Improved tribological properties, cyto-biocompatibility and anti-inflammatory ability of additive manufactured Ti-6Al-4V alloy through surface texturing and nitriding

Surface texture and nitride coating have been proved as effective ways to improve the tribological properties of biomedical titanium alloys. However, the influence of surface texture and nitride coating on cells behavior, especially on the polarization of macrophages, was rarely reported. In this work, Ti-6Al-4V parts with designed rhombus surface texture were successfully prepared by selective laser melting process. Followed by post heating treatment in N2, uniform and dense nitride coatings on the textured surfaces consisted of TiN, Ti2N, TiN0.9 and N-containing solid solution with a thickness of similar to 5 mu m were generated. The combination of surface texture and nitride coating reduced the frictional coefficient from 0.343 to 0.166, and significantly improved the wear resistance of the substrate. The nitride coating promoted the adhesion and proliferation of MC3T3-E1 cells in the early stages (1 d and 3 d). Textured surfaces provided larger area for cells growth that encouraged the cell adhesion and early spread. The significant increasing of the expression of Arg-1 and the ratio of CD206 positive cells (M2 phenotype) comparing with the uncoated group indicated that the nitride coating promoted the macrophages (Raw264.7 cells) polarization into anti-inflammatory type after co-culturing for 24 h. Surface texture combined with nitride coating further increased the ratio of CD206 positive cells and also reduced the inflammatory factors releasing.