New surfaces with hydrophilic/hydrophobic characteristics in relation to (no)bioadhesion.

The possibility of biosurfaces with high or low adhesiveness for protein, bacteria or eukaryotic cells is discussed. At the interface surface object/biological milieu, biocompatibility, (no) bioadhesion and (no) biocontamination are shown to be correlated with physico-chemical surface characteristics. First consequence is the (no) possibility of biofilm formation. Substrates with low surface energy could interact only with hydrophobic biomolecules. On substrates with high surface energy, a water monolayer spontaneously formed. Modification of a surface by plasma techniques is a way for engineering biomaterials. Plasma techniques are dry processes and more suitable for biomedical applications. In the field of biomaterial medical devices, in hygienic prevention of nosocomial diseases, in food packaging, the use of substrates with a very hydrophilic character may help to prevent the proliferation of cells and bacteria. Such a technique is so efficient that antibiotic molecules are not necessary. Therefore, surface engineering is a tool for modifying and adapting materials to specific biological applications.

Elaboration of highly hydrophobic polymeric surface--a potential strategy to reduce the adhesion of pathogenic bacteria?

Different polymeric surfaces have been modified in order to reach a high hydrophobic character, indeed the superhydrophobicity property. For this purpose, polypropylene and polystyrene have been treated by RF or µwaves CF4 plasma with different volumes, the results were compared according to the density of injected power. The effect of pretreatment such as mechanical abrasion or plasma activation was also studied. The modified surfaces were shown as hydrophobic, or even superhydrophobic depending of defects density. They were characterized by measurement of wettability and roughness at different scales, i.e. macroscopic, mesoscopic and atomic. It has been shown that a homogeneous surface at the macroscopic scale could be heterogeneous at lower mesoscopic scale. This was associated with the crystallinity of the material. The bioadhesion tests were performed with Gram positive and negative pathogenic strains: Listeria monocytogenes, Pseudomonas aeruginosa and Hafnia alvei. They have demonstrated an antibacterial efficiency of very hydrophobic and amorphous PS treated for all strains tested and a strain-dependent efficiency with modified PP surface being very heterogeneous at the mesoscopic scale. Thus, these biological results pointed out not only the respective role of the surface chemistry and topography in bacterial adhesion, but also the dependence on the peaks and valley distribution at bacteria dimension scale.

Relationship between ammonia sensing properties of polyaniline nanostructures and their deposition and synthesis methods.

The ammonia absorption properties of polyaniline nanostructures are studied in terms of sensitivity, response and recovery times and stability. These characteristics are obtained by measuring, at room temperature, the absorbance variations at 632 nm. The nanostructures are synthesized either by interfacial or rapid or dropwise polymerizations with the oxidant-to-monomer mole ratio equals to 0.5 or 1. The influence of the deposition method (in-situ or drop-coating technique) as well as the nature of the dopant (HCl, CSA or I(2)) on the gas detection properties are also studied. The results show a strong dependence of the morphology on the deposition method, the in-situ technique leads to the best sensitivity and response time. For this deposition method, the nanostructures sensitivity, response time and regeneration rate depend on the synthesis method, the dopant and the mole ratio. The ageing effect after 8 months under ambient conditions and the mechanism of interaction between the polyaniline nanostructures and ammonia molecules are also presented.

Improvement of the detection of neurodegenerative Alzheimer's disease through a specific surface chemistry applied onto the inner surface of the titration well.

The main objective of this paper was to illustrate the enhancement of the sensitivity of the ELISA titration of Tau proteins while reducing other non-specific adsorptions that could increase the optical densities and could lead to false positives. This goal was obtained thanks to the association of cold plasma and wet chemistries of the inner surface of the titration well. The PP surface was cold plasma-activated, then coated with different amphiphilic molecules bearing either ionic charges and/or long hydrocarbon chains. The support treated and coated with hexatrimethylammonium bromide improves the signal detection of proteins while reducing the background due to non-specific associations of biomolecules such as hyperphosphorylated Tau protein. However, coating with 3-butenylamine hydrochloride could also be suitable.

Study of the adhesion of neurodegenerative proteins on plasma-modified and coated polypropylene surfaces.

The inner polymeric surface of an ELISA titration well is plasma-modified and coated with different surfactant molecules. The titration of neurodegenerative proteins markers (prion, Tau and ß-synuclein), previously demonstrated as more efficient with such modified tubes, is related to the adhesion behaviour of these proteins and their corresponding capture antibodies. The adhesion process is studied in terms of anchoring and specific mechanisms. The proteins and antibodies binding onto such modified surfaces is related to the substrate hydrophilic character calculated from the angle contact measure, to the polymer surface charge measured through the streaming potential determination at different pH and the inner surface roughness determined from AFM images. Furthermore, the influence of the blocking agent used during the ELISA titration is also studied.

How to control the recombinant prion protein adhesion for successful storage through modification of surface properties.

Depletion of neuroproteins on the inner walls of storage tubes influences the accuracy of tests used for identification of various neurodegenerative disorders. In this paper, a strategy is described for surface modification of Eppendorf tubes leading to non-adhesive properties towards the recombinant human prion proteins (PrPrec(hum)). Tubes were pre-activated by helium plasma and grafted with three diverse coatings: pure poly(N-isopropylacrylamide) (PNIPAM), PNIPAM admixed with either neutral PEG(20)sorbitan monolaurate (PEG(20)) or positively charged cetyl trimethylammonium bromide (CTAB) at varying plasma activation times and polymer to surfactant ratios. New functionalized surfaces were analyzed by goniometry, streaming potential measurement and X-ray photoelectron spectroscopy, whereas the protein adhesion was monitored by enzyme linked immunosorbent assays and confocal microscopy. The mapping of PrPrec(hum) adhesion associated with surface analyses enabled us to determine that no or negligible depletion of PrPrec(hum) can be obtained by surfaces possessing basic component in the range between 50 and 60 mJ m(-2) and streaming potential ζ(7.4) - -50 mV.

Ammonia absorption study of pulsed-plasma polyaniline by quartz crystal microgravimetry and UV/vis spectrometry.

The ammonia absorption properties of polyaniline elaborated by the pulsed-plasma technique are studied. These properties depend on the structure of the polymer which is associated not only to plasma parameters such as peak power, ignition and extinction durations, pulse frequency and duty cycle, but also to the type of doping agent. Two methods of analysis are used: the UV/vis spectrometry and the quartz crystal microbalance. The results show that input power is the most influent plasma parameter on the sensitivity of the polyaniline film. Moreover, the oxidative doping is more efficient than the acidic one to create more polarons and then to obtain a more sensitive layer. The gravimetric study shows that the interaction between ammonia molecules and iodine-doped polyaniline corresponds to a multilayer reversible chemisorption.

Development of an optical ammonia sensor based on polyaniline/epoxy resin (SU-8) composite.

Polyaniline (PANI)/glycidyl ether of bisphenol A (SU-8) composite film is elaborated in order to detect ammonia gas. These composite films are characterized by ultraviolet-visible (UV-vis) spectroscopy, Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The sensitivity to ammonia is measured by optical absorption changes. The ammonia sensing properties of PANI/SU-8 composite films are studied, and then are compared to pure PANI films elaborated by chemical way. Experimental results show that the PANI/SU-8 optical sensor has simultaneously a rapid response to ammonia gas and regenerates easily, that is advantageous compared to pure PANI films.

A new evanescent wave ammonia sensor based on polyaniline composite.

A single-mode TE(0)-TM(0) optical planar waveguide ammonia sensor based on polyaniline/polymethyl methacrylate (PANI/PMMA) composite is designed and developed. The sensing properties of the photonic sensor to ammonia at room temperature are studied. A significant change is observed in the guided light output power of the sensor after it is exposed to ammonia gas. The metrological parameters (sensitivity, response time and recovery time) of the sensor are strongly influenced by the interaction length (length of sensing region). Compared with the conventional optical ammonia sensor based on absorption spectroscopy, the integrated optical sensor is more sensitive to ammonia.

New sensitive layer based on pulsed plasma-polymerized aniline for integrated optical ammonia sensor.

A new integrated optical sensor based on plasma-polyaniline sensitive layer for ammonia detection is designed and developed. The sensor is based on polyaniline elaborated by the plasma technique (Plasma Enhanced Chemical Vapor Deposition, PECVD) and deposited on a small section of a single-mode planar SU-8 waveguide. The sensing properties of the integrated optical sensor to ammonia at room temperature are presented. A significant change in the guided light output power of the sensor is observed after exposition to ammonia gas. This new ammonia sensor exhibits fast response and recovery times, good reversibility and repeatability. The metrological parameters (sensitivity, response time and recovery time) of the sensor are strongly influenced by the interaction length (length of sensing region), the type of dopant and the light polarization. The sensor has a logarithmic linear optical response within the ammonia concentration range between 92 and 4618ppm.

Azobenzene-containing monolayer with photoswitchable wettability.

A compact monolayer containing azobenzene has been prepared on silicon substrates. The elaboration route consisted of covalent grafting of freshly synthesized azobenzene moieties onto an isocyanate-functionalized self-assembled monolayer (SAM). The highly packed and ordered isocyanate-functionalized SAM and the azobenzene-functionalized SAM were monitored and characterized by contact angle measurements and X-ray reflectivity (XR). Photoswitching of the wettability of the film induced by the reversible cis-trans isomerization of the azobenzene chromophores is experimentally shown from water and olive oil contact angle measurements.

Surface engineering of biomaterials with plasma techniques.

In this study, 3 types of plasma techniques, i.e. plasma modification, plasma deposition and plasma followed by grafting reaction, are used for the fabrication of tools, medical devices and biomaterials. Depending on purpose, bioadhesion of cells and biomolecules is either looked for or avoided. Since the mechanisms of bioadhesion depend on the characteristics of the surface (hydrophilic or hydrophobic), modifying the surface by a treatment will alter the bioadhesion. These treatments are developed for the anti-fouling process, the sterilisation and the improvement of the formation of biofilms. They have also proved useful for the synthesis of biomimicking devices.