Effect of Nitinol surface treatments on its physico‐chemical properties

Abstract

The main purpose of this work is the study of different physicochemical treatments on Nitinol slabs and wires, with the aim of inducing the formation of a TiO(2) surface film capable of increasing the corrosion resistance of the material and of reducing the release of Ni when the Nitinol samples were immersed in simulated body fluid (SBF). To this end, a battery of measurements (surface roughness, contact angle, electrochemical corrosion, chemical analysis as a function of depth, and Ni release to SBF) has been used to characterize Nitinol commercial samples, as received, and also after the different treatments performed. The results clearly indicate the effectiveness of the passivation TiO(2) layer as a barrier against Ni leaching, and the detrimental effects of any processes (such as polishing or cutting) that result in exposure of areas not coated by the TiO(2) film. Chemical methods such as oxidation in nitric acid or hydrothermal treatment of the samples (by prolonged immersion in boiling water) seem to provide simple and efficient ways of forming TiO(2) films of adequate thickness on the Nitinol surface.

Structural analysis of HyFlex EDM instruments

“…, Milošev & Kapun ), minimizing the adverse cytotoxic effects that would result from the release of Ni into body fluids (Pérez et al . ).…”

“…Rutile‐based layers typically appear on NiTi alloys as a result of a high‐temperature oxidation treatment (Pérez et al . , Vojtěch et al . , Smialek et al .…”

Shape-memory NiTi with two-dimensional networks of micro-channels

“…The extent of leaching of Ni, which is cytotoxic, from the surfaces of NiTi implants remains a controversial issue [70,71], and several surface modifications exist to reduce this effect [4]. However, this effect is not expected to be significant in the present specimens because their specific surface area is smaller, by a factor of >4, than that of the commercially available porous NiTi spinal fusion device called Actipore™ (Biorthex Inc., Montreal, QC, Canada) [72].…”

Effects of Oxide Layer Composition and Radial Compression on Nickel Release in Nitinol Stents

“…Previous immersion testing demonstrated that polished Nitinol exhibits similar Ni release behavior to stainless steels and cobalt-based alloys [9,10]. Longer immersion studies (up to 6 months) found that surface treatments such as polishing and/or passivation of Nitinol wires can reduce Ni release compared to untreated controls [11][12][13][14]. Wire immersion tests have shown that thicker oxides, surface Ni particles, and Ni-rich phases contribute to increased Ni dissolution [15,16].…”