Introduction: While radial force (RF) is an important mechanical property used in designing stents, high RF is associated with some complications such as in-stent restenosis, an exuberant inflammatory response or thrombosis [1]. In contrast, low RF leads to poor support of artery which may increase the risk of thrombosis and stent migration in the artery [2]. Since there are no standards which determine the maximum and minimum RF for designing the stent, best references as a criterion are commercial stents. Thus, the aim of this study is to establish a validated simulation method for evaluating the RF of commercial stents.

Methods: Three self-expandable intracranial (Neuroform (open-cell), Enterprise and Solitaire (close-cell)) and two balloon-expandable cardiac (Integrity and Multi-Link) stents were selected for RF testing. Stents were scanned using micro CT and DICOM images were obtained. Three dimensional finite element models were then constructed using Simpleware software (Figure 1). The RF was simulated by compression of the stent between two plates using ABQUS software (Figure 2). Simulation results of self-expandable stents were verified by experimental testing using ElectroForce® Load Frame Systems 3200 products machine (Figure 3).

Results: The RF (in Newton, N) of the Neuroform, Enterprise, Solitaire stents was determined to be 0.142 N, 0.150 N, 0.196 N, respectively, by compression between two plate for 50% of the stent diameter experimentally (Figure 4). By comparison, the simulation results demonstrated the RF to be 0.140 N, 0.151 N, 0.195 N and for Integrity and Multi-Link1to be 15.3 N and 13.86 N, respectively (Figure 5). When comparing balloon-expandable vs. self-expandable stents, the balloon expandable stents had a much higher RF. When comparing self-expandable open-cell and closed-cell stents, the closed-cell had a slightly higher RF.

Conclusions: These studies have shown that simulation results of radial force testing are in excellent agreement with experimental results for self-expandable stents.

Patient Care: Knowledge of the RF between these different types of stents and correlation with clinical outcome can aid in the purposeful design of stents for the cardiac and intracranial circulations.

Learning Objectives: This study can be employed in future studies in order to decrease cost of the stent designing process.

References: 1. Julian Bedoya et al., Journal of Biomechanical Engineering, 2006, 128:757-765. 2. A. García, E. Peña and M.A. Martínez, Journal of the Mechanical Behavior of Biomedical Materials, 2012, 10:166-175.