Research On Structure Design And Mechanical Properties Of Magnesium Alloy Vascular Stent

In recent years,vascular stent intervention has gradually developed into the mainstream treatment for cardiovascular diseases.As a new type of vascular stent material,biodegradable magnesium alloy can avoid problems such as impaired vascular function and late restenosis caused by traditional stents being permanently left in the body.It is known as the fifth revolution in coronary interventional therapy,and it is also the current field of vascular stents.Research frontiers.However,under the same structural conditions,the mechanical properties of magnesium alloy stents are not perfect compared with traditional metal stents.If the structural design is unreasonable,the stent will not achieve good supporting effects.Therefore,improving the mechanical properties is a key issue for its development..In order to improve the mechanical properties of the stent,this paper proposes a large included angle W support ring structure and a J-shaped,V-shaped and S-shaped curved connecting rib structure to improve the mechanical performance of the stent by analyzing the force of the stent.Four different designs are designed.The structure is composed of I-shaped straight rod connecting ribs and W-shaped support rings,respectively,J-shaped curved connecting ribs and W-shaped supporting rings constitute JW stents,V-shaped curved connecting ribs and W-shaped supports The ring forms the VW bracket,and the S-shaped bending connecting rib and the W-shaped supporting ring form the SW bracket.The mechanical properties of these four stents were studied by finite element,The results showed that the W-shaped support unit improved the radial support performance of the stent,SW,VW,The radial support stiffness of IW and JW stents are increased by 23.7%,15.7%,13.9%,and 12.9%,respectively,compared with BVS.The radial recovery rate of the four stents is also reduced compared to the BVS stent;the axial shortening rate and the axial recovery rate of the IW,JW and VW stents are also less than that of the BVS,SW axial shortening rate and the axis In terms of flexibility,the bending stiffness of the SW bracket is the smallest,which is 56.98% lower than that of the BVS;VW and JW are the second,with 37% and 12% reduction respectively.Conclusion: The main factors affecting the radial stiffness and radial recovery rate of the stent are the structure of the support ring and the connection position of the connecting ribs.The use of the W-shaped support ring can effectively improve the radial support and radial retraction performance,and the connecting ribs are connected The position of the straight rod on the opposite side of the support ring shows better radial support force and radial recovery;the connecting rib structure and the connecting position of the connecting rib are the main factors affecting the axial shortening rate,and the curved connecting rib structure reduces the stent Axial shortening;the main factor affecting the bending stiffness is the structure of the connecting ribs,and the flexible performance of the bracket using the bending connecting ribs is better.The finite element model of the stenosis vessel-stent was established,and the stent was implanted into a stenosis vessel with a stenosis rate of 25%.It was concluded that the four types of W-shaped stents played a good role in supporting the stenosis vessel and recovered in the radial direction.In terms of rate and dog bone rate,it is also better than the BVS stent,and the improvement effect of the SW stent is the best.However,in terms of axial recovery and axial shortening,the SW was significantly larger than the BVS stent,increasing by 2.24 times and 2.95 times,respectively.After the five stents were implanted,the distribution of the vascular wall stress cloud map was consistent,and the stress peaks were different.If the peak stress on the vascular wall surface was used as the evaluation index,the VW and JW stents had less damage to the blood vessel.The fluid-structure coupling analysis after vascular stent implantation was carried out,and it was concluded that under the action of blood and blood vessel wall,the stress distribution of the five stents was the same.During the whole cardiac cycle,the stress value change law was the same,but the maximum stress value was different.,VW stent has a minimum of 114.8Mpa,and BVS and IW stents are the largest,greater than 140Mpa;after VW and SW are implanted,the effects on blood flow rate,wall shear force and shear shock factor in the blood vessel are better than those of BVS,IW and JW The bracket shows that the reverse distribution structure of the support ring is better than the same direction distribution.Comprehensive in vitro,in vivo,and fluid-structure coupling research results show that the overall performance of the VW stent is the best.Its radial support stiffness is1080.3MPa,which is 15.7% higher than BVS;the radial recovery rate is 3.628%,which is lower than BVS 12%;the axial shortening rate is 1.667%,which is 21.5% less than BVS;the bending stiffness is 3.51,which is 37% less than BVS;in the peak state of expansion,the peak stress of the vessel wall surface is 0.28 MPa,which is less than that of the BVS stent(0.33 MPa);under the action of blood flow,the maximum stress of the stent is 114.8 MPa,which is smaller than the BVS stent(141.4MPa);the area of the highwall shear stress and the high-wall shear oscillation factor area is smaller than that of the BVS.