Questions and Answers
Which characteristic is NOT typical of an infiltrating and embedding medium?
Colored and opaque
What is the purpose of infiltration in tissue processing?
To fill tissue cavities and give firm consistency to the specimen
Why is paraffin wax commonly used for tissue embedding?
It can be easily handled and is inexpensive
During tissue processing, at what temperature range should an ideal infiltrating and embedding medium be molten?
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What is the primary function of embedding or casting in tissue processing?
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Which substance is NOT commonly used as an impregnation and embedding medium?
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Which wax substitute has a melting point of 56-57 °C and is described as more elastic and resilient than paraffin wax?
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Which wax substitute is recommended for embedding 'eyes' and 'tissue mat' due to its less brittle nature compared to Paraplast?
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Which wax substitute is harder than paraffin, NOT soluble in water, but SOLUBLE in 95% ethanol or other clearing agents?
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Which type of wax substitute does not require dehydration and clearing due to being soluble and miscible with water?
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Which wax substitute requires 3-4 changes to ensure complete tissue impregnation, even without prior clearing of tissue?
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Which wax substitute is described as a product of paraffin that contains rubber and has similar properties to Paraplast?
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What is the purpose of vacuum embedding in tissue processing?
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Why is vacuum embedding recommended for urgent biopsies and delicate tissues?
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How does vacuum embedding impact the removal of air bubbles from tissue blocks?
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Which type of wax is commonly used for tissue embedding?
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What is the purpose of immersing the specimen in melted paraffin wax multiple times?
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Study Notes
Substitutes for Paraffin Wax
- Paraplast: a mixture of highly purified paraffin and synthetic plastic polymers with a melting point of 56-57 °C, more elastic and resilient than paraffin wax.
- Embeddol: a synthetic wax substitute similar to paraplast with a melting point of 56-58 °C, less brittle than paraplast.
- Bioloid: a semi-synthetic wax recommended for embedding "eyes" with similar properties to paraplast.
- Tissue mat: a product of paraffin containing rubber, with the same properties as paraplast.
Ester Wax
- Lower melting point of 46-48 °C, harder than paraffin, not soluble in water, but soluble in 95% ethanol or other clearing agents.
- Can be used for impregnation even without prior clearing of tissue, requires 3-4 changes of ester wax for complete tissue impregnation.
Water Soluble Waxes
- Carbowax: plastic polymers with a melting point of 38-42 °C or 45-56 °C, soluble and miscible with water, does not require dehydration and clearing.
Infiltration and Embedding
- Infiltration (impregnation): the process of replacing the clearing agent with a medium that fills tissue cavities, giving the specimen firm consistency and allowing easy handling and cutting.
- Embedding (casting/blocking): the process of surrounding the impregnated tissue with a medium that provides external support during sectioning.
Characteristics of an Infiltrating and Embedding Medium
- Soluble in processing fluids
- Suitable for sectioning and ribboning
- Molten between 30°C and 60°C
- Translucent or transparent, colorless, stable, homogeneous
- Capable of flattening after ribboning
- Non-toxic, odorless, easy to handle, inexpensive
Types of Impregnation and Embedding Medium
- Paraffin wax
- Celloidin (collodion)
- Gelatin
- Plastic
Paraffin Wax Impregnation and Embedding
- The simplest, most common, and best embedding medium used for routine tissue processing.
- Specimen is immersed in a series of melted paraffin wax solutions for 15 minutes each, followed by a final immersion for 3 hours.
- Vacuum embedding facilitates complete removal of transition solvents and prolongs the life of the wax.
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