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This work addresses the ubiquitous presence of organic contaminants at inorganic solid surfaces and the improvement of XPS analysis selectivity to cope with it. Water contact angle measurements showed that the adsorption of organic contaminants occurs readily in ambient air, and faster and more extensively under high vacuum. It is stronger on stainless steel (SS) compared to silica and is significantly reduced when SS is sterilized by autoclaving. The reliability of XPS data was evaluated (selectivity, precision, accuracy) by correlations between spectral data incorporating a large amount of results obtained with different XPS spectrometers on SS and glass samples cleaned in different ways and conditioned with several biomacromolecules. The methodology used allows a discrimination to be made between contaminants and deliberately adsorbed biomacromolecules, and offers perspectives for tracking the source of contamination. Furthermore, a discrimination can be made between oxygen from the organic adlayer and oxygen from the substrate, and the O 1s component above 532.0 eV observed for SS is shown to be due to organic contaminants rather than adsorbed water. This approach offers new perspectives to examine the interactions (displacement or not) between contaminants and compounds of interest, e.g. proteins, at the stage of the adsorption process.

Chitosan (Cs) and hydroxyapatite (Ha) were analysed by X-ray photoelectron spectroscopy (XPS). Phosphorylated Cs microparticles and hybrid Cs/Ha microparticles were prepared and analysed by XPS before and after immersion in a solution 1.5 times more concentrated than a simulated body fluid (SBF). The accuracy of spectrum recording, peak decomposition and peak component assignment was insured by a post-control of charge stabilization, and by the examination of correlations between spectral data guided by stoichiometry and charge balance. The concentration of organic oxygen was determined from the concentrations of the oxidized forms of carbon, allowing a sharper insight into speciation and O 1s peak shape. This indicated that the hydroxide ion of Ha, and hydrogenophosphate if present, give a contribution near 532.4 eV, which overlaps with organic oxygen. As a result of immersion in the 1.5*SBF solution, the formation of CaCO3 and of Ha material occurred. A quantification could be made for the constituents of biomaterial interest, contaminating salts and paraffin oil residues from the microparticle manufacturing process. The uncertainties regarding the nature of the model calcium phosphate used and the best marker for calcium carbonate were addressed by comparing the possible effect on the output, which was facilitated by using ternary composition diagrams. Whatever their formulation, the native microparticles were found to be coated by a thick layer of paraffin oil. The induction of calcium carbonate and phosphate precipitation or the retention of precipitates by the microparticles was favored by the presence of phosphate in the initial formulation either by phosphorylation or by incorporation of Ha.

Protein adsorption on surfaces placed in biological fluids is a ubiquitous and mostly irreversible phenomenon, desirable or not, but often uncontrolled. Understanding and control of protein adsorption has important implications in biotechnology, food industry, biosensor design, biomaterials science etc. The aim of this thesis is to create stimuli-responsive surfaces allowing the control of protein adsorption by a simple pH and ionic strength (I) trigger. The adopted strategy consists in grafting thiol-terminated poly(ethylene oxide) (PEO), a protein-repellent polymer, and disulfide-modified poly(acrylic acid) (PAA), a weak polyelectrolyte able to adsorb large amounts of protein or not depending on its conformation, together on a gold substrate. The effect of pH and I on homobrushes of PEO and PAA, and on mixed PEO/PAA brush conformation as well as on protein adsorption is investigated, and repeated cycles of adsorption and desorption of proteins are performed. Simultaneous grafting allows intimate mixing of PEO and PAA in brushes with PEO mass fraction ranging from 0.35 to 0.65, depending on PEO/PAA ratio in solution. The amount of albumin adsorbed on PAA brushes is 10 times higher when adsorbed at pH 5 and I = 10-5M (swollen PAA chains) compared to pH 9 and I = 10-1M (shrunk PAA chains). Based on these results, adsorption and desorption conditions of proteins with different isoelectric points were tentatively predicted. Cycles of adsorption and desorption of albumin, lysozyme, collagen and immunoglobulin G were then successfully performed on mixed PEO/PAA brushes, with adsorbed amounts in the range of the ones measured on PAA brushes and an efficient desorption ability, close to the one of PEO brushes. The smart coating developed here open perspectives in many bioengineering fields including enzyme immobilization, drug delivery and biosensing., (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2013

A facile method of using optical trapping to measure cell adhesion forces is presented and applied to the adhesion of Saccharomyces cerevisiae on glass, in contact with solutions of different compositions. Trapping yeast cells with optical tweezers (OT) is not perturbed by cell wall deformation or cell deviation from a spherical shape. The trapping force calibration requires correction not only for the hydrodynamic effect of the neighboring wall but also for spherical aberrations affecting the focal volume and the trap stiffness. Yeast cells trapped for up to 5 h were still able to undergo budding but showed an increase of doubling time. The proportion of adhering cells showed the expected variation according to the solution composition. The detachment force varied in the same way. This observation and the fact that the detachment stress was exerted parallel to the substrate surface point to the role of interactions involving solvated macromolecules. Both the proportion of adhering cells and the removal force showed a distribution which, in our experimental conditions, must be attributed to a heterogeneity of surface properties at the cell level or at the subcellular scale. As compared with magnetic tweezers, atomic force microscopy, and more conventional ways of studying cell adhesion (shear-flow cells), OT present several advantages that are emphasized in this paper. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4723566]

The 24 h stability of bare silicon wafers as such or silanized with CH 3O-(CH 2-CH 2-O) n -C 3H 6-trichlorosilane (n = 6-9) was investigated in water, NaCl, phosphate and carbonate solutions, and in phosphate buffered saline (PBS) at 37 °C (close to biological conditions regarding temperature, high ionic strength, and pH). The resulting surfaces were analyzed using ellipsometry, X-ray Reflectometry (XRR), X-ray Photoelectron Spectroscopy (XPS), and Atomic Force Microscopy (AFM). Incubation of the silanized wafers in phosphate solution and PBS provokes a detachment of the silane layer. This is due to a hydrolysis of Si-O bonds which is favored by the action of phosphate, also responsible for a corrosion of non-silanized wafers. The surface alteration (detachment of silane layer and corrosion of the non-silanized wafer) is also important with carbonate solution, due to a higher pH (8.3). The protection of the silicon oxide layer brought by silane against the action of the salts is noticeable for phosphate but not for carbonate. © 2012 Elsevier Inc. All rights reserved.

A survey of the literature is made for the XPS analysis of food products (mainly spray-dried powders, which reveal a considerable surface enrichment in lipids) and of microorganisms and related systems (extracellular polymer substances and biofilms). This survey is used as a background for discussions and recommendations regarding methodology. Sample preparation methods reviewed are freeze drying, analysis of frozen hydrated specimens and adsorption of surface-active biocompounds on model substrates. Peak decomposition is a way to increase the wealth of information provided by the XPS spectra. It should be performed after a check that sample charge stabilization is satisfactory. Moreover, ensuring the precision needed to make comparisons within sets of samples may involve a trade-off between imposing constraints and generating information. The examination of correlations between spectral data in the light of chemical guidelines is useful to validate or improve peak decomposition and component assignment, and may also upgrade the chemical information regarding speciation. Further upgrading may be achieved by expressing marker XPS data in terms of concentrations of compounds of interest. Different methods of computation are discussed, providing a composition in terms of ingredients, classes of biochemical compounds, or various organic and inorganic compounds. As an alternative or complement to this deterministic approach, multivariate analysis of suitable spectral windows provides spectral components, which may be used for comparing samples, and which may have a direct chemical relevance or be used to identify features of interest.

The factors influencing the adherence of starch were examined to improve the understanding of the mechanisms affecting soiling and cleanability. Therefore an aqueous suspension of starch granules was sprayed on four model substrates (glass, stainless steel, polystyrene and PTFE) and dried, and the substrates were cleaned using a radial-flow cell. The morphology of the soiled surfaces and the substrate chemical composition were also characterized. By influencing droplet spreading and competition between granule-substrate and granule-granule interfaces regarding the action of capillary forces, substrate wettability affected the shape and compactness of the adhering aggregates, the efficiency of shear forces upon cleaning, and finally the adherence of soiling particles. The rate of drying had an influence explained by the duration left to capillary forces for acting. X-ray photoelectron spectroscopy demonstrated the presence of macromolecules, mainly polysaccharides, which were adsorbed from the liquid phase, or carried by the retracting water film and deposited at the granule-substrate interface. These macromolecules acted as an adhesive joint, the properties of which seemed to be influenced by the detailed history of drying and subsequent exposure to humidity. In summary, the substrate surface energy affects the adherence of starch aggregates by different mechanisms which are all linked together: suspension droplet spreading, action of capillary forces, direct interaction with starch particles and interfacial macromolecules.

The removal of particulate soils from solid surfaces is the key process of cleaning many industrial devices, such as heat exchangers and spray dryers (food and pharmaceutical sector), and may be influenced by the presence of solutes, in particular of macromolecules. The present study deals with the influence of soluble polysaccharide on the adherence of particulate fouling of open surfaces and on subsequent cleaning. Model surfaces differing by hydrophobicity (glass and polystyrene) were soiled with a suspension of quartz particles, taken as a model of hard hydrophilic soil. Dextran was chosen as a model of soluble polysaccharide. The surfaces were soiled with or without previous conditioning with the polysaccharide solution (80mg/l). The quartz particles suspension was prepared in three ways: (i) suspension in a polysaccharide solution (80mg/l), (ii) same as (i) and subsequent washing three times, (iii) suspension in water. The surfaces were soiled by spraying the suspension and dried for 30min before cleaning treatment with a water flow in a radial flow chamber. The aggregates observed after soiling differed considerably between glass and polystyrene, whether the surface and/or the quartz particles are conditioned with dextran. Conditioning polystyrene with dextran increased slightly the adherence of quartz particles, while the opposite was observed when conditioning glass with dextran, whatever the mode of quartz particles conditioning. The effect of conditioning quartz particles with dextran at the concentration used was not significant.

In order to evaluate the respective influence of surface nanotopography and chemical composition on blood compatibility, plasma protein adsorption (fibrinogen - Fg and albumin - HSA, quantified simultaneously by dual radioassays) and platelet adhesion were investigated on a range of materials. Reference surfaces were glass, polystyrene and poly(vinyl chloride), as well as pieces of commercial blood bags. Colloidal lithography with 65 and 470nm polystyrene latex particles was used to prepare nanostructured surfaces with either one layer of colloids or with bimodal roughness. The surfaces were further conditioned by adsorption of poly(ethylene oxide) (PEO)-containing compounds (Pluronic F68 and PLL-g-PEG). Study of the simultaneous adsorption of Fg and HSA on reference substrates demonstrated that the Fg/HSA adsorbed amount ratio decreases as the substrate hydrophobicity increases, the lower ratio being obtained with commercial blood bag. This is due to the higher resistance of HSA adsorbed on hydrophobic substrates to displacement by proteins from the solution. Such higher resistance was also shown to occur in the case of displacement by constituents of non-diluted blood plasma. Nanostructured substrates gave about the same Fg/HSA ratio as polystyrene and poly(vinyl chloride). Surface conditioning with Pluronic F68 reduced the adsorption of Fg in competition with HSA on all substrates except glass, while PLL-g-PEG decreased the adsorbed amount of both Fg and HSA on glass but not on the other substrates. Positive correlations between the amount of adhering blood platelets and both the Fg/HSA ratio and the absolute amount of Fg adsorbed in competition with HSA were found for all substrates (reference and nanostructured, as such or after PEO conditioning, except native glass which had to be discarded due to the formation of clots in the liquid phase). These quantities were also related to the state of activation of adhering platelets. This supports the concept that bloo

The structure and the chemical composition of the layer adsorbed at interfaces involving champagne have been investigated using native champagne, as well as ultrafiltrate (UFch) and ultraconcentrate (UCch) obtained by ultrafiltration with a 10(4) nominal molar mass cutoff. The layer adsorbed at the air/liquid interface was examined by surface tension and ellipsometry kinetic measurements. Brewster angle microscopy demonstrated that the layer formed on polystyrene by adsorption or drop evaporation was heterogeneous, with a domain structure presenting similarities with the layer adsorbed at the air/liquid interface. The surface chemical composition of polystyrene with the adlayer was determined by X-ray photoelectron spectroscopy (XPS). The contribution of champagne constituents varied according to the liquid (native, UFch, and UCch) and to the procedure of adlayer formation (evaporation, adsorption, and adsorption + rinsing). However, their chemical composition was not significantly influenced either by ultrafiltration or by the procedure of deposition on polystyrene. Modeling this composition in terms of classes of model compounds gave approximately 35% (w/w) of proteins and 65% (w/w) of polysaccharides. In the adlayer, the carboxyl groups or esters represent about 18% of carbon due to nonpolypeptidic compounds, indicating the presence of either uronic acids in the complex structure of pectic polysaccharides or of polyphenolic esters. This structural and chemical information and its relationship with the experimental procedures indicate that proteins alone cannot be used as a realistic model for the macromolecules forming the adsorption layer of champagne. Polysaccharides, the other major macromolecular components of champagne wine, are assembled with proteins at the interfaces, in agreement with the heterogeneous character of the adsorbed layer at interfaces.