Creation of hierarchical micro/nano-porous TiO2 surface layer onto Ti implants for improved biocompatibility

• A hierarchical micro/nano-porous TiO2 layer was coated onto a Ti implant.
• Significant enhancement in in vitro osteoblastic cellular responses was achieved.
• Protein adsorption capability was also remarkably improved.

We created a hierarchical micro/nano-porous TiO2 surface layer onto a Ti substrate to enhance its biocompatibility by mimicking the hierarchical architecture of the native extracellular matrix. To accomplish this, a rough, micro-porous TiO2 layer with pore sizes in the range of 0.5–2 μm was first formed on the surfaces of a Ti substrate using micro-arc oxidation (MAO) and then coated with a thin layer of pure Ti, ~ 0.5 μm in thickness, using electron beam (e-beam) evaporation. Subsequently, anodic oxidation was conducted to create a uniform nano-porous TiO2 surface layer with a pore size of ~ 70 nm on the micro-porous layer. This hierarchical micro/nano-porous surface showed considerably enhanced hydrophilicity and in vitro biocompatibility compared to the dense surface and even the micro-porous and nano-porous surfaces. These improvements were attributed to the synergistic effect of micropores and nanopores created by a combination of MAO and anodic oxidation. In addition, protein adsorption capacity was remarkably improved due to the high affinity of the nano-porous TiO2 surface for proteins.