This image shows a zebrafish brain that was embedded in a swellable polymer and physically expanded about tenfold using expansion microscopy. The expanded brain shows the structural organization of the tissue, with individual cells outlined across the entire brain. Together, these outlines form a continuous mosaic-like pattern that reflects the overall architecture of the brain. The larger goal of this research project is to develop an expandable hydrogel platform that can physically magnify biological specimens up to ~1,500× linearly, or more than a billion-fold in volume. At this scale, individual protein residues and molecular interactions can be directly visualized using standard light microscopes.