ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

expansion of a stent, a metallic scaffold with the function of maintaining the vessel
dilation. At present this technique is used in more than 70% of percutaneous coronary
interventions, but the placement of a stent often results in in-stent restenosis (ISR), a renarrowing
of the artery due to neointimal hyperplasia [1-2].
Models of ISR can provide further detail of the factors involved. Boyle et al. [3] studied
development of neointima using a cell-centred lattice-based approach. This model
considers tissue growth as a result of vessel injury based on the stress state immediately
after stent deployment without evolution of the mechanical stresses over time. Evans et
al. [4] present a model of restenosis using an agent-based approach to describe smooth
muscle cell behaviour following stent deployment. This approach is able to capture the
rupture of the internal elastic lamina but does not consider the contribution of the
extracellular matrix. The mechanical environment of the vessel wall and how this
changes over time is currently not well understood. Anatomy, biochemical contents,
mechanical properties of arteries have been reported in the past [5], both for human and
animal vessels. The material properties alone are not sufficient to represent the
interaction between the stent and the vessel as the boundary conditions of the problem
will also determine the stress distribution within the vessel wall.
This study aims to address the importance of some of the spatial and temporal
parameters associated with vascular stress, evaluating in particular the effect of
considering the axial pre-stretch of the vessel and the viscoelastic long-term response
after the short-term stent deployment. These are considered in the context of a
simplified stent expansion in a 3D finite element model.
3. MATERIALS AND METHODS
A section of a coronary artery has been generated within ANSYS Mechanical APDL
version 12.0 (ANSYS Inc.): 1/6 of a straight tube represents a 3D vessel, with an initial
radius of 1.4 mm, thickness of 0.1 mm and a length of 30 mm, thus longer than the stent
length of 18 mm (Fig.1).
Fig. 1 - The Finite Element model of the vessel and the stent. The model is a 1/6 symmetry, on the
right the symmetry expansion and an example of stent deployment are shown.