Plastination

Introduction

Plastination is a new method of preservation of perishable biological specimens, especially for soft, putriable ones with high water contents, for example whole organ like brain, heart, liver, lung and kidney. In zoology, you can also plastinate small animal like chicken embryos, spiders, amphibians and small reptiles. In botany the Plastination of fungus has already been developed for general use, while the plastination of higher plant specimens is still in the experimental stage.

During the plastination process the tissue water and the part of the tissue fat is replaced by polymerize resin. Once the polymerization has taken place inside the specimen, it provides a higher stability than that of freeze dried specimen and paraffined specimen.

History of plastination

This technique is developed at the University of Heidelberg’s Institute of Anatomy in 1977, patented it between 1977 and 1982, and have been continually improving the process ever since.

Even though a major German encyclopedia (the 19th edition of the Brockhaus Encyclopedia, 1992) indicates that the word "Plastination" is derived from the Greek (from plassein = to shape, to form), the term is, in fact, a creation of Gunther von Hagens. He coined the term because "plastification" already had a fixed meaning in the field of polymer chemistry, and the expression used in the original patents of 1977/78 ("Polymer Impregnation of Perishable, Biological Specimens”) was not terribly catchy and was utterly inadequate for popularizing the new technology, particularly abroad. The following will provide an explanation of how Plastination works.

Plastination is carried out in four steps

1. fixation and staining

2. dehydration

3. forced impregnation

4. curing

Fixation and staining

Fixation is carried out using normal fixation techniques such as using formaldehyde solution. Coloration is achieved by injecting colored epoxy resin into the vascular system. Fixed specimens may be stained by microscopic staining methods. Color preservation can be attained by short fixation or utilizing the chemical influence of polymer components of the impregnation bath.

Dehydration

Dehydration of the specimen is necessary prior to impregnation with polymers. The easiest method is freeze-substitution. The specimen is placed in acetone at -25 ºC for several weeks. The acetone is changed until the water content is below 1%.

Forced impregnation

The process of forced impregnation is the central and important step of plastination. After saturation the specimen with a medium of high vapor pressure (low boiling point), it is immersed in a suitable polymer solution whose components have a low vapor pressure (high boiling point). The acetone inside the specimen is removed continuously by a vacuum pump. As the medium is removed from the specimen, a pressure difference will be generated causing the polymer solution to be drawn into the specimen.

The impregnation should be carried out slowly as to allow the polymer solution to penetrate inside the specimen,by which the acetone changes to the gaseous phase and is removed(pumped out “of boiledoff’). The impregnation takes 4 to 14 days depending primarily on the size of the specimen, the density of the tissue and the viscosity of the polymer solution.

Curing

The curing of the impregnated specimen carried out at room temperature or at +50ºC depending on the nature of the polymer used. It is a special method as gas-cure, where the impregnated specimen is brought into contact with a gaseous medium in order to complte polymerization.

Uses

The plastinated specimens are easy to handle as there are no formalin present which causes irritation to the eyes and skin. The specimens are more harder and could not be damaged easily. They can also used for longer period of time.