Fibroblast Response to Nanocolumnar TiO₂ Structures Grown by Oblique Angle Sputter Deposition

Abstract

The biocompatibility of Ti originates from the chemically passive oxide layer naturally forming on the Ti surface. [13] Previous research indicates that the surface properties such as, composition, hydrophilicity, and texture of the oxide on the Ti affect the cellular response. The micro-and nanoscale surface morphology has shown to be a highly-sensitive parameter that influences for instance cell adherence, proliferation, migration, gene expression, and differentiation. [16][17][18][19][20][21][22][23] Therefore, modifying the implant surface on the micro-and nanometer scale appears to be a promising approach for improving the interaction between tissue and implant. [20,[24][25][26][27][28][29] Various deposition methods are known to fabricate such thin TiO 2 films and comprise chemical (anodic oxidation, spray pyrolysis, chemical vapor deposition, etc.) or physical (DC or RF magnetron sputtering, ion-beam assisted sputtering, electron beam evaporation) approaches. Sputtering is widely used in research and industry due to the low vacuum requirements. Combining sputtering with an oblique angle deposition (OAD) geometry allows tailoring self-assembled, 3D nano-and microstructures over large substrate areas. [30] OAD is a physical vapor deposition technique based on the inter-columnar shadowing effect, which emerges from tilting the substrate normal to highly oblique angles with respect to the incoming vapor. [31][32][33] This deposition geometry results in the formation of a highly porous thin film that consists of nano-sized columns inclined toward the incoming particle flux. Moreover, these columns are separated from each other so that the resulting thin film exhibits an open pore-structure. These nanostructures might be beneficial for cell adhesion. For instance, Dolatshahi-Pirouz et al. and Pennisi et al. have reported that nanostructured platinum surfaces have a profound impact on the proliferation of primary human fibroblasts, suggesting that nanostructured surfaces affect cellular responses. [34,35] Although being in the focus of considerable research activities, the interactions of cells and such nanostructured surfaces still remain incompletely understood.In the present work, thin films composed of tilted TiO 2 nanostructures are fabricated by oblique angle ion-beam sputter deposition at room temperature. The columnar tilt angles, the distance between neighbored nanostructures, as well as, the roughness of the thin films were investigated with scanning electron microscopy (SEM) and atomic force microscopy Cells are established to sense and respond to the properties, including nanoand microscale morphology, of the substrate they adhere to, which opens up the possibility to tailor bioactivity. With this background, the potential of tilted TiO 2 nanostructures grown by oblique angle sputtering to affect fibroblasts with particular focus on inducing anisotropy in cell behavior is explored. By depositing TiO 2 at different oblique angles relative to the substrate normal, morphologies, columnar tilt angle, roug...