Osteoblast-like cells are sensitive to submicron-scale surface structure

Objectives: Studies showing that osteoblasts exhibit a more differentiated phenotype on rough titanium (Ti) surfaces and osteoclast-resorbed bone surfaces used materials characterized by average peak to valley distance (R_a). Other surface features impacting the cells include distance between peaks, curvature of the valleys, and relative distribution of flat and smooth regions. We used novel Ti surfaces prepared by electrochemical micromachining as models to examine specific contributions of individual design features to osteoblast response. Results show that micron-scale topography modulates cell number, cell morphology and prostaglandin E₂ (PGE₂). In the presence of the appropriate microtopography, submicron-scale rugosity modulates differentiation and transforming growth factor-β1 (TGF-β1) levels. In this study, we examined the role of different types of submicron-scale structures. Material and methods: Thirty micrometer diameter craters on Ti disks were produced by photolithography resulting in an electropolished smooth surface, and arranged so that inside crater area vs. outside flat area was 6 (30/6). Submicron-scale structures were superposed by acid etching and porous anodization. R_a's were 700, 400, 60 nm on acid-etched, porous anodized and smooth 30/6 surfaces, respectively. Results: MG63 osteoblast-like cells were sensitive to submicron-scale architecture. Cell morphology on anodized surfaces was similar to morphology on smooth surfaces, whereas on etched surfaces, cells had a more elongated differentiated shape. Cell number was greatest on smooth surfaces>anodized>etched. Osteocalcin and PGE ₂ were affected in a reverse manner. Active TGF-β1 was greatest on etched 30/6 surfaces>anodized>smooth; latent TGF-β1 was elevated on all rough surfaces. Conclusions: These results support our previous observations that submicron-scale structures modulate osteoblastic phenotype and show that the physical properties of the submicron-scale structures are important variables in determining osteoblast response to substrate topography.