Finite Element Analysis Of Mechanical Behavior On Biodegradable Magnesium Alloy Stents

Stent implantation now is an effective mean for the treatment of cardiovascular disease. Traditional permanent stent is prone to cause restenosis after implantation and is impossible to be implanted again when restenosis occurs. Gradual degradation of biodegradable stents in human body can reduce the long-term stimulation of blood vessel and then reduce the incidence of restenosis. Polymer materials iron and magnesium alloy are candidates for biodegradable stent materials. Magnesium alloy is the most potential materials for cardiovascular stents among them.As the degradation rate of magnesium stent was influenced by the stress caused by balloon expansion, finite element method was used to simulate the residual stress of stent after expansion. Comparison was made to residual stress in different parts of stent and to the change of stress with different strut size. Mechanical properties of two different types of stent were simulated. Radial force and compliant change of different types and sizes of stent with the size of strut were computed. The effect of material property to radial force of stent was also taken into consideration.Finite element analysis results show that the sites of the stress concentrating at are the two ends and central of the structure unit for different size of strut. The residual stress decreases when the size of strut decreases. Stress change at the minimum curvature point is most obvious and the stress is higher than that at other point. Stress at the inner surface of square cross-section stent is higher than that at the outer surface. Stress at circular cross-section stent is higher than the stress at other two cross-sections shapes stent. This phenomenon shows that circular cross-section is prone to cause stress concentration. Reaction forces provided by all sizes of open-loop structure stents are always higher than that by the closed-loop structure. When the compression is 1.5cm, reaction forces supported by closed-loop structure stent are 67% of that by open-loop structure. Compared with the same structure of magnesium stent, stent made of 316L stainless steel can provide much bigger reaction force. When the compression is 1.5cm, reaction forces supported by the magnesium stent are only 46% of that by stainless steel stents. Flexibility of the open-loop structure stent is better than that of the closed-loop stent. In the early stages of bending, difference of flexibility between the two types of stent is relatively small, while with the increase of deformation, the difference increases. When the deformation is 1mm, resistance of deformation of the open-loop structure stent is only about 60% of that produced by closed-loop structure stent.Structure of stent has great influence on the stress generated during the expanding process and the mechanical properties. Structural design can improve the performance of stent and is primary means to ensure magnesium alloy stent to have excellent performance.