EMBEDDING AND TRIMMING

• Embedding


  Also known as Casting or Blocking. Arranging the impregnated tissue to its precise position in a mold filled with a medium which is then allowed to solidify. The medium used in embedding is the same medium used to infiltrate the tissue sample.
• Embedding


  • The tissue is being oriented in embedding to its correct position in the mold to not miss out elements that needs to be studied
  • Done after impregnation
  • Utilizes different types of embedding medium and blocking out molds
• Embedding media


  • Paraffin Wax
  • Celloidin (Collodion)
  • Gelatin
• Paraffin Wax


  The simplest, most common and the best embedding medium that is used for routine tissue processing. Can store tissue blocks indefinitely without considerable distortion. Not recommended for fatty tissues.
• Celloidin (Collodion)


  Suitable for specimens with large cavities or hollow space (such as our eyes); for hard and dense tissues (such as our bones and teeth) and for large tissue sections (whole embryo). Sections are thicker than paraffin sections. Recommended for processing neurological tissues. Rubbery in consistency so when you cut a very hard tissue it would be cut without undue distortion. Disadvantages: Slow acting and tedious to work with, Serial sections are difficult to prepare.
• Gelatin


  Rarely used except when dehydration is to be avoided and for tissues that are for histochemical and enzyme studies. For delicate specimens and frozen tissue sections because it prevents fragmentation of tough and friable tissues. Water soluble. Low melting point.
• Blocking-out molds


  • Leuckhart's Embedding Mold
  • Compound Embedding Unit
  • Plastic Embedding Rings & Base Mold
  • Peel Away
  • Plastic Ice Trays
  • Paper Boats
• Plastic Embedding Rings & Base Mold


  Stainless steel base mold with a plastic embedding ring which later serves as the block holder during cutting. Advantages: No need to remove the tissue block from the embedding board, you just have to remove the base mold and then chuck it into the machine.
• Trimming


  Cutting of excess wax from the block to expose the tissue surface. To make the tissue block even to form a four sided prism. In preparation for section cutting.
• Trimming


  • Coarse Trimming
  • Fine Trimming
• Coarse Trimming


  Cutting away excess wax from the sides, top and bottom of the block until perfectly level and all sides are parallel to each other almost to the edge of the tissue. Done while the tissue is not clamped to the microtome.
• Fine Trimming


  Fine tuning. Tissue block is clamped on the chuck of the microtome. Adjust the thickness adjuster to 15 mm or advance the tissue block using the coarse feed mechanism towards the microtome knife. Tissue block is trimmed until the entire surface has been partly exposed.
• Equipment & Materials


  • Paper boats
  • Forceps
  • Bunsen burner
  • Pan of ice water
  • Melted paraffin wax
  • Paper wax (6x6 cm)
• Specimen Used: A well-infiltrated tissue
• Embedding Procedure


  1. Melt the paraffin wax at 60°C in an electric paraffin wax dispenser

  2. Make a paper boat using a 6x6 cm wax paper. Fold the wax paper into a box measuring 2cm in all sides

  3. Fill it with melted paraffin wax

  4. Warm a pair of blunt-nosed forceps in flame and use them to transfer the well-impregnated tissue to the mold

  5. Warm the forceps again and orient the tissues. Press the specimen down gently, making sure that all parts of the tissue are flat in order to achieve a flat surface for cutting

  6. Place the label against the side of the mold, adjacent to the tissue. The number should be placed in such a way it is always facing outside

  7. Allow the block to solidify partially in a cold plate or at room temp and then completely cool it down in an ice bath until it hardens

  8. Tear the paper mold or remove the base mold and trim to form a four-sided prism