Biomedical subjects

J-C Voegel

Publications and source records attributed to J-C Voegel.

4 recordsLinked to original sources

PubMed2003

Modeling of the detachment of a molecule from a surface: illustration of the "Bell-Evans effect".

This article deals with the modeling of the detachment of a molecule initially adsorbed on a surface and submitted to an external force whose strength increases with time. By means of an atomic force microscope (AFM), it is possible to measure the force when the molecule separates from the substrate. However, it is known that this force depends to a large extend on the rate at which the pulling force is applied ("Bell-Evans effect"). Two models are described to illustrate this behavior. First, a random walk approach is suggested to reveal the fundamental principle of the escape over a time-dependent energy barrier. Second, a multi bead-and-spring model is proposed to mimic the AFM experiment and numerical simulations, based on Brownian dynamics, are performed.

Binding Sites↗

PubMed2002

Molecular basis for the explanation of the exponential growth of polyelectrolyte multilayers.

The structure of poly(l-lysine) (PLL)/hyaluronan (HA) polyelectrolyte multilayers formed by electrostatic self-assembly is studied by using confocal laser scanning microscopy, quartz crystal microbalance, and optical waveguide lightmode spectroscopy. These films exhibit an exponential growth regime where the thickness increases exponentially with the number of deposited layers, leading to micrometer thick films. Previously such a growth regime was suggested to result from an "in" and "out" diffusion of the PLL chains through the film during buildup, but direct evidence was lacking. The use of dye-conjugated polyelectrolytes now allows a direct three-dimensional visualization of the film construction by introducing fluorescent polyelectrolytes at different steps during the film buildup. We find that, as postulated, PLL diffuses throughout the film down into the substrate after each new PLL injection and out of the film after each PLL rinsing and further after each HA injection. As PLL reaches the outer layer of the film it interacts with the incoming HA, forming the new HA/PLL layer. The thickness of this new layer is thus proportional to the amount of PLL that diffuses out of the film during the buildup step, which explains the exponential growth regime. HA layers are also visualized but no diffusion is observed, leading to a stratified film structure. We believe that such a diffusion-based buildup mechanism explains most of the exponential-like growth processes of polyelectrolyte multilayers reported in the literature.

Chemical Phenomena↗

PubMedDate not supplied

Secondary structure of proteins adsorbed onto or embedded in polyelectrolyte multilayers.

The structural changes of bovine serum albumin (BSA) and hen egg white lysozyme (HEL) upon their adsorption onto the surface or their embedding into the interior of poly(allylamine hydrochloride)-(poly(styrenesulfonate) (PAH-PSS) multilayer architectures were investigated by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The presence of the polyelectrolytes seems, as previously observed for fibrinogen (J. Phys. Chem. B 2001, 105, 11906-11916), to prevent intermolecular interactions and, thus, protein aggregation at ambient temperature. The secondary structure of the proteins was somewhat altered upon adsorption onto the polyelectrolyte multilayers. The structural changes were larger when the charges of the multilayer outer layer and the protein were opposing. The adsorption of further polyelectrolyte layers onto protein-terminated architectures (i.e., embedding the proteins into a polyelectrolyte multilayer) did not cause considerable further changes in their secondary structures. The capacity of the polyelectrolyte architectures to delay the formation of intermolecular beta-sheets upon increasing temperatures was not uniform for the studied proteins. PSS in contact with HEL could largely prevent the heat-induced aggregation of HEL. In contrast, PAH had hardly any effect on the aggregation of BSA. The differences are explained on the basis of protein-polyelectrolyte interactions, affected mostly by the nature and the strength of the ionic interactions between the polyelectrolyte-protein contact surfaces.

Adsorption↗

PubMedDate not supplied

Cell interactions with polyelectrolyte multilayer films.

The short-term interactions of chondrosarcoma cells with polyelectrolyte multilayer films built up by the alternate adsorption of poly(L-lysine) (PLL) and poly(L-glutamic acid) (PGA) was studied in the presence and in the absence of serum. The films and their interaction with serum proteins were first characterized by means of optical waveguide lightmode spectroscopy, quartz crystal microbalance, and zeta potential measurements. In a serum-containing medium, the detachment forces measured by the micropipet technique were about eight times smaller on PGA-ending than on PLL-ending films. For these latter ones, the adhesion force decreased when the film thickness increased. In a serum-free medium, the differences between the negative- and positive-ending films were enhanced: adhesion forces on PLL-ending films were 40-100% higher, whereas no cellular adherence was found on PGA-terminating films. PGA-ending films were found to prevent the adsorption of serum proteins, whereas important protein adsorption was always observed on PLL-ending films. These results show how cell interactions with polyelectrolyte films can be tuned by the type of the outermost layer, the presence of proteins, and the number of layers in the film.

Blood Proteins↗