We fabricated stepped gradient arrays containing nm-sized features coated with cell-attracting proteins to build surface of defined densities for chemoattractant cell migration studies. By challenging cells with a binary choice of low versus high densities, we discovered a threshold difference in density required for migration direction choice. With stepped gradients, we observed a behaviour consistent with directional persistence during cellular migration. This assay allows for the systematic study of cellular migration between low and high protein surface densities across multiple densities, and uncovers directional choices that are otherwise masked in continuous gradients. This assay provides a powerful platform for advancing the understanding of contact-mediated migration and signaling of motile cells to surface protein cues.
Cell migration assay on combinatorial nanodot strips
C2C12 myoblasts on netrin-1 coated nanodot gradient of 30% to 44% showed no directional preferences (A); but preferentially migrated onto higher density arrays in 1% to 30% gradient (B).
Directional persistence during cellular migration
A) Stepped gradient arrays on a silicon mold showing 1, 3, 10, 30 and 44% arrays (repeated twice), made of 800 × 800 nm2 nanodots. (B) Contrary to the absence of directional choice on binary 30 to 40% gradients, a multistep gradient with 1%, 3%, 10%, 30% and 44% showed high cell preference on the 40% arrays. We hypothesize that in the stepped gradient, cells are already motile migrating from the lower density arrays (1%, 3%, 10%), and continue migrating beyond the 30% onto the 44% arrays due to directional persistence