Epoxy resins: what must be done before embedding?

• A. Tissue must be completely dehydrated
• B. Tissue must be fixed with formalin
• C. Tissue must be decalcified
• D. Tissue must be cut into large pieces

Answer: (A)

Water must be removed from the tissue before embedding epoxy resin. Epoxy resins are hydrophobic and do not penetrate water, so any remaining water blocks resin infiltration and prevents proper polymerization, resulting in poorly embedded blocks and artifacts. The tissue is dehydrated through a graded series of alcohols to replace water with alcohol, and then cleared to make the tissue receptive to resin. While fixation is performed earlier to preserve structure, and decalcification is only necessary for mineralized tissues, dehydration is the essential prerequisite for successful epoxy resin embedding. Cutting tissue into large pieces would hinder penetration; smaller pieces improve resin infiltration.