**4. Conclusions**

The additively manufactured NiTi parts were found to have a corrosion behavior (electrochemical corrosion and Ni ion release) similar to that found for the conventionally fabricated NiTi alloy. This indicates that the proposed additive manufacturing process does not result in a deterioration in the corrosion resistance of NiTi parts. In addition, the SEM and XRD analysis of the corroded NiTi samples showed the formation of biocompatible corrosion products on the surface of the sample, which could be beneficial for bone implant applications. Adding porosity to the additively manufactured NiTi parts increased the exposed surface area, which results in a higher electrochemical corrosion current and hence a higher Ni ion release compared to the bulk NiTi samples. 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. It is worth mentioning that there have been several efforts to reduce the Ni ion release of conventionally fabricated NiTi parts in the literature using surface modification and coating techniques. Such techniques could be beneficial to implement for additively manufactured NiTi structures to further increase the corrosion resistance and reduce the Ni ion release rates.

**Acknowledgments:** The authors wish to acknowledge partial support for this research from Third Frontier (State of Ohio) gran<sup>t</sup> 15-791, titled "Additive Manufacture of Stiffness-Matched Skeletal Fixation Hardware".

**Author Contributions:** Hamdy Ibrahim and Mohammad Elahinia conceived and designed the experiments; AhmadReza Jahadakbar, Amir Dehghan, Narges Shayesteh Moghaddam, Amirhesam Amerinatanzi and Hamdy Ibrahim performed the experiments; Hamdy Ibrahim and Amir Dehghan analyzed the data; Mohammad Elahinia contributed reagents/materials/analysis tools; Hamdy Ibrahim, Amir Dehghan, AhmadReza Jahadakbar and Mohammad Elahinia wrote the paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
