A Computational Study of Mechanical Performance of Bioresorbable Polymeric Stents with Design Variations

Abstract

The study compared the mechanical behavior of bioresorbable polymeric stents with various designs during deployment, and investigated their fatigue performance under pulsatile blood pressure loading. Methods: Finite element simulations have been carried out to compare the mechanical performance of four bioresorbable polymeric stents, i.e., Absorb, Elixir, Igaki-Tamai and RevaMedical, during deployment in diseased artery. Tri-folded balloon was modelled to expand the crimped stent onto the three-layered arterial wall with plaque. Cyclic diastolic-systolic pressure loading was applied to both stent and arterial wall to study fatigue behavior. Results: Stents with larger U-bend and longer axial strut demonstrate more flexibility but suffer from severe dogboning and recoiling effects. Stress concentrations in the stent, as well as in the plaque and artery, are higher for stents designed with increased rigidity such as 2 those with smaller U-bends and shorter axial struts. Simulations of fatigue deformation for Elixir stent demonstrate that the U-bends, with high stress concentrations, have a potential risk of fatigue failure under pulsatile systolic-diastolic blood pressure as opposed to the counter metallic stents which are normally free of fatigue failure. Conclusion: The structural behaviour of bioresorbable polymeric stent is strongly affected by its design, in terms of expansion, dogboing, recoiling and stress distribution during the deployment process.

Effect of two-year degradation on mechanical interaction between a bioresorbable scaffold and blood vessel

“…Systolic-diastolic stress will introduce cyclic stresses within the scaffold. However, estimated fatigue stresses are considerably lower than the stresses imposed in the scaffold during acute 37 expansion of the scaffold (stress amplitude less than 5% of acute maximum stress during expansion; Qiu, 2017). Rigorous calculation of fatigue safety factors has been attempted for scaffolds in prior works (Li et al, 2010;Azaouzi et al, 2012), however, traditional Goodman analyses (mean stress effect) provide only a rough assessment of fatigue resistance suitable for simple comparisons between scaffold designs, given that this technique is best suited for predicting failure in ductile metals and not polymers.…”

“…The mechanical property for virgin PLLA was found in Pauck and Reddy (2015) who obtained stressstrain curve through performing uniaxial tensile tests. The stress-strain response was already reported in our recently published papers (Schiavone et al, 2016;2017) and thus omitted here.…”

“…For the PLLA material, the density is 1.4×10 -6 , Young's Modulus is 2200 MPa and Poisson Ratio is 0.3. In simulation, plastic behaviour was described by providing the yield stress as a function of plastic strain extracted from the stress-strain curve (Schiavone et al, 2016;2017). Yielding refers to the transition from linear elastic deformation to nonlinear plastic deformation, and the stress level corresponding to this transition point is called yield stress.…”

Mechanistic evaluation of long-term in-stent restenosis based on models of tissue damage and growth

“…Mesh sensitivity was systematically carried out in our previous studies, in terms of stent deployment (Schiavone 2015;Qiu 2017). For the stent, four different meshes, namely 2 × 2, 2 × 4, 4 × 4 and 6 × 6 layers of elements across the width and thickness, were compared.…”

Impact of Degradation and Material Crystallinity on the Mechanical Performance of a Bioresorbable Polymeric Stent

“…Finite element analysis (FEA) presents an attractive means to investigate the mechanical performance of BPS, and a number of such studies have examined the mechanical properties of PLLA for the BPS application [23][24][25][26][27][28]. Geometry and material stiffness were found to significantly impact the radial strength, recoil characteristics and short-term mechanical performance of BPS [23], whereas a similar influence of recoil behaviour on design was noted [28].…”