Cryofixation of suspensions and tissues by propane-jet freezing and high-pressure freezing

During the last few years, several techniques for the rapid freezing of thin aqueous layers of cells and tissues have been developed and successfully applied to various biological questions (spray-freezing, propane-jet freezing, metalmirror-freezing, plunge-freezing, high pressure freezing). For practical work, techniques where the biological material (mainly suspensions) is sandwiched between two metal platelets are most favourable, because the frozen sandwiches are easily freeze-fractured, freeze-substituted or freeze-dried. In addition, the thickness that is sufficiently well frozen (vitrified or in the microcrystalline state) is greater in a sandwiched sample than in a specimen cooled only from one side (1). Heat can be extracted from the specimen sandwich either by controlled rapid plunging into a suitable coolant (2) or by shooting the coolant simultaneously from opposite directions onto the specimen surface (propane-jet) (3).