Critical Point Drying of Freeze-Fractured Tissue For Scanning Electron Microscopy

Abstract

The critical point method eliminates distortion that might have been caused by surface tension during drying of specimens being prepared for scanning electron microscopy. Such preparations can be made rapidly and routinely, and the structural fidelity of surfaces of cells and tissues thus prepared is excellent. But attempts to look inside the tissues or cells with the scanning electron microscope have been less successful. Critical point dried tissue can be broken or cut, and the exposed surface viewed. But plastic deformation of the exposed surface structures caused by the cutting or breaking severely limits the usefulness of this approach. Plastic deformation is minimized when tissue is freeze-fractured to expose internal surfaces, and the water (ice) can be sublimed away from small fragments of tissue without surface tension distortion by freeze-drying the specimen in a vacuum. But freeze damage, resulting mainly from ice crystal formation, is very difficult to avoid.