Geometry parameterization and multidisciplinary constrained optimization of coronary stents

Abstract

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.

Comparing coronary stent material performance on a common geometric platform through simulated bench testing

“…The approach taken was similar to that commonly used in FE stent flexibility studies (Petrini et al, 2004;Wu et al, 2007;Pant et al, 2011) and allowed a direct comparison with previous experimental studies (Mori and Saito, 2005). Similar to the previous bench-tests, only two circumferential rings of the stent were modelled for stents A and C and three for stent B.…”

Multi-objective optimisation of stent dilation strategy in a patient-specific coronary artery via computational and surrogate modelling

“…The release of the drug was simulated as a steady state event by using the forced heat convection analysis capability of ABAQUS/Standard. The boundary conditions for the transport simulation were defined as in other studies (Feenstra and Taylor, 2009;Hose et al, 2004;Pant et al, 2012;Zunino, 2004).…”

“…It is an index indicating the average stress change within a fixed volume (intima-media wall). VAS has been presented by Holzapfel et al (2005b) and successfully implemented in recent studies (Pant et al, 2012;Pant et al, 2011;Ragkousis et al, 2015).…”

“…Similarly to the VAS index, a volume average index for drug release was proposed by Pant et al (2012) to measure the amount of drug transported into the tissue. VAD expresses the average drug diffusion within a fixed volume (intima-media wall).…”

Fabrication of Small Caliber Stent-grafts Using Electrospinning and Balloon Expandable Bare Metal Stents

“…But the development of small caliber stent-grafts is limited by the ability to maintain low profile and flexibility, which aids in deployment of the stent-grafts [11][12][13][14] . PU is an elastomeric polymer with good mechanical strength which is a desired trait for achieving a low profile and good flexibility 15,16 .…”