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Development of balloon-expandable stents for treatment of eccentric plaque considering surface roughening
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| Title: | Development of balloon-expandable stents for treatment of eccentric plaque considering surface roughening |
| Other Titles: | 偏心プラークのための表面性状を考慮したバルーン拡張ステントに関する研究 |
| Authors: | Syaifudin, Achmad Browse this author |
| Keywords: | surface roughness,Asymmetric stent,flexibility,plaque vulnerability,FEM |
| Issue Date: | 26-Sep-2016 |
| Publisher: | Hokkaido University |
| Abstract: | Stent, a tiny mesh tube that well known to treat narrow or blocked artery due to plaque obstruction, remains relevant to investigate after decades of development. In the case of balloon expandable stent (BES), its development remains necessity due to having superior material properties and affordable price. Nowadays, the development of BES should adapt latest issues. The physical properties of the stent surface affect the effectiveness of vascular disease treatment. During the expanding process, the stent acquires high-level deformation that alters the surface roughness level. To improve the surface roughness changes in the treatment of eccentric plaque, applying the symmetric expansion will generate the non-uniform stress distribution, which may aggravate the fibrous cap prone to rupture. Therefore, the development of a new stent design that adapts plaque shape is necessity. Mechanical characteristic assessment of new stent design should be conducted afterwards to improve stent performance during stenting process. FEM assessment is a good choice to save the cost and time of manufacturing. As a series of new stent development, rupture analysis after stent deployment is essential to investigate plaque vulnerability and arterial tissue rupture. All structural analysis was performed using ANSYS R15.0. To observe the effects of the plaque length on the changes in the surface roughness, two types of bare metal stents such as Palmaz and Sinusoidal stent are studied. Three different lengths of plaque, i.e. the plaque length longer than the stent, shorter than the stent, and the same length as the stent are chosen in the simulation. The material models was defined as a multilinear isotropic for the stent and the hyperelastic for the balloon, plaque, and vessel wall. The correlation between the plastic deformation and the changes in surface roughness was obtained by the intermittent pure tensile test using a specimen made of type 316NG. To develop a new stent design, a non-symmetric structural geometry of stent is derived from Sinusoidal stent type by modifying struts length, struts width, bridges, and curvature width of struts. An end ring of stent struts was also modified to eliminate the dogboning phenomenon and to reduce the ectropion angle. Two balloon types used to deploy stent, i.e. the ordinary cylindrical and the offset balloon. Positive modification results were used to construct a final non-symmetric stent design, called an Asymmetric stent. Analyses of the deformation characteristics, the surface roughness changes, and stresses within the intact arterial layer were subsequently examined. To assess the flexibility of Asymmetric stent, FEM assessments are conducted, i.e. flexibility tests on unexpanded and expanded condition. To investigate plaque vulnerability and arterial tissue rupture, Asymmetric stent is expanded inside an idealized human carotid artery, which has the eccentric plaque obstruction. The large lipid pool and the thin fibrous cap are accommodated in the model to behave the prone to rupture. The arterial tissue with the multilayer material parameters, including intima, media, and adventitia is also focused in the study. The study found that the plaque size relative to the stent length affected the changes in the surface roughness. It was also found that the stent should have the similar length with the plaque because of the moderate change in the surface roughness. As for the surface roughness changes in treatment of the eccentric plaque, Asymmetric stent has a comparable effect with Sinusoidal stent though Asymmetric stent drives the distribution of the surface roughening as expanded by the offset balloon. From the flexibility assessment, it is found that the flexibility of both stents is comparable in both the unexpanded or expanded condition. However, the inflated-side of Asymmetric stent is more flexible than its fixed-side. Finally, the analyses demonstrated that the expansion combination between Asymmetric stent – offset balloons might increase the plaque vulnerability. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第12454号 |
| Degree Level: | 博士 |
| Degree Discipline: | 工学 |
| Examination Committee Members: | (主査) 教授 佐々木 克彦, 特任教授 成田 吉弘, 教授 中村 孝, 教授 大橋 俊朗 |
| Degree Affiliation: | 工学院（人間機械システムデザイン専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/63333 |
| Appears in Collections: | 課程博士 (Doctorate by way of Advanced Course) > 工学院(Graduate School of Engineering)
学位論文 (Theses) > 博士 （工学）
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