The Study Of Some Problems Of The Mechanical Property Of Coronary Stents Expansion

Along with the stepping into the aging society of our country and the improving of the people’s diet, the incidence of Coronary Heart Disease (CHD) is increasing. Nowadays the Percutaneous Transluminal Coronary Angioplasty (PTCA) has become the standard therapy for CHD. The stent is the main equipment of the surgery, expanded in the narrowed artery in the surgery and remained to hold the vessel after. After stent is implanted in the lesion, there exist some problems, such as stent fracture and the non-uniformly expansion, which influence the clinical effectsIn order to reveal the mechanical properties and behavior of the stent during expansion in the narrowed coronary artery, and that estimate the relationship between stent expansion and the problems mentioned above, this paper adopted the deduction of mechanical formulas, planar stent experiment and Finite Element Method (FEM) to investigate the expansion.Based on the relative work of Yang et al, this paper analyzed the section internal forces of the Palmaz-Schatz stent during expansion, and deduced formulas of the elastic radial stiffness and the plastic limit pressure. These formulas were verified by FEM and could be an assistance of stent designing. They explained that the Palmaz-Schatz stent has a very high radial strength.Planar stent experiment employed MTS testing machine to do the tension of planar structure of stent symmetrical element. We obtained the radius-pressure curve of corresponding stent by the manufacture of test data acquired by joining the experiment. The experiment verified the formulas of stent mechanical properties and the hinge phenomenon. Meanwhile it showed a significant large deformation of the symmetrical element ends, which implied the easy fracture position.The finite element simulation put a coupling model of the balloon, stent, plaque and three-layered artery, which is based on the CT images of blocked coronary artery. The finite element computation showed the dilation status of balloon during stent expansion, the stress distribution of stent and the artery and the feasibility of CT imaging in finite element analysis. The structural form of the balloon dilation may cause the non-uniform expansion of the stent. The penetration of balloon through the stent interspaces was the direct driving power for the opening of narrowed artery, and aggravated the non-umiformity. The geometrical irregularity of coronary artery stenosis led to that the linking bridge of stent suffered from a large amount of stress, and revealed that the bridge had a high possibility of stent fracture.