Lec 16: Infiltration
Why?
•In order for tissue to be sectioned into thin slices, it must be supported by permeating it with a medium that will give it a proper consistency for sectioning
embedding media infiltrates the tissue (both intra and extracellularly)
Paraffin is the best infiltrating agent
Advantages
Time period for infiltration and embedding is shorter (for small tissues)
Sectioning can be easily done using rotary microtome
Tissues (after infiltration and embedding) can be kept longer without worrying its damage and conditions
Can change from solid to liquid very quickly when heated
When it become harden in a tissue, it maintain the tissue structure and this condition will allow the sectioning to be done easily
Disadvantages
Tissue distortion always occur
Paraffin artifacts always occur
Degree of artifacts depend on the type of fixative used; Formalin always produce distinct artifacts; Bouin’s fixative produce less artifact.
Time period for infiltration and embedding is longer for big tissues
Types of paraffin
Soft paraffin become liquid at 45-50C
Medium state paraffin become liquid at 50-55C
Hard paraffin Become liquid at 60-68C
How to choose paraffin?
Based on tissue hardness: Use hard paraffin for hard tissues
Based on the thickness of a tissue section: Use hard paraffin for thin section
Based on temperature where the tissue is sectioning: Use soft paraffin for low temperature
Time period for infiltration depends on?
Size of tissue
Thickness of tissue
Density of tissue
Type of tissue
Procedures
After clearing, tissue placed in several changes of melted paraffin for specific period of time
Infiltration occur under vacuum and heat
Vacuum helps infiltrate paraffin through the tissue and heat keeps paraffin liquefied
Paraffin permeates, impregnates or infiltrate the tissue, replacing clearing agent