For more than a decade, researchers have been etching grooves into silicon and plastic wafers, filling the spaces with living cells, and hoping that the resulting devices will mimic biological systems such as the liver or gut. Scientists at the Wyss Institute for Biologically Inspired Engineering at Harvard University in Boston, Massachusetts, have created one of the most sophisticated devices so far: a lung on a chip that represents several types of tissue1. "We started with the simplest embodiment of human airway and capillary cells, and then introduced immune cells" says Donald Ingber, head of the institute. The chip holds a pair of microchannels separated by a flexible, porous 10-micrometre membrane. One channel contains air and a layer of epithelial cells such as those lining the tiniest air sacs in the lung; the other holds the type of cell that lines capillaries, along with flowing liquid to simulate blood. The set-up even models breathing: vacuum chambers attached to the channels simulate the mechanical forces that cells encounter as a persons chest expands and contracts.
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