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Qiu et al. Vessel Plus 2018;2:12 I http://dx.doi.org/10.20517/2574-1209.2018.13 Page 9 of 15

A Absorb Xience V

B

C

D

Figure 5. Contour plot of the maximum principal stress (MPa) on the (A) plaque, (B) intima layer, (C) media layer and (D) adventitia layer,
after deployment of Absorb scaffold and Xience V stent in eccentric lesion [38]

A B C

Figure 6. Degradation degree distribution on the stent over time [40] . (A) 10 days degradation; (B) 20 days degradation; (C) 30 days
degradation

Stent degradation
BRSs have advantages in overcoming clinical complications (e.g., restenosis and ST) associated with
permanent metallic stents due to their biodegradation characteristics. Generally, constitutive models are
required to describe the mechanical response of stent materials during the process of degradation. For
instance, Soares et al. applied a thermodynamically consistent constitutive model to predict degradation
[39]
behaviour of PLLA stents. This model was suitable for simulating deformation-induced degradation,
especially for biodegradable PLLA. The model is based on a degradation-dependent Helmholtz potential
(material properties decrease as a function of degradation) and the rate of dissipation. Degradation of three
different stent designs was modelled, and results showed that high risk of degradation was mainly observed
at the bends of stent rings and junction points. Luo et al. developed a numerical model to study the
[40]
degradation behaviour of bioabsorbable PLLA stent. The constitutive degradation model combined the
degree of degradation with pre-stretched deformation, and the degree of degradation was used to describe
the change of material property as a function of degradation time. The degradation model was validated
against experimental tensile data at different degradation times. Results showed that degradation happened
throughout the whole stent over 30 days, but the degradation rate was not uniform [Figure 6]. The maximum
degradation was observed at the inner surface of U-bend strut where the stress concentration/maximum
strain occurred during stent expansion, which was in good agreement with experimental result. This
indicated that the degradation rate of material was influenced by the initial deformation.