Theory and Practice of High Pressure Freezing

Abstract

Pressure-freezing has often been regarded as a method for highly technical specialists. At the beginning of its development, this may have been true: it was introduced in 1968 by Moor and Riehle at the European conference on electron microscopy in Rome. The interest of the audience was not overwhelming, because everybody thought that this approach is oversophisticated and in principle unnecessary. In the following decade, many technically less pretentious freezing methods have been developed, which work in the absence of pressure. All of them became standardized and their methodology has been described in numerous reviews and textbooks (e.g. Rash 1983; Gilkey and Staehlin 1986; see also Sitte et al., Chap. 4, this Vol.). The compiled experience shows the manifold profits of applying impact-, plunge-, jet- and spray-freezing. In one aspect, however, all of these techniques are inadequate: namely they only enable satisfactory cryofixation of objects or superficial layers, which are not thicker than 10–20 μm. This limitation is caused by the physical properties of aqueous systems and it indicates that thicker specimens can be well cryofixed only if these properties are altered.