Paraffin Embedding And Sectioning Article

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Paraffin Embedding and Sectioning

Paraffin Embedding and Sectioning is extensively used in Histology Labs for the preparation of thin Tissue Sections so as to view them under a microscope.

Author: Abhinav Chaudhary

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Paraffin Embedding

The procedure involves transferring of the fixed object after thorough dehydration through graded alcohol and subsequent passage through paraffin –solvent intermediaries like xylene etc. to molten paraffin, to completely impregnate it with paraffin. Embedding Station is used to hold the tissue in paraffin, creating a block which eases the process of sectioning.

The choice of the hardness of the paraffin often depends on the room temperature. Commonly a paraffin of 56 to 58deg C melting point is used. In very warm laboratory rooms, or in hot countries, paraffin of higher melting points are used, but an embedding temperature of more than 65 deg C should be avoided as they produce additional artifacts in the object.

Research shows that fresh Paraffin has considerably poorer cutting properties than paraffin that has been standing in the hot thermostat for prolonged periods; this removes all the gaseous components. It is therefore advisable to prepare a large quantity of paraffin in stock, by boiling it for about five minutes and filtering and storing it in a thermostat. Filtering removes the dirt particles that can potentially damage the knife and can tear the sections.

In recent times, Pure Paraffin is being replaced by Tissue Embedding Media which are mixtures of pure paraffin and various plastic polymers. These plastic polymers considerably improve the embedding and cutting properties of both materials over those of pure paraffin. They are ready to use and do not require previous ageing or filtering.

Paraffin Sectioning

These days a variety of Microtomes are available to cut paraffin tissue sections. Microtomes can be manual, semi automatic or fully automatic. The difference is in the use of stepper motor for specimen feed and sectioning. A Semi-Automatic Microtome has a motorized specimen feed whereas a Fully Automatic Microtome in addition has motorized sectioning.

Steel Knives have been replaced by disposable blades which are more economical and increase throughput. Disposable Microtome Blades come in two types the Low Profile Blades and the High Profile Blades, the difference being in the thickness of the blade. High Profile Blades are ideal for sectioning hard tissues, industrial purposes and frozen sections.

The optimum range for the cutting of sections embedded in paraffin lies in a thickness range of 5 to 10 µm. Sections embedded in paraffin-polymer mixtures can be sectioned down to 3 µm thickness. Paraffin Sections are generally cut in ribbons. Before sectioning the paraffin block must be trimmed and aligned on the microtome so that its front and rear edge are parallel to each other and to the knife edge.

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Manager Business Promotion, Medimeas Instruments

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