We develop novel hydrogels for expansion microscopy; an imaging technique that isotopically magnifies biological samples to carry out superresolution imaging. We use photopolymerization reactions to fabricate expansion microscopy hydrogels (PhotoExM). Photopolymerization reactions are highly advantageous, as they proceed very rapidly, oxygen insensitive, and yield mechanically robust hydrogels post-expansion. Using two different strategies, we are capable of expanding samples 6.5 – 20 x of their original size, indicating a lateral resolution of 20-50 nm in a conventional confocal microscope. Furthermore, we use expansion microscopy to carry out nanoscale imaging inside 3d biomaterial cultures using a gel-to-gel (GtG) technology. This technology optically clears and expands cells and organoids in 3d biomaterials, which are conventionally hard to image using standard methods. Using PhotoExM and GtG technology, we study cell-matrix interactions, cellular matrix deposition, organoid growth and differentiation as well as skeletal muscle stem cell niche with unprecedented clarity.