Confinement by liquid-liquid interface replicates in vivo neutrophil deformations and elicits bleb based migration.

Leukocytes navigate through interstitial spaces resulting in deformation of both the motile leukocytes and surrounding cells. Creating an in vitro system that models the deformable cellular environment encountered in vivo has been challenging. Here, we engineer microchannels with a liquid-liquid interface that exerts confining pressures (200-3000 Pa) similar to cells in tissues, and, thus, is deformable by cell generated forces. Consequently, the balance between migratory cell-generated and interfacial pressures determines the degree of confinement. Pioneer cells that first contact the interfacial barrier require greater deformation forces to forge a path for migration, and as a result migrate slower than trailing cells. Critically, resistive pressures are tunable by controlling the curvature of the liquid interface, which regulates motility. By granting cells autonomy in determining their confinement, and tuning environmental resistance, interfacial deformations are made to match those of surrounding cells in vivo during interstitial neutrophil migration in a larval zebrafish model. We discover that, in this context, neutrophils employ a bleb-based mechanism of force generation to deform a barrier exerting cell-scale confining pressures.