A, b and c Side by side

on a soft substrate (a), moving cells quickly change direction, as a result of which they have less chance of ending up further from their starting point and therefore remain in the relatively small area around their starting point. On a stiffer substrate (b), cells move longer in a single direction, as a result of which they can end up further from their starting point and move over a larger surface area. If an environment exhibits a rigidity gradient (c), the cells spontaneously ‘walk’ towards the area with a firmer substrate. The local behaviour in (a) and (b) directly results in the global behaviour in (c).
Source: Elizaveta Novikova