Application Study Of NiTi Sma Vascular Stent

It’s highly concerned of the Niti shape memory alloys because of their outstanding shape memory effect (SME) and super-elasticity (SE). With their high recoverable elastic strain, high output strength and good biological compatibility of the NiTi Alloys, it’s regarded as one of the most promising developing targets to introduce the minimally invasive surgery using the Nitinol stent into the treatment of heart and vascular diseases. In this paper, the processing methods and as the result of its performance of a design of nitinol vascular stent are studied aiming the real commercial application.Firstly, the effect on superelasticity of the heat treatment process of a commercial NiTi (Ni 50%atm.) alloy is studied. The results show that the main purposes of heat treatment process are to set shape and enhance the mechanical performance, and the higher temperature or longer processing time should be applied in the second heat-treating process in a two-step heat treatment process. For the special application requirements of a commercial design of stent, it’s recommended a most reasonable heat treatment data which is 480 centigrade C x 5 minutes in the first heat-treating step and 500 centigrade C x 5 minutes in the second heat-treating step.Secondly, it’s studied of the effects of different surface finishing methods on the fatigue and anti-corrosion performance of a commercial nitinol wire. The results show that among several surface finishing processes, the electropolishig process can significantly improve the surface condition, extend the fatigue lifetime, and provide better anti-corrosion performances.Finally the interactive strain in the working state of a commercial design of stent is simulated using the Finite Element program MSC.MARC. The results show that the strain in different part of different design of stent pieces is different, while the maximal strain values are found on the surface of the apexes of the stent; stent with legs of different lengths shows higher strain and the maximal strain values are found on the apexes linking legs of different lengths; alternating strain shows a great impact on the fatigue performance of the stent, and higher alternating strain, worse fatigue performance.