English: MSC osteogenic differentiation on ordered and disordered nanotopographies. After 21 days of culture, MSCs on control (a, f) and symmetrically arranged 100 nm deep pits (b, g) appeared fibroblastic (k) and did not stain positively for osteopontin (OPN) or osteocalcin (OCN). Cells cultured on surfaces with pits displaced ± 20 nm (c, h) and ± 50 nm (d, i) from the true center expressed OPN and OCN, formed nodules (arrows), and had an osteoblast-like morphology with mineral nodules after 28 days (l). Cells cultured on surfaces with random pit placement (e, j) had morphology similar to those on displaced surfaces but did not express OPN or OCN. These findings illustrate the sensitivity of cells and MSC differentiation to nanoscale surface features. Reprinted with permission from Dalby et al. (2007). Copyright (2007) Nature Publishing Group.