<i>In Situ</i> XRD Stress Analysis during Expansion of Stents

Abstract

Stents are medical implants, which are applied to keep cavities in the human body open, e.g. blood vessels. Typically they consist of tube-like grids of suitable metal alloys. Typical dimensions depend on their applications: outer diameters in the mm-range and grid bar thickness in the 100 µm range. Before implantation, stents are compressed (crimped) to allow implantation in the human body. During implantation, stents are expanded, usually by balloon catheters. Crimping as well as expansion causes high strains and high stresses locally in the grid bars. These strains and stresses are important design criteria of stents. Usually, they are calculated numerically by Finite Element Analysis (FEA) [1,2]. The XRD-sin²ψ-technique is applied for in-situ-determination of stress conditions during crimping and expansion of stents of the CoCr-alloy L-605. This provides a realistic characterization of the near-surface stress state and an evaluation of the numerical FEA results. XRD-results show an increasing compressive load stress in circumferential direction with increasing stent expansion. These findings correlate with the numerical FEA results. Further residual stresses after removing the expansion device have been measured.