Enhanced Osseointegration of Ti6Al4V ELI Screws Built-Up by Electron Beam Additive Manufacturing: an Experimental Study in Rabbits

In the present study, the osseointegration of additively manufactured screws with a micro-rough surface structure and conventionally machined Ti6Al4V ELI screws with a smooth surface structure is compared. Screws were implanted in rabbit femurs or tibiae for two weeks. The additively manufactured screws exhibited a micro-rough surface with attached semi-molten powder with a size of 50-100 mu m and blunt threads, whereas the conventionally machined screws showed a smooth surface and sharp threads. The bonding strength of the additively manufactured screws was significantly higher than that of the conventionally machined screws. The additively manufactured screws showed higher bone-to-implant contact than the conventionally machined screws. Considerable amount of bone tissue on the surface of the additively manufactured screws remained after the push-out tests, and the rabbit tibiae with the additively manufactured screws were significantly damaged, indicating a higher osseointegration rate. Active osteogenesis was observed around the semi-molten powder of the additively manufactured screws, and new bone was well developed along the micro-rough surface. Overall, this study shows that the micro-rough surface improved the bone ingrowth and suggests that additively manufactured screws may be an alternative to conventionally machined screws.