Figure 4. Neutrophils migrating on Col-coated substrates toward fMLP show Td, DI<, and DI>, independent of substrate stiffness.
Human primary neutrophils migrating on Col-coated gels of 10 kPa, 50 kPa, or 100 kPa stiffness toward a fMLP point source were tracked over a 30-min period (Supplemental Video 2). (A) The MSD of neutrophil migration paths is plotted as a function of time between steps. (Inset) The average MSD at a 150-s time interval for each condition. Cells migrating on 10 kPa Col-coated gels show a significant increase in RMS speed over cells on 50 kPa or 100 kPa gels. *P < 0.05, 10 kPa versus 50 kPa and 100 kPa. (B) The average DI of each condition is plotted over time interval. (C) For each cell, index DI(Δt) was fit to an exponential DI fit function, yielding mean values of Td. The Td of cells migrating on Col-coated gels is independent of substrate stiffness. (D) The fit of DI(Δt) was also used to generate values for DI< and DI>. These data are plotted as the directionality transition. Cells migrating on Col-coated gels have no significant differences in DI< or DI>. Error bars represent sem.