Multiscale modelling of stent/vessel interactions

Angioplasty with stenting re-opens stenosed arteries, but in-stent restenosis remains a common negative outcome. Correlations between local mechanical stimuli and ISR have been reported, explained by mechanotransduction mechanisms that influence cell behaviour. This thesis investigates the loads imposed on the coronary artery following stent implantation. The changes in mechanical stimuli in a vessel following stent deployment were initially considered using a simple MATLAB model, followed by analysis of a 2D cross-section model to represent variation of stress with stent strut distribution. This model revealed the distribution of the stress through the thickness and around the circumference varied significantly for high expansion ratios and uneven strut distributions. A 3D continuum model of stent geometry post-expansion, obtained from micro-CT images, was used to analyse stent interaction with an idealised vessel geometry. The structural stress at the level of individual struts was compared to histological data and to fluid dynamic simulations of the same stent/vessel geometry. When structural and fluid dynamic stimuli were considered together, correlations with the amount of neointimal growth became more significant than when they were considered individually. This suggests that both stimuli contribute to the development of neointimal growth and their combination may accelerate the progression of ISR. Finally, the thesis describes a model of the evolution of in-stent restenosis. A cellular model of growth was developed to include feedback from a finite element model of the vessel and neointima. Change in the lumen geometry was captured with neointimal growth, an updated geometry was passed to the finite element model to compute the subsequent change of stress direction on cells during their growth. The results show encouraging resemblance with histological images of ISR, especially for the early phases of growth. The thesis concludes with a summary of the modelling results and a review of opportunities for further research