Abstract
Brain organoids are three-dimensionally reconstructed brain tissue derived from pluripotent stem cells in vitro. 3D tissue cultures have opened new avenues for exploring development and disease modeling. However, many physiological conditions, including signaling gradients in 3D cultures, have not yet been easily achieved. Here, we introduce brain organoid-on-a-chip platforms that generate signaling gradients that in turn enable the induction of topographic forebrain organoids. This creates a more continuous spectrum of brain regions and provides a more complete mimic of the human brain for evaluating neurodevelopment and disease in unprecedented detail.