Effect of geometrical configuration on mechanical performance of a tubular aortic valve prosthesis with dynamic fem stimulation.
Tan, Wei Ling.
Date of Issue2009
School of Mechanical and Aerospace Engineering
Recent development in aortic valve prosthesis design includes the Truly Stentless Pericardial Aortic Valve prosthesis having the leaflets connected to the sino-tubular junction at three Single Point Attached Commissures (SPAC). The leaflet geometry of this valve prosthesis can be constructed from either a simple tubular structure or a specially designed three-dimensional valve mold that mimics natural aortic leaflet geometry. This project aimed to elucidate the effect of the two leaflet geometrical designs, i.e. the tubular and the molded, on mechanical performance of the SPAC valves. Mesh Optimization was first carried out to determine the optimum mesh topology for the simulation. Approximately 6600 elements for each model represents a balance between accuracy and computing overheads and therefore were chosen as the optimum mesh size used for the subsequent simulation. Simulation was first performed to test on the validity of the SPAC implantation approach to examine if the single 2-mm stitch at the commissures would in any way compromise the valve performance. Models with incrementally increasing suture lengths (2, 4, 6, 8, and 10mm) at the commissures were compared. Results show that increasing the suture length at the commissures does not affect significantly the coaptation area for both the tubular and the molded valves, and the maximum compressive stress for the molded valve is lower at 2 mm than at the longer suture lengths. It is therefore suggested that a single 2-mm stitch at the commissures does not compromise the mechanical performance of the valve and the use of the SPAC technique is justified. Symmetric simulation was then carried out to simulate a situation where surgeons are able to implant the valve symmetrically into the aortic root. Again, the tubular and the molded valve designs were compared in terms of compressive stress and coaptation area. The molded valve is shown to give a larger coaptation area and lower compressive stress of the leaflets than the tubular valve and thus represents a better design. Asymmetrical simulation was then carried out to simulate the condition when the valves were not sutured symmetrically either due to errors of the operating surgeon or the asymmetrical anatomy of the aortic root. Due to the limitation of the simulation program, asymmetric simulation was only able to be carried out for 2mm displacement from the original symmetric suture position. Results show that such a slight asymmetry in the commissures does not affect appreciably the coaptation area and compressive stress compared to the results from the symmetrical simulation. In conclusion, the SPAC implantation approach does not compromise the mechanical performance of both tubular and molded valve designs and its use is justified. The SPAC-molded valve is superior to the tubular design as it gives a larger coaptation area and lower compressive stress on the leaflets for both symmetrical and asymmetrical implantations.
Final Year Project (FYP)
Nanyang Technological University