瘦身設計對鎂合金支架抗腐蝕性能之提升

Abstract

心血管疾病 (Cardiovascular Disease, CVD) 為全球最常見的死亡原因之一，根據美國心臟協會2022年之研究報告顯示，以冠狀動脈心臟病為最大的致死成因。過去在心血管疾病的治療上以藥物治療與開心手術為主，但如今心導管支架置放手術已經取代傳統的治療，成為心血管疾病最主要的治療方式。然而一般的金屬支架，雖然在置放入阻塞血管後能提供足夠的徑向支撐力，卻可能因為永久性存留在體內而引發發炎反應形成晚期血栓。生物可吸收支架在置放後，能提供阻塞血管所需之徑向力，並待完成階段性任務後被人體所吸收，因此生物可吸收式支架已成為現今主要的發展方向之一。 鎂合金以往作為骨材使用與人體有良好的生物相容性，被作為生物可吸收支架的主要發展材料，但由於其降解速度過快，在血管傷口處內皮細胞包覆完全前就已被降解吸收，無法達到心血管手術支撐阻塞血管的目的，因此本研究將針對此問題探討不同支架設計在施加應力與液體沖刷下的腐蝕情形。 本研究成功透過簡單的基本支架設計，更改其Strut構造，將Strut中段細化，達到支架瘦身的效果，透過FEA與CFD之電腦模擬來確認各瘦身比例在10%-50%間，支架擴張後支應力應變殘留，與血管置放支架後壁面之剪應力分布及最大流速。並以雷射切割方式製造鎂合金ZM21的生物可吸收支架雛形，以靜態浸泡與動態沖刷的方式進行雛型品的腐蝕實驗，成功確認瘦身設計在鎂合金支架上能增加腐蝕壽命的效果。根據本研究的模擬結果得到，鎂合金支架在瘦身20% 時能有最佳之腐蝕抗性，並成功以實驗證明其相比於未瘦身支架有較好的抗腐蝕集中能力。

Cardiovascular disease (CVD) is one of the most common causes of death globally, with coronary artery disease being the leading cause of death, according to a 2022 study report by the American Heart Association. In the past, drug treatment and open-heart surgery were the main treatments for cardiovascular disease. However, nowadays, percutaneous coronary intervention (PCI) has replaced traditional treatments and become the main treatment for CVD. Nevertheless, conventional metal stents, while providing sufficient radial support after placement, may cause late thrombosis due to their permanent presence in the body. Bioresorbable stents, on the other hand, can provide the necessary radial force for blocked blood vessels and be absorbed by the body after completing their tasks, making them one of the main development directions in CVD treatment. Magnesium alloys have good biocompatibility with the human body and have been used as bone material. They are also used as the main development material for bioresorbable stents. However, due to their rapid degradation rate, they are absorbed before complete endothelial cell coverage at the vascular injury site, making them ineffective in supporting the blocked blood vessels during cardiovascular surgery. Therefore, this study investigates different stent designs for corrosion under stress and liquid flushing. This study successfully modified the basic stent design by refining the Strut structure and achieving the effect of slimming down the stent. By using FEA and CFD computer simulations, the residual stresses and strains after stent expansion, the shear stress distribution, and the maximum flow velocity after placement in the blood vessel were confirmed for various slimming ratios between 10% and 50%. A prototype of a magnesium alloy ZM21 bioresorbable stent was manufactured by laser cutting, and the corrosion experiment of the prototype was carried out by static immersion and dynamic flushing methods, successfully confirming the effect of slimming design on increasing the corrosion life of the magnesium alloy stent. Based on the simulation results of this study, the magnesium alloy stent has the best corrosion resistance when slimmed down by 20%, and it has been experimentally proven to have better corrosion concentration resistance than non-slimmed stents.