Surface Interactions and Control of Microbial Locomotion

Interactions between swimming cells and surfaces are essential to many microbiological processes, from the formation of biofilms to the fertilization of human egg cells. Until recently, however, relatively little was known about the physical mechanisms that govern the scattering of flagellated or ciliated microorganisms from solid surfaces. A better understanding of cell-surface interactions not only promises new biological insights but may also advance microfluidic techniques for controlling microbial locomotion, with potential applications in diagnostics, therapeutic protein synthesis and photosynthetic biofuel production. One of our recent papers shows that the surface scattering of mammalian spermatozoa and unicellular green algae is dominated by direct ciliary contact interactions. Building on this insight, we were able to construct optimal microfluidic ratchets that maximize rectification of initially uniform algae suspensions. Furthermore, our related work on confined bacterial suspensions demonstrates how curved boundaries can be used to control and stabilize the collective motion of microorganisms.