**6. Conclusions**

The porous sti ffness-modulated NiTi bone fixation plates with di fferent levels of sti ffness were designed and modeled via a FE analysis. It was shown that specific levels of sti ffness could be achieved by introducing engineered levels of porosity to the bulk plate, and the mechanical properties can be captured using the properties of standard coupons. Due to the complex geometry of porous bone fixation plates, the SLM technique was employed to fabricate the NiTi plate. This methodology can be applied to complex geometries and plates as thin as 1.5 mm. The as-fabricated parts were tested mechanically, and the experimental results were in a good agreemen<sup>t</sup> with the FE model. After modeling verification and confirming the design methodology, Ni-rich bone fixation plates were fabricated to achieve superelastic behavior. The DSC results of the porous Ni-rich bone fixation plate showed a small variation in TTs of di fferent locations of the plates. Various thermal histories that the parts experienced during the SLM process were the main reason for the variation in TTs. Two tensile samples using Ni-rich powder were fabricated along with Ni-rich bone fixation plates and tested to measure the mechanical properties used for FE modeling. The as-fabricated porous Ni-rich bone-plate fixation was tested and the predicted superelastic behavior was achieved. In order to test methods to remove un-melted powder particles from the surface following AM, the bone-plates were chemically polished under six di fferent conditions. SEM analysis revealed that an etching solution with a composition of HF (10%), HNO3 (40%), H2O (50%), and the e ffective time of 4 min, was the optimal etching solution to remove un-melted powder particles. The chemical composition analysis of our Ni-rich SLM bone fixation plates confirmed that the composition was in a good agreemen<sup>t</sup> with the ASTM 2063 requirements.

**Author Contributions:** Conceptualization, M.E. and D.D.; additive manufacturing, M.N.; simulation and validation, A.J. and K.S.; characterization P.B., K.S., A.J., M.N., G.G. and H.D.; all authors contributed to the writing of initial draft and final draft and reviewed the manuscript. All authors have read and agree to the published version of the manuscript.

**Funding:** This research was partially funded by a gran<sup>t</sup> from the Third Frontier (Ohio Development O ffice) of Ohio (grant # TECG20170372).

**Acknowledgments:** The authors would like to acknowledge the financial support of the Ohio Third Frontier Technology Validation and Start-up Fund.

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