Surface characteristics of NiTi cardiovascular stents by selective laser melting

Abstract

Selective laser melting (SLM) has gained great attention to manufacture cardiovascular stents given its potential of fabricating customized stents with complex shapes to satisfy clinical requirements. In this study, the surface characteristics of NiTi cardiovascular stents by SLM were explored. The effect of SLM machining parameters on surface morphology, geometry accuracy, phase composition, surface roughness and contact angle were analyzed. The results demonstrated that the surface morphology of stent became more irregular and the surface roughness was enhanced accompanied by the volume energy density (VED) increased. SLMed stents exhibited hydrophobic properties, and the rougher surface obtained a lower contact angle. The deviation of strut thickness was more than 200% than the nominal value under 194 J/mm3. The lowest VED displayed strong cubic B2 structure with less content loss of Ni, satisfying the self-expand NiTi stent requirements. Then electrochemical polishing (ECP) process distinctly improved the surface quality, providing smoother surfaces. The surface roughness reduced minimum to 0.45 µm from 6.64 µm for SLMed stent, and the average strut thickness was reduced to 230 µm at most. Finally, electrochemical test results revealed that SLM-ECPed stents showed a more obvious tendency to resist corrosion compared to SLMed stents.