Polyester Resin Embedding for Sectioning of Hard and Soft Tissues

Soft and calcareous tissues embedded in polyester resin may be cut on a sledge microtome to produce thin sections of 3-4 β thickness. Fixed tissues, dehydrated in ethyl alcohol, cleared in methyl benzoate and chloroform, are taken into a wide-necked bottle containing equal parts of polyester resin and chloroform with 0.75% catalyst. The bottle kept in water bath at 37°C is connected to a vacuum pump. With the evaporation of the chloroform under reduced pressure (approximately 10 mm Hg) infiltration is complete. Tissues transferred into a blocking form containing pure polyester resin with 1.5% catalyst are polymerized at 37° C until blocks are firm (48 hr or more). Blocks are prepared with at least 5 mm margin of plastic surrounding the tissue. The edge of the block adjacent to the knife is then filed at an angle of 45° to the cutting movement. Sections are cut with a wide-backed biplanar knife having a cutting edge of 40-44° positioned at an angle of 30° to the plastic block. As the resin is permeable to most stains, staining is carried out through the plastic Sections carried through staining procedures in wire baskets are floated onto slides and mounted in polystyrene; the cover-glass is compressed with a spring-clamp. Microscopic examination shows no staining of plastic, minimal shrinkage and good cellular detail.