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

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 0.5-2μm 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, ~0.5μm 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 ~70nm 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.