Pitch-dependent acceleration of neurite outgrowth on nanostructured anodized aluminum oxide substrates.

Nervous systems are composed of microstructured scaffolds with three-dimensional nanofeatured textures. These textures enable the systems to give nanometer-scaled physical cues to the overlying cells, along with biochemical cues. However, the topographical effects on the neurons are still an unexplored territory, although there have been many reports on the biochemical cues for neuronal behavior. It is practically very difficult to investigate the topographical environments in vivo in the biological systems and/or to mimic them precisely in vitro. There is much recent evidence that the cellular response is affected by the physical properties of artificial materials. Studies with such materials could therefore provide us with new insight into the developmental processes of the brain and enable elucidation of the unexplored nanotopographical effects on neuronal behavior. The responses of nerve cells to surface roughness have been studied on various substrates, such as porous silicon, thin titanium nitride films, carbon nanotubes, topographically molded poly(dimethylsiloxane), silicon pillar arrays, gallium phosphide nanowires, aligned nanofiber arrays, and silicon nanowires. Previous studies showed that nerve cells exhibit enhanced attachment and viability as well as the axonal guidance effect on rough surfaces, as opposed to topographically flat surfaces. However, there have been few reports on how nanometer-scaled features regulate neuronal behavior in terms of neurite development. To generate nanotopographical stimuli to neurons in a controllable and systematic manner, it is necessary to make reproducible, rigid structures with variable topographical features. Among the methods for creating topographies on surfaces at the nanometer scale, the fabrication of anodized aluminum oxide (AAO) is highly effective, straightforward,