a, Biphasic discs with smooth and rough surface; scale bar, 1 μm (image: Joerg Lahann). b, Pillar arrays for mapping force of epithelial cell migration134; scale bar, 5 μm (© 2005 PNAS). c, Asymmetrically coated particles136; scale bar, 5 μm (© 2003 RSC). d, Micropatterned particles114; scale bar, 100 μm (© 2007 PNAS). e, Control of spreading of an endothelial cell through a micropatterned substrate27; scale bar, 10 μm (© 1997 AAAS).