high-pressure freezing

High pressure freezing is one of physical fixation methods to freeze water-containing specimens such as living organisms, foods and paints under a high-pressure environment, by keeping them close to their original form for scanning electron microscope (SEM) observation.
In this method, a specimen is loaded into a dedicated cartridge, and then, the specimen in the cartridge is frozen under applying a high pressure of about 210 MP with a jet of liquid nitrogen to the cartridge using a dedicated tool.
The high-pressure freezing enables a uniform and ice-crystal-free freezing to a depth of several tens of times greater (around 200 μm) than freezing under atmospheric pressure (ordinary rapid freezing). The high pressure lowers the melting point of water and increases its viscosity, thus suppressing ice-crystal formation which can destroy the morphological structure of the specimen.

The frozen specimen is observed with a cryo-SEM while keeping its frozen state, or observed at room temperature with an ordinary SEM after freeze substation and freeze drying.