Comparison of chemokinetic and chemotactic behavior. (A) The MSDs for neutrophils on 10- and 100-kPa substrates are shown for both random and directed migration. The cells move more efficiently on the stiffer substrate. (B) The angular distribution of steps is shown for neutrophils undergoing both chemokinesis and chemotaxis on a 60-second interval. Neutrophils chemotaxing toward a pipette tip showed more peaked distributions than neutrophils randomly migrating. For both chemokinetic and chemotactic behavior, however, the angular distribution of steps showed a greater peak on the 100-kPa substrates compared with the 10-kPa substrate for each condition. Migration is thus more persistent on stiffer substrates.