PSI - Issue 15

Ran He et al. / Procedia Structural Integrity 15 (2019) 28–32 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 1. Artery-plaque-stent-balloon assembly.

2.2. Interactions, loadings, and boundary conditions Both ends of the artery were fixed in the longitudinal and circumferential directions throughout the simulation. Stent deployment consists of balloon inflation, deflation and removal steps. The inflation step was performed by applying pressure on the inner surface of balloon. The uniform pressure was linearly increasing from 0 to 1.8 MPa. Interactions between the artery, stent and balloon were modelled as general hard contacts with a frictional coefficient of 0.25 (Ju et al., 2008). The deflation step was modelled by releasing the pressure on the inner surface of balloon, which allowed the expanded stent to recoil freely. Interactions between stent, the balloon and the plaque were maintained in this step. In the final step, the contact of the balloon with the stent and artery was removed. 2.3. Material models The first-order Ogden model with the Mullins effect were adopted to describe the mechanical behaviour of the plaque, for which the parameters were determined by fitting the experimental data for echolucent (soft) and calcified (stiff) plaques in Maher et al. (2011). The modified HGO-C model with damage were adopted to describe the mechanical behaviours of the arterial layers, for which the parameters were determined by fitting the experimental data in Weisbecker et al. (2012) and Fereidoonnezhad et al. (2016). The material of the Resolute Integrity™ drug-eluting coronary stent was MP35N, a nickel-cobalt base alloy, with a density of 8.5772E-9 tonne/mm 3 , Young’s modulus of 176000 MPa, Poisson’s ratio of 0.22 (Fallen et al., 2001). Its plastic behaviour was provided by Han et al. (2002). The material of the balloon was Pebax with a density of 1.01E-9 tonne/mm 3 , Young’s modulus of 963.16 MPa and Poisson’s ratio of 0.4 (Foster Polymer Distribution, 2017). 3. Results Table 1 shows the lumen areas and the maximum/minimum diameters obtained from simulations for soft and stiff plaques, in comparison with clinical results before and after stenting. The 13 positions were illustrated in Fig. 1. Both simulations achieved the desired outcomes; however, those simulated with stiff plaque were closer to the clinical outcomes. The stenting-induced stress and damage in the stiff plaque were about 2 and 1.5 times those in the soft plaque, respectively.

Table 1. Comparison of clinical and simulated results for lumen dimensions after stenting.

Position Before stenting

Clinical after stenting

Simulation after stenting (soft plaque) Simulation after stenting (stiff plaque)

A

MaxD MinD A

MaxD MinD A

MaxD

MinD

A

MaxD

MinD