Mechanical and fatigue performance of multidirectional functionally graded Ti6Al4V scaffolds produced via laser powder bed fusion for orthopedic implants

Abstract

Orthopedic implants require porosity gradients to achieve tissue integration and mechanical support. This study presents a novel design of Multidirectional Functionally Graded (MDFG) porous Ti6Al4V scaffolds, fabricated via Laser Powder Bed Fusion (LPBF) to mimic natural bone porosity for orthopedic applications. Four scaffold types were developed: Gyroid and Primitive (sheet-based TPMS) and Kelvin and Voronoi (strut-based lattices). A pore size of 1000 µm was maintained to promote tissue ingrowth, while strut thickness grading (0.3–0.7 mm) enhanced mechanical stability. Quasi-static compression tests showed Young’s moduli of 9.5 GPa (Gyroid) and 9.3 GPa (Primitive), with ultimate strengths of 240 MPa and 190 MPa, respectively. Energy absorption was 47.74 MJ/m³ for Gyroid and 46.68 MJ/m³ for Primitive, demonstrating excellent resistance to mechanical failure. Fatigue testing revealed that the Gyroid lattice sustained 25 MPa after one million cycles, highlighting its long-term durability. Fractographic analysis showed that fatigue cracks initiated at surface defects and propagated along strut intersections, providing insights into failure mechanisms. These findings confirm that MDFG scaffolds, particularly Gyroid and Primitive lattices, enhance mechanical robustness and biological compatibility, making them strong candidates for load-bearing orthopedic implants.