Additive manufacturing and heat treatment of zero poisson’s ratio self-expanding nitinol stents

Abstract Additive manufacturing (AM) has recently gained attention as an effective approach for printing patient-specific, self-expanding Nitinol (NiTi alloy) stents with complex structural designs for the treatment of peripheral arterial disease (PAD). However, achieving the desired phase transformation temperature and superelastic performance remains challenging due to compositional variations, phase imbalance and microstructural inhomogeneities introduced during the printing process. In this study, self-expanding Nitinol stents with a zero Poisson’s ratio (ZPR) structural design were fabricated via laser powder bed fusion (PBF-LB). The printed stents showed no evidence of cracks or structural defects, confirming PBF-LB’s capability to produce mechanically sound stent geometries. However, the as-printed stents exhibited an austenite finish (A f ) temperature above 80 °C, which is incompatible with body-temperature functionality. To address this, a systematic post-heat treatment strategy was developed by varying temperature and time, with the effects evaluated through transition temperature measurements and previously unreported cyclic three-point compression testing. The optimised treatment, solution annealing at 850 °C for 15 min followed by aging at 500 °C for 15 min, produced a homogenised microstructure with surface Ni diffusion, effectively reducing the A f temperature to 35 °C. Under these conditions, the stents demonstrated excellent superelastic performance at body temperature, achieving a 93.6% recovery ratio in the first compression cycle, and 97.9% after ten cycles, representing outstanding superelastic recovery compared with previously reported PBF-LB-printed NiTi. Therefore, this study establishes a viable post-processing heat-treatment protocol that provides a practical framework for manufacturing NiTi implants via AM, while maintaining the desired functional properties of self-expanding ZPR stents. Graphical abstract