Papers by Author: P. Chevallier

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Authors: Alejandra Reyna-Valencia, P. Chevallier, D. Mantovani
Abstract: Collagen hydrogels are widely used as three-dimensional scaffolds for cells and tissue in culture environments. These materials, which consist of crosslinked biopolymer (protein-based) networks in aqueous media, are particularly suitable for recreating part of the extra-cellular matrix, but their poor mechanical properties represent a major limitation. One strategy to enhance the strength of this kind of hydrogels might be to incorporate clay nanoscopic particles. In fact, it has been observed that the charged surface of clay nanosheets can interact with certain functional groups belonging to polymer molecules, yielding stronger networks. Moreover, clay particles are recognized to be biocompatible. In the present work, the gelation process and the resulting morphological and mechanical properties of collagen/laponite clay nanocomposite hydrogels were invastigated. Upon gelation, the biopolymer molecules assemble into nanoscale fibrils, which bundle into fibers and entangle into a three-dimensional network. The network characteristics depend on tunable parameters such as pH and clay concentration.
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Authors: Maryse Touzin, P. Chevallier, Stéphane Turgeon, Paula Horny, D. Mantovani
Abstract: Commonly made of 316L stainless steel and nitinol, metallic intravascular stents are medical devices used to scaffold a biological lumen, most often diseased arteries. While stenting procedures reduce the risk of restenosis, they do not eliminate it completely. Furthermore, other common complications observed are thrombosis, inflammation and corrosion of the stents. The corrosion of the device is induced by blood flow which provokes a degradation of its mechanical properties and leads to a high risk of release of potentially toxic metallic compounds, such as nickel-based oxides and metal ions. To lower these clinical complication rates and to prevent the corrosion of the metallic stent structure, coated stents have been developed during the last decade. Indeed, the coating is expected to improve the surface biocompatibility and corrosion resistance without compromising the stainless steel mechanical properties required for the stent implantation. The Food and Drug Administration (FDA) has already provided guidance on a series of non-clinical test protocols, methods and reports to evaluate the safety and effectiveness of intravascular stents. Properties such as the stability, durability, and adhesion of a stent coating, prior and after deployment, must be clearly assessed to demonstrate its efficiency. This study wants to evaluate the effectiveness against general and local corrosion of an ultra-thin fluorocarbon film deposited by plasma on pre-treated stainless steel. Cyclic polarization tests were used to measure the coating capacity to protect the substrate from localized corrosion and Tafel plot corrosion measurements were used to evaluate the general corrosion behaviour of uncoated and coated, flat and deformed samples.
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Authors: Francesca Boccafoschi, P. Chevallier, A. Sarkissian, D. Mantovani
Abstract: Materials in contact with tissue and biological fluids affect cell reaction that could eventually lead to clinical complications (i.e. thrombosis, restenosis). Improving the biological performances of the materials used for biomedical applications is the main goal of this study. In particular, cardiovascular devices require excellent haemo- and biocompatibility properties. PTFE is currently the main material used for vascular prostheses. After long contact periods with blood, clinical complications leading to thrombosis and restenosis are often reported. Improving the haematological performances of PTFE could significantly increase its life-time and decrease long-term complications. However, inadequately engineered surfaces could trigger the coagulation cascade with the formation of a clot, the first step towards a thrombosis. Plasma carbon-based coatings with varying nitrogen contents deposited on PTFE have been studied as promising coating to improve the haematological performances of PTFE implants. In this work, several techniques were applied to study the viscoelastic properties of blood after contact with virgin and treated PTFE as well as the presence and the clot morphology eventually formed onto the surfaces. The chemical composition of the surfaces was analysed with XPS and FTIR.
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Authors: Francesca Boccafoschi, P. Chevallier, A. Sarkissian, D. Mantovani
Abstract: Materials in contact with tissue and biological fluids affect cell reaction that could eventually lead to clinical complications (i.e. thrombosis, restenosis). Improving the biological performances of the materials used for biomedical applications is the main goal of this study. In particular, cardiovascular devices require excellent haemo- and biocompatibility properties. PTFE is currently the main material used for vascular prostheses. After long contact periods with blood, clinical complications leading to thrombosis and restenosis are often reported. Improving the haematological performances of PTFE could significantly increase its life-time and decrease long-term complications. However, inadequately engineered surfaces could trigger the coagulation cascade with the formation of a clot, the first step towards a thrombosis. Plasma carbon-based coatings with varying nitrogen contents deposited on PTFE have been studied as promising coating to improve the haematological performances of PTFE implants. In this work, several techniques were applied to study the viscoelastic properties of blood after contact with virgin and treated PTFE as well as the presence and the clot morphology eventually formed onto the surfaces. The chemical composition of the surfaces was analysed with XPS and FTIR.
606
Authors: A.M. Escamilla-Pérez, D.A. Cortés-Hernández, J.M. Almanza-Robles, D. Mantovani, P. Chevallier
Abstract: Powders of Mg0.4Ca0.6Fe2O4 were prepared by sol-gel using ethylene glycol and Mg, Ca and Fe nitrates as starting materials. Those powders were heat treated at different temperatures (300, 400, 500 and 600 °C) for 30 min. The materials obtained were characterized by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). The Ca-Mg ferrite with the most appropriate magnetic properties was further analyzed by transmission electron microscopy (TEM). The heating capability of the nanoferrites was also tested via magnetic induction. The XRD patterns of these Ca-Mg ferrites showed a cubic inverse spinel structure. Furthermore, neither traces of hematite nor orthorhombic Ca ferrite phases were detected. Moreover, all the Ca-Mg ferrites are superparamagnetic and the particle size distribution of these Ca-Mg magnetic nanoparticles exhibits an average diameter within the range of 10-14 nm. The needed temperature for hyperthermia treatment was achieved at around 12 min.
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Authors: Marie Claude Boivin, P. Chevallier, Stéphane Turgeon, Jean Lagueux, Gaetan Laroche
Abstract: Several studies have shown that 65 % of expanded poly (tetrafluoroethylene) (ePTFE) vascular prostheses had to be explanted within 10 years of implantation in humans. The reasons for these explantations relied on thrombosis formation and poor hemocompatibility of synthetic polymers. It has been shown that surface modification of ePTFE arterial prostheses could enable their endothelialization therefore improving their biocompatibility and hemocompatibility. Indeed, endothelial cells naturally cover the biological blood vessel wall and consequently, an endothelial layer constitutes the best achievable hemocompatible surface. In this context, our strategy consisted in micropatterning cell adhesion (RGD) and proliferation (WQPPRARI) peptides on the surface of plasma-functionalized PTFE, therefore enabling covalent conjugation of the peptides. Basically, the technology consisted in spraying a solution of the adhesion peptide, therefore leading to 10 µm-diameter RGD spots semi-randomly distributed over the sample and covering 20 % of the whole polymer surface. In a second step, proliferation peptide was applied to the remaining surface by soaking, therefore covering the unreacted surface. The 20 % coverage was obtained by using an x-y table, programmed to move from side to side of the surface on x value, with an increment on y value that has been calibrated.
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Authors: Maxime Cloutier, Stéphane Turgeon, P. Chevallier, D. Mantovani
Abstract: As intravascular biomedical devices, metallic stents are particularly susceptible to corrosion induced by the physiological environment, causing the degradation of mechanical properties and leading to the release of toxic and carcinogenic ions from the SS316L bulk. Therefore, several works have been focused on the development of an ultra-thin fluorocarbon coating that could act both as a drug-carrier for in-stent restenosis and as an anti-corrosion barrier. However, the increase of the corrosion performance was limited by the inevitable permeability of the coating, which exposed some of the sensitive interfacial region to the corrosive environment. Indeed, in previous works, adhesion and growth rate of the film were promoted by the removal of the native oxide layer of the stainless steel which is inhomogeneous, brittle and mechanically unstable. Further refinements of the interface are therefore required in order to enhance the overall corrosion performance without compromising the fluorocarbon film properties and adhesion. Hence, the aim of this work was to enhance the corrosion behaviour of coated SS316L by the creation of a controlled interfacial oxide layer. The native oxide layer was first removed under vacuum and the bare metal surface was subjected to a plasma-reoxidation treatment. Tafel measurements were used to assess the corrosion rates of the specimens. Coated and uncoated modified interfaces were also characterized by X-Ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM).
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Authors: Eléonore Michel, P. Chevallier, Amélie Barrère, Didier Letourneur, D. Mantovani
Abstract: Metallic intravascular stents are medical scaffolds commonly used to heal diseased arteries and to restore blood flow in vessels after a balloon angioplasty. Although clinical complications occurs (mainly in-stent-restenosis, representing 30-40% of cases within six months after angioplasty), this clinical procedure reduces the risk of restenosis. In order to improve the long-term clinical performances of stents, different coatings, bioactives or not, are investigated. However, the adhesion of the coating within the substrate is often weak and delamination after stent deployment could be observed. Therefore, our approach was to consider a plasma fluorocarbon film deposit on stainless steel substrates, improving adhesion and providing protection against the stent corrosion, as a carrier for the subsequent grafting of a polysaccharide (dextran). Indeed, a copolymer made of dextran and metacrylate has already demonstrated interesting results toward cell proliferation and appropriate mechanical properties regarding stent deployment. Hence, the aim of this project is to covalently graft the copolymer of dextran-methacrylate to plasma-aminated fluorocarbon film. In this study, dextrans were functionalized in order to conjugate them to amino groups. Two different ways of functionalization were investigated: by carboxylmethylation reaction and by periodate oxidation. Characterizations were performed by FTIR, for organic syntheses and by XPS for the subsequent grafting on the surface. Coatings topography and stability were also investigated. Preliminary results suggest the use of polysaccharides grafted by plasma on fluorocarbon films to provide a stable stent surface.
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Authors: Sébastien Meghezi, P. Chevallier, D. Mantovani
Abstract: Collagen gels constitute an adequate scaffold for supporting the adhesion, proliferation and tissue regeneration of vascular cells inside a bioreactor. However, their mechanical properties should be enhanced not only for their manipulation but also to resist the mechanical constraints applied in the bioreactor. Actually, assessing the mechanical properties of a hydrogel requires many precautions since they are very sensitive to the environmental conditions (temperature, ionic strength, aqueous environment, etc). Whereas mechanical properties are usually measured directly in the air, the aim of this work was to evaluate the effects of a pseudo-physiological environment (PPE) on the mechanical properties of collagen gels. Furthermore, reinforcement was also tested using UV treatments (λ = 254 nm, 20 J/cm2), known to induce crosslinking. Irradiated samples were more resistant to enzymatic degradation and swelling tests showed that the crosslink density was increased by a factor of 30. This increase was thereafter correlated to the mechanical properties. Results showed that the UV-treated samples were stiffer and more brittle than the non-treated ones when tested in air. However, a 20% decrease and 40% increase were respectively measured on the linear modulus and strain at rupture when the gels were tested in the PPE. In the perspective of vascular tissue regeneration, these results show that the mechanical properties of a hydrogel should be performed in PPE in order to take into account the plasticization phenomenon that will occur in a bioreactor.
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