| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 107 === Stenting procedure has received great attention from the medical society since its introduction in 1990s. However, these intravascular stents could suffer from various repetitive motions due to pulsatile blood pressure and daily body activities after implantation, especially in the applications of peripheral arteries. Such motions oscillate the stents repeatedly, leading to the potential risk of stent fracture and fatigue failure. Such fatigue-related stent fracture has drawn much attention within the medical society in recent years and as a result, stent fatigue performance has become a major issue for stent design.
In this paper, an intriguing stent design concept aimed at enhancing fatigue life is proposed. The concept of this design is to shift the highly-concentrated stresses away from the crown region and re-distribute them along the stress-free bar arms by tapering the strut width. Finite element models (FEA) and Goodman fatigue life analysis were developed to evaluate the mechanical integrity and fatigue safety factor of the stent to various loading conditions. Simulation results show that the fatigue safety factor of our novel stent design jumped to 4 times that of a conventional stent. Conceptual stent prototypes were first cut by a pulsed-fiber optic laser module, followed by a series of expansions and heat treatments to gradually shape the stent to its final size and lastly, processed by electrochemical polishing to refine their surface roughness. A rotating bending fatigue tester was built for this study and stent fatigue tests were conducted for proof of concept. Experimental results show that our novel stent concept successfully enhanced the fatigue life as designed. The fatigue cycle number of our novel stent increased by 6-7 times that of a conventional stent, which agreed well with the trend predicted by the simulations, no matter whether the stents are tested in room temperature or in body temperature. Furthermore, the result of radial force test also indicates that compared to a conventional stent, which sacrifices even more radial strength for the sake of increasing the fatigue life, our pioneering stent only decreases slightly under 20% in radial strength. In conclusion, the findings of this paper provide an excellent guide to the optimization of future stent design to greatly improve stent fatigue life.
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