Project Summary To reduce the burden of neurological disease, induced pluripotent stem cell-derived human brain cells offer the potential for unprecedented insight. But the capabilities of the nervous system arise from the interactions of its cells, so to use them as a model of brain pathology, they must be investigated in a context where they can reciprocally influence one another as they do in vivo. The field is in need of facsimiles with architectural arrangements that recapitulate brain circuits. To study the dentate gyrus-hippocampal CA3 circuit that is critical for memory and often altered in diseases such as epilepsy, this project will place neuronal and glial precursor cells at precise locations. The project consists of two aims. First, we will create a matrix suitable for capture of fluid droplets containing individual glial and neuronal cells. This surface must be soft enough to minimize cell trauma during deposition and must encourage the growth of these cells and extension of their processes. A porous scaffold constructed of the brain extracellular component hyaluronic acid is the starting point for development of this capture substrate. Embedding of signaling molecules will help specify cell identities and encourage cell growth, and regional modulation of matrix properties will help guide cell organization. Secondly, adapting methods from cell-sorting technology, we will develop a microfluidic system for optical cell identification. When the droplet containing the cell is released, a charge is applied. As the droplet falls through a voltage field, this charge determines its position. In this way cells will be deposited in precise patterns. The resulting array of neurons and glial cells will yield a robust, reproducible model -- composed of human brain cells -- of neural circuit function and pathology. Given the great toll of neurologic diseases involving hippocampus such as epilepsy, depression, and dementia, improved means of investigating these conditions and possible treatments could benefit millions of individuals and families. Indeed, this project will provide a framework for construction of a microphysiological system to model any brain circuit. This has potential to yield significant value to public health.