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Philippe Lavalle

Publications and source records attributed to Philippe Lavalle.

10 recordsLinked to original sources
PubMed2006

From exponential to linear growth in polyelectrolyte multilayers.

There exist two types of polyelectrolyte multilayers: those whose thickness increases linearly with the number of deposition steps, which are nicely structured, and those whose thickness increases exponentially, which resembles hydrogels. This simple picture has recently slightly evolved with the finding that some exponentially growing films enter into a linear growth phase after a certain number of deposition steps. In this study, we investigate the buildup process of hyaluronic acid/poly(L-lysine) (HA/PLL) multilayers that constitute one of the best known exponentially growing systems. The films are built by using two deposition methods: the well-known dipping method and the more recent spraying method where the polyelectrolyte solutions are sprayed alternately onto a vertical substrate. The goal of this study is twofold. First, we investigate the influence of the main parameters (i.e., spraying rate and spraying time) of the spraying method on the film growth process. We find that, as for the dipping method, the film thickness first evolves exponentially with the number of deposition steps, and after a given number of deposition steps, it follows a linear evolution. We find that similar behavior is observed with the dipping method. Second, because the spraying method allows the very fine variation of the different parameters of the buildup, we use this method to investigate the exponential-to-linear transition. We find that this transition always takes place after about 12 deposition steps whatever the values of the parameters controlling the deposition process. We discuss our results in light of a model proposed by Hübsch et al. (Hübsch, E.; Ball, V.; Senger, B.; Decher, G.; Voegel, J. C.; Schaaf, P. Langmuir 2004, 20, 1980-1985) and later by Salomäki et al. (Salomäki, M.; Vinokurov, I. A.; Kankare, J. Langmuir 2005, 21, 11232-11240) in which it is assumed that the exponential-to-linear transition is due to a film restructuring that progressively forbids the diffusion of one of the polyelectrolytes constituting the film over part of the film. This "forbidden" zone then grows with the number of deposition steps so that the outer zone of the film that is still concerned with diffusion keeps a constant thickness and moves upward as the total film thickness increases.

Journal Article↗
PubMed2006

Control of drug accessibility on functional polyelectrolyte multilayer films.

A surface coating based on polylysine/hyaluronic acid multilayers was designed and acted as a reservoir for an antiproliferative agent, paclitaxel (Taxol). Absolutely no chemical modification of polyelectrolytes or of the drug was needed and the final architecture was obtained in an extremely simple way using the layer-by-layer method. The paclitaxel dose available for human colonic adenocarcinoma cells HT29 seeded on the films could be finely tuned. Moreover, the accessibility of the drugs was controlled by adding on the top of the drug reservoir a capping made of synthetic polyelectrolyte multilayers. This capping was also required to allow adhesion of HT29 cells. Paclitaxel activity was maintained after embedding in the polyelectrolyte multilayers and cellular viability could be reduced by about 80% 96 h after seeding. The strategy described in this paper could be valuable for various other drug/cell systems.

Antineoplastic Agents, Phytogenic↗
PubMed2006

Immunogold detection of types I and II chondrocyte collagen fibrils: an in situ atomic force microscopic investigation.

Chondrocyte tissue engineering is a major challenge in the field of cartilage repair. The phenotype of chondrocytes consists of cartilage specific proteoglycan and type II collagen. During serial passages, chondrocytes dedifferentiate into cells, presenting a fibroblast-like phenotype consisting predominately of type I collagen synthesis. Observation of native collagen fibers could be visualized by atomic force microscope. Here, we developed an original and useful atomic force microscopy-based immunogold technique allowing biochemical distinction between types I and II collagen fibers. Imaging of 40-nm gold particles staining collagen fibers was performed in tapping mode. Rat 1 fibroblasts and human chondrosarcoma cells were used as positive models for types I and II collagen, respectively. As demonstrated by our data, primary rat chondrocytes adhering for 48 h on a glass substrate synthesize type II collagen native fibers. This technique allows analyses of local areas of the extracellular matrix of fixed cells, providing complementary data about cartilage phenotype. This simple approach could be of major interest for the biologist community in routine laboratory investigations, to localize in situ, macromolecules of the extracellular matrix.

Animals↗
PubMed2006

Polyelectrolyte multilayer films as substrates for photoreceptor cells.

Reconstruction of extracellular matrix substrates for delivery of functional photoreceptors is crucial in pathologies such as retinal degeneration and age-related macular degeneration. In this study, we assembled polyelectrolyte films using the layer-by-layer deposition method. The buildup of three different films composed of poly(L-lysine)/chondroitin sulfate (PLL/CSA), poly(L-lysine)/poly(styrenesulfonate) (PLL/PSS), or poly(L-lysine)/hyaluronic acid (PLL/HA) was followed by means of quartz crystal microbalance measurements, optical waveguide light mode spectroscopy, confocal microscopy, and atomic force microscopy. The exponential growth regime and the diffusion of PLL chains from the bulk through the PLL/CSA, PLL/PSS, and PLL/HA films was examined. Evaluation of photoreceptor cell viability was optimal on one layer of PLL (PLL(1)), followed by 10 bilayers of PLL/HA [(PLL/HA)(10)] and 10 bilayers of PLL/CSA [(PLL/CSA)(10)]. The number of bilayers and the type of terminating layer also had a significant influence on the number of photoreceptor cells attached. Functionalized polyelectrolyte multilayer films were obtained by adsorbing basic fibroblastic factor (bFGF) or the insoluble fraction of interphotoreceptor matrix (IPM) on or within polyelectrolyte multilayers. bFGF and IPM adsorption on top of the (PLL/CSA)(10)/PLL polyelectrolyte films increased the number of photoreceptor cells attached and maintained the differentiation of rod and cone cells.

Animals↗
PubMed2005

Polyelectrolyte multilayers and degradable polymer layers as multicompartment films.

Polyelectrolyte multilayers are now a well established concept with numerous potential applications in particular as biomaterial coatings. To timely control the biological activity of cells in contact with a substrate, multicompartment films made of different polyelectrolyte multilayers deposited sequentially on the solid substrate constitute a promising new approach. In a first paper (Langmuir 2004, 20, 7298) we showed that such multicompartment films can be designed by alternating exponentially growing polyelectrolyte multilayers acting as reservoirs and linearly growing ones acting as barriers. In the present study, we first demonstrate however that these barriers composed of synthetic polyelectrolytes are not degraded despite the presence of phagocytic cells. We propose an alternative approach where exponentially growing poly(L-lysine)/hyaluronic acid (PLL/HA) multilayers, used as reservoirs, are alternated with biodegradable polymer layers consisting in poly(lactic-co-glycolic acid) (PLGA) and acting as barriers for PLL chains that diffuse within the PLL/HA reservoirs. We first show that these PLGA layers can be deposited alternatively with PLL/HA multilayers leading to polyelectrolyte multilayer/hydrolyzable polymeric layer films and acting as a reservoirs/barriers system. Bone marrow cells seeded on these films ending by a PLL/HA reservoir rapidly degrade it and internalize the PLL chains confined in this reservoir. Then the cells degraded locally the PLGA barrier and internalize the PLL localized in a lower (PLL/HA) compartment after 5 days of seeding. By changing the thickness of the PLGA layer, we hope to be able to tune the time delay of degradation. Such mixed architectures made of polyelectrolyte multilayers and hydrolyzable polymeric layers could act as coatings allowing us to induce a time scheduled cascade of biological activities. We are currently working on the use of comparable films with compartments filled by proteins or peptides and in which the degradation of the barriers results from a hydrolysis over tunable time scales.

Journal Article↗
PubMed2005

Natural polyelectrolyte films based on layer-by layer deposition of collagen and hyaluronic acid.

The aim of the present work was to assemble extracellular matrix components into polyelectrolyte multilayers using the layer-by-layer deposition method. The films are constructed with type-I collagen and hyaluronic acid. The construction exhibits the general features observed during polyelectrolyte multilayer buildup: alternate positive and negative values of the zeta potential of the film during its construction and regular increase of the film thickness with the number, n, of deposition step. This increase is shown to be linear with n. As expected for a linearly growing film, the confocal microscopy shows that when the film is brought in contact with a collagen solution, collagen does not diffuse into the film but interacts only with its outer layer. However, the films are not constituted of homogeneously distributed polyanion/polycation complexes as it is usually observed, but they are formed of fibers as imaged by AFM. The typical width of these fibers increases with the number of deposition steps. Finally, it is found that chondrosarcoma cells spread well and synthesize extracellular matrix components only on the collagen ending films, whereas no cellular matrix was found for HA ending ones. Such architectures may be further functionalized by inclusion of active drugs, peptides, proteins..., and could be used as tunable biomaterial interfaces.

Biocompatible Materials↗
PubMed2004

Multicompartment films made of alternate polyelectrolyte multilayers of exponential and linear growth.

The layer by layer deposition process of polyelectrolytes is used to construct films equipped with several compartments containing "free polyelectrolytes". Each compartment corresponds to a stratum of an exponentially growing polyelectrolyte multilayer film, and two consecutive compartments are separated by a stratum composed of a linearly growing multilayer that acts as a barrier preventing polyelectrolyte diffusion from one compartment to another. We use hyaluronic acid/poly(L-lysine) as the system to build the compartments and the poly(styrene sulfonate)/poly(allylamine) system for the barrier. Using confocal microscopy, it is shown that poly(L-lysine) diffuses only within the compartment in which it was initially introduced during the film construction and is thus unable to cross the barriers. Using fluorescein isothiocyanate as a pH indicator, it is also shown that although poly(styrene sulfonate)/poly(allylamine) multilayers act as a barrier for polyelectrolytes, they do not prevent proton diffusion through the film. Such films open the route for multiple functionalization of biomaterial coatings.

Journal Article↗
PubMed2004

Layer by layer buildup of polysaccharide films: physical chemistry and cellular adhesion aspects.

The formation ofpolysaccharide films based on the alternate deposition of chitosan (CHI) and hyaluronan (HA) was investigated by several techniques. The multilayer buildup takes place in two stages: during the first stage, the surface is covered by isolated islets that grow and coalesce as the construction goes on. After several deposition steps, a continuous film is formed and the second stage of the buildup process takes place. The whole process is characterized by an exponential increase of the mass and thickness of the film with the number of deposition steps. This exponential growth mechanism is related to the ability of the polycation to diffuse "in" and "out" of the whole film at each deposition step. Using confocal laser microscopy and fluorescently labeled CHI, we show that such a diffusion behavior, already observed with poly(L-lysine) as a polycation, is also found with CHI, a polycation presenting a large persistence length. We also analyze the effect of the molecular weight (MW) of the diffusing polyelectrolyte (CHI) on the buildup process and observe a faster growth for low MW chitosan. The influence of the salt concentration during buildup is also investigated. Whereas the CHI/HA films grow rapidly at high salt concentration (0.15 M NaCl) with the formation of a uniform film after only a few deposition steps, it is very difficult to build the film at 10(-4) M NaCl. In this latter case, the deposited mass increases linearly with the number of deposition steps and the first deposition stage, where the surface is covered by islets, lasts at least up to 50 bilayer deposition steps. However, even at these low salt concentrations and in the islet configuration, CHI chains seem to diffuse in and out of the CHI/HA complexes. The linear mass increase of the film with the number of deposition steps despite the CHI diffusion is explained by a partial redissolution of the CHI/HA complexes forming the film during different steps of the buildup process. Finally, the uniform films built at high salt concentrations were also found to be chondrocyte resistant and, more interestingly, bacterial resistant. Therefore, the (CHI/HA) films may be used as an antimicrobial coating.

Animals↗
PubMedDate not supplied

Improvement of stability and cell adhesion properties of polyelectrolyte multilayer films by chemical cross-linking.

Poly(L-lysine)/hyaluronan (PLL/HA) films were chemically cross-linked with a water soluble carbodiimide (EDC) in combination with a N-hydroxysulfo-succinimide (NHS) to induce amide formation. Fourier transform infrared spectroscopy confirms the conversion of carboxylate and ammonium groups into amide bonds. Quartz crystal microbalance-dissipation reveals that the cross linking reaction is accompanied by a change in the viscoelastic properties of the films leading to more rigid films. After the cross-linking reaction, both positively and negatively ending films exhibit a negative zeta potential. It is shown by fluorescence recovery after photobleaching measured by confocal laser scanning microscopy that cross-linking dramatically reduces the diffusion of the PLL chains in the network. Cross linking also renders the films highly resistant to hyaluronidase, an enzyme that naturally degrades hyaluronan. Finally, the adhesion of chondrosarcoma cells on the films terminating either with PLL or HA is also investigated. Whereas the non cross-linked films are highly resistant to cell adhesion, the cells adhere and spread well on the cross-linked films.

Cell Adhesion↗