Dynamic characteristics of composite coronary stents after implantation

Abstract The dynamic characteristics of composite coronary stents of poly-l-lactic acid (PLLA) coated magnesium (Mg) alloy were investigated using the finite element method (FEM). Firstly, the effects on dynamic performances of stents were considered, such as stent materials, large deformation of expansion and springback during stent implantation, residual stress after implantation, degradation of PLLA coating, and vascular constraints. Secondly, variations in the dynamic characteristics of the blocked artery after stent implantation were calculated. The natural frequencies and corresponding vibration modes of stents and arteries, as well as the response under harmonic excitation were numerically simulated. The results show that, the natural frequency of the composite stent is much smaller than that of the Mg alloy stent. Each natural frequency of the stent after a large deformation of expansion and springback significantly decreased compared with that of the initial stent. The existence of residual stress has a minor effect on the natural frequencies of the stent and does not change the vibration modes. However, degradation of the PLLA coating and vascular elastic constraint have distinct influences on the frequencies of stents. Modal analysis results indicate that bending, torsional and breathing modes occur in the first five vibration modes. Moreover, there are differences in the natural frequencies and vibration modes among healthy, blocked and stent-implanted arteries. These results are helpful for understanding the dynamic behavior of the vascular system after stent implantation and have guiding significance in stent design.