Influence of Storage Conditions on Clinically Relevant Properties of Peripheral NiTi Stents

The temperature-dependence of the mechanical properties of NiTi is well known in the community for many years. However, most manufacturers do not consider the conditions their devices are being subjected to during transportation or longer-term storage on the shelf during the design process. The present paper reports on the influence of time and temperature on clinically relevant performance parameters of peripheral NiTi stents, including elastic recoil after deployment, radial force and A_f-temperature. All three parameters are of utmost importance for the success of a vascular intervention in the catheter lab. The unintended change of any of these characteristic and carefully designed stent properties may result in an increased risk for the patient, due to a reduction of the effectiveness of the device. Fully processed NiTi stents were stored at temperatures between 50 – 90°C for up to 30 days, simulating the exposure to elevated temperatures well beyond the clinically intended range. Subsequently, the stents were examined regarding changes of the mechanical properties and a shift in A_f-temperature and compared to devices stored at ambient temperature. As a result, the paper identifies critical storage conditions for NiTi medical devices, which should be avoided to prevent a degradation of these important properties.