Si nano-columns were deposited in 2-D and 3-D in the form of well-defined geometries by physical vapor deposition. The films were grown by e-beam evaporation with an angle between source and substrate. The Si nano-columns were deposited in the shape of spiral with two different incoming atomic flux angle so that the manipulation of nano-columns in 3-D (out-of-plane) was obtained. The Si nano-columns were also grown as vertical stick with square, triangle and linear cross sections in 2D (in-plane). Rat bone marrow mesenchymal stem cells (MSCs) were cultured on these different Si nanosurfaces. MTS assay was carried out to determine the cell proliferation and viability based on different nanotopographies. For the evaluation of cell distribution and morphology, a SEM (Scanning Electron Microscopy) analysis was performed. Any CaP deposition on Si nanosurfaces was observed using energy dispersive X-Ray spectroscopy in SEM (SEM-EDX). After 4 days of culture, there was a higher value of cell proliferation on square columns and spiral Si nano-columns grown with 85 degrees of incoming atomic flux. The cell attachment and spreading was also affected by the geometry of Si nano-columns. While there were still cells showing round/spherical morphology with minimal spreading on conventional Si surfaces, most of the cells cultured on different Si nanotopographies attached on the surface and displayed flattened morphology, especially on the square columns surface. Moreover, CaP deposition was discovered on square columns and spiral films with 85 degrees substrate angle. So, it can be concluded that there is a clear correlation between cell responses and nano-sized geometry on Si surface and it is possible to induce cellular differentiation and CaP formation in certain geometrical constraints.

Controlling the wettability of nano textured surface structures is essential for understanding of its role particularly in biomedical applications. The main objective of this study is to explore the wetting mechanism of a water drop on a nano textured Si surface. Si nano-columns with 4-, 3and 2-fold in-plane symmetries were grown on p-type (100) Si wafer by oblique angle deposition (OAD). The surface morphology was characterized by scanning electron microscopy (SEM). The contact angle technique was used to reveal the wetting characteristics of these textured surfaces. Experimental results were compared with the theoretical contact angle calculations derived from the Young, Wenzel and Cassie-Baxter equations in order to identify the conditions for the minimum free energy of the drop. Water droplets on all plenary symmetries water droplets showed good agreement with the Cassie-Baxter model of Sunny side up. These findings were used to simulate the extent of the hydrophilicity on the fabricated textures by taking the contact angle hysteresis (CAH) into account.

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