Nanograin-enhanced surface-layer strengthening of 3D printed intervertebral cage induced by sandblasting.

3D-printed customized titanium alloy (Ti6Al4V, TC4) as load-bearing prostheses and implants, such as intervertebral cages, have been widely used in clinical practice. Native biological inertia and inadequate bone in-growth of porous titanium alloy scaffolds hampered their clinical application efficiency and then extended the healing period. To improve the osseointegration capacity of 3D-printed intervertebral cages, sandblasting was selected to execute their surface treatment. On the one hand, sandblasting treatment can efficiently eliminate incomplete unmelted powder that adheres to struts in intervertebral cages during the manufacture of 3D printing, resulting in high surface area and low surface flatness induced by the rough surface could favor osseointegration. On the other hand, sandblasting can also induce ultrafine grains and nanograins in the near-surface layer that are conductive to mechanical strength enhancement. This can be verified by both microhardness and residual compressive stress reaching peak values (404.2 HV, 539.1 MPa) in the transverse section of its near-surface layer along the depth from the surface. This is attributed to the fact that more grain boundaries can impede dislocation movement. Sandblasting surfaces in intervertebral cages could favor osseointegration and in-growth, providing a foundation for sandblasting treatment of 3D-printed intervertebral cages in clinical applications.