The Influence of Stent Geometry on Haemodynamics and Endothelialisation

Every year, millions of people worldwide undergo stent implantation to widen narrowed arteries or to redirect blood away from aneurysms. The rapid post-operative regrowth of a healthy endothelial layer, a key factor in stented artery repair, would reduce complications and improve quality of life for many patients. While this has long been a clinical or pharmaceutical issue, this project considers the role of local haemodynamics, specifically the effects of stent-modified wall shear stress on the endothelium. Endothelial cells have a strong mechanobiological response to wall shear stress magnitude, direction and time variance. To understand the impact of stent geometry on this response through altered fluid dynamics, a novel model vessel was developed for the deployment of a wide range of coronary and flow diverter stents in vitro. The model allowed the observation of both endothelial cell migration and, via particle tracking, disturbed flow within the stents. High-resolution micro-computed tomography scanning techniques replicated stent geometry in silico, enabling computational fluid dynamics simulations for the assessment of wall shear stress distribution. Coronary stents greatly influenced fluid flow. The orientation and distribution of tracked particle streamlines were transformed proximal to stents struts, which were also areas of reduced wall shear stress. These areas correlated with zones of reduced cell migration. Flow diverter stents had a lesser impact on observable particle flow; yet endothelial cell migration within them was completely arrested. This is likely due to their structure directing flow away from the wall and reducing shear stress to an even greater extent that coronary stents, over a more substantial area. Dissimilar cell migration between coronary and flow diverter stents is a point of possible significance as the two are treated alike with respect to post-operative care and medication. Continued analysis of various geometries may enable the efficacy of individual stent designs to be quantified or predicted. By applying this knowledge in the future, careful stent design could reduce their impact, or exert an intentional, active influence on endothelial cells, to optimise the healing proces