Epoxy embedding serves a dual purpose - it fixates and preserves the structural integrity of biological material of interest without drastically altering the sample and encloses the material in a solid, hard environment that is suitable for cutting semi-thin and thin sections for TEM viewing.
Fixation is done using a 2.5% glutaraldehide solution and a 1% osmium tetraoxide solution, the latter also used in tandem with a 2% uranilacetate solution for negative staining. Dehydration is performed by immersing the material in graduated solutions of distilled water and ethanol with a subsequent immersion in pure propylene oxide to fully substitute the materials’ water for a liquid miscible with the epoxy resin of the embedding medium. The tissue is then sent through a mixture of epoxy and acetone, and then through pure epoxy to substitute any liquid for resin components. The prepared tissue is placed into plastic capsules, which are filed with epoxy, and cured for up to 4 days in an incubator (60 oC) until ready for sectioning.