Event Abstract

MRI-compatible Nb-60Ta-2Zr alloy used for vascular stents: mechanical properties, corrosion resistance and haemocompatibility

  • 1 Institute of Metal Research, Chinese Academy of Sciences, China
  • 2 School of Stomatology, China Medical University, China

Introduction: With the increased usage of magnetic resonance imaging (MRI) as a diagnostic tool in clinical trials, the currently-used metals for vascular stents, such as 316L stainless steel (SS), Co-Cr alloys and Ni-Ti alloys, are challenged by their MRI incompatibility, due to their constituents containing ferromagnetic or paramagnetic elements.

To provide new MRI compatible vascular stents, the Nb-xTa-2Zr (30≤x≤70) series alloys were selected in the current work. Several key properties of these alloys were optimized in terms of stent requirements, including magnetic susceptibility, elastic modulus and tensile properties [1]. Using revised simulated body fluid (r-SBF), the electrochemical corrosion behavior of an Nb-60Ta-2Zr alloy for MRI compatible vascular stents was characterized [2]. To assess the hemocompatibility, platelet adhesion (lactate dehydrogenase activity), platelet activation (P-selectin expression), coagulation and hemolysis of Nb-60Ta-2Zr alloy were investigated, For comparison, parallel assessments for these factors were performed for the Nb, Ta, 316L SS and L605 Co-Cr alloy (L605) [3].

Experimental Methods: The Nb-60Ta-2Zr alloy ingot was fabricated using electron beam melting (EBM), with subsequent forging and annealing. Magnetic susceptibilities of the alloys were measured using a MPMS-7S superconducting quantum interference device (SQUID).  

The chemical composition of the sample surface of the alloy was analyzed using X-ray photoelectron spectrometry (XPS). Simulated body plasma solution was used as the electrolyte. The r-SBF was selected to mimic the ion concentrations of human blood plasma. Electrochemical measurements were performed in a standard three-electrode cell filled with approximately 300 mL r-SBF solution.

Platelet adhesion on the material surface is also characterised by lactate dehydrogenase (LDH) activity. Measurements of prothrombin time (PT), activated partial thrombin time (APTT) and thrombin time (TT) were performed with an automated blood coagulation analyser. Haemolysis testing was performed according to ASTM F 756-00

Results and Discussion: In the as-cast state, a single-phase solid solution with bcc structure was formed in the alloys. The volume magnetic susceptibility (χv) and Young’s modulus (E) of the alloys scaled linearly with the Ta content. Increasing the Ta content gave rise to the decreased χv and the increased E, together with the elevated yield strength but less-changed elongation. From multiple requirements for the stents, the Nb-60Ta-2Zr alloy exhibits an optimal properties, including the χv of nearly 20-fold lower than 316L SS, the E of 149 GPa superior to pure niobium, high mass density of 12.74 g/cm3 favored to the X-ray visibility, yield strength of ∼330 MPa comparable to the 316L SS and a elongation of ∼24%.

After immersion in the solution of r-SBF, the surface passive oxide film of the alloy was identified as a mixture of the Nb, Ta and Zr oxides, with a thickness of approximately 1.3 nm, as shown by XPS analysis. In terms of potentiodynamic polarization curves and EIS, the Nb-60Ta-2Zr alloy manifests a low corrosion rate and high polarization resistance. No localized corrosion was detected.

The propensity for platelet adhesion and activation on the Nb-60Ta-2Zr alloy was at nearly the same level as that for Nb and Ta but was slightly less than those of 316L SS and L605. The mitigated platelet adhesion and activation of the Nb-60Ta-2Zr alloy is associated with its decreased adsorption of fibrinogen. The Nb-60Ta-2Zr alloy has a longer clotting time and exhibits significantly superior thromboresistance than 316L SS and L605. Moreover, the haemolysis rate of the Nb-60Ta-2Zr alloy satisfies the bio-safety requirement of the ISO 10993-4 standard.

CONCLUSIONS: Among the Nb-xTa-2Zr (30≤x≤70) series alloys, the Nb-60Ta-2Zr alloy provides optimal properties, considering the multifactorial requirements of the stent. The Nb-60Ta-2Zr alloy possesses a significant advantage in corrosion resistance in the human blood environment, in contrast to current stent metals such as 316L SS and Co-Cr alloys. Regarding blood coagulation, the Nb-60Ta-2Zr alloy has a longer clotting time and exhibits significantly superior thromboresistance compared to 316L SS and the L605 Co-Cr alloy.

References:
[1] H.Z. Li, J. Xu, J. Mech. Beh. Biomed. Mater. 32 (2014)166-176.
[2] H.Z. Li, X. Zhao, J. Xu, Mater. Sci. Eng. C. 56 (2015)205-214.
[3] X.M. Li, et al.,Mater. Sci. Eng. C. 42 (2014)385-395

Keywords: MRI, corrosion, mechanical property, hemocompatiblility

Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016.

Presentation Type: Poster

Topic: Metallic biomaterials and alloys

Citation: Xu J, Li H, Li X and Ai H (2016). MRI-compatible Nb-60Ta-2Zr alloy used for vascular stents: mechanical properties, corrosion resistance and haemocompatibility. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.01239

Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters.

The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated.

Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed.

For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions.

Received: 27 Mar 2016; Published Online: 30 Mar 2016.