Freeze fracturing is a process where a frozen specimen is cracked to reveal a plane through the tissue. The fracture occurs along weak hydrophobic planes such as membranes or surfaces of organelles. The technique is extremely powerful when applied to the study of membrane structure and organisation.
Once fractured, replicas of fractured surfaces are prepared and separated from the tissue leaving a thin metal (eg platinum-carbon) replica to examine in a transmission electron microscope (TEM). Replicas are uniquely suited for the study of membrane structure, notably the internal aspects of the lipid bilayer, thus providing a three-dimensional representation of the tissue and cellular landscape. This technique is very technically demanding and slow with the fragile replica requiring careful cleaning before being collected on a TEM grid for viewing.
Instrument advances now allow fully hydrated fracture faces to be directly imaged at high resolution in a cryogenic field emission gun scanning electron microscope. The technique relies on vitrification of tissues by high pressure freezing, fracturing and ion beam coating at high vacuum conditions and cryogenic temperatures.
