SUMMARY
Examples of plastic deformation are illustrated from a wide range of specimens that have been prepared for electron microscopic examination by fracturing at low temperature prior to replication of the frozen surface. Deformation has been shown to occur in some specimens when fractured at temperatures as low as 4 K.
Plastic deformation is recognized in non‐biological polymers such as polystyrene and polyacrylate latex spheres, as well as in similar biological molecules such as poly‐β‐hydroxybutyrate (PHB). However, it is also demonstrated that plastic deformation occurs widely in more complex biological systems, including membranes and protein macromolecules.
The interpretation of the structure of fracture faces of frozen membranes, and particularly the lack of complementarity on opposing fracture faces, is discussed in relation to deformation artifacts.
It is concluded that very considerable energy must be dissipated as heat during the cleavage process. In the case of some of the latex spheres, the glass transition temperature (Tg) of the bulk polymer can be more than 200 K above the cleavage temperature, and yet plastic deformation still occurs.
Once a molecule has deformed, its appearance in the final replica may be significantly changed by heating during evaporation of the replica. An empirical attempt has been made to define the factors leading to the ‘survival’ of a deformed particle.
Although the evidence in this review has been drawn from freeze‐fracture and freeze‐etching studies, it is emphasized that the process of cleaving at low temperature—whether in freeze‐fracture techniques or in cryoultramicrotomy—is essentially the same. Therefore the interpretation of structure in ultra‐thin frozen sections will also need to allow for the possibility of deformation artefacts.