Study, characterization and implementation of a cutting device for aortic valve removal

Aortic stenosis is a widespread cardiac valve disease with a prevalence of 2 to 4% for the U.S. population between the age of 65 and 80. Current treatments such as SAVR (Surgical Aortic Valve Replacement) and TAVI (Transcatheter Aortic Valve Implantation) have substantial limitations. Therefore a minimally-invasive device is being developed by several researchers of the Université Catholique de Louvain. This thesis takes root in Xavier Bollen’s PhD thesis and focuses on the resection cone of the AVATAR2 instrument he designed. It contains three separate but interconnected parts:(i) an extensive review of the literature and an experimental investigation of the failure behavior of the cone, which is limited by elastic buckling; (ii) a material selection process; and (iii) a systematic design process for the miniaturization of the resection mechanism. The buckling behavior of 54 cone specimens under axial compression has been tested and statistically analyzed using a multiple linear regression model. The influence of several properties has been investigated. These properties include geometric imperfections, cone semi-vertex angle, diameter, thickness and material properties of the cone specimens. There is a major discrepancy between the critical buckling load obtained during the experimental tests and the classical buck- ling load derived among others by P. Seide from linear theory. It is deduced from both the tests and the literature review that the main source for this discrepancy are the initial geometric imperfections. Furthermore, the experiments show that the sensitivity to these imperfections increases significantly with decreasing thickness. Finally, a new equation for the critical buckling load of the resection cone is suggested. It results from a multiple linear regression of the experimental results. The material selection process starts from the full CES Selector 2015 database and then systematically narrows it down with every new constraint. The implemented constraints include minimal hardness, biocompatibility and sterilizability, resistance to buckling and elastic return. These constraints reduce the number of acceptable materials from 3938 to only 14. A further analysis of these materials and especially their processability for the manufacturing of the resection cone narrows this list down to 8. From these 8 materials, Nitinol is selected as the best fit. Indeed, this nearly equiatomic Nickel-Titanium shape memory alloy stands out for its hardness, processability and excellent mechanical properties. The design process followed for the miniaturization is the prescriptive method established by Pahl and Beitz and further developed by N. Cross. The conceptual design resulted in a principle solution, which has been further analyzed during the embodiment design phase. Furthermore, a preliminary lay-out, a first functional aluminum prototype and a thin sheet Solidworks® drawing of the designed solution have been developed. The buckling behavior of the resection cone is a critical aspect of the AVATAR2 instrument and should be taken into account in any design decision. Given its intended function, the best fitted material for this cone is Nitinol. The miniaturization of the instrument designed by X. Bollen is a very complex task but could have a considerable impact on cardiac surgery