physical fixation

Physical fixation is a freezing method to preserve the morphological structure of biological specimens such as cells and tissues extracted from living organisms, by keeping them close to their living states for scanning electron microscope (SEM) observation.
The method physically fixes water in cells or tissues. If the freezing rate is low, ice crystals are formed in the cells and the crystals destroy the cell structure in the cells. To avoid this, rapid freezing or high-pressure freezing is applied. There are two rapid freezing methods available. One is immersion freezing, in which a biological specimen is directly immersed into liquid nitrogen or liquid ethane. Another is metal mirror freezing (slam freezing), in which a biological specimen is punched against a metal block cooled by liquid nitrogen or liquid helium. In high-pressure freezing, a specimen is frozen at the liquid nitrogen temperature under the pressure of a few 100 MPa.
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.