Micron-scale positioning of features influences the rate of polymorphonuclear leukocyte migration

Microfabrication technology was used to create regular arrays of micron-siz e holes (2 mum X 2 mum X 210 nm) on fused quartz and photosensitive polyimi de surfaces. The patterned surfaces, which possessed a basic structural ele ment of a three-dimensional (3-D) network (i.e., spatially separated mechan ical edges), were used as a model system for studying the effect of substra te microgeometry on neutrophil migration. The edge-to-edge spacing between features was systematically varied from 6 mum to 14 mum with an increment o f 2 mum. In addition, collagen was used to coat the patterned quartz surfac es in an attempt to change the adhesive properties of the surfaces. A radia l flow detachment assay revealed that cell adhesion was the strongest on th e quartz surface (similar to 50% cell attached), whereas it was relatively weaker on polyimide and collagen-coated quartz (similar to 25% cell attache d). Cell adhesion to each substrate was not affected either by the presence of holes or by the spacing between holes. A direct visualization assay sho wed that neutrophil migration on each patterned surface could be characteri zed as a persistent random walk; the dependence of the random motility coef ficient (mu) as a function of spacing was biphasic with the optimal spacing at -10 mum on each substrate. The presence of evenly distributed holes at the optimal spacing of 10 mum enhanced mu by a factor of 2 on polyimide, a factor of 2.5 on collagen-coated quartz, and a factor of 10 on uncoated qua rtz. The biphasic dependence on the mechanical edges of neutrophil migratio n on 2-D patterned substrate was strikingly similar to that previously obse rved during neutrophil migration within 3-D networks, suggesting that micro fabricated materials provide relevant models of 3-D structures with precise ly defined physical characteristics. In addition, our results demonstrate t hat the microgeometry of a substrate, when considered separately from adhes ion, can play a significant role in cell migration.