Ti-6Al-4V intervertebral fusion cage with compatible stiffness, enhanced fatigue life, and osteogenic differentiation

The 3D-printed Ti-6Al-4V intervertebral fusion cage is fabricated to be biocompatible with improved stiffness, fatigue life, and osteogenic differentiation, which are greatly enhanced by heat treatment and surface modification. The flexible cage's life, which exceeds the standard dynamic fatigue requirement of 5 × 10⁶ cycles based on the ASTM F2077 and F2267 test methods, is achieved by heat treatment at 800 ℃ in argon atmosphere, shot peening, and adjusting the α to β phase ratio to increase mechanical toughness. Surface modification via sandblasting and chemical etching removes the surface oxide layer and forms submicron pores on the surface of the cage, which significantly boosts cell proliferation, differentiation, and osteoblast mineralization. This work exhibits a novel design of Ti-6Al-4V intervertebral fusion cage with biocompatible stiffness, enhanced fatigue life, and improved osteogenic differentiation achieved by reducing residual stress, modifying surface micro-pores, and optimizing microstructure.