血管支架設計對於軸向強度與可撓度的影響

Abstract

動脈粥狀硬化是造成心臟疾病的主要原因之一，以往通常使用開心手術或心臟繞道手術進行治療。近十年來，隨著醫療科技的進步，血管支架已經成為治療相關疾病的一大重要準則。血管支架是一種微型的網狀管形醫療器材，能夠藉由導管及導線植入人體，並在血管中擴張以維持該處血管的管徑大小。然而，在近期的冠狀動脈支架手術過程中，發生了所謂的支架軸向變形臨床現象。原因通常是在支架順利放置後，導管、導線或擴張支架用的氣球收回時，不慎與支架的結構發生擠壓，使支架局部或整體發生嚴重的變形扭曲。此現象可能導致血管的嚴重阻塞，甚至對病患的生命造成危害，因此在眾多醫學會議上都有著熱烈的討論。 本論文首先針對支架的設計進行參數化分析，透過有限元素軟體模擬 L-605 鈷鉻合金氣球擴張式支架的部署過程，並建立三種不同的台架試驗機械模型，分析支架受到軸向壓縮、軸向拉伸和側向彎曲負載時對應的變形狀況，再分別定義不同的性能指標，以量化各個設計參數相對於比較基準的變動對上述機械性質的影響。結果顯示當 Connector 的數量從兩個增加到三個的時候，抗壓勁度增加了十二倍、抗力高原幅值成長至三倍、抗拉勁度增加了十三倍之多；而改變 Connector 的分佈方式也讓抗壓勁度變為原先的二點五倍、抗力高原幅值成長了 80%、抗拉勁度成長至六倍左右。除此之外，提升單元結構的大小、Strut 的寬度或厚度也都能有效提升支架的軸向機械強度。最後也利用有限元素軟體，模擬支架在真實血管內發生軸向變形的情況，讓我們對於該現象有更精確的預測與認識。 透過本論文的結果，可以清楚了解各項設計參數對於支架軸向強度與可撓度的影響，對於未來支架設計有著更為全方面的參考資訊。此外，對於醫師以及臨床人員在未來選用支架時也能提供更完備的評估準則，以避免類似的臨床案例再次發生。

Atherosclerosis is one of main factors of cardiovascular diseases. In the past, open heart surgeries and bypass surgeries were usually performed for treatment. In the recent decade, intravascular stents have been a gold standard to treat such disorders with the advancement of medical technology. A stent is a tiny, tube-like, wire-mesh medical device which can be implanted into a human body via a catheter and a guide wire, and expanded in the artery to maintain the size of lumen. In recent percutaneous coronary interventions, however, the longitudinal stent deformation (LSD) occurred. This phenomenon occurs when the delivery devices such as catheter, guide wire, or post-dilation balloon conflicted against the deployed stent, causing entire or part of stent to dramatically distort. It could clog the artery severely and threaten the patient’s life, so related issues have soon become hot topics in western medical society. In this paper, we implied the parametric analysis on stent design, and simulated the deployment of a L-605 cobalt-chromium balloon-expandable stent. Three different models were created to assess the deformation of the stent when the stent was exerted longitudinal compression, longitudinal elongation, and bending loads. Several performance indices were defined to quantify the effects of variation relative to the standard case of each design parameter on the mechanical behaviors. Results showed that when the number of connectors changed from two to three, the compression stiffness grew twelve times, the plateau amplitude rose to tripled, and the elongation stiffness grew thirteen times. Changing the arrangement of connectors made the compression stiffness grow to 2.5 times, the plateau amplitude rise 80 percentages, and the elongation stiffness grow to about six times. Besides, increasing strut width, strut thickness and the size of unit cell could also promote the longitudinal integrity of stents. Finally, we simulated LSD in a virtual artery by finite element software, and made a more accurate knowing and prediction to this phenomenon. These results can make us understand the influences of each design parameter to the longitudinal strength and flexibility of stents more clearly, and give reference information on more aspects in stent designing. In addition, the results can provide doctors and clinicians more comprehensive standard when they choose stents to prevent similar cases taking place.