Papers by Author: Farzaneh Arefi-Khonsari

Abstract: We present a process for rapid post-discharge deposition of liquid monomer to form functional coatings at atmospheric pressure. The post-discharge polymerization of dense polyacid and polyether coatings is first depicted versus the energy density deposited by the preliminary surface treatment of polyethylene and polystyrene substrates in air Dielectric Barrier Discharge (DBD) with respect to SEM, to XPS and FTIR-ATR analysis and to polymerization yield determined by mass measurements. The paper focuses on the effect of the filamentary air DBD on surface of the polymer substrates and on post-discharge polymerization mechanism. Indeed, the grafting yield is shown to depend on the energy density deposited by DBD and on the time exposure to air between DBD and monomer deposition, controlling respectively the surface density of radicals and labile peroxides, both triggering the polymerization of vinyl precursors. Then, the effect of deposition conditions on the polymerization yield and related thickness of the functional polymer coatings is shown and special attention is paid to the stability of the coating upon washing.

Abstract: Plasma processing has been developed to produce selective chemistry in the inner surface of a microfluidic system. This dry process is an alternative solution to the Chemical Vapor Deposition (CVD) process that allows us to work at low temperatures thus avoiding the degradation of the substrate by heat. The present study focused on the surface modification of PDMS in order to make them more hydrophilic and capable to exhibit a high percentage of COOH functions which will provide a good asset for future cell attachment.

Abstract: Coronary stents are metallic (316L stainless steel) devices employed during balloon angioplasty to reopen and prevent the re-obstruction of a diseased narrowed area within a coronary artery. To reduce restenosis rate, bare metal stent coating is a promising solution. The coating can act as an anticorrosive barrier against the aggressive properties of biological environment, improving the long-term safety of the device. The goal of this study is to develop a dry process to isolate metallic surface from the biological environment by depositing a thin plasma polymerized allylamine (CH2=CH-CH2-NH2) film on the metallic surface. Plasma polymerized allylamine films were deposited on flat electropolished 316L stainless steel samples in a low pressure plasma reactor (70 kHz). Chemical composition of the coatings has been analysed as a function of the discharge power and treatment time. Moreover, special attention has been paid on the stability of the coating after immersion during 24 hours in D.I. water. Finally, to mimic stent expansion conditions, a “small punch test” has been used to investigate the adhesive properties of the coating. Our results demonstrate that is possible to deposit a stable, cohesive and adhesive plasma polymerized allylamine thin film which can be used as a coating for cardiovascular stents

Abstract: Metallic Intravascular stents are medical devices used to scaffold a biological lumen, mostly diseased arteries, after balloon angioplasty. They are commonly made of 316L stainless steel or Nitinol, two alloys containing Nickel, an element classified as potentially toxic and carcinogenic. Although they are largely implanted, the long-term safety of such metallic elements is still controversial, since the corrosion processes may lead to the release of several metallic ions. In order to avoid the metallic ion release in the body and to improve the biocompatibility of metallic stents with their biological environments, polymer coatings have been deposited by two different technologies, i.e. plasma surface modifications and Electrospraying. The role of the polymer coating is then to encapsulate the stainless steel device, and to favour the chemical grafting of Phosphorylcholine, a molecule known for its hemocompatible properties.1 In this talk, the state of the art on low pressure and atmospheric pressure plasmas for deposition of organic coatings will be given and we will present the advantages and drawbacks of each process. Then, we will present an original technology that combine a Dielectric Barrier Discharge and an electrospraying system to deposit well-defined Polyacrylic acid and Polyallylamine films. The advantage of such system is the possibility to limit the extent of the monomer fragmentation and to give rise to rapid deposition of a highly functionalised plasma polymer layer, and also the possibility to cover three dimensional objects, such as stents. Thus, the theory of EHDA technology will be explained: special attention has been paid to define the Electrospray parameters (Voltage, flow of precursor, nozzle-substrate distance…) which control the size distribution of the charged droplets and as a consequence, the structure of the film coating. The film coatings have been analysed with XPS and by ATR. Moreover, special attention will be paid on the stability of the coating which is related to both spraying conditions as well as to the preliminary plasma treatment. The potentiality and the features of the EHDA process will be then presented.