Application of cryosectioning to x-ray microanalysis of biological tissue.

Cryosectioning biological tissue is a critical and difficult step when applied to x-ray microanalysis of diffusible elements. Conventional metal machining theory can explain and predict results obtained by cryosectioning more consistantly than a freeze-thaw model. Temperature of a critical zone where shearing occurs is probably the most important factor for cryosectioning. This is presumed to be a result of thermally induced changes in tissue brittleness. Two other factors which may change effective cutting temperature are section thickness and cutting speed. Tissue brittleness also depends upon the extent of ice crystal damage from initial freezing which is largely determined by heat removal rate (freezing rate), water content, size, and composition. Antiroll plates are effective devices for counteracting bending forces which occur as the section is sheared from the block. Cryosectioning does not appear to affect elemental distribution or tissue morphology in either bounded or unbounded systems. Thus cryosectioning appears to be a predictable and controllable step which is suitable for x-ray microanalysis of diffusible elements in biological tissue. Deterioration of spatial and analytical resolution does not appear to occur through the process of cryosectioning; rather these limits are set by initial freezing.