Anisotropic Behavior of Radiopaque NiTiPt Hypotube for Biomedical Applications

Abstract

Nitinol (NiTi) has become one of the most important implant materials in biomedical applications such as endovascular stents, embolic protection filters, and endodontic files. However, NiTi stents sometimes do not provide satisfactory visibility under fluoroscopy during angioplasty. A new ternary alloy, radiopaque nitinol (NiTiPt), exhibits much better radiopacity than NiTi and has great potential for future biomedical applications. This paper presents the first characterization of anisotropic stress-strain behavior in micron-sized specimens cut directly from hypotubes of this new alloy NiTiPt. Experimental results show that NiTiPt hypotube has very different anisotropic characteristics and high stress-strain nonlinearity when compared to its NiTi counterpart. Its ultimate tensile strength and strain are approximately 15-40% higher than NiTi with statistically significant difference for all three cutting angles measured. Its stress-strain behavior has several unique features including lower initial austenite elastic modulus, smaller hysteresis loop, and sharper tails during the loading-unloading cycle. The 458 behavior is particularly different from other angles, with stronger hardening effect and an approximately 25-30% reduction in ultimate strain when compared to 08.

Radiopaque Shape Memory Alloys: NiTi–Er with Stable Superelasticity

“…Among the radiopaque elements, so far only the addition of Pt has been investigated in some useful form, e.g. wire and hypotube, but without describing any details on the materials processing or any quantitative value of the improvement in radiopacity [1,4,5]. Mehrabi et al [23] reported a high hardness of W-alloyed NiTi.…”

“…stainless steel and Co-Cr alloys) used in minimally invasive surgery are inherently less visible due to their weak X-ray absorption ability (radiopacity) [1,3]. Dense and high atomic number elements such as platinum (Pt) have been added to NiTi [1,[4][5][6] and stainless steel [7] to enhance radiopacity.…”

Rhombic-Shaped Channel Stent with Enhanced Drug Capacity and Fatigue Life

“…The nitinol material behavior for the ABAQUS UMAT subroutine inputs was obtained from Pham et al [ 46 ]. The material ultimate strain and fatigue endurance limits used in the fatigue life analysis were 10% and 1%, respectively [ 47 , 48 ].…”

A novel multifunctional NiTi/Ag hierarchical composite

“…Unfortunately, conventional NiTi SMAs exhibit also high electrical resistance, low mechanical damping and low visibility under fluoroscopy1617, which severely limit their usefulness in applications. Ag has good visibility under fluoroscopy and is one of the best electrically conductive materials possessing high electrical conductivity.…”

“…NiTi shape-memory alloys (SMAs), due to their excellent shape-memory effect, superelasticity and biocompatibility, are used for many products, such as cellular phone antennae, spectacle frames, medical guidewires and stents 13 14 15 . Unfortunately, conventional NiTi SMAs exhibit also high electrical resistance, low mechanical damping and low visibility under fluoroscopy 16 17 , which severely limit their usefulness in applications. Ag has good visibility under fluoroscopy and is one of the best electrically conductive materials possessing high electrical conductivity.…”