Micro/nanoscale multistructures of oxide layers on Ti6Al4V achieved by acid etching and induction heating for high osteogenic activity in vitro

Current development of nano/microscale modification technology of Ti-based implants was focused on the acceleration of ossification and consequent reduction of immunological rejection after implantation. Here, we rationally designed and produced the multistructures with microscale etched pits and nanodot-like oxide crystallites using, a two-step method, HF/HCl etching and induction heating treatment (IHT). IHT oxidation achieved the initially generating of nanocrystallites on the microscale surface and continually growing into dense spherical particles. The dual-scale oxide structures mostly contained rutile-TiO2 with mixture thickness of 402 nm, and remarkably improved the surface wettability with surface roughing. The oxide multistructures showed favorable osteogenic differentiation of human bone marrow-derived mesenchymal stem cells with promoting expressions of osteogenesis-related genes (ALP, Runx2, OCN and COL-1) and proteins. Otherwise, it practically confirmed that the stem cells owned relatively weak 24 h cell adhesion and proliferation on the special oxide structures via comparation with histiocytic types (ST2 cells), and the samples acquired better cell fates when oxidized for 30 s than 20 s due to the larger surface roughness and better hydrophilicity. This study provided theoretical and experimental foundations for construction and further clinical application of high-performance bone implants with multistructures.