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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 μm 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.

Graphene quantum dots (GQDs) prepared by pulsed laser ablation in liquid (PLAL) process face barriers to commercialization due to their poor optical properties and the use of expensive carbon precursors. In this work, we report a one-step route for the preparation of N-doped graphene quantum dots (NGQDs) with excellent optical properties using a low-cost carbon precursor. The as-prepared NGQDs exhibited excellent optical properties and high quantum yield compared to pristine graphene quantum dots (0.8% → 9.1%) due to the presence of the N atoms. A possible recombination mechanism of NGQDs was investigated by time-resolved photoluminescence spectroscopy. The increase of N atoms incorporated in the GQDs resulted in an increased fraction of the short recombination lifetime from the intrinsic state. We also report a possible mechanism for the formation of the N atoms in the GQDs structure during the PLAL process, which is explained based on the plasma plume, cavitation collapse, and nitrogen precursor decomposition model.