with the antibiofilm agent (dispersin B). In a third step, the properties and antibiofilm performance of the loaded-membranes were evaluated. Exposure of Staphylococcus epidermidis biofilms to such systems weakly inhibited biofilm formation (weak preventive effect) but caused their detachment and disaggregation (strong curative effect). These initial results are promising since they open the way to a new generation of effective tools in the struggle against persistent bacterial infections exhibiting enhanced antibiotherapy resistance, and in particular in the case of infected chronic wounds.

Elaboration of antibacterial plastic surfaces by a combination of antiadhesive and biocidal coatings of natural products

Antibacterial polyolefins surfaces, combining biocidal and antiadhesive properties, were elaborated by a covalent grafting of antimicrobial peptides (AMPs), able to kill adherent bacteria, on a pre-immobilized hyaluronic acid (HA) layer, able to repel the micro-organisms. Different HA activation rate for its immobilization, were used to change HA layer morphology and number of residual free carboxylic acid functions for AMPs grafting. Based on adhesion tests on Staphylococcus epidermidis and microscopy fluorescent observations, the presence of the two combined properties was shown to be depended on the HA activation rate. Thus, the best addition effect was observed for an AMP grafting on a surface based on a high HA activation, data pointing out a decrease of the bacterial adhesion up to 99.8% and a perturbation of the bacterial membrane integrity of adhered bacteria. On the contrary, a decrease of the antibacterial activity was observed for an AMP grafting on a surface based on a low HA activation.