Chemical reactivity assay and surface characterization of a poly(vinylidene fluoride) microfiltration membrane ("Durapore DVPP")

Sur-face functionalization of a commercially available poly(vinylidene fluoride) (PVDF) filtration membrane (Millipore DVPP) was performed using organic synthesis at the solid-liquid interface. Hydroxyl groups present on this hydrophilic membrane were activated by reaction with several activating and coupling agents prior to the covalent grafting of lysine. Transamination was used as well as a grafting method. The apparent surface of the PVDF membrane was characterized using SEM and XPS techniques before and after the wet chemical treatments. On the other hand, chemical reactivity of the open surface was assayed by the coupling to tritiated lysine and liquid scintillation counting (LSC) of the radioactivity associated to the samples. (c) 2004 Elsevier B.V. All rights reserved

Surface hydroxylation of poly(vinylidene fluoride) (PVDF) film

The surface of PVDF film was selectively modified by wet chemistry. Treatment with aqueous LiOH produced HF-elimination and the emergence of an oxygen-containing functionality. The XPS analysis clearly indicated the presence of ketone-, ether(epoxide)-, and alcohol motifs. The percentage of alcohols could be significantly increased by reduction of the ketones with NaBH4 in 2-propanol, followed by reduction of the epoxides with DIBAL-H in hexane. Thus, the full treatment led to a PVDF surface displaying 7 to 16% of oxygen-containing units, of which about 60% consisted in alcohol motifs. The reactvity of the surface-displayed hydroxyl functions was assayed by radiolabeling with [H-3]-Ac2O. (C) 1997 John Wiley & Sons, Inc

Combined Time-of-flight Secondary-ion Mass-spectrometry and X-ray Photoelectron-spectroscopy Study of the Surface Segregation of Poly(methyl Methacrylate) (pmma) in Bisphenol-a Polycarbonate Pmma Blends

Phase segregation at the surface of Bisphenol A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) blends is studied by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF SIMS). Blends with different compositions were solution-casted onto silicon wafers with dichloromethane (CH(2)CL(2)) as the mutual solvent. A sharp PMMA segregation is observed at the surface of the blends. In fact, the quantitative analysis of the XPS data shows that the PMMA surface molar concentration increases first steeply with the PMMA bulk concentration (the surface concentration reaches 70% of PMMA for a 2.5% bulk concentration), and then it continues to increase slowly and saturates for a 38.8% hulk concentration. The ToF SIMS results show that PC remains detected even for high PMMA surface concentration. A semiquantitative ToF SIMS analysis is also presented, which correlated with the XPS results and confirmed the segregation even if matrix effects are detected when the surface concentration of each polymer is comparable. The segregation is explained by the difference of surface tension between the two polymers. The surface morphology is also sampled by the ToF SIMS imaging mode, but no contrast is detected although optical images reveal a two-phase system in the bulk

Reactivity Assay of Surface Carboxyl Chain-ends of Poly(ethylene-terephthalate) (pet) Film and Track-etched Microporous Membranes Using Fluorine Labeled And/or H-3 Labeled Derivatization Reagents - Tandem Analysis By X-ray Photoelectron-spectroscopy (xps) and Liquid Scintillation-counting (lsc)

Poly(ethylene terephthalate) (PET) films and track-etched microporous membranes of two different porosities were pretreated by hydrolysis and/or oxidation in order to enhance the amount of carboxyl chain-ends displayed on their surface. The reactivity of these carboxyl functions was determined by derivatization assays in which the reactions were carried out under conditions likely to be encountered in the coupling of water-soluble biochemical signals on the surface of biomaterials. Original reagents, fluorine-labelled and/or H-3-labelled aminoacid compounds, were used. The derivatized PET samples were examined by X-ray photoelectron spectroscopy (XPS) to characterize their apparent surfaces, and by liquid scintillation counting (LSC) to quantify the amount of tags fixed on their open surfaces. Using this dual assay technique, we analyzed the surface of microporous membranes which are currently used as substrates for cell culture systems

PMMA surface modification under keV and MeV ion bombardment in relation to mammalian cell adhesion

Spin casted poly methyl methacrylate (PMMA) films were submitted to Ga+ (15 keV), Xe+ (4 keV) and He+ (1 MeV) ion bombardments with fluences varying between 10(+12) and 10(+16) ions/cm(2). The surface modifications were studied by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The evolution of ToF-SIMS peaks characteristic of the polymer and of the degradation were followed as a function of the ion fluence. Surface deoxygenation and loss of the methacrylate pendent group were observed. These results are discussed regarding the kind of energy deposition mode (electronic and nuclear). The XPS results confirmed the surface deoxygenation. Finally, the influence of the ion beam modifications on the adhesion of mammalian cells were investigated. For this purpose, the samples were reconditioned by a solution containing both a protein and a surfactant prior to inoculation with human epithelial cells in a serum free nutritive medium. The results showed a preferential cell adhesion in the bombarded areas

Chemical-composition and Physicochemical Properties of Polymer Surfaces

The analysis of polymer surfaces in terms of functional groups can be undertaken by X-ray photoelectron spectroscopy. Correlations between chemical composition and water contact angle indicate the dependence of polymer wettability on the surface concentration of oxygen carrying a high electron density, whatever the specific functional groups present. Electrokinetic methods, which can be applied to plates or films, provide tools for examining the surface electric properties and for detecting ionizable groups at polymer surfaces. Surface characterization provides basic information for understanding the adhesion process through molecular interactions. However the study of polypropylene has shown that adhesiveness is not only influenced by surface properties but also by the deformability of the polymer and, consequently, by its crystallinity and its thermal history

Surface Study of Polycarbonate Membranes Used As a Substratum for Animal-cell Culture

The aim of this work is to investigate the relationships between the chemical composition of a polymer surface and its physico-chemical properties. The study of track-etched membranes was undertaken in order to understand and control better the attachment of epithelial cells for reconstituting a highly differentiated cell tissue. The bis-phenol A polycarbonate membrane surface properties have been modified by various procedures: sulphochromic acid, nitration, oxygen and ammonia radio frequency (rf) glow discharge, corona discharge. The surface chemical composition was determined by x-ray photoelectron spectroscopy and the surface free energy was computed from the contact angle of various liquids. The presence of sulphur and nitrogen-containing groups bound to the surface has been demonstrated after application of the corresponding wet surface treatments. All surface treatments lead to an increase of the oxygen surface concentration, the highest value being obtained after nitration. As a result, the polar contribution to the surface free energy also is increased; this seems to be correlated with the surface concentration of oxygen bearing a high electron density. The cell adhesion and growth on the membranes is improved by the surface treatments applied, in particular by oxygen rf glow discharge. However, steam sterilization tends to remove the effects of earlier surface modifications; this seems to be more pronounced when the sample is in direct contact with liquid water

Multitechnique Study of Hexatriacontane Surfaces Modified By Argon and Oxygen Rf Plasmas - Effect of Treatment Time and Functionalization, and Comparison With Hdpe

Hexatriacontane (C36H74) has been used as a model molecule for the study of the surface modifications of high-density polyethylene (HDPE) in argon and oxygen radio-frequency (RF) plasmas. The combination of static secondary ion mass spectrometry (SIMS), ion scattering spectroscopy (ISS), X-ray photoelectron spectroscopy (XPS), and contact angle measurements has constituted a powerful method for the investigation of the surface modifications induced by the plasma treatments. The surface degradation and functionalization are shown to depend on both the nature of the treated material and the nature of the plasma atmosphere. The SSIMS results obtained on plasma-modified hexatriacontane and HDPE are compared in order to identify the nature of the functionalities present at the plasma-treated surfaces. Finally, plasma treatment 180 atmosphere was performed on HDPE, C36H74, and polystyrene (PS). In that case, the isotopic specificity of both ISS and SIMS allowed the determination of the relative concentrations of O-16 and O-18 in relation to the probed depth and plasma atmosphere

Adhesion to the extracellular matrix is positively regulated by retinoic acid in HepG2 cells

Aims: In this work, we aimed to investigate the possible modulation of cell–matrix interactions by retinoic acid (RA), in view of the well-known role of the extracellular matrix (ECM) and integrins in hepatocyte differentiation and proliferation. For this purpose, we analysed the adhesion ability of HepG2 cells on different substrates in the presence and absence of RA evaluating both the expression and cellular localisation of major proteins involved in focal contacts, using Western blot and confocal microscopy. Results: A positive and substratedependent effect of RA on cell–matrix adhesion was observed after long-term culture. The increased adhesiveness in the treated cells was accompanied by an enhanced expression of b1 and a3 integrin subunits, together with a redistribution of b1 receptors clustered at the basal surface. In contrast, the levels of focal adhesion kinase (FAK), paxillin and a-actinin were unchanged, as was the phosphorylation state of FAK. Nonetheless, a stronger association between b1 integrin and intracytoplasmatic proteins of focal contacts was observed in coimmunoprecipitation experiments after RA treatment, suggesting improved connection with the actin cytoskeleton.These results are consistent with previously described antiproliferative and differentiative effects of RA on transformed hepatocytes, and confirm the hypothesis of a direct influence of RA on specific adhesion molecules