Biomedical subjects

J C Voegel

Publications and source records attributed to J C Voegel.

At least 19 recordsLinked to original sources

PubMed2004

Multilayer polyelectrolyte films functionalized by insertion of defensin: a new approach to protection of implants from bacterial colonization.

Infection of implanted materials by bacteria constitutes one of the most serious complications following prosthetic surgery. In the present study, we developed a new strategy based on the insertion of an antimicrobial peptide (defensin from Anopheles gambiae mosquitoes) into polyelectrolyte multilayer films built by the alternate deposition of polyanions and polycations. Quartz crystal microbalance and streaming potential measurements were used to follow step by step the construction of the multilayer films and embedding of the defensin within the films. Antimicrobial assays were performed with two strains: Micrococcus luteus (a gram-positive bacterium) and Escherichia coli D22 (a gram-negative bacterium). The inhibition of E. coli D22 growth at the surface of defensin-functionalized films was found to be 98% when 10 antimicrobial peptide layers were inserted in the film architecture. Noticeably, the biofunctionalization could be achieved only when positively charged poly(l-lysine) was the outermost layer of the film. On the basis of the results of bacterial adhesion experiments observed by confocal or electron microscopy, these observations could result from the close interaction of the bacteria with the positively charged ends of the films, which allows defensin to interact with the bacterial membrane structure. These results open new possibilities for the use of such easily built and functionalized architectures onto any type of implantable biomaterial. The modified surfaces are active against microbial infection and represent a novel means of local host protection.

Adsorption↗

PubMed2003

Endothelial cells grown on thin polyelectrolyte mutlilayered films: an evaluation of a new versatile surface modification.

Endothelial cell seeding constitutes an appreciated method to improve blood compatibility of small-diameter vascular grafts. In this study, we report the development of a simple innovative technique based on multilayered polyelectrolyte films as cell adhesive substrates. Polyelectrolyte multilayered films ending by poly(sodium-4-styrenesulfonate)/poly(allylamine hydrochloride) (PSS/PAH) or poly(L-glutamic acid)/poly(D-lysine) (PGA/PDL) could enhance cell adhesion by modification of the physico-chemical properties of the surface. The biological responses of human umbilical vein endothelial cells seeded on the polyelectrolyte multilayer films, on PDL or PAH monolayers, and on control surfaces, were evaluated in terms of initial attachment, growth, cellular metabolic activity, endothelial phenotype, and adhesion. The results showed that polyelectrolyte multilayers neither induce cytotoxic effects nor alter the phenotype of the endothelial cells. The polyelectrolyte multilayered films enhanced initial cell attachment as compared to the polyelectrolyte monolayer. Cell growth observed on the films was similar to that on TCPS. Among the different coating tested, the film ending by PSS/PAH exhibited an excellent cellular biocompatibility and appeared to be the most interesting surface in terms of cellular adhesion and growth. Such films could be used to cover hydrophobic (cell resistant) substrates in order to promote cell colonization, thereby constituting an excellent material for endothelial cell seeding.

Biocompatible Materials↗

PubMed2002

[Bioactive films for biomaterial coating and intended for tissue engineering: new original methods?].

Numerous functionalized biomaterials aimed to induce specific cellular or tissular responses have been developed in the last decade. They result often from a specific treatment of the interface of the material. Techniques like physisorption, covalent binding or deposition of a Langmuir-Blodgett film have been employed to modify surface properties. We describe here a novel approach based upon an alternated adsorption of polyelectrolytes (polyanions or polycations) leading to the build-up of a film. These films can be functionalized through protein insertion (ligands) or by covalent peptide bindings able to interact with cellular receptors. Combined with a high affinity for calcium or phosphate complexing properties such functionalized architectures could constitute an original way to favour osseointegration.

Adsorption↗

PubMed2001

Semi-automatized processing of AFM force-spectroscopy data.

Atomic force microscopy operated in the force-spectroscopy mode is now a widespread technique, often used to investigate ligand-receptor interactions with the goal of measuring forces at the individual molecule level. However, in an experiment, the simultaneous interaction of several ligand/receptor pairs cannot be excluded. This may produce complicated force curves, although unambiguous ruptures are sometimes observed. In the case of the non-specific adhesion of molecules, such as fibrinogen, to a surface, it is usually difficult to identify the real events on the force curves. This can render the application of fixed rules uneasy and in addition can introduce some degree of arbitrariness if the analysis has to be performed by hand. In the present paper a computer algorithm, aimed at speeding up the processing, and at applying selection rules in a reproducible manner, is proposed. It is applied to force recordings performed at various retraction velocities, thus various loading rates. The influence on the evaluation of the rupture forces of the different parameters that can be set by the operator is discussed.

Adsorption↗

PubMed2001

Peptide hormone covalently bound to polyelectrolytes and embedded into multilayer architectures conserving full biological activity.

We report the development of new bioactive coatings of biomaterials based on the alternate deposition of oppositely charged polyelectrolytes. We selected polylysine (PLL) and poly(glutamic acid) (PGA) for the polyelectrolytes and murine melanoma cells as a biological test model system. These cells respond specifically to a small peptide hormone, alpha-melanocortin, which is a potent stimulator of melanogenesis. We show that a synthetic alpha-melanocortin derivative, covalently coupled to PLL forming the outer layer of a multilayer film remains as biologically active as the free hormone. Furthermore, the long time activity of the hormone is maintained when embedded in multilayer architectures whereas its short time activity depends on integration depth. The embedding of bioactive molecules not only anchors them irreversibly on the biomaterial, but opens also the possibility to control their activity. In comparison to conventional coating methods, polyelectrolyte multilayers are easy to prepare and retain their biological activity after storage as dry material. These very flexible systems allow broad medical applications for implant and tissue engineering.

Animals↗

PubMed2000

High-resolution electron microscopy study of synthetic carbonate and aluminum containing apatites.

Aluminum (Al)-containing calcium-deficient carbonated hydroxyapatites were produced by a precipitation method from aqueous solution with carbonate (0-6.1%) and aluminum (0.1-0.5%) concentrations close to those found in biological materials. Two series of apatites were prepared: one at pH 7.0 and another at pH 9. 0. High-resolution electron microscopy has shown that many of them possess structural defects such as screw dislocations, grain boundaries, and central defects. Samples with high carbonate content and high water and high Al(3+) content had a high amount of structural defects. Accordingly, a sample (7Al1) with a relatively high carbonate content (6.1%) and a sample (7Al6) without carbonate but with a relatively high water (2.0 mol) and Al(3+) content (0. 39%) presented the highest amount of structural defects, 54% and 47%, respectively. A sample (7Al13) with a low level of crystalline water (1 mol) and low carbonate (2.5%) showed a small amount of defects. The presence of water associated with Al(3+) induced a high number of crystals having a central defect with a great similarity to the so-called water layer of octacalcium phosphate (OCP). Observed images of all these crystals have shown good correspondence with the computer-simulated image based on the crystal structure of hydroxyapatite, indicating that the addition of Al(3+) and carbonate does not perturb the apatitic structure.

Aluminum↗

PubMed2000

Protein interactions with polyelectrolyte multilayers: interactions between human serum albumin and polystyrene sulfonate/polyallylamine multilayers.

The interactions between polystyrenesulfonate (PSS)/polyallylamine (PAH) multilayers with human serum albumin (HSA) were investigated by means of scanning angle reflectometry (SAR). We find that albumin adsorbs both on multilayers terminating with PSS (negatively charged) or PAH (positively charged) polyelectrolytes. On films terminating with PSS only, an albumin equivalent monolayer is found whereas when PAH constitutes the outer layer, albumin interacts with the multilayer in such a way as to form a protein film that extends over thicknesses that can be as high as four times the largest dimension of the native albumin molecule. Once the protein film is formed, it is found that when the albumin solution is replaced by a pure buffer solution of same ionic strength as the adsorption solution almost no desorption takes place. On the other hand, when a buffer solution of higher ionic strength is brought in contact with the albumin film, a significant amount of adsorbed proteins is released. One also observes that, for albumin solutions of a given protein concentration, the adsorbed protein amount depends on the ionic strength of the adsorption solution. On surfaces terminating with PAH, the adsorbed protein amount first increases rapidly but passes through a maximum and decreases with the ionic strength. The ionic strength corresponding to the maximum of the adsorbed albumin amount itself depends on the albumin concentration. On the other hand, on films terminating with PSS the adsorbed amount increases with the salt concentration before leveling-off. These results show that the underlying complexity of concentration and pH dependent adsorption/desorption equilibria often simply termed "protein adsorption" is the result of antagonist competing interactions that are mainly of electrostatic origin. We also propose two microscopic models, that are compatible with our experimental observations.

Adsorption↗

PubMed2000

[Leukocyte adhesion on a fibrinogen-coated surface under static conditions: experimentation and creation of a model].

The adhesion of polymorphonuclear leukocytes (PMNs) on the vascular endothelium is a complex process that occurs during different biological and pathological events and involves numerous molecules. The adhesion cascade is induced after PMN stimulation by various molecular or cellular signals. Fibrinogen is one of the substrates for CD11b/CD18 B2-integrins expressed at the PMN surface; fibrinogen-neutrophil binding is induced by inflammatory reactions. In order to understand this process, we have carried out studies on the basis of preliminary experiments on red blood cells and synthetic particles. The modelization of quiescent PMNs adhesion on a fibrinogen substrate was investigated with a sedimentation cell chamber. Two different physiological conditions were tested: the activated state of PMN by a synthetic pro-inflammatory activator (FMLP). The activated state of PMNs was both quantified by flow cytometry and controlled by fluorescence microscopy. The results suggest that quiescent neutrophils deposit in accordance with the ballistic deposition model. This random adsorption model differs from random sequential adsorption (RSA) in that the cells arriving at the surface are able to roll along cells previously adsorbed introducing the notion of gravitational attraction of cells. The preliminary results obtained with stimulated PMN do not allow to choose between one of this two deposition models. Nevertheless, the qualitative and quantitative effects of FMLP on neutrophils were demonstrated by modifications of adhesion molecules expression.

Antigens, CD↗

PubMed1999

Extended random sequential adsorption model of irreversible deposition processes: from simulations to experiments.

An experimental study of the irreversible deposition of colloidal particles of various radii R on a solid surface is presented over a wide range of the Péclet number, Pe, or reduced radius R* (Pe = R*(4)). The experimental data are analyzed by means of a new generalized random sequential adsorption model that takes explicitly the diffusion of the particles during the deposition into account. It allows description of the continuous transition from a random sequential adsorption-like to a ballistic-like deposition behavior. It depends on three parameters: d(s), related to the diffusion of the particles before adhesion; n(s), related to the number of allowed adhesion trials of a particle; and R(e), representing the effective particle radius. The model allows accounting for all of the experimental observations relative to the radial distribution functions and the number density fluctuations over the whole coverage range and all investigated values of R*. In addition, it is found that d(s)/R is proportional to R*(-2) as expected for a diffusional process. Moreover, the parameters d(s) and n(s) appear to be connected through the empirical relation (d(s)/R)n(s)(2/3) = C, where C is found to be of the order of 50. This unique statistical model allows an accurate description of the irreversible deposition process, whatever the influence of gravity with respect to diffusion.

Journal Article↗

PubMed1999

Matrix-assisted laser desorption ionization mass spectrometry: a new tool for probing interactions between proteins and metal surfaces. Use in dental implantology.

The fixation in the bone of an artificial titanium tooth root is believed to be initiated by the rapid adsorption of the proteins present in the surgical cavity on the titanium surface. The study of this adsorption should make it possible to predict the osseointegration capacities of new implant surface treatments. We describe here a new method, based on matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), for quantifying proteins adsorbed on titanium surfaces fully identical to these designed for implantology. The key step of this method is a new MALDI-MS sample preparation allowing the adsorbed proteins to be removed from the surface and to be homogeneously dispersed in the matrix crystals. The adsorption of a model protein (lysozyme) on two titanium surfaces (polished and sandblasted) was studied in order to evaluate the method. The absolute MALDI-MS intensity was shown to vary linearly with the amount of adsorbed lysozyme. After dipping the titanium surfaces for different times in lysozyme solutions at different concentrations, the maximum amount of adsorbed lysozyme was measured by MALDI-MS and was shown to correspond to a lysozyme monolayer, which is consistent with results described in the literature.

Adsorption↗

PubMed1999

Direct observation of the anchoring process during the adsorption of fibrinogen on a solid surface by force-spectroscopy mode atomic force microscopy.

Atomic force microscopy in a force-spectroscopy mode has been used to investigate the kinetics of the adsorption process of fibrinogen molecules on a silica surface. An original "approach/retraction" cycle of the tip/surface was used for this purpose. Fibrinogen molecules were adsorbed on the atomic force microscopy tip and were brought into contact with the silica surface for different interaction times varying from 5 to 2,000 ms. Multiple consecutive ruptures were observed. The mean number of ruptures nr per cycle increases steadily with the interaction time as well as the mean strength fr which varies from 300 pN for 5 ms to 1,400 pN for 2,000 ms. The minimal interaction time for a fibrinogen molecule to bind strongly to a silica surface during an adsorption process appears to lie between 50 and 200 ms. The histograms of the distances between two consecutive ruptures in one cycle exhibit maxima around 20-25 nm. This length is comparable to the characteristic distance between D and E globules of one fibrinogen molecule and suggests that fibrinogen molecules mainly adsorb through their D and E globules.

Fibrinogen↗

PubMed1999

Dissolution of synthetic hydroxyapatite in the presence of acidic polypeptides.

This article deals with the effect of two acidic polypeptides [polyaspartic acid (PA) and polyglutamic acid (PG)] onto hydroxyapatite (HAP) dissolution by separately considering their influence when they are present only at the HAP interface and when they are both adsorbed and present in the bulk solution. We first determined the amount of adsorbed PA and PG at pH 7.0 and 5.0 onto 10 mg of HAP. Dissolution experiments were performed at pH 5.0 under pH stat conditions by continuously following the consumed protons and released calcium versus time with the aid of specific electrodes. The released phosphate ions were determined by spectrophotometric analysis. The data show that, because of their calcium chelating properties, the polypeptides act as a driving force for HAP dissolution when PA and PG remain present in solution and the interfacial beneficial effect of the adsorbed peptides is erased by the chelating properties of PA and PG present in the solution. When the polypeptides are only adsorbed at the interface, even if a partial PA or PG desorption occurs, HAP dissolution inhibition is still observed.

Adsorption↗

PubMed1999

Characterization and histological analyses of a coral-collagen composite used for bone-replacement graft material: a report of clinical cases.

Several studies, devoted to the osteogenic potentialities of natural CaCO3 have already been reported. However, it seems questionable if the data obtained from natural calcium carbonates can be extrapolated to a composite biomaterial incorporating coralline material. For these reasons, in the present investigations the structural and crystallographic features of the biomaterial (Biocoral gel) were thoroughly analyzed prior to implantation, with the aid of X-ray diffraction and electron microscopy. Then, biopsied samples, taken from Biocoral gel-filled sites, respectively after 7, 8, 9, 12 and 29 mon implantation, were studied with optical and electron microscopy. It could be concluded from the histological analyses of the biopsies, that mineral still remained after long implantation periods. This composite biomaterial may thus be considered for uses in clinical situations where neither incorporation nor dissolution of the implanted biomaterial are essential, i.e. maintenance of edentulous ridge volume.

Journal Article↗

PubMed1999

Extended (n/v)-Stillinger cluster for use in the theory of homogeneous nucleation.

In this paper we develop a theory for an extended version of the (n/v)-Stillinger cluster that has been used in nucleation theory, where n means the number of particles constituting the cluster characterized by the volume v. The "extended cluster" incorporates some of the surrounding supersaturated vapor. This cluster, although requiring more extensive simulation than the original (n/v)-Stillinger cluster, is almost devoid of approximation. It maintains the non-ad-hoc nature of the original (n/v)-Stillinger cluster implicitly. The theory of the cluster is also applicable to clusters which avoid redundancy by some other means than the so-called "connectivity requirement." Simulation of the extended cluster is now being implemented and will be used in the theory of the homogeneous nucleation rate.

Journal Article↗

PubMed1999

Modelisation of leukocyte adhesion on a fibrinogen coated surface in static conditions.

The adhesion of polymorphonuclear leukocytes (PMNs) on the vascular endothelium is a complex process that occurs during biological and pathological events and involves a large family of molecules. This phenomenom could be approached by a modelisation study of the adhesion of PMNs on a biological substrate, fibrinogen. Two different physiological conditions were tested such as the activated state of PMNs with a synthetic pro-inflammatory activator (N-Formyl-Methionyl-Leucyl-Phenylalanine, FMLP). The activated state of PMNs was both quantified by flow cytometry and controlled by fluorescence microscopy. The results suggest that quiescent PMNs deposit in accordance with the ballistic deposition model. The preliminary results obtained with FMLP-stimulated PMNs show a different deposit process compared to quiescent PMNs but do not allow to determine exactly a deposition model.

Activated-Leukocyte Cell Adhesion Molecule↗

PubMed1998

Influence of magnesium substitution on a collagen-apatite biomaterial on the production of a calcifying matrix by human osteoblasts.

The induction of a calcifying matrix is of great interest in the restoration of bone defects. In a previous in vitro study we demonstrated that a collagen sponge constituted of type I collagen fibrils, chondroitin sulfates, and hydroxyapatite crystals induces an earlier and a more abundant synthesis of a new extracellular calcifying matrix than do other biomaterials such as collagen or hydroxyapatite alone. Bone mineral contains various amounts of magnesium ions, either adsorbed at the surface of apatite crystals or incorporated inside the crystal structure. Magnesium is known to reduce the degradation rate of tricalcium phosphate ceramics and to influence the crystallization of mineral substance. Thus we evaluated two sponges modified with different substituted apatites. The substituted low magnesium-containing apatite sample decreased the osteoinductive properties of the sponge whereas the substituted high magnesium-containing apatite sample had a toxic effect on bone cells and prevented the formation of any extracellular matrix. Such a toxic effect can be explained by the presence of large numbers of magnesium ions released into the culture medium even though at physiological level magnesium is able to promote bone mineralization and to control the growth of hydroxyapatite crystals. Thus collagen sponges containing hydroxyapatite remain one of the most appropriately evaluated biomaterials used for the restoration of periodontal pockets and bone defects.

Apatites↗

PubMed1998

First experimental evidence for human dentine crystal formation involving conversion of octacalcium phosphate to hydroxyapatite.

Biological apatite-crystal formation is a complex process starting with heterogeneous nucleation of inorganic calcium phosphate on an organic extracellular matrix [Cuisinier et al. (1995), J. Cryst. Growth, 156, 443-453]. Further stages of crystal growth are also controlled by the organic matrix and both nucleation and growth processes are under cellular control [Mann (1993), Nature (London), 367, 499-505]. The final mineral in calcified tissue is constituted by poorly crystalline hydroxyapatite (HA) with a low Ca:P ratio, containing foreign ions such as carbonate and fluoride. This study reports the first observation of octacalcium phosphate (OCP) [Brown (1962), Nature (London), 196, 1048-1055] in a biological tissue; OCP was found in the central part and HA at the extremities of the same crystal of calcifying dentine. This observation is of key importance in understanding the first nucleation steps of biological mineralization. The presence of OCP in a forming human dentine crystal and the observation in the same tissue of nanometer-sized particles with a HA structure [Houllé et al. (1997), J. Dent. Res. 76, 895-904] clearly proves that two mechanisms, direct nucleation of non-stoichiometric HA crystals and nucleation of OCP, occur simultaneously in same area of mineralization. OCP is found to be a transient phase during the growth of biological crystals. In small crystals, OCP is completely transformed into HA by a hydrolysis reaction (Brown, 1962) and can only be detected in larger crystals because of its slow kinetics of transformation.

Calcium Phosphates↗

PubMed1998

Kinetics of the homogeneous exchange of alpha-lactalbumin adsorbed on titanium oxide surface.

The homogeneous exchange process whereby alpha-lactalbumine molecules adsorbed on hydrophilic titanium oxide particles are replaced by alpha-lactalbumine molecules in solution has been investigated by means of a 125I radio-labeling technique, alpha-lactalbumine is a compact and highly negatively charged protein, making this study complementary to previous work devoted to the general understanding of the exchange mechanisms of adsorbed proteins on solid surfaces. The isotherm of alpha-lactalbumine exhibits bimodal adsorption shape, and the exchange process whereby adsorbed proteins are replaced by new incoming ones from the bulk solution has been studied at both the upper and the lower plateau of the isotherm. In the upper plateau the exchange process was found to be of first order with respect to the bulk molecules, and the release rate constant was equal to 0.914 L. mol-1.s-1. This behavior is identical to what has been observed with other proteinic systems. In the lower plateau domain, in contrast, the protein release process is independent of the concentration of proteins in the bulk, but the release rates are higher than the pure desorption rates. This constitutes, to our knowledge, a behavior that never before has been observed and that remains to be explained.

Adsorption↗