fixation methods

Methods 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 fixation methods are classified into chemical fixation and physical fixation. The former method chemically fixes proteins, lipids, etc., by using chemicals and the latter method physically fixes water in cells or tissues by freezing them.
For chemical fixation, immersion fixation is widely used, in which cells or tissues are directly immersed into a fixation solution. In addition, two other methods are often used: One is perfusion fixation used for animals, in which a fixation solution is injected into a specimen through the vascular system. Another is vapor fixation used for mold, in which the specimen is exposed to the vapor of a fixation solution.
For physical fixation, immersion freezing is widely used, in which tissues are directly immersed into liquid nitrogen or liquid ethane. In addition, two methods are often used: One is metal mirror freezing (slam freezing), in which a tissue is punched against a metal block cooled by liquid nitrogen or liquid helium. Another is high-pressure freezing, in which a tissue is frozen at the liquid nitrogen temperature while high pressure is applied.