RESUMEN
Objective To analyze mechanical properties of stent retrievers with different structures, and provide theoretical support for the design and clinical selection of stent retrievers. Methods Three kinds of stent retrievers with different structures (B3, K4, X) were evaluated by finite element analysis and in vitro simulation experiment. The analytic parameters were radial support force, withdrawal force and thrombosis state during the thrombotomy test. Results The radial support forces of B3, K4, X stent retrievers obtained from the experiment were 0.48 N, 0.43 N, 0.51 N, respectively. The larger the crimping distance, the greater the radial support force of stent retrievers. The radial support force of the stent increased significantly when the crimping distance was larger than 3 mm. The simulated thrombus removal experiment results showed that the peak withdrawal forces of B3, K4, X stent retrievers were 0.410 N, 0.451N, 0.501 N, respectively. The experimental results were consistent with the finite element analysis results. Conclusion sBoth the experimental results and the finite element results showed that the X stent has better mechanical properties. This method can be used as an analytic method to evaluate performance of the stent retrievers, and provide references for performance improvement and development of the stent retrievers.
RESUMEN
Objective To simulate the process of thrombus removal from the open-type stent retrievers, so as to provide theoretical references for the design and clinical application of the open-type stent retrievers. Methods Finite element models of the open-type stent retrievers with 3,4,5 supporting units (K3,K4,K5), the crimping tools, simulated vessels and simulated thrombus (three types) were established. Radial displacement load was applied on the crimping tool until the stent was crimped to 0.5 mm, and the maximum principal strain (MPS) peak and radial force (RF)of the stent were analyzed. When displacement of the crimping tool was restored, the stent self-expanded and contacted with blood vessels, and MPS of the stent and von Mises stress (VMS) of blood vessels were analyzed. Axial displacement was applied to proximal end of the stents to allow the stent to drive the clots to migrate, and the blood vessel VMS and withdrawal force of the stents (the ability to capture thrombus) were analyzed. ResultsThe MPS peaks for 3 types of stent retrievers during crimping process were 6.94%, 8.30% and 5.48%, which were all smaller than the 12% fracture limit. When the outer diameter of the stent was 3 mm (equal to the inner diameter of blood vessels), the K4 stent had the largest RF. The results of self-expanding release process showed that the larger the number of support units, the greater the VMS of blood vessels. At the stage of thrombus migration and removal,the VMS of blood vessels was generally small and concentrated on the thrombus. The withdrawal force of the stent reached the maximum at the initial stage of thrombus migration and removal, then gradually decreased. The peak withdrawal force of the K4 stent was larger than that of the K5 and K3 stent. Conclusions Although the MPS and VMS for 3 types of open-type stent retrievers were within the safe range, the K4 stent showed better performance in RF and withdrawal force with the three types of thrombus. The research findings can provide the analysis methods and ideas for optimizing the open-type stent retrievers, to avoid clinical complications such as vascular injury and improve safety and effectiveness of the stent retrievers.