Study for the optimization of interfacial properties between metallic substrates and polymeric coatings by plasma-based surface modification methods to improve performance of vascular stents

Authors: Dorri, Megan Mahrokh
Advisor: Mantovani, D.
Abstract: Over the past 15 years, ischemic heart disease and stroke have remained the leading causes of death, worldwide. According to the World Health Organization, 15 million of the 56.4 million global deaths, in 2015, were caused only by ischemic heart disease or stroke. For the treatment of these diseases, surgical treatments have been introduced and improved to hold the blood vessels open. Among the surgical treatments, angioplasty with stenting is the most popular and the least invasive treatments. Stents, which are wire mesh tubes, prepare a mechanical support for blood vessels and hold them open to restore the blood flow. They are mostly made up of AISI316L stainless steel (SS316L), cobalt-chromium, and titanium alloys. More than half a century ago, when a stent first used, it has considerably evolved. However, release of potentially-toxic metallic ions and deterioration of mechanical properties due to corrosion, and decrease of polymeric coatings adhesion, in case of coated stents, still constitute major concerns in SS316L stents. In the case of SS316L stents, to circumvent the release of metallic ions, in the laboratory for biomaterials and bioengineering of Université Laval (LBB), a fluorocarbon (CFx) coating was previously investigated to isolate the stent completely from the biological environment. The coating also enables subsequent grafting of bioactive molecules to improve its integration in the body. The results were promising; however, the interface of SS316L/CFx needed to be modified to improve the adhesion of the CFx coating. In this Ph.D. research project, a new interface between the SS316L substrate and the CFx coating was created by plasma oxidation. The properties of this new interface, which was an oxide layer, was modified by varying the plasma-process parameters in order to preserve its properties after a 25% plastic deformation. This deformation is the maximum plastic deformation that imposes on a stent during its implantation. The new interface decreased the release of ions by decreasing the corrosion rate of the SS316L substrate by a factor of three. It was also found that the new interface produced an adequate adhesion of the CFx coating to the substrate after deformation as well as after immersion in an aqueous saline solution. The new oxide layer on SS316L was an amorphous oxide layer with an approximately 6 nm thickness, which was clearly distinguished from the polycrystalline microstructure of the substrate. The enhancement of the interface properties was ascribed to this nano-thick amorphous oxide layer, which was found to be more resistant to plastic deformation. This new oxide layer can be produced on bare-metal stents made of passivating metals. Moreover, it can create a favorable interface for coated stents, which have been used in drug-eluting stents, and also to improve stents integration in the human body.
Document Type: Thèse de doctorat
Issue Date: 2017
Open Access Date: 24 April 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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