Défense de thèse de doctorat en sciences chimiques

Design of polymer coatings on Nitinol by surface-initiated polymerization : towards cardiovascular applications

Jury

Laetitia MESPOUILLE (UMons) co-promoteur, Philippe DUBOIS (UMons), Jean-François VANHUMBEECK (CRM Group), Stéphane LUCAS (UNamur) président, Zineb MEKHALIF (UNamur) promoteur

Résumé

Over the last decade Nitinol (NiTi) has become very appealing owing to its attractive properties (good impact and heat resistance, high fatigue strength, low density, ...). Nowadays, it is commonly used as a support material for the treatment of cardiovascular disease where it is used as a stent. However, its implementation in the biomedical fields is still hampered by nickel inclusions, making this alloy sensitive to pitting corrosion and leading therefore to the release of carcinogenic Ni²⁺ ions.

The present thesis is devoted to the improvement of NiTi properties. The main objectives are to increase the material corrosion resistance, its biocompatibility, as well as its hydrophilicity to prevent the adhesion of fat and proteins on its surface. In this context, three steps are considered and investigated: (a) the hydrothermal reinforcement of Nitinol native oxide layer; (b) the elaboration of an organic monolayers containing polymerization moieties; and (c) the subsequent growth of a biocompatible layer. More specifically, the electro-assisted elaboration of self-assembled monolayers (SAM) is proven to allow fast preparation of protective coatings in mild conditions while preventing degradation of sensitive molecules such as the ATRP initiating sites. However, the steric hindrance of ATRP initiating sites interferes with the formation of ordered and compact SAMs, leading to a bad reinforcement of the metal surface corrosion resistance. To face this issue, the elaboration of alternative initiating layers, i.e. mixed- or bisphosphonic-made monolayers, are investigated. Finally, the behaviour of modified Nitinol plates in human blood plasma simulated fluid, and its ability to grow endothelial cells are investigated.

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