A method for investigating the mechanical properties of intracoronary stents using finite element numerical simulation

The proliferation of stent designs poses difficult problems to clinicians, who have to learn the relative merits of all stents to ensure optimal selec tion for each lesion. and also to regulatory authorities who have the dilem ma of preventing the inappropriate marketing of substandard stents while no t denying patients the benefits of advanced technology. Of the major factor s influencing long-term results, those of patency and restenosis are being actively studied whereas the mechanical characteristics of devices influenc ing the technical results of stenting remain under-investigated. Each diffe rent stent design has its own particular features. A robust method for the independent objective comparison of the mechanical performance of each desi gn is required. To do this by experimental measurement alone may be prohibi tively expensive. A less costly option is to combine computer analysis, emp loying the standard numerical technique of the finite element method (FEM), with targeted experimental measurements of the specific mechanical behavio ur of stents. In this paper the FEM technique is used to investigate the st ructural behaviour of two different stent geometries: Freedom stent geometr y and Palmaz-Schatz (P-S) stent geometry. The effects of altering the stent geometry, the stent wire diameter and contact with land material propertie s off a hard eccentric intravascular lesion (simulating a calcified plaque) on stent mechanical performance were investigated. Increasing the wire dia meter and the arterial elastic modulus by 150% results in the need to incre ase the balloon pressure to expand the stent by 10-fold. Increasing the num ber of circumferential convolutions increases the pressure required to init iate radial expansion of mounted stents. An incompressible plaque impinging on the mid portion of a stent causes a gross distortion of the Freedom ste nt and an hour-glass deformity in the P-S stent. These findings are of rele vance for future comparative studies of the mechanical performance of stent s, in designing newer stents and also in clinical practice. (C) 2001 Elsevi er Science Ireland Ltd. All rights reserved.