Design and characterization of a novel nickel-free cobalt-base alloy for intravascular stents

- A new nickel-free cobalt-base alloy for intravascular stent was prepared.
- Compared with L605 alloy, the tensile strength of the new alloy is > 1000 MPa, and elongation is above 55%.
- New cobalt-base Co-20Cr-12Fe-18Mn-2Mo-4W-N alloy shows excellent corrosion resistance and biological properties.
- New cobalt-base Co-20Cr-12Fe-18Mn-2Mo-4W-N alloy has the potential to be used for intravascular stent.

Co-Cr-W-Ni alloy (L605) with high tensile strength is used in coronary stents. The thickness of individual strut of the stent is reduced which can decrease the stent restenosis rate. However, about 10% Ni element content in L605 is found to cause allergic reactions and pulmonary embolism, similar to the traditional 316L stainless steel. In this study, a novel nickel-free cobalt-base alloy Co-20Cr-12Fe-18Mn-2Mo-4W-N (wt%) was designed and fabricated in order to efficiently avoid the potential hazards of Ni element. Fe and Mn, essential elements of human body, were added in the alloy to substitute part of Co element. In comparison to L605 alloy, the tensile strength of the new alloy was higher than 1000 MPa while elongation was above 55%. The pitting potential of the new alloy was measured close to 1000 mV, also higher than that of L605 alloy. CCK-8 test indicated that the cytotoxicity of the new alloy is grade 1, reflecting that Co-20Cr-12Fe-18Mn-2Mo-4W-N alloy has no cytotoxic effects. There was no significant difference in the apoptosis rates between Co-20Cr-12Fe-18Mn-2Mo-4W-N and L605 alloy. The newly developed cobalt-base alloy showed excellent mechanical, corrosion resistance and biological properties, which could make it a desirable material for future clinical investigations.