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Lapraille_76551600_2022.pdf
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- Cardiovascular diseases are the leading cause of death globally in 2019 [1]. More than 80 % of the deaths due to cardiovascular diseases involve a severe form of atherosclerosis [1]. The gold standard treatment for this disease is drug-eluting stents (DES), that are implanted permanently, although necessary during only a short amount of time [2]. DES are associated with long term complications that could be avoided by using a bioresorbable stent that disappears harmlessly when not needed anymore. The ideal metallic material that meets all the criteria for this application has not been found yet. This master thesis is part of the research field aiming at finding the ideal metallic material for producing bioresorbable stents. More particularly, in vitro static immersion tests were conducted during 1 day, 4 days and 7 days on four different metals, namely Cobalt-Chromium, pure Iron, pure Zinc and quinary Zinc alloy. A novel candidate material evaluation approach based on microfocus X-ray computed tomography (micro-CT) imaging was developed. Images were acquired prior to and after immersion, giving useful information to qualitatively evaluate the degradation behaviour, assess the corrosion rate and analyse the surface properties. Micro-CT allowed to obtain images with unprecedented quality used to qualitatively evaluate the corrosion behaviour of biometallic materials. Uniform degradation was observed on pure Iron wires, wide pitting corrosion shape was exhibited by the pure Zinc samples and deep and horizontal pitting shape was visible on quinary Zinc alloy samples. Although very precise, the information given by micro-CT images is limited, as only approximately 10 % of the wires were imaged. This lead to difficulties to properly assess and interpret the corrosion rates based on volume loss method, especially for pure Zinc and the quinary Zinc alloy that exhibited highly localized corrosion. Finally, the surface properties determined using micro-CT images highlighted the favorable surface properties of pure Iron after immersion. The quinary Zinc alloys surface properties are slightly less favorable while the pure Zinc does not degrade harmlessly in vitro. This work highlights the usefulness and potential of micro-CT for evaluating candidate materials for bioresorbable stents. Although it is needed to improve some aspects of the methodology like the corrosion rate assessment, results obtained with this imaging technique are encouraging for the quinary Zinc alloy. In fact, this candidate material for bioresorbable stents exhibits only slight shape modification when highly corroded and appropriate surface properties.