Different micro/nano-scale patterns of surface materials influence osteoclastogenesis and actin structure

The surface topography of a material can influence osteoclast activity. However, the surface structural factors that promote osteoclast activity have not yet been investigated in detail. Therefore, we investigated osteoclastogenesis by testing various defined patterns with different dimensions and shapes. The systematic patterns, made of a cyclo-olefin polymer, were prepared at a micron-, submicron-, and nano-scale with a groove, hole, or pillar shape with a 1:1 pitch ratio. RAW264.7 cells were cultured on these patterns in the presence of the receptor activator of NF-κB ligand (RANKL). Osteoclast formation was induced in the order: pillar > groove ≥ hole. The two-dimensional factors also indicated that submicron-sized patterns strongly induced osteoclast formation. The optimal pillar dimension for osteoclast formation was 500 nm in diameter and 2 µm in height. Furthermore, we observed two types of characteristic actin structure, i.e., belt-like structures with small hollow circles and isolated ring-like structures, which formed on or around the pillars depending on size and height. Furthermore, resorption pits were observed mainly on the top of calcium phosphate-coated pillars. Thus, osteoclasts prefer convex shapes, such as pillars for differentiation and resorption. Our results indicate that osteoclastogenesis can be controlled by designing surfaces with specific morphologies.