RESUMO
BACKGROUND:Restenosis easily occurs after stent implantation,thus it is worthy optimizing the stent design and evaluating its structural safety.OBJECTIVE:To simulate the deformation of balloon-expandable stainless steel stents by the finite element method,and calculated the radial displacements and stresses after expansion in different designs.DESIGN:A comparative calculated analysis.SETTING:Laboratory of Laser Processing Technology,South China Normal University.MATERIALS:The experiment was carried out in the Laboratory of Laser Processing Technology,South China Normal University in October,2006.The model of slotted-tube stent was used.METHODS:The simulations were carried out to expand a stainless steel stent with 2 mm in outer diameter,10 mm in length and 0.09 mm in strut width.Due to the symmetry of the stent by utilizing the correct boundary conditions,a half model was used to simulate the deformation process.①In stent I,the slot length was 2.0,4.0 and 4.0 mm for a,b and c respectively.In stent Ⅱ,the slot length was 1.5,4.5 and 4.0 mm for a,b and c respectively.In stent Ⅲ,the slot length was 1.8,4.2 and 4.0 mm for a,b and c respectively.Three points(A,B and C)in vary strut were selected to study the displacement during the process of deformation.The pressure applied as a surface load on the inner stent surface was 0.5 Mpa.②The dimensions and radial displacements of the three stent designs in the process of expansion were calculated,and the changes of deformation stresses were observed in the third design.MAIN OUTCOME MEASURES:① The dimensions and radial displacements of the three stent designs in the process of expansion were calculated;②The changes of deformation stresses were observed in the third design.RESULTS:The shape of the expended stent I looked like a dumbbell.The maximum radial displacement of point C obtained is found to be 2.1 mm,and the point B obtained the smallest radial displacement of 0.3 mm in the three defined points.In stent Ⅱ,the maximum radial displacement obtained is found to be point B of 2.1 mm,and the point C obtained the smallest radial displacement of 1.20 mm in lhe three defined point,which obtained a spindly shaped stents.In stent Ⅲ,the maximum radial displacement obtained is found to be point B of 2.2 mm,and the point A obtained the smallest radial displacement of 1.85 mm in the three labeled point,which produce more uniform expansion than the last two stent designs.②In stent Ⅲ,the stresses and the radial displacements achieved as the pressure increased gradually.CONCLUSION:The stress concentrations and the uniformity of the expanded stent can be decreased through optimizing the stent design by finite element method,which can be used in optimizing the stent design and evaluating the structural safety of stents.
RESUMO
As an important medical instrument in percutaneous transluminal coronary angioplasty, endovascular stents must have excellent biocompatibility. In this paper, after a description of the performance and fabrication process of stents, we analyzed the technology to improve the biocompatibility of stents during the fabrication process which is the effective method for decreasing the rate of restenosis.
