School of Engineering Sciences, Computational Engineering Design Group, University of Southampton, SO17 1BJ, Southampton, UK.
Biomech Model Mechanobiol. 2012 Jan;11(1-2):61-82. doi: 10.1007/s10237-011-0293-3. Epub 2011 Mar 4.
Coronary stents are tubular type scaffolds that are deployed, using an inflatable balloon on a catheter, most commonly to recover the lumen size of narrowed (diseased) arterial segments. A common differentiating factor between the numerous stents used in clinical practice today is their geometric design. An ideal stent should have high radial strength to provide good arterial support post-expansion, have high flexibility for easy manoeuvrability during deployment, cause minimal injury to the artery when being expanded and, for drug eluting stents, should provide adequate drug in the arterial tissue. Often, with any stent design, these objectives are in competition such that improvement in one objective is a result of trade-off in others. This study proposes a technique to parameterize stent geometry, by varying the shape of circumferential rings and the links, and assess performance by modelling the processes of balloon expansion and drug diffusion. Finite element analysis is used to expand each stent (through balloon inflation) into contact with a representative diseased coronary artery model, followed by a drug release simulation. Also, a separate model is constructed to measure stent flexibility. Since the computational simulation time for each design is very high (approximately 24 h), a Gaussian process modelling approach is used to analyse the design space corresponding to the proposed parameterization. Four objectives to assess recoil, stress distribution, drug distribution and flexibility are set up to perform optimization studies. In particular, single objective constrained optimization problems are set up to improve the design relative to the baseline geometry-i.e. to improve one objective without compromising the others. Improvements of 8, 6 and 15% are obtained individually for stress, drug and flexibility metrics, respectively. The relative influence of the design features on each objective is quantified in terms of main effects, thereby suggesting the design features which could be altered to improve stent performance. In particular, it is shown that large values of strut width combined with smaller axial lengths of circumferential rings are optimal in terms of minimizing average stresses and maximizing drug delivery. Furthermore, it is shown that a larger amplitude of the links with minimum curved regions is desirable for improved flexibility, average stresses and drug delivery.
冠状动脉支架是管状支架，使用导管上的可充气气球展开，最常用于恢复狭窄（患病）动脉节段的管腔大小。当今临床实践中使用的众多支架之间的一个常见区别因素是它们的几何设计。理想的支架应该具有高径向强度，以在扩张后提供良好的动脉支撑；具有高柔韧性，以便在扩张过程中易于操纵；在扩张时对动脉造成的损伤最小；对于药物洗脱支架，应在动脉组织中提供足够的药物。通常，对于任何支架设计，这些目标都是相互竞争的，因此一个目标的改进是其他目标的权衡结果。本研究提出了一种通过改变环的形状和连接来参数化支架几何形状的技术，并通过模拟球囊扩张和药物扩散过程来评估性能。有限元分析用于通过球囊充气将每个支架（通过球囊充气）扩展到与代表性的患病冠状动脉模型接触，然后进行药物释放模拟。此外，还构建了一个单独的模型来测量支架的柔韧性。由于每个设计的计算模拟时间非常长（约 24 小时），因此使用高斯过程建模方法来分析与所提出的参数化相对应的设计空间。建立了四个评估回弹、应力分布、药物分布和柔韧性的目标，以进行优化研究。特别是，建立了单目标约束优化问题，以相对于基线几何形状来改进设计，即在不损害其他目标的情况下改进一个目标。分别获得了 8%、6%和 15%的应力、药物和柔韧性指标的改进。以主效应的形式量化了设计特征对每个目标的相对影响，从而提出了可以改变以提高支架性能的设计特征。特别是，结果表明，较大的支柱宽度与较小的环轴向长度相结合，在最小化平均应力和最大化药物输送方面是最优的。此外，结果表明，链接的幅度较大且最小弯曲区域，对于提高柔韧性、平均应力和药物输送是有利的。
