A human neutrophil is initially exposed to a linear chemoattractant gradient (IL8) pointing towards the top of the screen. After 5 minutes, the direction of the gradient is switched downwards. Interestingly, the neutrophil does not just make a U turn, instead it stops and rounds up before starting to move in the new direction of the gradient. The neutrophil is followed for another 5 minutes after the switch. The direction of the gradient is switched in just 4 seconds inside the microfluidic device.