Page 86 - Read Online

Page 8 of 15 Qiu et al. Vessel Plus 2018;2:12 I http://dx.doi.org/10.20517/2574-1209.2018.13

A 1.2
Absorb
1.0 Xience V
Pressure (MPa) 0.6
0.8

0.4

0.2
0.0
1 1.5 2 2.5 3
Diameter (mm)
B 50% Recoiling
Dogboning
40%
Dogboning/recoiling (%) 30%

20%

10%

0%
Absorb Xience V
Figure 4. (A) Stent outer diameter change against pressure and (B) recoiling and dogboning effects for Absorb scaffold and Xience V
stent in concentric lesion [38]

trend with the increase of stent expansion, which was 4.19%, 2.92% and 1.81% obtained for stent with
expanding to 3.1 mm, 3.7 mm and 3.92 mm, respectively. They also modelled re-crimping of the expanded
stent to evaluate the radial strength and stiffness, and calculated radial strength and stiffness was 1.46 N/
mm (close to the experimental value of 1.55 N/mm) and 1.40%, respectively. Shanahan et al. developed a
[37]
viscoelastic material model for a biodegradable polymeric braided stent, and evaluated the time-dependent
viscoelastic behaviour using finite element method. They simulated the crimping of stent by enforcing
radial displacement on 8 rigid plates, and the linear viscoelastic material model was validated against
their experimental data. However, no significant difference was observed for the crimping behaviour of
braided stent modelled as either linear elastic or viscoelastic material. However, all these simulation work
neglected the diseased artery in their models and was unable to assess the performance of polymeric stents
comprehensively.

Very recently, Schiavone et al. carried out a comparative study for polymeric Absorb stent and metallic
[38]
Xience stent by including diseased artery in finite element simulations. The Absorb stent showed a lower
rate of expansion in diseased artery, with higher dog-boning and recoiling when compared to Xience stent
[Figure 4]. This was due to the difference in material property and stent design. It was suggested that post-
dilatation of Absorb stent is required in order to achieve an effective treatment of stenosis, especially for
patients with stiffer vessels and highly calcified plaques. However, significantly lower stress was induced to
the plaque-artery system treated with the Absorb stent, which is a clinical benefit in terms of causing less
injury to the vessels. Effect of plaque eccentricity was also evaluated in their simulations, and higher stress
was found for the media and adventitia tissue layers with the increase of plaque eccentricity [Figure 5].
Eccentric plaque also caused complications to stent implantation, such as non-uniform stress distribution
and artery expansion. As such, the selection of stents, in terms of designs and materials, will be of high
importance for patients in order to achieve the most effective clinical outcomes.