Numerical simulations of stent-based local drug delivery: 2D geometric investigations and the evaluation of 3D stent designs on the basis of local delivery effectiveness.

摘要

Drug-eluting coronary stents have been identified as a promising means of treating in-stent restenosis. Animal models used to investigate these devices can deliver results for restenosis rates, but cannot provide accurate dose delivery information which would be very useful for refining stent geometries and apposition techniques to optimize dose delivery. In this study, a two-dimensional numerical model is constructed to explore geometrical situations of interest following stent implantation. Metallic stents with a polymer coating and biodegradable solid polymeric stents represent two different vehicles for local delivery. A comparison between these stent types is carried out through the variation of geometric parameters of interest. An investigation of solid polymeric stent struts in a curved vessel is then done through a comparison of dose delivery characteristics on inner and outer walls. Dose delivery success is measured using three quantities: the dose homogeneity in a defined therapeutic region, the percentage of mass remaining in that therapeutic region after a defined therapeutic duration, and the amount of contact between the stent and the vascular wall. The appropriateness of a quasi-stationary hypothesis is then justified in two dimensions through analysis of flow and diffusion parameters. This simplification is applied to stent geometries in three dimensions and a single local delivery effectiveness score based on the three dose delivery parameters is calculated. This tool for evaluating stent designs on the basis of local delivery effectiveness provides a starting point for similar, more sophisticated methods that could eventually be applied to a larger sample of existing stent geometries. Ultimately, the output of such a tool could be used to optimize drug-eluting stent designs.