MRI-compatible Nb–60Ta–2Zr alloy used for vascular stents: Haemocompatibility and its correlation with protein adsorption Xiu-Mei Li a , Hui-Zhe Li b , Shao-Ping Wang b , Hsun-Miao Huang c , Her-Hsiung Huang c , Hong-Jun Ai a, ⁎, Jian Xu b, ⁎⁎ a School of Stomatology, China Medical University, 117 Nanjing North Street, Shenyang 110002, China b Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China c Biomaterials & Electrochemistry Lab, Department of Dentistry, National Yang-Ming University, Taipei City 112, Taiwan abstract article info Article history: Received 15 January 2014 Received in revised form 29 April 2014 Accepted 23 May 2014 Available online 2 June 2014 Keywords: Haemocompatibility Platelet adhesion Protein adsorption Niobium Stent Nb–60Ta–2Zr is a newly developed MRI-compatible alloy used for vascular stents. In this work, its haemocompatibility was investigated, including platelet adhesion (lactate dehydrogenase activity), platelet activation (P-selectin expression), coagulation and haemolysis. For comparison, parallel assessments for these factors were performed for the niobium, tantalum, 316L stainless steel (316L SS) and L605 Co–Cr alloy (L605). In addition, albumin and fibrinogen were selected to examine the correlation of protein adsorption with platelet adhesion and metal surface properties. 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. The favourable haemocompatiblity of the Nb–60Ta–2Zr alloy provides evidence of its good biocompatibility and of its suitability as a candidate stent material. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The percutaneous coronary intervention (PCI) approach is increasingly used for patients recovering from blockage in the coronary arteries. Currently, balloon-expandable vascular stents are manufactured primarily from austenitic stainless steel (e.g., AISI 316L) or cobalt–chromium alloys (e.g., L605) [1,2]. When considering stent materials, apart from the mechanical properties, corrosion resistance and biocompatibility, radiography visibility is also a critical issue during the rigorous deploy- ment process for the stent. To reduce X-ray radiation-induced damage to the surgery operator, stent deployment navigated by magnetic resonance imaging (MRI) is a highly promising approach. Furthermore, cardiac MRI examination is also an important tool for the diagnosis of cardiovascular disease, such as the assessment of cardiac vessel morphol- ogy and plaque characterisation [3]. Consequently, compatibility of stent materials with MRI becomes a considerably important property. However, paramagnetic metals, such as the 316L SS and the Co–Cr alloy, exhibit high volume magnetic susceptibility (χ v ), owing to their constituent ferromagnetic elements, such as iron, cobalt and nickel. Under a magnetic field with intense strengths, artefacts in the images are generated as a result of a distortion in the magnetic field [4]. In order to reduce image artefacts, the χ v of stent metals should be as comparable to the surrounding tissue as possible, which is in a range of (-11.0)–(-7.0) × 10 -6 [5]. Recently, niobium- based alloys, such as the Nb–28Ta–3.8W–1.3Zr [6,7] and Nb–60Ta–2Zr al- loys [8], have been considered as an MRI-compatible metal for stent fabri- cation due to their remarkably lower χ v values. As such, the χ v of the Nb– 60Ta–2Zr alloy is only approximately 3% of the value of 316L SS, pro- viding a significant advantage in MRI compatibility. Meanwhile, the Nb–60Ta–2Zr alloy has a Young's modulus of 142 GPa, a yield strength of ~ 330 MPa (comparable to 316L SS), an elongation of ~ 24%. As the stent materials contacted with blood, understanding the blood compatibility of Nb-based alloys is essential. Blood–material interactions trigger a complex series of events including protein adsorption, platelet and leukocyte activation/adhesion, and complement and coagulation activation, which are highly interlinked [9]. Interaction between an im- planted material and blood starts with the adsorption of plasma proteins onto the material surfaces within a few seconds, leading to the formation of a protein adsorption layer of 10–20 nm. The type and quantity of the proteins that are first adsorbed onto the surface will influence the subsequent coagulation process. Fibrinogen (Fb) is a key structural glycoprotein involved in blood clotting by assembling to form a fibrin clot following thrombin activation. Additionally, Fb is largely responsible for mediating platelet–surface interactions by serving as a ligand for the Materials Science and Engineering C 42 (2014) 385–395 ⁎ Corresponding author. Tel.: +86 24 22891420. ⁎⁎ Corresponding author. Tel.: +86 24 23971950; fax: +86 24 23971215. E-mail addresses: aih0620@yahoo.com.cn (H.-J. Ai), jianxu@imr.ac.cn (J. Xu). http://dx.doi.org/10.1016/j.msec.2014.05.051 0928-4931/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec