Stresses at the Cell-to-Substrate Interface during

Recent technological improvements in the elastic substrate method make it possible to produce spatially resolved measurements of the tractions exerted by single motile cells. In this study we have applied these developments to produce maps of the tractions exerted by 3T3 fibroblasts during steady locomotion. The resulting images have a spatial resolution of 5 m and a maximum intensity of 10 kdyn/cm (10 pN/ m). We find that the propulsive thrust for fibroblast locomotion, 0.2 dyn, is imparted to the substratum within 15 m of the leading edge. These observations demonstrate that the lamellipodium of the fibroblast is able to generate intense traction stress. The cell body and posterior seem to be mechanically passive structures pulled forward entirely by this action.