Nitinol Stents Printed by Selective Laser Melting

Abstract

Nitinol alloys stents have been printed by Selective Laser Melting from a gas atomized powder with a composition of 50.8 at% Ni. The energy density has been adapted to set the austenite finish temperature just below the human body temperature, therefore the stent diameter can be reduced by plastic strain at lower temperature and recover its former expanded shape after being inserted in the artery. Several mesh geometries have been mechanically analyzed by finite elements modeling to ensure that the local strain will not exceed superelastic reversible capacity of 4% while squeezing the stent diameter by a factor of 4. The stent surface has been treated by electropolishing to reduce its roughness to Ra < 0.02 mm. After polishing, some samples have been coated by a 50 nm thick TiO₂ layer by Atomic Layer Deposition. Biocompatibility and hemocompatibility analysis demonstrated that the TiO2 coating significantly improved hemocompatibility. Nevertheless, uncoated stents are also biocompatible and hemocompatible according to ISO-10993–12 guidelines.