A fixed tissue sample is incubated in the X-CLARITY™ Hydrogel Solution Kit to allow hydrogel monomers to diffuse uniformly throughout the sample. Once the solution has permeated the tissue, the sample is placed in the X-CLARITY™ Polymerization System. Monomers polymerize in the anaerobic environment, covalently linking the biomolecules to a sturdy hydrogel network, preserving molecular information and structural integrity.