The Freeze Drying

Freeze drying specimen preparation reduces the distortion and shrinkage effects that occur when a wet specimen dries by normal evaporation. Distortion is due to the forces of surface tension that occur when going from a liquid to a vapour phase, such as from water to water vapour - the normal situation with biological specimens. The freeze drying method overcomes this problem by careful sublimation of frozen specimens under vacuum - a process that avoids the liquid phase and thereby reduces distortion effects. The rate of sublimation is a function of temperature and vacuum, with typical drying times being several hours or longer.