ALT Cartoon showing types of durotaxis. On stiffness gradients, single cells can exhibit either positive durotaxis (moving towards stiffer substrate), negative durotaxis (moving towards softer substrate), or adurotaxis (unbiased migration between soft and stiff substrates). During directed migration, cells polarize, forming lamellipodia and/or filopodia at their leading edge. Larger monolayers and small clusters of cells have both been observed to undergo positive collective durotaxis that is dependent on intact cell–cell junctions, intercellular propagation of forces and, in some cases, polarized signaling gradients. Although only collective positive durotaxis has been conclusively demonstrated, preliminary findings suggest that small cell clusters might also undergo negative durotaxis along self-generated stiffness gradients.