Effect of modification of oxide layer on NiTi stent corrosion resistance

Abstract

Because orits good radiopacity, superelasticity, and shape memory properties, nickel-titanium (NiTi) is II potential material for fabrication of stents because these properties Clln facilitate their implantation and precise positioning. However, ill vitro studies of NiTi alloys report the dependence of alloy biocompatibility and corrosiun behavior on surface conditions. Surface oxidation seems to be very promising for improving the corrosion resistancc and biocompatibility of NiTi. In this work, we studied the effect on corrosion resistancc and surface chanlcteristics of electropolishing, heat treatment, and nitric acid passivation of NiTi stents. Characteri zation techniques such as potentiodyna mic polarization tests, scanning electron microscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy were used to relute corrosion behavior to surface ch.mlcteristics and surface treatments. Results show that all of these surface treatments improve the corrosion resistance of the alloy. This imprOl'ement is attributed to the plastically deformed nath'e oxide layer removul und replacement by a newly grown, more uniform one. The uniformity of the oxide layer, rather than its thickness and composition, seems to he the predominant factor to explain the corrosion resistance improvement. 0 t998 John Wiley & Son~. Inc.

Enhanced Corrosion Resistance of Silicone-Coated Stents by Plasma Treatment

“…The production of a protective Ti-rich oxide layer on the surface of NiTi alloys used in medical applications also improves the corrosion resistance of the material in physiological conditions [17][18][19]. However as shown in Fig.…”

“…2b). This is why the stent even with the silicone coverage shows toxicity when the NiTi strips are exposed to the aqueous environment of the human body [17]. This observation implies that not only thick oxide layer but also well-structured oxide layer is necessary for better corrosion-resistance.…”

Electrochemical Polarization Characteristics of a DLC-Coated Magnesium Alloy Stent in a Saline Solution

“…A stent is a small metal mesh tube that is inserted in a stenosis site of a coronary artery or cerebral artery to expand the blood vessel. Materials used for stents today include stainless steel (SUS316L) [1], cobalt chromium (Co-Cr) alloys [2], and Nitinol (Ni-Ti) alloys [3]. However, these stents remain inside the living body, and the incompatibility of the metal with the living body may cause restenosis (reblockage of arteries) at the stent insertion site.…”

Corrosion Mechanism in Artificial Sweat Solution of In-Bearing White Bronze Alloy

“…12 Recently, two more directives were issued to reduce further the nickel permitted release down to 0.2 μg cm -2 week -1 from "post assemblies" 12 and extend these limits to nickel compounds. 13 Since the end of the 1990s, several studies were carried out to determine, and eventually reduce, Ni release from objects designed to be in contact with the human body, such as medical devices, [14][15][16][17][18][19] cutlery, [20][21] coins, [22][23] and guitar strings, 24 in various types of synthetic body fluids. [25][26][27][28][29][30] However, all these studies have focused on the properties of bulk materials, leaving the field of decorative coatings practically unexplored.…”