A study of balloon type, system constraint and artery constitutive model used in finite element simulation of stent deployment

This paper carried out a comparative study of different practices used in finite element simulation of stent deployment, with a focus on the choice of balloon type, system constraint and artery constitutive model. Folded balloon produces sustained stent expansion under a lower pressure when compared to rubber balloon. The maximum stresses on the stent and stenotic artery are considerably higher for simulations using a folded balloon, due to the assumed elastic behaviour of the folded balloon which signified the contact stresses between the balloon and the stent. The achieved final diameter is larger for folded balloon than that for rubber balloon, with increased dogboning and decreased recoiling effects. Fully constrained artery reduces the final expansion when compared to a free artery and a partially constrained artery due to the increased recoiling effect. The stress on the plaque-artery system has similar distribution for all three types of artery constraints (full, partial and free of constraints), but the magnitude is higher for a free artery as a result of more severe stretch. Stenotic plaque model plays a dominant role in controlling stent expansion, and calcified plaque model leads to a considerably lower expansion than hypocellular plaque model. Simulations using Ogden and 6-parameter polynomial models generate different behaviour for stent expansion. For Ogden model, stent expansion approaches the saturation at a certain stage of balloon inflation, while saturation is not observed for 6- 2 parameter polynomial model due to the negligence of the second stretch invariant in the strain energy potential. The use of anisotropic model for the vessel layers reduced the expansion at peak pressure when compared to the simulation using an isotropic model, but the final diameter increased due to the significantly reduced recoiling effect. The stress distribution in the arteryplaque system is also different for different combination of artery and plaque constitutive models. In conclusion, folded balloon should be used in the simulation of stent deployment, with the artery partially constrained using spring elements with a proper stiffness constant. The blood vessel should be modelled as a three-layer structure using a hyperelastic potential that considers both the first and second stretch invariants as well as the anisotropy. The composition of the plaque also has to be considered due to its major effect on stent deployment.