Numerical assessment of fatigue strength of transcatheter mitral bioprosthetic stent based on the titanium nickelide model

This study is devoted to assessing the fatigue strength of a self-expanding Nitinol frame for a prosthetic heart valve when reconstructing the conditions of primary implantation in the mitral position. The object of research is a stent-like supporting frame, which is a cellular structure that performs the function of the main fastening and maintaining the shape of the leaflets and cover. The study included two stages of the formation of the stress-strain state of the frame: the creation of a mathematical model that provides an assessment of the state of the structure of the support frame in the final state and an assessment of the fatigue strength. It is shown that during the packaging of the frame in the delivery system (compression), a high degree of localization of inelastic deformations leading to surface destruction of a number of cells and joints at the final stage of the compression process, is noted. In a number of cell vertices and frame junctions, the fatigue strength coefficient exceeded its limit value, which indicates their destruction under the influence of long cyclic alternating loads. The main effect on the fatigue strength of the structure is the stress-strain state obtained at the stages of compression and implantation. To meet the conditions of static and fatigue strength, a modification of the support frame structure is required.