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International audience; Foams are inherently unstable objects, that age and disappear over time. The main cause of foam aging is Ostwald ripening: smaller air bubbles within the foam empty their gas content into larger ones. One strategy to counter Ostwald ripening consists in creating armored bubbles, where solid particles adsorbed at the air/liquid interface prevent bubbles from shrinking below a given size. Here, we study the efficiency of coating air bubbles with fat crystals to prevent bubble dissolution. A monoglyceride, monostearin, is directly crystallized at the air/oil interface. Experiments on single bubbles in a microfluidic device show that the presence of monostearin fat crystals slows down dissolution, with an efficiency that depends on the crystal size. Bubble ripening in the presence of crystals exhibits intermittent dissolution dynamics, with phases of arrest, when crystals jam at the interface, followed by phases of dissolution, when monostearin crystals are ejected from the interface. In the end, crystals do not confer enough mechanical strength to the bubbles to prevent them from fully dissolving.

Silk fibroin (SF) is a versatile material with biodegradable and biocompatible properties, which make it fit for broad biomedical applications. In this context, the incorporation of nanosized objects into SF allows the development of a variety of bionanocomposites with tailored properties and functions. Herein, we report a thorough investigation on the design, characterization, and biological evaluation of SF hydrogels incorporating gold, silver, or iron oxide nanoparticles. The latter are synthesized in aqueous media using a biocompatible ligand allowing their utilization in various biomedical applications. This ligand seems to play a pivotal role in nanoparticle dispersion within the hydrogel. Results show that the incorporation of nanoparticles does not greatly influence the mechanism of SF gelation and has a minor impact on the mechanical properties of the so-obtained bionanocomposites. By contrast, significant changes are observed in the swelling behavior of these materials, depending on the nanoparticle used. Interestingly, the main characteristics of these bionanocomposites, related to their potential use for biomedical purposes, show the successful input of nanoparticles, including antibacterial properties for gold and silver nanoparticles and magnetic properties for iron oxide ones.

Understanding the wetting properties of chemically modified inorganic surfaces with random nanoscale topographies is of fundamental importance for diverse applications. This issue has hitherto continuously been the subject of considerable controversies. Herein, we report a thorough investigation of the wettability-topography-chemistry balance for a nanostructured surface with random topography, the main challenge being decoupling topography from surface chemistry. For this purpose, we use a superficially nanostructured aluminum substrate chemically modified by fatty acid monolayers. From atomic force microscopic data, we extract a variety of parameters describing the surface topography by means of variogram calculations, a method originally developed by geostatisticians to explore large surfaces. Moreover, by using log and power transforms, we establish a consistent relationship relating wettability, topography, and surface chemistry. Interestingly, we demonstrate that the water contact angle comprises a contribution due to the surface composition, originating from hydrophobization through alkyl chains, and a contribution due to the surface topography, particularly its stochastic feature. This model is valid in the Wenzel region; it provides guidelines for tuning the wetting properties of inorganic surfaces with random nanoscale topographies.

International audience; Alsingle bondSi coated boron steels have been of interest for many years because of their superior mechanical properties and their excellent oxidation resistance. These high strength steels are particularly used in hot stamping processes during which the Alsingle bondSi coating undergoes multiple microstructural transformations. In this study, morphology and structure transformations are investigated using an original approach. Most of the time, the coating evolution is studied in cross section, by ex situ characterization of its different layers after heat treatment. In this work, the evolution of the surface is explored for the first time using in situ high-temperature Environmental Scanning Electron Microscopy (HT-ESEM). The austenitization step reproduced in the ESEM chamber allows a precise description of several surface changes occurring, depending on the temperature range. Among them, the main change in morphology is occurring between 650 and 800 °C and is linked to different reactions between aluminium and bi- and ternary Fe-Al-Si phases. The heating rate is also pointed out as a key parameter that affects the surface morphology. In fact, with low heating rates the surface is mostly composed of hexagonal and rectangular elements coming from τ5 (Fe2Al8Si) structuration, while needle-shaped FeAl3 structures are found for higher heating rates. In addition, it is observed that the heating rate also affects the surface roughness depending on the surface morphology. Finally, the origin of the presence of micrometrics pores appearing between 800 and 900 °C at the coating surface is discussed. Our hypothesis supported by ex situ characterization is that they result from formation of a crystallized oxide layer, probably close to α-Al2O3 structure.

International audience; Herein, we investigate the adsorption behavior of a small peptide, Glu-Cys-Gly, in aqueous solution onto copper surface and unravel a mechanism of growth of a hybrid peptide-copper multilayer the thickness of which may exceed a hundred of nanometers. Thanks to a combined set of surface characterizations supported by theoretical considerations, we provide a comprehensive understanding of the driving force and parameters influencing multilayer growth. (i) The generation of Cu+ ions due to the dissolution of copper surface, modulated by pH, results in the formation of cuprous-thiolate complex made of two peptide molecules anchoring one Cu+ cation. (ii) The stability of this hybrid multilayers is ensured by intermolecular interactions between peptide-copper entities mainly through a combination of electrostatic interaction and hydrogen bonds which stabilize the supramolecular edifice.

International audience; A rotaxane scaffold incorporating two dithiolaneanchoring units for the modification of gold surfaces hasbeen functionalized with multiple copies of a redox unit,namely ferrocene. Surface modification has been first assessedat the single molecule level by atomic force microscopy(AFM) and scanning tunneling microscopy (STM) imaging,while tip enhanced Raman spectroscopy (TERS) providedthe local vibrational signature of the ferrocenyl subunitsof the rotaxanes grafted onto the gold surface. Finally, oxidationof the redox moieties within a rotaxane scaffold graftedonto gold microelectrodes has been investigated by ultrafastcyclic voltammetry. Intramolecular electron hopping isindeed extremely fast in this system. Moreover, the kineticsof charge injection depends on the molecular coverage dueto the influence of intermolecular contacts on molecular motions.

International audience; Biomineralization is the process by which organisms produce hard inorganic matter from soft tissues with outstanding control of mineral deposition in time and space. For this purpose, organisms deploy a sophisticated “toolkit” that has resulted in significant evolutionary innovations, for which calcium phosphate (CaP) is the biomineral selected for the skeleton of vertebrates. While CaP mineral formation in aqueous media can be investigated by studying thermodynamics and kinetics of phase transitions in supersaturated solutions, biogenic mineralization requires coping with the inherent complexity of biological systems. This mainly includes compartmentalization and homeostatic processes used by organisms to regulate key physiological factors, including temperature, pH and ion concentration. A detailed analysis of the literature shows the emergence of two main views describing the mechanism of CaP biomineralization. The first one, more dedicated to the study of in vivo systems and supported by researchers in physiology, often involves matrix vesicles (MVs). The second one, more investigated by the physicochemistry community, involves collagen intrafibrillar mineralization particularly through in vitro acellular models. Herein, we show that there is an obvious need in the biological systems to control both where and when the mineral forms through an in-depth survey of the mechanism of CaP mineralization. This necessity could gather both communities of physiologists and physicochemists under a common interest for an enzymatic approach to better describe CaP biomineralization. Both homogeneous and heterogeneous enzymatic catalyses are conceivable for these systems, and a few preliminary promising results on CaP mineralization for both types of enzymatic catalysis are reported in this work. Through them, we aim to describe the relevance of our point of view and the likely findings that could be obtained when adding an enzymatic approach to the already rich and creative research field dealing with CaP mineralization. This complementary approach could lead to a better understanding of the biomineralization mechanism and inspire the biomimetic design of new materials.

We report an original approach to synthesize hybrid gold nanostructures in which doxorubicin (DOX), mixed to Poliethylenglycole diacid (PEG-COOH) led to original hybrid gold nanovector (DOX IN PEG AuNPs). In this work, we investigate the ability of DOX IN PEG-AuNPs to detect the amplification of the hybridization process by a sensitive Quartz crystal Microbalance with dissipation (QCM-D) by intercalation process. The sensing layer was carried out by self-assembled monolayer of β mercaptoethylamine (cysteamine) on gold-coated quartz crystal sensor composed by a rigid homobifunctional cross-linker 1,4 phenilenediisothiocyanate (PDITC) linked covalently with amino-probe oligonucleotides. By QCM characterization in the range from 8 µM to 20 nM, we demonstrate high specificity of DOX IN PEG-AuNPs-DNA with a limit of detection (LOD) of 9 nM. This result is very promising for development of sensitive and effective nanoparticle-based biosensor for quantifying small biomolecules concentration in physiological liquids. These results open a possibility to realize a new class of nanovector which will be tailored for different biomedical application, such as imaging, targeting and drugs delivery. Keywords: Quartz Crystal Microbalance (QCM), Chemical surface, DNA hybridization, Gold nanoparticles, Doxorubicin

Herein, we report the coating of a surface with a random nanoscale topography with a lipid film formed by an anchoring stearic acid (SA) monolayer and phospholipid (DPPC) layers. For this purpose, different procedures were used for phospholipid coating, including adsorption from solution, drop deposition, and spin-coating. Our results reveal that the morphology of the obtained lipid films is strongly influenced by the topography of the underlying substrate but also impacted by other factors, including the coating procedure and surface wettability (modulated by the presence of SA). These coated surfaces showed a remarkable antifouling behavior toward proteins, with different yields of repellency (Yrp) depending on the amount/organization of DPPC on the nanostructured substrate. The interaction between the proteins and phospholipids involves a partial detachement of the film. The use of characterization techniques with different charcateristics (accuracy, selectivity, analysis depth) did not reveal any obvi...

Cu-Ni alloys are extensively used in contact with natural waters and are impacted by microbial activities of biofilms. The mechanisms by which surface changes occur upon immersion remain not well understood. Herein, an aerobic microbial activity of natural biofilms is mimicked by the enzymatic generation of an oxidizing agent and an organic acid. Surface changes are probed through a detailed analysis of XPS spectra which allowed a distinction between compounds of organic and inorganic nature to be made. Results show that the surface is composed of copper oxides/hydroxides, presumably Cu2O and Cu(OH)2 and Ni hydroxides. The enzyme-catalyzed reaction causes a significant depletion of Ni and inorganic oxygen, while the concentration of copper, CuI and CuII, varies only slightly. Surface changes concern the organic phase; the amount of organic compounds strikingly increases in the presence of enzymes, and the XPS spectra reveal the accumulation of compounds with high oxidized carbon content, attributed to adsorbed gluconate. Correlations between spectral data suggest the formation of Cu-gluconate complex, probably through coordinative bonds between gluconates and CuII on the oxide layer. These findings are particularly important to properly evaluate the impact of microbial activities on the sustainability of Cu-Ni alloys upon natural exposures.

The use of Pd nanoparticles (Pd-NPs) to realize several important organic reactions allows efficient catalysis with low metal loading (

Inhibition of TIEG1 gene provides changes within the musculoskeletal system. Recently, hypertrophy, hyperplasia and a metabolic glycolytic switch for slow and fast fibers has been observed in TIEG1...

Hypothesis The crystallization of calcium phosphate (CaP) is a ubiquitous process that occurs in several mineralized tissues and involves a variety of biochemical and chemical reactions. This issue has been hitherto continuously studied from supersaturated solutions (chemical procedure), i.e. by adding calcium and orthophosphate ions in a homogenous phase. Yet, both in vivo and in vitro investigations have clearly shown the implication of enzymes, namely alkaline phosphatase (ALP), to initiate the mineralization process by generating orthophosphate ions. Experiments We report a thorough investigation on the mechanism of enzyme-induced mineralization in homogenous phase (enzymatic procedure). For this purpose, ALP is introduced in Ca2+/Mg2+-containing solution (pH = 7.4; 37 °C), and its activity modulated by the concentration of its substrate. Findings Results show that after 24 h of mineralization both chemical and enzymatic procedures lead to the formation of well-crystalline hydroxyapatite nano-objects, however with noticeable impact on their shape and dimensions. Remarkably enough, by combining in situ monitoring and ex situ characterizations, we identify several intermediate phases, including amorphous phase, dicalcium phosphate dehydrate phase (DCPD or brushite) and Whitlockite (WH). Besides, mineralized nano-objects with a core-shell structure is observed, and hydroxyapatite platelets are shown to grow on the surface of their shell.

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.

International audience; We investigate the evolution of the surface of a highly alloyed stainless steel (Sanicro 28) upon immersion in aqueous phosphoric acid solutions. For this purpose, both short-(few hours) and long-term immersion (several days) were carried out. A detailed analysis of XPS spectra allowed a distinction to be made between oxygen originating from the organic adlayer (adventitious contamination), the passive oxide layer, and adsorbed phosphate species. By estimating the fraction of oxygen due to phosphate species (O-ph), it was shown that the O-ph/P molar concentration ratio was ranging from about 2 to 3. This suggests the presence of a polyphosphate layer at the stainless steel surface, as also supported by Raman analysis, which influence the electrochemical behavior of SS in the acidic media. (c) 2017 Elsevier B.V. All rights reserved.

International audience; IGF tri-peptide adsorption on Au(110)-(1 × 2) under Ultra High Vacuum (UHV) conditions has been investigated using surface science techniques such as synchrotron based Angle Resolved X-ray Photoemission Spectroscopy (AR-PES or AR-XPS), Low Energy Electron Diffraction (LEED) and Scanning Tunnelling Microscopy (STM). The behaviour of IGF molecules has been revealed to be coverage dependent; at low coverage, there is formation of islands presenting a chiral self-organised molecular network with a (4 2, − 3 2) symmetry as shown by Low Energy Electron Diffraction (LEED) and Scanning Tunnelling Microscopy (STM) on the unaltered Au(110)-(1 × 2) reconstruction, suggesting significant intermolecular interactions. When the coverage is increased, the islands grow bigger, and one can observe the disappearance of the self-organised network, along with a remarkable destruction of the (1 × 2) substrate reconstruction, as shown by STM. The effect of IGF on the surface gold atoms has been further confirmed by angle-resolved photoemission measurements which suggest a modification of the electronic states with the (1 × 2) symmetry. The resulting molecular organisation, and overall the gold surface disorganisation, prove a strong surface-molecule interaction, which may be probably be explained by a covalent bonding.

International audience; We investigated the mechanism of enzyme immobilization on silanized surfaces through coupling agents (cross-linkers) in order to understand the role of these molecules on interfacial processes and their effect on catalytic activity. To this end, we used a model multimeric enzyme (G6PDH) and several cross-linking molecules with different chemical properties, including the nature of the end-group (-NCO, -NCS, -CHO), the connecting chain (aliphatic vs aromatic), and geometrical constraints (meta vs para-disubstituted aromatics). There did not seem to be radical differences in the mechanism of enzyme adsorption according to the linker used as judged from QCM-D, except that in the case of DIC (1,4-phenylene diisocyanate) the adsorption occurred more rapidly. In contrast, the nature of the cross-linker exerted a strong influence on the amount of enzyme immobilized as estimated from XPS, and more unexpectedly on the stability of the underlying silane layer. DIC, PDC (1,4-phenylene diisothiocyanate), or GA (glutaraldehyde) allowed successful enzyme immobilization. When the geometry of the linker was changed from 1,4-phenylene diisothiocyanate to 1,3-phenylene diisothiocyanate (MDC), the silane layer was subjected to degradation, upon enzyme adsorption, and the amount of immobilized molecules was significantly lowered. TE (terephtalaldehyde) and direct enzyme deposition without cross-linker were similar to MDC. The organization of immobilized enzymes also depended on the immobilization procedure, as different degrees of aggregation were observed by AFM. A correlation between the size of the aggregates and the catalytic properties of the enzyme was established, suggesting that aggregation may enhance the thermostability of the multimeric enzyme, probably through a compaction of the 3D structure.

International audience; The mechanism of interaction of Zn porphyrin (ZnPP) with TiO2 surfaces is investigated with a view to optimizing the synthesis of hybrid nanomaterials. The strategy consists of studying the adsorption of ZnPP on TiO2 flat surfaces by taking advantage of complementary surface characterization techniques. Combining a detailed X-ray photoelectron spectroscopic analysis with AFM imaging allows ZnPP-surface and ZnPP intermolecular interactions to be discriminated. Probing the adsorption of ZnPP on TiO2 nanoparticles (NPs) reveals the dominant role of ZnPP-mediated interactions, which are associated with the formation of ZnPP multilayers and/or with the state of aggregation of NPs. These preliminary investigations provide a guideline to synthesizing a novel ZnPP-TiO2 hybrid nanomaterial in a one-step protocol. In this material, ZnPP molecules are presumably involved in the TiO2 lattice rather than on the NP surface. Furthermore, ZnPP molecules preserve their electronic properties within the TiO2 NPs, and this makes the ZnPP-TiO2 hybrid nanomaterial an excellent candidate for nanomedicine and related applications, such as localization of nanoparticles in cells and tissues or in photodynamic therapy.

International audience; In this work the mechanism of (3-aminopropyl)triethoxysilane (APTES) interaction with silicon surfaces is investigated at the molecular level. We studied the influence of experimental parameters such as time, temperature, and concentration on the quality of the APTES layer in terms of chemical properties, morphology, and stability in aqueous medium. This was achieved using a highly sensitive IR mode recently developed, grazing angle attenuated total reflection (GA-ATR). This technique provides structural information on the formed APTES layer. The topography of this layer was investigated by atomic force microscopy in aqueous medium. The hydrophilicity was also studied using contact angle measurement. Combining these techniques enables discussion of the mechanism of silane grafting. Considerable differences were observed depending on the reaction temperature, room temperature or 90 C. The data suggest the presence of two adsorption sites with different affinities on the oxidized silicon layer. This also allows the optimal parameters to be established to obtain an ordered and stable silane layer. The adsorption of proteins on the APTES layer was achieved and monitored using in situ quartz crystal microbalance with dissipation monitoring and ex situ GA-ATR analyses.

International audience; We report the synthesis of diacid-terminated PEG cubic TiO2 nanocrystals by a simple one-step solvothermal method, and their further use to form nanostructured surfaces for protein immobilization. The relevance and major interest of the so-obtained nanocrystals are the presence of terminal carboxylic acid groups at their surface, as confirmed by infrared analyses, in addition to the surrounding PEG chains, essential to avoid non specific interactions. These functional chemical groups were used to (i) immobilize the synthesized nano-cubes on a cysteamine-modified Au surface, and to (ii) attach proteins via a presumable covalent link. AFM images show that the shapes and the narrow size distribution of the nano-cubes, observed by TEM, were preserved after their immobilization on the modified Au surface. Moreover, the efficiency and specificity of antigen recognition were demonstrated using spectroscopic analyses. Our successful approach provides a versatile and facile way to elaborate specific and sensitive nanostructured surfaces for biosensors.

We investigate the interaction between D-Ala-D-Ala peptide and a stainless steel (SS) surface by AFM force spectroscopy with view to understand the role and nature of interfacial processes at the single molecule level. For this purpose, force-distance curves were recorded between the D-Ala-D-Ala modified tip and the SS surface in NaHCO 3 -enriched medium. The SS surface was prepared in a way that allows iron oxide species, presumably FeOOH, to be formed and remains stable during AFM measurements. Dynamic force measurements show that the unbinding force linearly increases with the logarithm of the loading rate, as generally observed for receptor-ligand complexes. Our results reveal also the existence of two regimes, suggesting the presence of multiple energy barriers in the energy landscape. From these dynamic force spectroscopy measurements, the kinetic off-rate constant is determined. An average unbinding force in the range of 50-300 pN is obtained, depending on the loading rate. Accordingly, in a medium in which the electrostatic interactions are not dominating, the binding mechanism of the peptide and SS surface cannot be attributed to covalent bonds and may be due to a combination of van der Waals and hydrogen bonds. Our findings open up new way to probe peptide-inorganic surface interactions and to understand the mechanism of peptide specific binding which is of particular interest in the design of hybrid materials. Single molecule level: The surface interaction of the D-Ala-D-Ala peptide with a stainless steel surface is measured by means of single molecule force spectroscopy (see picture). An average unbinding force in the range of 50-300 pN depending on the loading rate is found, suggesting weak interactions of the peptide with the surface due to a combination of van der Waals and hydrogen bonds. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Short peptides interact strongly with copper surfaces. We report here a full charac-terization on the interaction of Gly-Pro and Gly-Pro-Glu with the Cu(110) surface. By combining infrared analysis with X-ray photoelectron spectroscopy, two binding centers have been identified: the carboxylate and the amino groups. Moreover, spectral data were used in an innovative way to evaluate the number of nitrogen atoms per molecule bound to the surface. The presence of additional glutamate fragment in the peptide modifies the adsorption mechanism radically, leading to multilayer self-assembling growth. Our findings open up new insights into interfacial phenomena involved in intermolecular bonds and molecule−surface interactions.

Times Cited: 1 Article English Cited References Count: 45 703pk; The aim of this work was to create patterned surfaces for localized and specific biochemical recognition. For this purpose, we have developed a protocol for orthogonal and material-selective surface modifications of microfabricated patterned surfaces composed of SiO2 areas (100 mu m diameter) surrounded by Au. The SiO2 spots were chemically modified by a sequence of reactions (silanization using an amine-terminated silane (APTES), followed by amine coupling of a biotin analogue and biospecific recognition) to achieve efficient immobilization of streptavidin in a functional form. The surrounding Au was rendered inert to protein adsorption by modification by HS(CH2)(10)CONH-(CH2)(2)(OCH2CH2)(7)OH (thiol-OEG). The surface modification protocol was developed by testing separately homogeneous SiO2 and Au surfaces, to obtain the two following results: (i) SiO2 surfaces which allowed the grafting of streptavidin, and subsequent immobilization of biotinylated antibodies, and (ii) Au surfaces showing almost no affinity for the same streptavidin and antibody solutions. The surface interactions were monitored by quartz crystal microbalance with dissipation monitoring (QCM-D), and chemical analyses were performed by polarization modulation-reflexion absorption infrared spectroscopy (PM-RAIRS) and X-ray photoelectron spectroscopy (XPS) to assess the validity of the initial orthogonal assembly of APTES and thiol-OEG. Eventually, microscopy imaging of the modified Au/SiO2 patterned substrates validated the specific binding of streptavidin on the SiO2/APTES areas, as well as the subsequent binding of biotinylated anti-rIgG and further detection of fluorescent rIgG on the functionalized SiO2 areas. These results demonstrate a successful protocol for the preparation of patterned biofunctional surfaces, based on microfabricated Au/SiO2 templates and supported by careful surface analysis. The strong immobilization of the biomolecules resulting from the described protocol is advantageous in particular for micropatterned substrates for cell-surface interactions.

Understanding the behavior of enzymes at solid surfaces requires coping with the complexity of the interfaces. Examples are given to illustrate key considerations: (i) influence of the adventitious contamination; the amount of glucose oxidase adsorbed on stainless steel in conditions producing an electrochemical effect is very low compared to the amount of organic contaminants; (ii) structure (multilayered, random) of an adsorbed phase containing an enzyme and other organic constituents (self-assembled monolayer, adventitious contaminants); (iii) competition between proteins for adsorption and influence of the adsorption procedure (simultaneous or sequential) and (iv) reality vs. expectation in enzyme (glucose oxidase) immobilization by tentative covalent grafting. The study of enzyme adsorption in several model systems (catalase on surface-modified carbon blacks, beta-glucosidase on clay at different pHs, beta-glucosidase on sand and surface-modified sand) showed that a strong adsorption, whether by electrostatic or hydrophobic interactions, provokes an extensive deactivation. After adsorption, which is a quick process, the enzyme activity may continue to decrease both in the adsorbed phase and in the solution owing to dynamic processes which involve the adsorbed enzyme and exchanges between the adsorbed phase and the liquid phase. (c) 2008 Elsevier Ltd. All rights reserved.

International audience; The electrochemical behavior of stainless steels (SS) in natural waters is characterized by the ennoblement of their free corrosion potential (Ecorr). This phenomenon depends strongly on the settlement of biofilms on SS surfaces. Many hypotheses have been proposed to explain the biofilm action, in particular the enzymatic catalysis plays an important role by shifting the cathodic and/or anodic processes. However, there are still only few studies relating the use of purified enzymes. In contrast with bacteria-associated corrosion, the direct influence of enzymes is still poorly documented. The aim of this review is to show the benefits of the enzymatic approach in the study of biocorrosion. Indeed, enzymatic systems may constitute convenient models to mimic microbial influenced corrosion and to evaluate the behavior of metallic materials in natural waters.

The corrosion behaviour of Sanicro28, in industrial phosphoric acid and simplified solution of pure H3PO4 containing sulphates and chlorides, is investigated during 48 h between 20 and 80 °C. Results show higher corrosion resistance in the industrial medium. Film thickness evaluated by EIS remains constant in industrial acid due to polyphosphate that promotes crystallisation of the Cr2O3 inner layer. Conversely, the passive film is partially destroyed at 80 °C in simplified acid. XPS and Raman analysis show that phosphate and molybdenum are both present in the passive film and in corrosion products. The role of Ca present in the industrial acid is discussed.

The Fe(II–III) hydroxycarbonate green rust, GR(CO 3 2− ), can be prepared by oxidation of aerated aqueous suspensions of Fe(II) hydroxide. The effects of phosphate species on the formation and transformation of GR(CO 3 2− ) were then studied by adding Na 2 HPO 4 before the precipitation of the initial Fe(II) hydroxide or once GR(CO 3 2− ) was obtained. The final products of the oxidation processes were characterized by X-ray diffraction (XRD) and Raman spectroscopy. When Na 2 HPO 4 was added to a suspension of well crystallized GR(CO 3 2− ), various effects were observed depending on the Na 2 HPO 4 concentration. (i) The formation of α-FeOOH was inhibited. (ii) Nanophase lepidocrocite was the main final product for the lowest phosphate concentrations (0.001 M, that is Fe/P = 120). (iii) “Ferric GR(CO 3 2− )”, a Fe(III) oxyhydroxycarbonate keeping a layered structure similar to that of GR(CO 3 2− ), was the only final product when [Na 2 HPO 4 ] was increased. When phosphate species were present together with Fe 2+ , OH − and HCO 3 − ions before precipitation, the crystallization and growth of GR(CO 3 2− ) particles were inhibited. The intermediate Fe(II–III) product was characterized for the first time. It is amorphous and may consist of nanoparticles showing a local ordering of atoms similar to that of GR(CO 3 2− ), isolated from each other by adsorbed phosphate species. Its oxidation led to ferrihydrite. The effects of phosphate species may also depend on the type of GR considered.

The adsorption of a globular protein on chemically well controlled surfaces was investigated in order to correlate its orientation to the surface properties. To this end, three different alkyl thiols, differing by their end group (-COOH, -CH3, and -NH2), were used to build up self-assembled monolayers (SAMs) on gold substrates. β-Lactoglobulin (βLG) was then adsorbed on these SAMs by immersion in a phosphate buffer solution. The surface modification with alkyl thiols and the subsequent adsorption of proteins were characterized ex situ by polarization modulated infrared reflection-absorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). The adsorption behavior of proteins was also monitored in situ using quartz crystal microbalance with dissipation measurements (QCM-D). Direct evidence regarding the protein orientation in the adsorbed state was obtained by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). Principal component analysis (PCA), performed on the ToF-SIMS results, enables to separate the samples and shows that the proteins display different distributions of amino acids at the surface depending on the conditioning thiol layer. Our results revealed that the adsorption mode of the protein is influenced by the thiol end groups, and specific orientations of the protein on the surface are proposed for the different substrates. © 2013 American Chemical Society.

International audience; In this work, we investigate the influence of crosslinkers on the operational and heat stability of immobilized enzymes on a silanized silicon surface. To this end, glucose-6-phosphate dehydrogenase (G6PDH), a model multimeric enzyme, was attached through bifunctional crosslinkers able to bind covalently the -NH2 in the silane layer and of amine residues in the enzyme. Five bifunctional crosslinkers in the form of "X-spacer-X" were used, differing by the reactive functional groups (X=aldehyde: -CHO, isothiocyanate: -NCS, isocyanate: -NCO), by the nature of the spacer chain (aromatic or aliphatic) or by the geometry (bifunctional groups positioned in meta- or para- on an aromatic ring). A thermostability enhancement has been obtained for enzymes immobilized using 1,4-phenylene diisothiocyanate (PDC) and 1,4-phenylene diisocyanate (DIC). Moreover, using the latter crosslinker, activity was the mostly preserved upon successive uses, thus giving the best operational stability achieved. Changing the geometry of the cross-linker, i.e., 1,4- as compared to 1,3-phenylene diisothiocyanate (PDC and MDC, respectively), has a crucial effect on operational and thermal stabilities. Indeed, among all used crosslinkers, the most important loss was observed for MDC (residual activity after 6 times use is ~16%). Using dialdehyde crosslinkers: glutaraldehyde (GA) and terephtalaldehyde (TE), activity was significantly less well preserved than with DIC and PDC (for GA and TE, a loss of about 50% at 30°C against no loss for PDC and DIC). These effects can be explained by a multipoint attachment model, in which a higher number of anchoring points stabilizes the three-dimensional structure and especially the binding of the two subunits in the active dimer, at the expense of a greater rigidity which is detrimental to the absolute activity. The differences observed with the crosslinkers are mainly due to steric hindrance at the interface which seems to be greatly influenced by the structure and the reactivity of the linkers.

International audience; We investigate the nanoscale organization of a superficially hydroxylated Al substrate and its effect on subsequent protein adsorption using atomic force microscopy (AFM). For this purpose we used a mode which allows a direct mapping of a variety of surface properties (adhesion, elasticity, dissipation, etc.) to be probed simultaneously with topographical images. The hydroxylation treatment leads to a drastic modification of the surface morphology, owing to the formation of AlOOH compounds. In air, AFM images revealed the formation of regular nanorod-like structures randomly distributed, inducing the appearance of nanoporous domains on the surface. In buffer solution, prior to the adsorption of proteins, the surface nanoscale organization is preserved, mainly due to the chemical stability of AlOOH compounds under these conditions. The adsorption of proteins on the obtained nanostructured surface was performed using either a globular (b-lactoglobulin) or a fibrillar (collagen) protein and by modulating the adsorbed amount through the incubation time or the concentration of proteins in solution. At low amounts, collagen adsorbs on the whole surface without preferential localization. The surface topography remains similar to the bare surface, while significant changes were evidenced on adhesion and elasticity maps. This is due to the fact that the surface became adhesive and less stiff, owing to the presence of a soft and hydrated protein layer. By contrast, b-lactoglobulin tends to diffuse into the nanoporous domains, leading to their filling up, and the surface is blurred with a thick and dense protein layer upon increasing the amount of adsorbed molecules. Our findings demonstrate the interest in using AFM for surface mapping to investigate the mechanism of protein adsorption at the nanoscale on materials with high surface roughness.

Biointerfaces, involving peptides or proteins and solid surfaces, have been investigated with the aim of controlling the behavior/reactivity of inorganic materials in biological environments. This chapter presents a comprehensive overview of the basic aspects governing the interaction of short peptides (≤ 3 amino acids) with metal and oxide surfaces. Factors influencing peptide adsorption are defined and exemplified by describing literature results obtained either from model conditions (adsorption of peptides under vacuum) or in the liquid phase. The chemical form of an adsorbed peptide, and thus the possible groups interacting with a solid surface, appears to be strongly dependent on the chemical nature and structure of the surface as well as on the adsorption conditions, e.g. the pH value of peptide solutions. Intermolecular forces also play an important role, sometimes prevailing over surface-peptide interactions, and leading to remarkable, possibly chiral, self-assembling. Some examples also show the role of water molecules upon adsorption and self-assembling. Such a review is expected to help both to understand and anticipate the behavior of peptides on metal and oxide surfaces.

International audience; Adsorption of proteins at interfaces is an ubiquitous phenomenon of prime importance. Layers of poly(ethylene oxide) (PEO) are widely used to repel proteins. Conversely, proteins were shown to adsorb deeply into brushes of poly(acrylic acid) (PAA), and their subsequent partial release could be triggered by a change of pH and/or ionic strength (I). Mixed brushes of these polymers are thus promising candidates to tune protein adsorption onto new smart surfaces. In this work, the synthesis of such mixed brushes was performed based on a "grafting to" approach, the two polymers being either grafted sequentially or simultaneously. Detailed characterization of the obtained brushes using static water contact angle measurements, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and polarization-modulation reflection-absorption infrared spectroscopy is presented. While sequential grafting of the two polymers for different reactions times did not give rise to a broad range of composition of mixed brushes, simultaneous grafting of the polymers from solutions with different compositions allows for the synthesis of a range of mixed brushes (mass fraction of PEO in the mixed brushes from 0.35 to 0.65). A key example is then chosen to illustrate the switchable behavior of a selected mixed PEO/PAA brush toward albumin adsorption. The adsorption behavior was monitored with a quartz crystal microbalance. The mixed brush could adsorb high amounts of albumin, but 86% of the adsorbed protein could then be desorbed upon pH and I change. The obtained properties are thus a combination of the ones of PEO and PAA, and a highly switchable behavior is observed toward protein adsorption.

International audience; We investigate the mechanism of self-assembly of fatty acids (FA) and methyl oleate on an Al oxy-hydroxide surface with a view to deciphering the role and nature of interfacial processes (adsorption, chemical binding, molecular organization, etc.). For this purpose, we focus on parameters related to intrinsic properties of molecules, namely the level of unsaturation and the nature of the head group (carboxylic acid or ester). After the FA adsorption, the presence of coordinative bonded carboxylate species on the Al oxy-hydroxide surface is demonstrated by means of PM-IRRAS analysis. We observe that contact of methyl oleate with the surface leads to its chemical transformation through a saponification reaction. As a consequence, it binds to the surface in a manner similar to that for fatty acids. Through an innovative mode of atomic force microscopy (AFM), the organization of the adsorbed molecules is demonstrated. Our results reveal the existence of highly ordered nanostructures guided by the FA self-assembly. The size of these nanostructures was determined with accuracy, suggesting that it exceeds one FA monolayer. By contrast, no organization was observed with methyl oleate.

International audience; The formation of a Cr-free conversion layer on hot-dip galvanized (HDG) steel involves various interfacial processes which radically influence the composition of the coating and thus its performance. Here, we investigate the role of the main constituents contained in the treatment bath, the polymeric compounds and manganese phosphate species, by using derivative versions from the standard solution. A detailed X-ray photoelectron spectroscopy (XPS) analysis allowed distinction between oxygen originating from polymeric compounds and oxygen of inorganic nature in oxides/hydroxides or phosphate species. Our results revealed that manganese phosphate present in the treatment bath promotes the polymer adsorption on HDG substrate. Angle-resolved XPS and depth profile showed the presence of TiO2 layer on the outer part of the conversion layer, when polymeric compounds are not detected.

Times Cited: 0 Article English Cited References Count: 29 659bp; This paper focuses on the physicochemical characterization and on the electrochemical behaviour of a Cr-free treatment applied on Hot-Dip Galvanized (HDG) steel. The treatment is composed of fluorotitanic acid, manganese phosphate, phosphoric acid and an organic compound Effects of the two major constituents of the solution e the organic phase and manganese phosphate) on the homogeneity, defects, electrochemical behaviour and composition of the conversion layer were investigated For this purpose, electrochemical tests were performed in a 3 5% NaCl medium for HDG samples treated with the standard version of the Cr-free treatment or with derivative versions without either manganese phosphate or the organic compound The conversion coating obtained with the standard Cr-free solution leads to a significant decrease in the corrosion current density (I-corr). On the basis of polarization curves and electrochemical impedance spectroscopy (EIS) analyses, it was shown that it also limits oxygen diffusion to the HDG substrate. In the absence of either manganese phosphate or the organic compound, the surface morphology is noticeably different. Depth profiling analyses using Glow Discharge Optical Emission Spectroscopy (GDOES) indicate the formation of thinner layers when compared with the standard-treated sample. As a consequence, the performance of the conversion layer is significantly affected. (C) 2010 Elsevier B.V. All rights reserved

We investigate the mechanism of polyelectrolyte multilayer (PEM) assembly in nanoporous templates with a view to synthesizing nanotubes or nanowires under optimal conditions. For this purpose, we focus on the effect of parameters related to the geometrical constraints (pore diameter), the size of the macromolecules (their molar mass and the ionic strength), and the interaction between the pore walls and the adsorbed chains (modulated by the ionic strength). Our results reveal the existence of two regimes in the mechanism of PEM growth: (i) the first regime is comparable to that observed on flat substrates, including the influence of ionic strength and (ii) the second regime, which is slower in terms of kinetics, results from the interconnection established between polyelectrolyte chains across the pores and leads to the formation of a dense gel. As a consequence, the diffusion of polyelectrolytes in nanopores becomes the controlling factor of PEM growth in this second regime. The dense gel, owing to its peculiar structure, enhances the formation of nanowires or of partially occluded nanotubes in some cases, depending on initial pore dimensions.

The ennoblement of the free corrosion potential (E-corr) of AISI 316L stainless steel which did not occur in synthetic fresh water (SFW), was observed after introduction of glucose oxidase (Gox) and glucose, or of hydrogen peroxide (H2O2). The composition of the surface was monitored using AFM and XPS, a detailed XPS analysis being based on the discrimination between oxygen of organic and inorganic nature proposed in a previous study. In H2O2 medium, the main changes regarding the inorganic phase were the increase of the oxygen concentration in the passive film, the increase of the molar concentration ratio of oxidized species Fe-ox/Cr-ox and the growth of nanoparticles, presumably made of ferric oxide/hydroxide. In Gox medium, no significant changes were observed in both oxygen concentration and Fe-ox/Cr-ox ratio, but the density of colloidal particles decreased, indicating a dissolution of Fe oxide/hydroxide under the influence of gluconate. In contrast with H2O2, in SFW and Gox the amount of organic compounds increased due to the accumulation of polysaccharides and proteins. The influence of glucose oxidase on the ennoblement of stainless steel is not due to indirect effects of H2O2 through the change of surface composition. The E-corr ennoblement seems to be directly due to the presence of H2O2 and to the electrochemical behavior of H2O2 and related oxygen species. This consideration is important for understanding and controlling microbial influenced corrosion. (C) 2008 Elsevier Inc. All rights reserved.

The evolution of the surface of a conventional stainless steel (AISI 316L) immersed in aqueous medium simulating fresh water (pH similar to 8) was studied using XPS and AFM. A detailed analysis of XPS spectra allowed a distinction to be made between oxygen of organic and inorganic nature. During the first 48 h, the main changes concern the inorganic phase: the oxygen concentration in the passive layer increases, owing both to oxidation of metal elements, including conversion of Fe-II to Fe-III, and to hydration; the molar ratio of oxidized species Fe-ox/Cr-ox decreases slightly; the formation of colloidal particles, presumably made of ferric hydroxide, is observed by AFM. After longer periods of immersion, the Fe-ox/Cr-ox is higher, while the coating of colloidal particles reaches a full surface coverage. The amount of organic compounds increases further and the XPS spectra reveal the accumulation of polysaccharides and proteins, which indicate that these organic compounds are of biological origin. (c) 2007 Elsevier Inc. All rights reserved.

Surface treatments and coatings are the practical approaches used to extend the lifetime of components and structures especially when the surface is the most solicited part of the considered engineering component. Hard thermally sprayed coating is one of the most wear resistance coating widely used in many practical mechanical applications. In the construction of articulating parts of medical devices, titanium and its alloys have to be surface coated to improve their tribocorrosion behavior. In this way, the use of porous thermal coatings is known to be a strategy for better binding bone or tissue on femoral stem for example. It is, thus, important to evaluate the corrosion and the wear behaviors of such materials for biosecurity considerations in the human body. In this study, we investigate the behavior of new nano ZrO2 and Al2O3-13 wt.% TiO2 thermal sprayed coatings on commercially pure (cp)-Ti (grade 4) and titanium alloy substrates. Friction and wear tests against Al2O3 balls showed that the wear resistance of Al2O3-13 wt.% TiO2 is better than that ZrO2 coating. Both plasma sprayings have similar abrasive wear behavior; however, the average friction coefficient is higher for alumina–titania coating. Electrochemical tests, open circuit potential monitoring and potentiodynamic polarization, were performed in simulated body conditions (Hank’s solution, 37 °C). Results showed that corrosion resistance was appreciably higher for alumina–titania coating.