Immune cells such as natural killer (NK) cells migrate with high speeds of several µm/min through dense tissue, but the traction forces are unknown. We present a method to measure dynamic traction forces of fast migrating cells in non-linear biopolymer matrices. The method accounts for the mechanical non-linearity of the 3D tissue matrix and can be applied to time series of confocal or bright-field image stacks. The method is highly sensitive over a large range of forces and object sizes, from ∼1 nN for axon growth cones up to ∼10 µN for mouse intestinal organoids. We find that NK cells display bursts of large traction forces that increase with matrix stiffness and facilitate migration through tight constrictions.

Dynamic traction force measurements of migrating immune cells in 3D matrices