Migration of purified human neutrophils in a 3D collagen matrix. (A-B) Neutrophils tracked using JEX analysis, migrating in a 100nM gradient of fMLP compared with no observable migration in the control (gel with no chemoattractant). Colors represent the formation of the chemical gradient: red represents maximum chemoattractant source concentration; and yellow, the chemoattractant concentration at the sink. (C-E) Comparison of neutrophil migration in a 100nM gradient of fMLP for the 2D and 3D embodiments of the KOALA platform, showing the chemotactic index, speed, and directional velocity. Standard purification protocols were used for 3D migration experiments (see “3D neutrophil migration”). (A-B) Scale bars represent 100 μm. Error bars represent SEM. Phase-contrast images acquired using Slidebook Version 5.0.0.14 software with an Olympus IX-81 microscope using a 10× objective (NA = 0.30) at 37°C. Additional details on imaging are given in “Microscopy.”