New oxidation treatment of NiTi shape memory alloys to obtain Ni‐free surfaces and to improve biocompatibility

Abstract

Various oxidation treatments were applied to nearly equiatomic NiTi alloys so as to form a Ni-free protective oxide on the surface. Sample surfaces were analyzed by X-ray Photoelectron Spectroscopy, and NiTi transformation temperatures were determined by differential scanning calorimetry (DSC) before and after the surface treatment. An ion release experiment was carried out up to one month of immersion in SBF for both oxidized and untreated surfaces. The results show that oxidation treatment in a low-oxygen pressure atmosphere leads to a high surface Ti/Ni ratio, a very low Ni surface concentration and a thick oxide layer. This oxidation treatment does not significantly affect the shape memory properties of the alloy. Moreover, the oxide formed significantly decreases Ni release into exterior medium comparing with untreated surfaces. As a consequence, this new oxidation treatment could be of great interest for biomedical applications, as it could minimize sensitization and allergies and improve biocompatibility and corrosion resistance of NiTi shape memory alloys.

Thermal Stabilization of NiTiCuV Shape Memory Alloys: Observations During Elastocaloric Training

“…Superelastic shape memory alloys have been known for biocompatibility [1][2][3] and good damping properties [4,5]. Ni-Ti-based stents have been established in the market for years [6], and the damping properties have been studied in a large number of scientific works [7,8].…”

Quantum parameters for guiding the design of Ti alloys with shape memory and/or low elastic modulus

“…Some controversy exists on the risk of Ni ions release from the implant to the surrounding tissue, which can produce adverse reactions [11][12][13]. Two ways of overcoming this problem have been proposed: surface modification by means of surface coating oxidation [14,15] and substitution of Ni by biocompatible and non-citotoxics alloying elements that preserve the excellent shape memory properties of Ti-Ni alloys [16][17][18].…”

Oxidized NiTi surfaces enhance differentiation of osteoblast‐like cells

“…This suggests that roughness has not been a key factor for MG63 adhesion in this study, since Ti and untreated surfaces are topographically similar and smoother than oxidized NiTi, as determined in a previous work. 13 As a consequence, this observation could be attributed to similar chemical composition and/or surface energy of Ti and oxidized NiTi surfaces (previously studied in Refs. 13 and 19), two physicochemical parameters known to influence cell adhesion.…”

“…The methods of NiTi fabrication, surface preparation, and oxidation are described in detail elsewhere. 13 The metallic disks studied (8 mm in diameter) were placed in a culture dish made of Teflon that was machined to carry out the different in vitro experiments (Fig. 1).…”

“…13 It has been shown that this surface treatment significantly decreases Ni ion release into the exterior medium. As a consequence, if the risks of toxic reactions associated with Ni are minimized because of this new surface treatment, it could be expected a better cytocompatibility of NiTi materials treated with OT.…”