A microfluidic device could make it easier to control pluripotent stem cells for use in tissue engineering and developmental biology, according to Jiro Kawada, a graduate student in Teruo Fujii’s group at the University of Tokyo. Pluripotent stem cells can differentiate into a variety of cell types in response to chemical signals, but controlling the spatial distribution of the chemical factors—and thus the resulting cell types—is difficult. Kawada reported a two-layer microfluidic device for controlling the spatial distribution of the chemical factors that induce stem cell differentiation. He places stem cells in the upper channel and delivers growth medium containing retinoic acid and leukemia inhibitory factor (LIF) into the lower channel through three inlets. Retinoic acid induces differentiation, whereas LIF inhibits it. Adjusting the laminar flow pattern of the medium in the lower level changes the spatial distribution of the chemical factors entering the upper channel and thus controls stem cell differentiation. Because the flow velocity in the upper channel is much less than that in the lower channel, the cells aren’t damaged by shear stress, a common problem in microfluidic devices.