In Vitro Corrosion Assessment of Additively Manufactured Porous NiTi Structures for Bone Fixation Applications

Abstract

NiTi alloys possess distinct functional properties (i.e., shape memory effect and superelasticity) and biocompatibility, making them appealing for bone fixation applications. Additive manufacturing offers an alternative method for fabricating NiTi parts, which are known to be very difficult to machine using conventional manufacturing methods. However, poor surface quality, and the presence of impurities and defects, are some of the major concerns associated with NiTi structures manufactured using additive manufacturing. The aim of this study is to assess the in vitro corrosion properties of additively manufactured NiTi structures. NiTi samples (bulk and porous) were produced using selective laser melting (SLM), and their electrochemical corrosion characteristics and Ni ion release levels were measured and compared with conventionally fabricated NiTi parts. The additively manufactured NiTi structures were found to have electrochemical corrosion characteristics similar to those found for the conventionally fabricated NiTi alloy samples. The highest Ni ion release level was found in the case of 50% porous structures, which can be attributed to their significantly higher exposed surface area. However, the Ni ion release levels reported in this work for all the fabricated structures remain within the range of most of values for conventionally fabricated NiTi alloys reported in the literature. The results of this study suggest that the proposed SLM fabrication process does not result in a significant deterioration in the corrosion resistance of NiTi parts, making them suitable for bone fixation applications.

On Coating Techniques for Surface Protection: A Review

“…Moreover, these alloys provide high biocompatibility as they are used as bone implants that could be combined with SME, SE, or both, to develop new biomedical devices for micro-surgeries inside the human body. However, the corrosion process of NiTi in physiological environments releases Ni ions as byproducts, which are a toxic and harmful category of materials for living organs [2]. Copper is a material with high thermal and electrical conductivity with many applications such as brazing advanced materials; however, it suffers from low stiffness…”

Design, Modeling, Additive Manufacturing, and Polishing of Stiffness-Modulated Porous Nitinol Bone Fixation Plates Followed by Thermomechanical and Composition Analysis

“…As a solution, our group has proposed and introduced a new generation of bone fixation plates that are stiffness matched to the bone tissue and are fabricated via additive manufacturing [2][3][4][5][6][7]. Stiffness modulation and the matching is achieved via replacing the Ti64 with Nitinol, as well as incorporating engineered porosity to the bone fixation plates.…”

“…This is mostly due to the freedom of fabrication and the superior properties of NiTi, as mentioned earlier. However, most of the research is fundamental, aimed at finding optimal fabrication process parameters and their effects on the part's properties [31], lattice structures [18], corrosion behavior [3], modeling [32], and biocompatibility [33]. It should also be noted that all the SLM fabricated porous structures in the literature have been evaluated only in compression mode and no study, as far as we know, has been done on a realistic stiffness-matched porous bone fixation plate, which is under tension.…”

Epitaxial Versus Polycrystalline Shape Memory Cu-Al-Ni Thin Films

“…Typical application fields for these materials are encountered in sensing-actuating systems in automotive, aerospace, robotics, and biomedical technologies [8]. Of the most functional shape memory alloys, Ni-Ti [9][10][11] Cu-Zn-Al [12], and Cu-Al-Ni [13,14] are some of the most widely used. Even though the Ni-Ti SMA system is widely studied and commercialized on account of its high percentage of shape recovery, Cu-based SMAs have become long-term proposed held at 700 • C, taking advantage of the epitaxial relationship between MgO(001) and austenitic β-Cu-Al-Ni as a bottom-up approach.…”