Optimization of the Nitinol Framework of an Aortic Valve Bioprosthesis Using Numerical Simulation.

Abstract

The application of numerical analysis methods when developing novel heart valve bioprostheses is an integral stage of their design; it enables to optimize the bioprosthetic construction and accelerate their development process. The aim of the study was to conduct hydrodynamic tests of a prototype of a self-expandable transcatheter aortic valve bioprosthesis and, based on the findings, using numerical simulation, improve the geometry of the bioprosthetic nitinol frame.

Materials and methods: The study investigated an aortic valve bioprosthesis with a self-expanding nitinol frame and the leaflet apparatus of three biological leaflets fixed to the frame through the holes in the commissural posts. The bioprosthesis was tested on a test bench to evaluate the hydrodynamic characteristics of heart valve prostheses. A computer model of the valve frame was created for a finite element analysis in the COMSOL Multiphysics software environment, and validated based on the observed deformations of the bioprosthesis in a full-scale experiment. The obtained model was used for parametric optimization of the commissural post geometry to reduce their deformities.

Results: Bench hydrodynamic tests revealed significant deformities of the bioprosthetic commissural posts (bending up to 5 mm) in leaflet closure under diastolic pressure. The numerical simulation using the finite element method enabled to precise the load on the posts (1.3 N instead of 1.52 N according to preliminary calculations). Based on the results obtained, an optimized frame design was developed with increased width and thickness of the beams in the area of commissural posts (from 0.3 to 0.5 mm and from 0.4 to 0.5 mm, respectively). Finite element analysis showed the suggested modification to significantly increase the structural stiffness, reducing the deformation value to 0.7 mm under the load of 1.3 N.

Conclusion: The suggested approach to the application of numerical simulation demonstrated its effectiveness for optimizing the design of the nitinol frame of a transcatheter aortic valve bioprosthesis. The suggested modification of the commissural post geometry significantly reduced their deformity under the hydrodynamic load on the valve, which contributed to the preservation of the leaflet coaptation, reduced the risk of paravalvular regurgitation and prosthesis dislocation. The findings demonstrate the promise of using numerical simulation methods at a bioprosthetic design stage enabling to reduce the number of necessary physical prototypes and accelerate the development process.