Typically, Microtomes Are Used To Slice Embedded Tissue into Very Thin Slices in Microbiology

 

Microtomes

Microtomes are the most commonly used apparatus/instrument in histology labs for obtaining sample sections for further microscopic examination. Knife clamps, a sample holder, a thickness gauge, and other accessories are included. It is a mechanical device that moves the sample towards the blade/knife in small steps of a few microns in length to obtain the required thickness section (thickness of the section mostly ranges from 5-10 nm). One of the most important tools in microtomy procedures is the knife (microtome knife). In most cases, a wedge (C type) knife is used to cut the sample section during a routine microtomy procedure.

The benefits provided by microtomes in histopathology practises are expected to drive microtome growth. Microtomes are used in clinical and diagnostic research laboratories, as well as industrial labs, to obtain routine paraffin sections and plastic-embedded specimens, high-quality sections with less fatigue, and to ensure the safety, reliability, and consistency of results. This has created a significant opportunity for manufacturers to create innovative microtomes using cutting-edge technologies.

According to Coherent Market Insights, The global Microtomes Market is estimated to be valued at US$ 128.5 million in 2019 and is expected to exhibit a CAGR of 6.2% during the forecast period (2020-2027).

A Microtome is a specialised precision cutting instrument that slices sections from a block of embedded tissue accurately and repeatedly. Different types of microtomes, as well as specialised microtomes, are used to section paraffin and plastic-embedded tissues and frozen tissues. A sharp knife and a tissue block are held in a fixed relationship in any microtome. Each pass of the tissue through the knife advances the tissue block by a predetermined amount—the section thickness.

The thickness of frozen sections is typically 8 to 15 m, wax sections 4-10 m, and plastic histological sections 0.5-3 m. Sections for electron microscopy must be extremely thin, about 200 times thinner than wax sections. Plastic sections used in transmission electron microscopy (TEM) are typically cut in the 60-100 nm range.

Samples must be chemically fixed with aldehydes, dehydrated in ethanol, clarified with xylene, and embedded in paraffin before microtome sectioning. Most samples are commonly referred to as Formalin Fixed Paraffin Embedded (FFPE) samples because they are fixed in a 10% formalin solution (composed of approximately 4% buffered formaldehyde solution stabilised with methanol). The use of the chemicals described will result in overall poor ultrastructural preservation.

This technique, however, preserves tissue microstructure and is still considered the gold standard for pathology assessment in human and animal disease models. When planned sample collection for CLEM is not possible, pre-prepared FFPE samples must be investigated further. Although not ideal for ultrastructural preservation, these samples can still be used for CLEM to answer specific biological questions. When possible, it is strongly advised to use electron microscopy grade aldehydes that have not been stabilised with methanol for sample fixation.