An apparatus to measure the shape memory properties of nitinol tubes for medical applications

A new apparatus has been developed to characterize the shape memory properties of Nitinol tubes and stents. In tests run on this apparatus, the samples are deformed in the radial direction in the martensitic state to a prescribed outer-fiber strain. Recovery strain and force are monitored continuously on heating. Values of properties as measured on this apparatus are compared to corresponding values from three-point and four-point bending tests, as well as DSC. We have found that this is a fast and reliable system to test transformation temperatures and recovery forces of tubes and stents.