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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.

Glass and stainless steel (StSteel, AISI304-2R), previously cleaned with ethanol (-Eth) or with ethanol and UV–Ozone treatment (-UVO), were soiled with quartz suspensions in water and in a β-lactoglobulin (β-LGB) solution, and dried. The cleanability (ease of quartz particle detachment) in water was evaluated using a radial-flow cell. The soiling suspension containing β-LGB was used as such or after heating for 4 h at 75 °C, which provoked coagulation of about 75% of β-LGB. The substrate–solution interfaces were characterized by X-ray photoelectron spectroscopy (XPS) analysis of conditioned substrates and by contact angle measurements. The substrate surfaces are covered by a layer of organic contaminants which are not removed by pre-cleaning or are adsorbed from the surroundings. The presence of β-LGB in the soiling suspension leads to protein adsorption, but a significant amount of contaminants remains at the surface. For three of the substrates tested (Glass-Eth, Glass-UVO, StSteel-UVO) the increase of cleanability when the soiling suspension contained β-LGB may be explained by lower capillary forces acting upon drying. Capillary forces are proportional to the liquid surface tension and depend in a less important way on substrate contact angle. However the order of cleanability observed for the substrates soiled with a suspension of quartz particles in water (Glass-Eth≅Glass-UVO

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.

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.

Grafting silicon wafers with CH(3)O(CH(2)CH(2)O)(n)C(3)H(6)-trimethoxysilane and -trichlorosilane (n=6 to 9) was performed in different conditions (solvent, reaction time, washing) in order to select procedures compatible with the design of nanostructured surfaces for biomaterial applications, using electron-beam lithography. After a first screening by principal component analysis (PCA), the X-ray photoelectron spectroscopy (XPS) data were analyzed by plotting the carbon to oxygen molar ratio vs the molar ratio of carbon singly bound to oxygen [CO] over carbon bound only to carbon and hydrogen [C(C,H)]. This was found to be a convenient method for discarding samples containing free polymerized silane. Such excess occurred as a result of insufficient washing or unsuitable solvent for the reaction (ether), as confirmed by AFM and thickness measured by X-ray reflectometry. Angle resolved XPS analysis indicated that the grafted silane layer had a 1-2 nm thickness and was covered by a thin layer of adventitious contaminant. As a result, the surface chemical composition obtained covered a broad range (O/C of 0.4 to 1.1; CO/C(C,H) of 2.5 to 6.5); variations could not be related to the nature of the silane reagent and no significant difference was found between hexane and toluene as solvent for the reaction. The grafted silane layer was not stable upon incubation during 24 h in phosphate buffered saline (PBS) at 37 degrees C, which mimics biological environments. As a consequence, the grafted wafers did not show protein repellent properties. This alteration was not observed at room temperature. XPS analysis demonstrated that silane layer detachment was due to a hydrolysis within the SiO(2) layer initially present at the wafer surface.

The adsorption of collagen (type I from calf skin) was studied, comparing different collagen sources and using substrates which differ according to surface hydrophobicity (polystyrene, either native, with OH substitution of each repeat unit, with COOH substitution of a small fraction of repeat units, or surface modified by oxygen plasma discharge). The atomic force microscopy observation of the adsorbed layers showed that aggregation in the solution acts in competition with the formation of fibrils in the adsorbed phase; more aggregated solutions behave like less concentrated solutions regarding adsorption. The fibrils formed in the adsorbed phase are much smaller than the fibrils formed in the suspension, and, in contrast with the latter, do not show regular band pattern. It is confirmed that fibrils formation occurs more readily on more hydrophobic surfaces, which is tentatively attributed to a greater mobility of individual molecules adsorbed on more hydrophobic substrates. This interpretation is supported by previously published radiochemical measurements. However, the comparison of strongly different adsorption procedures (progressive on the one hand; quick and massive on the other hand) did not provide any additional clue.

Collagen (type I from calf skin) adsorption on polystyrene (PS) and plasma-oxidized polystyrene (PSox) was studied, using a quartz crystal microbalance with energy dissipation measurements (QCM-D) and atomic force microscopy (AFM) in tapping mode. Radio-labeled collagen was used to measure the adsorbed amount and the ability of adsorbed collagen to exchange with molecules in the solution. The results show that the collagen adlayer consists of two parts: a dense and thin sheet in which fibrils are formed (directly observed by AFM) and an overlying thick layer (up to 200 nm) containing protruding molecules or bundles which are in very low concentration but modify noticeably the local viscosity. The thickness and viscosity of the semi-liquid adlayer both increase with adsorption time and collagen concentration. Fibril formation near the surface also increases with time and collagen concentration and occurs more readily on PS compared to PSox. Radiochemical measurements show that this may be related to the larger mobility of molecules adsorbed on PS, presumably owing to a smaller number of binding points.

PAN-based carbon fibres obtained by carbonisation at relatively low temperature and submitted to high-temperature treatment and oxidation in wet conditions provided a range of materials differing according to surface composition and hydrophobicity. The adsorption of catalase by these fibres was studied by XPS and by activity measurements in the liquid and in the adsorbed state. Three typical situations are featured: limited adsorbed amount in the case of low hydrophobicity; significant adsorption and preservation of an appreciable enzyme activity for samples of moderate hydrophobicity; strong adsorption with deactivation of the enzyme in the case of high hydrophobicity.

The treatment of stainless steel surfaces with responsive polymers was investigated using X-ray photoelectron spectroscopy and scanning electron microscopy. Poly (N-isopropylacrylamide) (PNIPAAM) is a temperature-sensitive polymer which is soluble in water below 32 degrees C (Lower Critical Solubility Temperature (LCST)) but collapses and aggregates above 32 degrees C. This polymer was adsorbed at 50 degrees C from solutions at different concentrations, followed by rinsing and different drying procedures. Thereby, a large variety of surface structures could be obtained, from smooth films to surfaces showing marked relief features due to residues of PNIPAAM aggregates. Two poly(styrene)b-poly(acrylic acid), PS-PAA, with different block lengths, were spin-coated on stainless steel and showed preferential exposure of PS blocks at the outermost surface. PNIPAAM-conditioning was shown to strongly reduce yeast cell adhesion and to facilitate the removal of oil soil due to its high water affinity and chain mobility below the LCST. PS-PAA coatings also reduced yeast cell adhesion; this may partly be due to a reorganization of the surface, leading to exposure of PAA chains in contact with water and thus to electrostatic repulsion of the yeast cells.

The supramolecular organization of collagen adsorbed from a 7 microg/ml solution on polystyrene was investigated as a function of the adsorption duration (from 1 min to 24 h) and of the drying conditions (fast drying under a nitrogen flow, slow drying in a water-saturated atmosphere). The morphology of the created surfaces was examined by atomic force microscopy (AFM), while complementary information regarding the adsorbed amount and the organization of the adsorbed layers was obtained using radioassays, X-ray photoelectron spectroscopy (XPS), and wetting measurements. The collagen adsorbed amount increased up to an adsorption duration of 5 h and then leveled off at a value of 0.9 microg/cm2. For samples obtained by fast drying, modeling of the N/C ratios obtained by XPS in terms of thickness and surface coverage, in combination with the adsorbed amount, water contact angle measurements and AFM images, indicated that the adsorbed layer formed a felt starting from 30 min of adsorption, the density and/or the thickness of which increased with the adsorption time. Upon slow drying, the collagen layers formed after adsorption times up to about 2 h underwent a strong reorganization. The obtained nanopatterns were attributed to dewetting, the liquid film being ruptured and adsorbed collagen being displaced by the water meniscus. At higher adsorption times, the organization of the collagen layer was similar to that obtained after fast drying, because the onset of dewetting and/or collagen displacement were prevented by the high density of the collagen felt.

The adsorption of collagen on polystyrene (PS) and polystyrene oxidized by oxygen plasma discharge (PSox) was studied as a function of time using radiolabeling, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Radiolabeling and XPS indicated that the initial step of adsorption was faster on PS than on PSox. AFM imaging under water revealed very different supramolecular organization of the adsorbed films depending on time and on the nature of the substrate: PS showed patterns of collagen aggregates at all adsorption times (from 1 min to 24 h); PSox was covered with a smooth layer except at long adsorption times (24 h), for which a mesh of collagen structures was observed. After fast drying, the collagen layer remained continuous and showed a morphology which recalled that observed under water. The mechanical stability of the adsorbed films was assessed under water by scraping with the AFM probe at different loading forces: no perturbations were created on PSox; in contrast, the layer adsorbed on PS was sensitive to scraping, the minimum force required to alter the collagen layer morphology increasing with time. These differences in the film properties were correlated with force measurements upon retraction: multiple adhesion forces were observed with collagen adsorbed on PS samples, whereas such an effect was never observed on PSox. The results show that the amount adsorbed and the organization of the adsorbed film respond differently to the adsorption time and that this is influenced by surface hydrophobicity. The quick initial adsorption on PS, compared to PSox, is thought to leave dangling collagen segments that are responsible for the observed morphology, for adhesion forces, and for lower mechanical resistance of the adsorbed layer.

Adsorption of collagen (300 nm length, 1.5 nm diameter) on poly(ethylene terephthalate) and the influence of Pluronic PE6800, a triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer, were investigated by the combination of three techniques. The adsorbed amounts of the two adsorbates were determined by radiolabeling. X-ray photoelectron spectroscopy was used to get quantitative information on the adsorbed layer. Selected samples were observed by atomic force microscopy (AFM) under water and in air; data on morphology, mechanical resistance, and molecular interactions were obtained. In the absence of Pluronic, two collagen layer morphologies were observed. Under water, at an adsorbed amount equal to half the maximum, collagen formed a dense granular layer; at the maximum adsorbed amount (equivalent to six layers of lying molecules), the adsorbed layer was soft, appeared as a pattern of elongated structures, and showed adhesion of the AFM probe with rupture lengths as long as several hundred nanometers. This was attributed to collagen molecules or bundles protruding into the solution. After fast drying, the collagen layer was smooth with a low surface fraction occupied by holes at the lower protein adsorbed amount, while it showed spindle-shape relief features at the maximum adsorbed amount. In the presence of Pluronic, the amount of adsorbed collagen was reduced considerably, due to rapid adsorption of the surfactant. In these conditions, the collagen layer obtained from high protein concentration solutions was also constituted by granules and was very sensitive to the alteration by the AFM probe.

PAN-based carbon fibres carbonised at relatively low temperature, i.e. type III carbon fibres, were submitted to heat treatment at 2300 °C (GR) or oxidation in nitric acid. The samples were characterised by XPS, FTIR, wetting measurements, gas adsorption, elemental analysis and acid/base titration. While oxidation only slightly affects the nitrogen concentration, it produces an appreciable change in the nature of the chemical functions, namely the conversion of pyridine-type nitrogen and quaternary nitrogen into aliphatic functions. Oxidation treatment modifies all the material constituting the fibre, the oxygen concentration being about 1.5 times higher at the fibre external surface compared with the whole material. Three components (531.2, 532.6 and 533.8 eV) are clearly identified in the oxygen XPS peak, allowing a comparison to be made between the whole material and the external surface regarding chemical species. The acidic groups are mainly carboxyl. Fibres submitted to extensive oxidation also show a high basicity, attributed mainly to calcium carboxylate. Although the acidic and basic groups present in the whole material can be titrated with aqueous solutions, the fibres develop only a very small surface area and no microporosity as determined by krypton adsorption. The material may be viewed as a sponge, collapsed when dry but able to swell in water and developing a high cation-exchange capacity.

To evaluate the influence of substratum surface characteristics on protein adsorption processes, we have investigated the adsorption (adsorbed amount, supramolecular organization) of collagen on model substrata exhibiting controlled topography and surface chemistry. Substrata were prepared in two steps: (i) gold deposition onto silicon wafers (smooth substrata) and onto a support with nanoscale protrusions created by colloidal lithography (rough substrata); (ii) functionalization with CH3 (hydrophobic) and OH (hydrophilic) groups, using alkanethiol self-assembly. Atomic force microscopy (AFM) images were recorded under water, prior to and after collagen adsorption, and the images were analyzed quantitatively using two independent approaches. On smooth substrata, collagen formed a similar to6 nm thick, homogeneous layer with low roughness on hydrophilic surfaces, and a similar to20 nm thick layer exhibiting elongated aggregated structures on hydrophobic surfaces. Film thickness measurements (AFM) together with X-ray photoelectron spectroscopy (XPS) revealed larger adsorbed amounts on hydrophobic surfaces compared to hydrophilic ones. On rough substrata, the adsorbed amounts were similar to those found on smooth substrata; however, the collagen molecules no longer formed aggregated structures on the hydrophobic surfaces. It is concluded that while the adsorbed amount is only affected by the surface chemistry, the supramolecular organization of the adsorbed layer is controlled both by surface chemistry and topography. The approach presented here will have great value in biophysics for investigating bioadsorption and bioadhesion processes on substrata of defined surface properties.

The influence of substrate hydrophobicity and biomacromolecules (dextran, bovine serum albumin – BSA) adsorption on the cleanability of surfaces soiled by spraying aqueous suspensions of quartz particles (10–30 lm size), then dried, was investigated using glass and polystyrene as substrates. The cleanability was evaluated using radial flow cell (RFC). The surface composition was determined by X-ray photoelectron spectroscopy (XPS). The interpretation of XPS data allowed the complexity due to the ubiquitous presence of organic contaminants to be coped with, and the surface composition to be expressed in terms of both the amount of adlayer and the mass concentration of adlayer constituents. When soiled with a suspension of particles in water, glass was much less cleanable than polystyrene,which was attributed to its much lower water contact angle, in agreement with previous observations on starch soil. Dextran was easily desorbed and did not affect the cleanability. The presence of BSA at the interface strongly improved the cleanability of glass while the contact angle did not change appreciably. In contrast, soiling polystyrene with quartz particles suspended in a BSA solution instead of water did not change markedly the cleanability, while the contact angle was much lower and the aggregates of soiling particles were more flat. These observations are explained by the major role of capillary forces developed upon drying, which influence the closeness of the contact between the soiling particles and the substrate and, thereby, the adherence of particles. The capillary forces are proportional to the liquid surface tension and depend in a more complex way on contact angles of the particles and of the substrate. The dependence of cleanability on capillary forces, and in particular on the liquid surface tension, is predominant as compared with its dependence on the size and shape of the soiling aggregates, which influence the efficiency of shear forces exerted by the flowing water upon cleaning.

Adsorption of collagen on polystyrene (PS) and plasma-oxidized PS (PSox) was investigated using atomic force microscopy (AFM) as the main tool. The extent of alteration produced by the AFM tip upon scanning at controlled loading forces in water was used to obtain semiquantitative information on the properties of the interfacial phase. This information was completed by observing the extent of reorganization of the adsorbed collagen layer after drying. The PSox surface was altered by scanning at high loading force in water. This behavior, which was not observed on PS, was attributed to the presence of a solvated polyelectrolyte layer at the surface of PSox, as demonstrated by previous works. Collagen adsorbed on PS gathered together under the action of the AFM tip while no perturbation was observed for collagen adsorbed on PSox. After drying at low rate of a thin adsorbed collagen layer, a netlike structure was formed on PS, in contrast with PSox. These differences were attributed to the formation of a dense, mechanically strong mat of collagen molecules adsorbed on PSox and/or to anchoring of collagen molecular ends in the swollen surface layer of PSox, in contrast with PS.

The collagen layer formed by adsorption of collagen on native (PETn) and surface oxidized poly(ethylene terephtalate) (PETox) was studied by X-ray photoelectron spectroscopy and atomic force microscopy (AFM). On PETox, for adsorption times up to a few hours. the collagen molecules form a network, the nodes of which seem to be responsible for a dot-like morphology, On PETn, at very short adsorption times and consequently low surface coverages, the adsorbed molecules are displaced by the AFM tip. This effect reveals lower interactions between the collagen and the surface after drying compared to PETox. At higher coverages, the surface morphology is similar to that obtained for PETox. After an adsorption time of 24 h, an aggregation of collagen molecules is observed for both substrates. The results are discussed with regard to the interactions between collagen and the substrate in water, the events occurring during the drying process and the mobility of collagen molecules in the dry state, (C) 2001 Elsevier Science B.V. All rights reserved.

The surface of oxygen-plasma-treated polystyrene (PSox) was investigated using X-ray photoelectron spectroscopy (XPS), streaming potential measurements and a dynamic study of the wetting properties at different pH (Wilhelmy plate method). The PSox surface is functionalized with various oxygen-containing groups, including carboxyl functions, and must be viewed as covered by a poly-electrolyte which swells depending on pH. The wetting hysteresis, its evolution upon repeated cycles and the influence of pH are controlled by the dissolution of functionalized fragments and the retention of water upon emersion; the retained water may evaporate progressively and allow macromolecule compaction and/or reorientation. Modification of the PSox surface upon aging in dry atmosphere, humid atmosphere, and water was studied using XPS and dynamic wetting measurements. Aging in water provoked the dissolution of PSox macromolecular chains, as indicated by adsorption of released fragments on a check PS sample placed nearby. However, the concentration of functionalized molecules at the surface of water-aged PSox was still sufficient to allow swelling at pH 5.6 and 11.0. Hydrophobicity recovery was faster in humid air (R. H. 95%) compared to dry air (R. H. 5%), due to the plasticizing effect of water. Hydrophobicity recovery upon aging in air was reversed quickly by immersion at pH 5.6 or 11.0, due to deprotonation and swelling.

Collagen adsorbed on poly(methyl methacrylate) (PMMA) was investigated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle measurement, after either fast drying or slow drying. Quantification by :XPS of the amount of adsorbed collagen is shown to be influenced by the drying procedure; This is explained by AFM images, which reveal the formation of a net-like structure at slow drying rates. Comparison between the surface organization, as observed by AFM, surface models provided by XPS and contact angle measurements, indicates that chemically heterogeneous surfaces are produced at slow drying rates, PMMA being exposed at the outermost surface in the holes left by the collagen net. (C) 1999 Society of Chemical Industry.

Atomic force microscopy (AFM) has been used to investigate the organization of the collagen layer present on polymer substrata after adsorption and drying, while the adsorbed amount was monitored using X-ray photoelectron spectroscopy (XPS) and radiochemical measurements. Differences in the organization of the adsorbed collagen layer (surface coverage, layer thickness) observed by AFM fitted well with those found by models obtained from XPS and radiolabeling data. (C) 1999 Elsevier Science B.V. All rights reserved.

Atomic force microscopy (AFM) imaging and force-distance curves have been used to investigate, in situ, the nanoscale organization of collagen adsorbed on polymer substrata covering a wide range of surface roughness and surface hydrophobicity: bisphenol A polycarbonate (PC), poly(ethylene terephthalate) (PET), and poly(vinylidene difluoride) (PVdF) used as such or treated by an oxygen plasma discharge (ox). After collagen adsorption, PC and PCox showed patterned structures under water, the size of which was influenced by substratum surface oxidation. These structures are attributed to aggregated ends of collagen molecules. Extended rupture lengths were observed in the force-distance curves, suggesting that bundles of collagen molecules adhere to the AFM probe and are progressively torn out upon probe retraction. In contrast, on PET, PETox, PVdF, and PVdFox, adsorbed collagen formed a smooth, homogeneous film devoid of any topographic feature, and no extended rupture lengths were observed. After drying, holes in the collagen film were observed on PET and PVdF and not on PETox and PVdFox. The influence of substratum roughness and physicochemical properties is discussed, considering the mobility of collagen molecules at the interface.

The adsorption of catalase on calcium hydroxyapatite is reported in this study. In all the solutions investigated, catalase adsorption takes place under conditions where the adsorbent and the adorbate are both negatively charged and is accompanied by the release of phosphate ions. This suggests that electrostatic attraction does not play a leading role in the adsorption process. However, electrostatic repulsion does play a role as evidenced by the influence of the solution composition on the maximum amount adsorbed. In fact, the amount adsorbed increases when the surface charge tends to be less negative (decrease of pH and phosphate concentration, presence of calcium) or when the electrical charges are screened as a result of the ionic strength increase. This was confirmed by the electrophoretic mobility which becomes more negative after protein adsorption. The rate of catalase adsorption is extremely low; the time required to reach a stationary concentration is 60 and 125 h in potassium nitrate and phosphate solution, respectively. The reversibility of catalase was examined with respect to changes in the bulk solution concentration. No significant desorption was obtained after several days of observation. The adsorption, desorption, and kinetic aspects have been discussed in relation to changes in the the protein structure upon interaction and to the microstructural characteristics of the mineral. Copyright 1998 Academic Press.

The influence of Pluronic F68 [a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer surfactant], serum albumin (HSA), and fetal calf serum (FCS) on the adsorption of type I collagen by polymer substrates was investigated using radiolabeling and XPS analysis. Three different kinds of polystyrene substrates with increasing level of hydrophobicity were used. Change in the state of hydration of the sorbent and protein surfaces appears to be the main driving force for collagen adsorption. Pluronic F68 strongly reduces collagen adsorption, the reduction being more pronounced with higher substrate hydrophobicity. This explains why epithelial cell adhesion on substrates preconditioned with a solution of Pluronic F68 and collagen is strongly influenced by substrate hydrophobicity. Collagen adsorption is also reduced in the presence of HSA and FCS, but the reduction and its sensitivity to substrate hydrophobicity are lower than with Pluronic F68.

Carbon black is tested as a support for iron-phthalocyanine within the frame of the oxidation of hydrocarbons with t-butyl-hydroperoxide as oxygen donor. The increased hydrophobicity of the carrier surface, with respect to zeolite Y, changes the adsorption behavior of the components in the reaction mixture towards the alkane. A major improvement in the oxidation conversion and efficiency of cyclohexane has been established, Furthermore, the kinetic isotope effect and the reactivity order of secondary and tertiary carbon atoms measured with adamantane provide evidence for an ''oxygen rebound'' reaction mechanism, a non-free-radical oxidation pathway where the metallo-complex is responsible for the hydrogen abstraction. (C) 1996 Academic Press, Inc.

The adhesion of the soil bacterium Azospirillum brasilense to polystyrene has been investigated using a parallel-plate chamber in conditions allowing cell transport to the support by sedimentation and rinsing under controlled hydrodynamic conditions. The adhesion pattern, which was heterogeneous, and the density of adhering cells were determined by cell aggregation at the support surface and detachment of aggregates upon rinsing. Determination of the support surface composition by X-ray photoelectron spectroscopy after detachment of adhering cells and analysis of the supernatant of cell suspensions revealed that, during the course of adhesion, extracellular proteins are released progressively into the aqueous phase and adsorb at the support surface. Support preconditioning by contact with a cell suspension promoted adhesion after a short contact time (2 h) due to protein adsorption at the support surface. Cell ageing prior to the adhesion test also enhanced adhesion after 2 h due to protein accumulation at the cell surface. Moreover, when supports were preconditioned and when cells were aged prior to the test, adhesion was still dependent on cell-support contact time, which pointed to the influence of in situ secretion of proteins by the adhering cells. It was therefore concluded that the role played by proteins at the cell-support interface is twofold. In the first stage, proteins accumulate at the cell surface, are liberated into the solution and adsorb at the support surface; the increase of the protein concentration at the interface promotes initial adhesion. In the next stage, in situ secretion of proteins during the prolonged contact between the cells and the support strengthens adhesion.

The influence of ionic strength on the adhesion of Azospirillum brasilense to polystyrene has been examined by comparing water and phosphate buffer saline (PBS) as suspending media. Polystyrene supports analysed by X-ray photoelectron spectroscopy (XPS) after adhesion in PBS for 2 h or 24 h and detachment of adhering cells showed a higher protein surface concentration, reflected by the N/C atomic concentration ratio, compared to supports analysed after adhesion in water. It was shown that PBS both favours protein release by the cells into the solution and enhances the tendency of proteins to adsorb at the support surface. After 2 h contact time, the increase in the concentration of adsorbed proteins in PBS was related to an increase in adhesion density. However, the observation that the adhesion density after 24 h was lower in PBS than in water indicated that the amount of proteins adsorbed at the support surface controls cell adhesion in a complex way. In PBS, a thick layer of proteinaceous material retaining the bacterial cells is formed; this leads to underestimation of the density of adhering cells as well as to a heterogeneous adhesion pattern and to a relatively low adhesion density due to detachment of pellicles upon rinsing. The ionic strength thus influences bacterial adhesion in a more subtle way than simply through double layer interactions between the cells and the support.

The influence of substratum surface hydrophilicity and of a surfactant on human epithelial cell adhesion and protein adsorption was investigated. Therefore, tissue culture grade polystyrene (TCPS) and bacteriological grade polystyrene (BGPS) substrata were treated with different media, with or without Pluronic F68 [a poly(ethylene oxide) and poly(propylene oxide) triblock copolymer surfactant], and with or without type I collagen as a typical extracellular matrix protein. The conditioned substrata were submitted to XPS analysis and assayed for cell adhesion by inoculating Hep G2 cells in a chemically defined nutritive medium. The presence of collagen at the substratum surface is required to obtain attachment and spreading of Hep G2 cells. With PS substrata, treating with a solution of collagen does not promote cell adhesion if the solution contains Pluronic; XPS data show that this is due either to prevention of collagen adsorption or to its desorption by rinsing. With less hydrophobic TCPS substrata, the presence of Pluronic in the conditioning solution does not preclude cell adhesion, nor collagen adsorption. The effect of BGPS and TCPS substrata on Hep G2 cell adhesion is thus mediated by the presence of a surfactant that affects the adsorption of collagen.

Homologous series of carbon samples were prepared from a non-porous thermal carbon black by oxidation with various concentrations of hydrogen peroxide at 95 degrees C. The samples were characterized by X-ray photoelectron spectroscopy, gas adsorption, and electrophoretic mobility measurement; the enzymatic activity of catalase adsorbed on the carbons blacks was also examined. No significant variation of texture was produced by oxidation. The oxygen surface concentration increased as a function of the H2O2 concentration up to 0.8 M, and tended to decrease above this concentration; this is attributed to the competition between surface modification and release of products of oxidation. The surface was found to be more negative as the oxygen concentration increased. The specific activity of catalase adsorbed (degree of coverage about 0.5%) on non-oxidized carbon is much lower that the specific activity of dissolved catalase, indicating a modification of the enzyme conformation in the adsorbed slate. The activity increases with the oxygen surface concentration; this is attributed to a weaker interaction with the surface, due to its lower hydrophobicity, or a stronger contribution of electrostatic repulsion. Catalase activity measurements appear as a promising way to probe carbon surface properties.

From bioengineering to optics and electronics, a great deal of work has been conducted on the development of new materials with structured surfaces. A large range of methods has been used, such as plasma etching, electron beam and colloidal lithography (Denis et al., 2002), electrical deposition (Yang et al., 2009), phase separation (Dekeyser et al., 2004) and polyelectrolyte assembly in order to produce structured surfaces (Agheli et al., 2006). The combination of different methods is also more and more explored. Schaak et al. (2004) described a simple approach to achieve colloidal assembly on a patterned template obtained by lithography. Densely packed layers of colloidal particles can be produced by lifting a substrate vertically from a suspension (Fustin et al., 2004; Li J. et al., 2007) or by spin coating (Yang et al., 2009). Colloidal lithography utilizes the ability of particles to adhere on oppositely charged surfaces (Johnson & Lenhoff, 1996; Hanarp et al., 2001, 2003)), possibly using surface modification by inorganic or organic polyelectrolytes. The surface coverage is influenced by several factors: ionic strength, particle size and time. The adhesion of microbial cells on various substrates was also achieved by surface treatments with inorganic or organic polycations (Changui et al., 1987; Van haecht et al., 1985) or with positively charged colloidal particles (Boonaert et al., 2002). A review on colloidal lithography and biological applications was published recently (Wood, 2007). Adsorption of polyelectrolytes is influenced by ionic strength, pH and the polyelectrolyte characteristics (molecular mass, charge density) (Lindquist & Stratton, 1976; Davies et al., 1989; Choi & Rubner, 2005). At low ionic strength, highly charged polyelectrolytes adopt extended conformations and are fairly rigid due to the strong repulsion between charged units. The maximum adsorbed amount and the adsorbed layer thickness do not vary markedly according to molecular weight. As the salt concentration is increased and the electrostatic intrachain repulsion is decreased, the polyelectrolyte becomes more coiled. In this case, the maximum amount adsorbed (expressed in mass) increases as a function of molecular weight (Roberts, 1996; Lafuma, 1996; Claesson et al., 2005; Boonaert et al., 1999). Build up of polyelectrolyte films may be achieved using layer-by-layer assembly through alternating adsorption of oppositely charged polyelectrolytes (Decher & Hong, 1991).

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 surface properties of calcium-deficient hydroxyapatites (HAps) prepared under different synthesis conditions (e.g. by precipitation at pH 10, or by hydrolysis of dicalcium phosphate at pH 6.5) were studied. All the products tested were pure, well crystallized calcium-deficient HAps. The samples prepared under slightly acidic conditions exhibit larger crystallite sizes and higher calcium deficiency compared with those prepared under alkaline conditions. Electrophoretic mobilities were measured as a function of pH in 1.0 x 10(-3) M KNO3 aqueous solutions. The isoelectric points (iep) of HAp appear to depend strongly on the synthesis conditions; iep values of 4 were found for samples prepared under more acidic conditions, while values ranging from 5.5 to 7.2 were found for solids precipitated from alkaline solutions. The adsorption of hen egg-white lysozyme was measured at ambient temperature, in 1.0 x 10(-3) M KNO3 aqueous solutions buffered at pH 6.8 with 2.0 x 10(-3) M phosphate buffer. The parameters of the Langmuir-type adsorption isotherms were found to depend significantly on the specific surface of the samples; the monolayer coverage goes through a maximum of 40 x 10(-9) mol m-2 at S(BET) = 80 m2 g-1, while the affinity constant culminates at 355 mM-1 at the same value of S(BET). The decay of both monolayer coverage and affinity constant beyond S(BET) = 80 m2 g-1 can be ascribed partly to the lower accessibility of smaller pores to lysozyme molecules, particularly when electrostatic repulsion exists between the lysozyme molecules and the HAp surface. It is thought that specific bonds between lysozyme and the hydroxyapatite surface must exist, which are very sensitive to the nature and the relative amounts of crystallographic planes exposed on the solid surface.

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 470 nm 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 F 68 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 F 68 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 blood compatibility of materials is primarily governed by the presence of Fg in the adsorbed phase, as a result of the competition with other plasma proteins. This is in turn strongly influenced by surface hydrophobicity. Surface nanostructuration as performed here (relief in the range of 50-500 nm) did not affect significantly the relationship between Fg adsorption and platelet adhesion.

International audience; 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.

The overall properties of the cell surface of Streptococcus thermophilus and Leuconostoc mesenteroides, two fouling microorganisms from dairy industry, were determined by a variety of physico-chemical methods. The study was carried out as an interlaboratory comparison to identify seemingly unimportant but yet critical steps in the experimental methods, i.e., contact-angle measurements, electrophoresis, X-ray photoelectron spectroscopy (XPS) and transmission Fourier-transform IR spectroscopy (FTIR). Particularly with regard to the contact-angle measurements, it turned out that the original papers, in which the technique was explained, did not contain enough detail. On the basis of the present experience, more emphasis is put on a slow preparation of bacterial samples and monitoring of the drying process by contact-angle measurements. Furthermore, the known importance of the suspending buffer in zeta potentials becomes extremely obvious since one of the strains employed preferentially adsorbed K+ from the buffer. Artefacts created during freeze-drying for XPS and FTIR analyses are mentioned. It is pointed out that the above four methods form a unique set of techniques for studying microbial cell surfaces, in the sense that the results of the various methods allow an interpretation of the physico-chemical properties of the cells in terms of their chemical composition.

A range of substrates made of polystyrene (PS) and poly(methyl methacrylate)-poly(methacrylic acid) copolymer (PMMA-PMAA) containing 98 and 80% PMMA (PA98, PA80) and presenting a homogeneous or a patterned surface were used to study fibronectin adsorption and neuronal cell behavior. Fibronectin adsorption showed weak differences regarding the adsorbed amount (evaluated by XPS), but large differences in adsorbed layer morphology as observed by AFM. A fine granular morphology, with dimensions up to 8 nm height and 50-150 nm width, was observed on top of a thin adsorbed layer in the case of PS, PA98, and of a surface made of nanoscale inclusions of the latter in PS. In contrast, the layer adsorbed on PA80, which carries more ionizable groups, showed a higher roughness on the PA80 zones with differences in height up to 30 nm and characteristic lateral dimensions of 400 nm. On substrates of the former category, the cells formed large clusters, revealing poor interactions with the substrate. On PA80, the cells formed large networks with only a few small clusters. The adsorbed layer roughness, resulting from aggregation of fibronectin upon adsorption and from the substrate surface chemical composition, is responsible for neuronal cell spreading and growth. Its effect is not prevented by the presence of inclusions (< 30% of the surface) responsible for smoother areas of adsorbed fibronectin and for protrusions below 40 nm. (c) 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008.

The cleaning of cellulosic hemodialysis membrane Cuprophan and model materials (glass; polystyrene and polypropylene, as such and surface-oxidized), conditioned by adsorption of blood plasma proteins (HSA, fibrinogen, IgG) was investigated in vitro. Sodium hypochlorite (NaClO) and Renalin, a product containing hydrogen peroxide and peroxyacetic acid, were used as cleaning reagents. X-ray photoelectron spectroscopy and the use of radiolabeled fibrinogen demonstrated the presence of varying amounts of a polypeptidic residue, with sulfur brought to a high oxidation stage (sulfonate-like). The trends were the same for the three proteins regarding the effectiveness of the oxidizer and the influence of the surface properties. NaClO was much more effective than Renalin to remove the adsorbed proteins. The proteins adsorbed on Cuprophan were more sensitive to the oxidizers, when compared with proteins adsorbed on other materials. This may be due to both the lower protein-surface affinity, as indicated by radiochemical measurements, and the sensitivity of the material itself to the oxidizer, as revealed by weight loss measurements. These results support the attribution of hemocompatibility improvement after regeneration of Cuprophan with Renalin to the masking of the activating surface by a residue from previously adsorbed proteins.

Adsorption (at 37 degrees C) of type I collagen, in native and heat-denatured (30 min at 40 and 90 degrees C) forms, on polystyrene was studied using quartz crystal microbalance with energy dissipation monitoring (QCM-D), atomic force microscopy (AFM) in tapping mode and X-ray photoelectron spectroscopy (XPS). The significance of the parameters deduced from QCM-D data was examined by comparing different approaches. The adsorbed layer of native collagen has a complex organization consisting of a thin mat of molecules near the surface, in which fibrils develop depending on concentration and time, and of a thicker overlayer containing protruding molecules or bundles which modify noticeably the local viscosity. As a result of drastic denaturation, the ability of collagen to assemble into fibrils in the adsorbed phase is lost and the protrusion of molecules into the aqueous phase is much less pronounced. The adsorbed layer of denatured collagen appears essentially as a monolayer of flattened coils. At low concentration, this is easily displaced upon drying, leading to particular dewetting figures; at high concentration, aggregates add to the first layer. Moderate denaturation leads to an adsorbed phase which shows properties intermediate between those observed with native and extensively denatured collagen, regarding the ability to form fibrillar structures and the adlayer thickness and viscosity.

The behavior of endothelial cells (HUVECs) in contact with thin collagen films presenting different supramolecular organizations was investigated. Collagen was adsorbed on polystyrene (PS) and plasma-oxidized PS (PSox) in conditions ensuring the formation of continuous layers presenting an increasing density of fibrillar structures. Discontinuous collagen layers were also prepared on PS by adsorption followed by dewetting. The morphology of the obtained collagen films was checked by using atomic force microscopy. HUVECs adhesion was evaluated in terms of cell number, cell area, cell shape, and actin structure after 4 h of contact with the prepared collagen layers. In the presence of serum, no adhesion was observed on PS, whereas a substantial adhesion was found on PSox. This is explained by the competition for adsorption, which turns in favor of adhesive proteins secreted by the cells on the hydrophilic PSox, but turns in favor of serum albumin on the hydrophobic PS. The progressive coating of PS by smooth collagen films increased cell adhesion and spreading. However, cell spreading and cytoskeleton organization were adversely affected by the appearance of a high density of collagen fibrillar structures. This latter trend was similarly observed on PSox. On the other hand, HUVECs spreading and cytoskeleton organization were clearly enhanced on discontinuous collagen layers compared with continuous ones. A possible explanation for these observations lies in the modification of exposure and/or spatial distribution of recognition sequences due to spontaneous collagen self-assembly on fibril formation or to collagen aggregation on dewetting.

The supramolecular organisation of collagen adsorbed on polymer substrates was investigated as a function of properties of the substrates (chemical nature, roughness) and of characteristics of the collagen solution (concentration, state of aggregation) as well as details of the preparation procedure (adsorption time, drying rate). Elongated structures are formed at the interface by assembly of collagen molecular segments protruding into the solution. This is favoured by using a hydrophobic and smooth substrate, by increasing the adsorbed amount and by increasing the adsorption time, even beyond stages at which the adsorbed amount does no longer vary. Collagen adsorbed at low amount on hydrophobic substrates strongly reorganises into a net-like pattern if drying is performed at low rate. This is due to dewetting and collagen displacement by the water meniscus. Applications derived from the control of collagen organisation are presented. Nanostructured polymer surfaces were created starting from a collagen template. The attachment and the cytoskeletal organisation of mammalian cells (MCF-7/6) were also shown to depend on collagen organisation.

In the last years, adsorbed collagen was shown to form layers with a supramolecular organization depending on the substrate surface properties and on the preparation procedure. If the concentration of collagen and the duration of adsorption are sufficient, fibrillar collagen structures are formed, corresponding to assemblies of a few molecules. This occurs more readily on hydrophobic compared to hydrophilic surfaces. This study aims at understanding the origin of such fibrillar structures and in particular at determining whether they result from the deposition of fibrils formed in solution or from the building of assemblies at the interface. Therefore, type I collagen solutions with an increasing degree of aggregation were prepared, using the "neutral-start" approach, by ageing pH 5.8 solutions at 37 degrees C for 15 min, 2 or 7 days. The obtained solutions were used to investigate the influence of collagen aggregation in solution on the supramolecular organization of adsorbed collagen layers, which was characterized by X-ray photoelectron spectroscopy and atomic force microscopy. Polystyrene and plasma-oxidized polystyrene were chosen as substrates for the adsorption. The size and the density of collagen fibrils at the interface decreased upon increasing the degree of aggregation of collagen in solution. This is explained by a competitive adsorption process between monomers and aggregates of the solution, turning at the advantage of the monomers. More aggregated solutions, which are thus depleted in free monomers, behave like less concentrated solutions, i.e. lead to a lower adsorbed amount and less fibril formation at the interface. This study shows that the supramolecular fibrils observed in adsorbed collagen layers, especially on hydrophobic substrates, are not formed in the solution, prior to adsorption, but are built at the interface, through the assembly of free segments of adsorbed molecules.

The nanometer-scale organization of collagen (type I) adsorbed on polystyrene (PS) and plasma-oxidized PS (PSox) was investigated using atomic force microscopy (AFM) as well as radioassays and X-ray photoelectron spectroscopy. The surface properties induced by plasma treatment of PS were examined: PSox was more hydrophilic than PS, owing to oxygen incorporation, and was covered by a layer of polyelectrolyte which could be swollen by water. Collagen adsorbed on PS formed elongated structures, the density and the height of which increased with the adsorption duration. On PSox, a smooth and homogeneous collagen layer was formed after up to 2 h of adsorption, but elongated structures appeared after 24 h. A similar contrast was found between CH3- and OH-terminated self-assembled monolayers, indicating the role of surface hydrophilicity. The adsorption duration affected the nanostructure of adsorbed collagen layers, not only through the adsorbed amount but also owing to reorganizations of the adsorbed phase. Compared with collagen adsorbed on PSox, collagen adsorbed on PS was more easily picked up for attachment to the AFM probe and more easily displaced along the surface plane by scanning with the atomic force microscope or by drying. This suggests that collagen molecules adsorbed on PS leave segments protruding into the solution, while they form a felt of lying molecules on PSox. The observed elongated structures may be due to association of collagen segments, and/or to particular interactions with the atomic force microscope probe. The respective importance of these two mechanisms may depend on the chemical nature of the substratum. Nanostructured collagen layers offer attractive perspectives to control mammalian cell response or as a template to create nanostructured polymer surfaces.

The adsorption of poly(N-isopropylacrylamide) (PNIPAAM), a well known thermosensitive polymer, on glass was investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The polymer was dissolved in water at low (0.02 g/L) and high (2 g/L) concentration and the tested temperatures were below (25 degrees C) and above (50 degrees C) the lower critical solubility temperature (LCST). Whatever the conditions, a smooth layer of adsorbed molecules spread along the surface was observed. The thickness was about twice higher for high concentration compared to low concentration. The cohesion in the adsorbed layer, as revealed by scraping tests performed by AFM, was higher above the LCST than below the LCST. On top of this adsorbed layer, single-chain coils, globules, or aggregates were present, depending on concentration and temperature. The observation of these additional adsorbed entities was poorly reproducible, presumably due to the lack of shear control upon rinsing. These results emphasize the importance of the characterization of surface morphology to interpret amounts of adsorbed polymers.

A new pathway for the radiolabeling of Pluronic PE6800 was developed. In a first step, the CH(2)-OH end groups of the copolymer were substituted by tosylates; in a second step these were reduced by [3H]-NaBH(4) to obtain tritiated chain ends. The final product was shown to be a mixture of native, tosylated, and reduced Pluronic containing 1 tritium atom per 1110 Pluronic molecules. The labeling procedure did not affect the molecular weight distribution nor the adsorption isotherm of the copolymer on polystyrene plates. A plateau value of about 0.7 microg/cm(2) is reached at a concentration in solution of 500 microg/ml, i.e., much lower than the cmc. Upon drying, the Pluronic adsorbed layer reorganizes in particles with a size of about 30 to 60 nm which cover about 15% of the substratum surface. This observation is of great importance for the design of protein-resistant surfaces by adsorption of Pluronic.

Terminology Methods to Study Microbial Adhesion Physicochemical Aspects of Primary Adhesion Complexity of Microorganism—Substratum Interfaces Keywords: adhesion of microorganisms onto surfaces; adsorption; attachment of microorganisms; immobilization of microorganisms on solid substrata; retention of microorganisms on solid substrata; surfaces

High-resolution patterns of grooves have been made in poly(methyl methacrylate) films, PMMA, by an electron-beam microlithographic process. The surface of films processed over a large width was characterized in terms of chemical composition (X-ray photoelectron spectroscopy (XPS). time of flight secondary ion mass spectroscopy), wettability (sessile drop) and topography (atomic force microscopy). Collagen adsorption was also studied (radiocounting, XPS) as such or in competition with Pluronic F68. The chemical alteration of the surface induced by the electron-beam irradiation disappeared after the dissolution involved in the development process. W138 human fibroblasts cultivated on microgrooved substrata (grooves 1 microm deep and 0.5-10 microm wide) showed a strong orientation parallel to the grooves. The contact guidance is induced by the topography of the surface and not by the alternation of zones with different physico-chemical properties. It may be explained in terms of probability of successful substratum contact by cell protrusions.

The adsorption of gossypol, a toxic pigment and the major colorant in cottonseed oil, has been studied, using silicas and aluminas of different surface areas and pore size distributions. Gossypol has a high affinity for alumina surface, the adsorption isotherm follows the Langmuir equation, and the maximum amount adsorbed is compatible with a monolayer of molecules on the surface; this is indicative of chemisorption. The affinity for a silica surface is much lower and the adsorption isotherm follows the Freundlich equation. The amount adsorbed is also influenced by the pore size distribution, the useful surface area being that developed by pores larger than 3 nm, i.e., 2 to 3 times the size of the adsorbate. Copyright 2000 Academic Press.

The adhesion of Hep G2 cells was investigated using different substrata (commercial substrata, polystyrene modified by oxygen or ammonia plasma discharge), the surface properties of which were characterized (surface chemical composition, water contact angle, zeta potential). Some substrata were pre-conditioned with solutions of extracellular matrix (ECM) protein (collagen, laminin, fibronectin), solutions of albumin or polylysin, fetal calf serum or culture medium. The culture medium contained the surfactant Pluronic F68; cycloheximide was added in certain tests to inhibit protein synthesis. Cells spread within 1.5 h provided ECM proteins were present at the surface. Adsorption of ECM proteins was subject to competition with adsorption of Pluronic F68. When the substratum was exposed simultaneously to ECM protein and Pluronic F68, either by pre-conditioning or through protein cell secretion, a weaker substratum hydrophobicity favored adsorption of the proteins and subsequent cell adhesion. On the other hand, when ECM proteins were pre-adsorbed, they were not displaced by Pluronic F68 and cell adhesion was not influenced by substratum hydrophobicity. When ECM proteins were present, no difference was observed between substrata of similar hydrophobicity carrying positive or negative charges, respectively. In absence of ECM proteins, the presence of cationic sites at the substratum surface (NH3 plasma treatment, adsorption of polylysine) allowed cell attachment but no spreading within 1.5 h.

The study of the adsorption of type I collagen from a solution containing Pluronic F68 has shown that the latter prevents collagen adsorption on polystyrene and does not prevent it on surface-oxidized polystyrene. This explains the control of mammalian cell adhesion by substrate surface hydrophobicity and composition of pre-conditioning solution. On that basis, selective adhesion of different types of mammalian cells (PC12 pheochromocytoma, MSC80 schwannoma, Hep G2 hepatoblastoma, rat hepatocytes) on patterned surfaces was achieved. Therefore tracks (width in the range of a few tens of microm) of reduced hydrophobicity were produced on polystyrene by photolithography and oxygen plasma treatment. After conditioning by a solution containing both Pluronic F68 and extracellular matrix protein (collagen, fibronectin), the latter adsorbed selectively on these paths thus allowing selective adhesion of the cells.