Investigation of Stent Implant Mechanics Using Linear Analytical and Computational Approach

Revisiting SFA stent technology: an updated overview on mechanical stent performance

OBJECTIVES

The study investigated mechanical parameters of stent systems indicated for treatment of femoropopliteal (FP) arterial disease to support interpretation of clinical results and the related causalities.

METHODS

Eight stent system types of same dimensions were investigated (n=2). Parameters were the profile of stent delivery system (SDS), radiopacity, trackability and pushability, bending stiffness (flexibility) and axial stiffness of expanded stents, length change during expansion, radial force, crush resistance, strut thickness and general surface condition.

RESULTS

The trackability ranged from 0.237 to 0.920 N and the pushability was 47.9-67.6 %. The bending stiffness of SDS was between 108.42 and 412.68 N mm2. The length change during stent release to 5 mm was low, with one exception. The bending stiffness of the expanded stents was 2.73-41.67 N mm2. The normalized radial forces at 5 mm diameter ranged from 0.133 N/mm to 0.503 N/mm. During non-radial compression by 50 %, the forces were 3.07-8.42 N, with one exception (58.7 N). The strut thickness was 153-231 µm.

CONCLUSIONS

Large differences occurred for flexibility, radial force and length change during expansion. The data should be used when choosing the proper device for restoring vascular function.

A study on the accuracy and efficiency of the improved numerical model for stent implantation using clinical data

BACKGROUND AND OBJECTIVES

Stent implantation procedure should be carefully planned and adapted to the particular patient in order to minimize possible complications. Numerical simulations can provide useful quantitative data about the state of the artery after the implantation, as well as information about the benefits of the intervention from the hemodynamical point of view.

METHODS

In this paper, a numerical model for stent implantation is presented. This numerical model simulates the stent expansion, the interaction of the stent with arterial wall and the deformation of the arterial wall under the influence of the stent. FE method was used to perform CFD simulations and the effects of stenting were analyzed by comparing the hemodynamic parameters before and after stent implantation.

RESULTS

Clinical data for overall 34 patients was used for the simulations, and for 9 of them data from follow up examinations was used to validate the results of simulations of stent implantation.

CONCLUSIONS

The good agreement of results (less than 4.1% of SD error for all the 9 validation cases) demonstrated the accuracy of the presented numerical model. The developed approach can be a valuable tool for the improvement of pre-operative planning and patient-specific treatment optimization.

INVESTIGATION OF MECHANICAL BEHAVIOR OF NiTi STENT UNDER DIFFERENT LOADINGS

Biocompatible stent implants that have been made of shape memory alloys (SMA) are being used in arteries which are restoring normal blood flow. A high failure rate of stent implants in femoral artery causes the investigation of the mechanical behavior of stent implants, and its design and manufacturing, a necessity study. In this paper, two different stent designs, with different geometries, have been simulated. One is a Diamond-shaped profile stent and the other one is a V-shaped profile stent. These stents have been simulated under different loadings such as tensile and bending loadings that are very similar to the loading environment imposed by the arterial wall and blood flow. Two different temperatures have been selected to investigate superelasticity as well as shape memory effect of NiTi stents. During unloading for the shape memory case, the residual strains are recovered by heating the stents. The verified model based on microplane model is numerically considered for simulation of the stents. Numerical results show that the V-shaped stent design stretches more than the Diamond-shaped stent design under tensile loading. In addition, the V-shaped stent bends more than Diamond-shaped stent under the same bending loading, which shows more flexibility.