Fig. 2.

Schematic representations of on-demand and competing chemotaxis assay. A. Chemokines are loaded in both side compartments (CK1 and CK2) and cells are plated in a middle cellular compartment. These compartments are separated by two side valves (default-closed) and one central valve (default-open), respectively. Sinks between those compartments are designed to balance the difference in priming time of chemokine gradients caused by different diffusivity. Inset shows a photo of the platform visualized by food dyes. B. Two side valves are opened shortly to prime chemokine chambers and migration channels with chemokines and then closed to prevent any disturbing convection flow into the migration channels during chemotaxis assay. C. To plate the cells in the central compartment, the central valve is kept closed, sealing the compartments and avoiding early exposure to chemokines. To expose the cells to chemokine gradients and start the chemotaxis, the central valve is released without any pressure. D. The platform operates in two steps: chemokine priming and chemotaxis. (1–2) With opening of the side valves and closing of the central valve, chemokines fill the chemokine chambers and the migration channels. (3–4) With closing of the side valves and opening of the central valve, chemokines release and activate cell chemotaxis. Scale bars, 2 mm (A) and 200 μm (D).