**Laurent Weiss 1,2,\*, Yaël Nessler 2, Marc Novelli 1, Pascal Laheurte 1,2 and Thierry Grosdidier 1,2**


Received: 20 November 2019; Accepted: 6 December 2019; Published: 13 December 2019

**Abstract:** Additive manufacturing allows the manufacture of parts made of functionally graded materials (FGM) with a chemical gradient. This research work underlines that the use of FGM makes it possible to study mechanical, microstructural or biological characteristics while minimizing the number of required samples. The application of severe plastic deformation (SPD) by surface mechanical attrition treatment (SMAT) on FGM brings new insights on a major question in this field: which is the most important parameter between roughness, chemistry and microstructure modification on biocompatibility? Our study demonstrates that roughness has a large impact on adhesion while microstructure refinement plays a key role during the early stage of proliferation. After several days, chemistry is the main parameter that holds sway in the proliferation stage. With this respect, we also show that niobium has a much better biocompatibility than molybdenum when alloyed with titanium.

**Keywords:** surface mechanical attrition treatment (SMAT); ultrasonic shot peening (USP); functionally graded materials (FGM); titanium niobium alloys; titanium molybdenum alloys; human mesenchymal stem cells culture; cell adhesion; cell proliferation
