This is an artist's conception of the microbrain bioreactor. The upper chamber contains the neurons and an artificial capillary that carries blood to the brain surrounded by the cells that make up the blood-brain barrier. The lower layer is filled with cerebral spinal fluid (CSF) and contains an artificial choroid plexus (red) that makes CSF and a venule (blue) that carries blood away from the brain, along with a collection of cells that form the blood-CSF and CSF-brain barriers. Collectively, all these cells will reproduce the microenvironment found in the brain. The entire device will be about the size of a grain of rice.