Principles of Plastination -dehydration of Specimens

Specimens to be plastinated are often moist which necessitates the removal of tissue fluid (dehydration) before forced impregnation or plastination can be carried, out. Dehydration removes the specimen fluid (water), as well as, some fat. The tissue fluid is replaced with an organic solvent. To be a dehydrating agent, the solvent must be miscible with water and may consist of a variety of chemical structures (ketones or alcohols). Either alcohol or cold acetone maybe used as a dehydrant for plastination. Methylene chloride (chlorinated hydrocarbons) is not a dehydrating agent. Shrinkage accompanies dehydration and may be minimized by: 1) using cold acetone (known as freeze substitution) or 2) starting dehydration in a lower % of ethanol. With freeze substitution, the ice in the specimen is replaced by the dehydrating liquid (acetone). It is essential to use an adequate volume of dehydrating liquid (either cold acetone or ethanol). The recommended ratio is: 10 volumes of dehydrating fluid to 1 volume of tissue. It is necessary to monitor the concentration of the dehydration fluid at weekly intervals. Once the fluid content has remained similar for a few days, the specimen is moved to a fresh dehydrating solution. Cold ACETONE (-15° to -25°C): usually has been considered the best method of dehydration. However, dehydration with acetone must be carried out in the cold and not at room temperature; warm acetone will cause excessive shrinkage and complete dehydration may not occur.