Compression fatigue behavior of gyroid porous titanium scaffolds manufactured by laser powder bed fusion for bone-implant applications

Additively manufactured porous metals involving Triply Periodic Minimal Surfaces (TPMS) are being paid great attention due to their noteworthy osteogenic potential and ability to eliminate the stress concentrations caused by strut curvatures and nodal points of unit cells in other porous structures. In this study, gyroid porous commercially pure titanium (CP-Ti) scaffolds with porosities of approximately 83, 74, 64, and 54 % and corresponding pore sizes of about 0.89, 0.73, 0.56, and 0.42 mm, respectively referred to as GN8, GN7, GN6, and GN5, were fabricated via selective laser melting using laser powder bed fusion. The quasi-static compressive and compression fatigue behaviors of the scaffolds were systematically investigated. Both their elastic modulus (E) and yield strength (σ y ) were observed to increase with decreasing porosity, with E increasing from 1.032 to 4.264 GPa and σ y increasing from 20.46 to 98.13 MPa. The scaffolds exhibited normalized fatigue strength values ranging over 0.49 to 0.78 at 10 6 cycles and their normalized fatigue strength and fatigue life demonstrated a power-law relationship. Further, both the porosity and the pore size influenced the fatigue performance of the scaffolds; in particular, the normalized fatigue strength and porosity correlated with a power-law relationship at a high confidence level (≥ 0.92). In early cyclic compression, ratcheting drove plastic deformation, while in later stages, fatigue crack initiation and propagation dominated, leading to scaffold fracture. The GN5 showed the highest cell viability of 113 % and the GN8 showed the lowest cell viability of 95 %; the cell viability is believed to have been affected by both the porosity and the pore size of the scaffolds.