Reconfigurable microfluidic circuits for isolating and retrieving cells of interest

Microfluidic devices are widely used in many fields of biology, but a key limitation is that cells are typically surrounded by solid walls, making it hard to access those that exhibit a specific phenotype for further study. Here, we provide a general and flexible solution to this problem that exploits the remarkable properties of microfluidic circuits with fluid walls─transparent interfaces between culture media and an immiscible fluorocarbon that are easily pierced with pipets. We provide two proofs of concept in which specific cell subpopulations are isolated and recovered: (i) murine macrophages chemotaxing toward complement component 5a and (ii) bacteria (Pseudomonas aeruginosa) in developing biofilms that migrate toward antibiotics. We build circuits in minutes on standard Petri dishes, add cells, pump in laminar streams so molecular diffusion creates attractant gradients, acquire time-lapse images, and isolate desired subpopulations in real time by building fluid walls around migrating cells with an accuracy of tens of micrometers using 3D printed adaptors that convert conventional microscopes into wall-building machines. Our method allows live cells of interest to be easily extracted from microfluidic devices for downstream analyses

Assaying macrophage chemotaxis using fluid‐walled microfluidics

While many tools exist to study immune-cell chemotaxis in vitro, current methods often lack desirable features. Using fluid-walled microfluidics, circuits are built around primary murine macrophages deposited in pre-defined patterns on Petri dishes or microplates. Concentration gradients of complement component 5a (C5a) are established in flow-free or flowing environments, image cell migration, and relate cell directionality and velocity to calculated local C5a concentrations. In flow-free circuits built around patterned macrophages, only cells nearest the C5a source migrate regardless of local attractant concentration. Conversely, in flowing circuits free from intercellular signaling and attractant degradation, only cells distant from the source migrate. In both systems, cells respond to lower C5a concentrations than previously reported (≈0.1 pM). Finally, macrophages follow instantly-shifted gradients better than slowly-shifting ones, suggesting that migration depends on both spatial and temporal responses to concentration