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

immediately after stent expansion and after a time of 2500 seconds, under a cyclic
pressure (diastolic/systolic = 80/120 mmHg).
4. RESULTS
4.1 Influence of initial conditions: pre-stretch and systolic pressure
The radial displacement imposed by the stent struts expanding is similar in the two
models, as the vessel radius after application of both systolic pressure and pre-tension
increases by less than 10% relative to the zero-stress condition. However, the
application of the physiological initial conditions results in a stiffening of the vessel
response. This is illustrated in figure 2 which shows the radial stress in the two models
after stent expansion for the region directly under the stent strut.
Fig. 2 - Radial stress distribution on a central section of the stress-free model (a) and the prestretched
model with systolic pressure (b).
Both the magnitude and distribution of stresses show differences: in the second case, the
maximum compressive stress is much higher (-298 kPa vs. -107 kPa), due to the
increased stiffness of the vessel after application of initial conditions.
4.2 Influence of viscoelasticity: stress relaxation
The temporal variation in radial stress is shown in figure 3 at both systolic and diastolic
pressure, both immediately after stent deployment and after a further elapsed time of
2500 seconds. A reduction in the peak compressive stress (29%) is observed after stress
relaxation has occurred along with a reduction in the area of the vessel subject to higher
compressive stress at the end of the stent. It is also noted that the changes in vessel
geometry between systolic and diastolic pressure values are influenced by the state of
relaxation.