Vascular Stent Design Optimisation Using Numerical Modelling Techniques

Since their first introduction in 1985 by Palmaz et al. (1985), balloon-mounted vascular stents have revolutionised the treatment of atherosclerosis, and in particular coronary artery disease. Vascular stents were developed to restore blood flow in stenosed arteries of the body, thereby preventing ischemia and myocardial infarction in peripheral and coronary arteries, respectively. A modification to these first stents by Schatz et al. (1987) led to the development of the first commercially successful stent, the Palmaz–Schatz stent. This redesign of the very first stent led the way in a new era of vascular medical device design, with a vast range of new stent designs, materials and adjunct drug therapies subsequently emerging at an ever increasing pace. Now over 25 years on, stents have undeniably become the gold standard in the non invasive treatment of atherosclerosis with 3 million implanted worldwide each year (van Beusekom & Serruys, 2010). To-date, vascular stents have been developed using an extensive range of high grade metals, from tantalum and titanium to the more common medical grade stainless steel, and more recently high yield strength materials such as cobalt chromium and platinum chromium alloys have also been used (Lally et al., 2006; Gopinath et al., 2007; Huibregtse et al., 2011). Self-expanding stents have been developed from shape memory alloys for peripheral anatomies to eliminate the need for expansion using angioplasty balloons (Gopinath et al., 2007). Biodegradable stents have been developed to allow for removal of the stent following successful revascularisation, whilst stents have also been developed to incorporate complementary drug, gene and radiation therapies and even pre-seeded with endothelial cells to lower thrombosis and encourage re-endothelialisation (Serruys et al., 2006; Sharif et al., 2004; Kay et al., 2001; Van der Giessen 1988; Dichek et al., 1989).While many of these new stent designs have offered improvements on their predecessors, no single design has successfully incorporated all of the characteristics of the ideal stent and one significant limitation in the long-term success of stents still remains, namely in-stent restenosis.