According to Merriam Webster, cryostat is defined as "an apparatus for maintaining a constant low temperature especially below 0°C" — which is, essentially, the same thing as a Dewar. However, most use the word as shorthand for "cryostat microtome", which is a lab instrument used to section tissue samples in a controlled, cryogenic environment. Certain applications, like sectioning tumors for diagnosis, demand that tissue samples be kept at cryogenic temperatures in order to preserve the molecular structure of the tissue. If that structure is not preserved, the sample cannot be properly analyzed under a microscope. Hence, the invention of the cryostat microtome.
Here's a rundown of how cryostats are used along with some of their common features.
Using a cryostat
Before sectioning a sample in the cryostat, the user must prepare both the sample and the cryostat. Prepping the cryostat may consist of running a disinfection protocol and then setting the desired chamber temperature. While the chamber is cooling, the pathologist may then freeze the tissue sample. Tissue must be frozen immersed in a specialized solution to support its cellular morphology during sectioning; if its cellular structure crumbles, the tissue can't be stained and examined properly.
Once the sample is embedded and the chamber is at its set temperature, the pathologist can then mount the sample to its holder on the microtome and begin sectioning it. Sectioning may be performed manually with the handwheel on the side of the cryostat or, in the case of more sophisticated units, with a motorized microtome that sections automatically.
Microtomy can be messy; after sectioning a sample there may be small scraps littering the chamber. The user can sweep up the shavings manually or, if waste trays are installed, empty the trays. If one decides to remove the tray, they must allow the chamber temperature to equilibrate with the room's ambient temperature — otherwise, the tray will condensate when removed from the chamber and then freeze to the chamber once placed back in.
Alternatively, the user can also vacuum them up if their cryostat is equipped with a vacuum assist feature.
Many cryostats come with advanced features to make disinfection easier, quick-freeze samples, and more. Here's a few of the options you can find on cryostats here at New Life Scientific:
Vacuum systems keep tissue sections flat, which ensures they'll be suitable for coverslipping onto microscope slides later. By pulling on the section with a light vacuum, it's kept taut and won't bunch up or fold as it is sliced. As stated earlier, vacuum assist tubes can also be used to quickly and easily clean up scraps of tissue.
For the sake of safety and convenience, many cryostats come with automatic chamber disinfection systems built in. There are two types of automatic disinfection:
Fumigation systems are ideal for deep cleaning. These systems release a gas, usually O2 or peroxide, that expands to fill every nook and cranny of the chamber and wipe out any pathogens. While highly effective, fumigation systems are far from perfect. They take a long time to complete a cycle, and there is risk posed to those working around the cryostat should the gas start leaking.
- UV disinfection
In UV disinfection systems, a bulb seated within the chamber illuminates and coats every exposed surface with ultraviolet light that eradicates any pathogens that could be lurking. Ultraviolet disinfection is fast, efficient, and completely safe for those near the cryostat. However, it's not as thorough as fumigation systems — if any angle of the chamber is shielded from light, it won't be disinfected.
Automatic motorized sectioning
Also found on benchtop microtomes like the Tissue-Tek AutoSection, motorized cryostat microtomes offer fully-automated sectioning that frees up valuable time for the pathologist and ensures consistent sections.
Shopping for a cryostat?
View our available cryostats here, all of which have been serviced and tested to perform at manufacturer specifications.