The researchers fabricated a microfluidic device with two important features: a three-dimensional environment, and compartments that separate muscles from nerves to mimic their natural separation in the human body. They suspended muscle and neuron cells in a hydrogel and injected them in the millimeter-sized compartments (thin channels shown in blue) and supplied culture medium from each side of the neuron/muscle tissue (large channels shown in blue) to mimic a three-dimensional environment.  Image: Sebastien Uzel