What is a cryostat?

The cryostat is a piece of equipment used in the processing of samples for histological or histopathological diagnosis or identification. It is mainly used to freeze and obtain frozen tissue sections or samples that have not been previously fixed by chemical methods, to avoid losing some important characteristics necessary for observation.

In other words, it is an instrument used in pathological anatomy laboratories in order to obtain tissue sections from frozen material and thus achieve thicknesses ranging from 8 to 40 ยตm, for observation under the light microscope.

Tissue freezing is a quick way to harden them without the need for embedding, so molecular preservation is maximized. But to correctly preserve the structure of the tissue, it must be a very fast freezing which prevents the formation of ice crystals that deteriorate the cellular structures.

How does this team work?

The two most commonly used devices for freezing cuts are the freezing microtome and the cryostat. In the case of the cryostat, the rotation and cut-off mechanism of the cryostat is located inside a refrigerated chamber, at a temperature between -20 and -30 ยฐ C. In this chamber is the sample, the blade and it is where the sections are collected, a process by which the sections are glued to a slide.

Freezing is usually done on a platform within the refrigerated chamber itself with the Peltier system. You can also freeze the tissue externally as quickly as you want, for example with liquid nitrogen, but it is convenient to place the sample in the cryostat chamber until its temperature is equal to that of the cryostat to obtain homogeneous sections. Before freezing, the sample is embedded in a medium that is liquid at room temperature and solid at cut-off. Therefore, we have our sample in a solid block, embedded but not included. This allows the sample to be manipulated and attached to a sample holder, which will be fixed to a shaft that advances on the blade.

Cryostat types

Single compressor: Single compressor models can control both the temperature inside the freezing plate and the cooling chamber. This process generally involves an evaporation system, which allows the cooling chamber and freezing plate to reach cryogenic temperatures.

Double compressor: With the double compressor model, there is one compressor to control the temperature of the freezing plate and another to control the cooling chamber. Because of this, you can cool samples faster with quick freeze and reach lower temperatures compared to a single compressor model.

Rotating Cryostat: These are cryostats that have flyers on the side of the device. Turning the handwheel clockwise starts the cutting process. As the samples go down with the steering wheel, the sections are made. The cutting thickness is also done at the upper reversal point of the cutting movement.

Motorized Cryostat: These have a motorized cutting drive for sectioning samples. The cutting speed can be adjusted so that harder materials can section more slowly than softer materials.

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