About Plastination

In the traditional curriculum anatomy is thought and learned in the preclinical years. According to local circumstances more or less work is devoted to dissection or prosected specimen. Whereas this may be a method to acquire knowledge in systematic anatomy and topography it does not help very much in understanding applied aspects, f.i. x-ray anatomy.

With the rise of modem imaging methods the demand for correlated sections increased. Such specimen should be available in later phases of the curriculum when students deal with patient -oriented material. Plastination is a technique to preserve such specimen without any preserving fluids.
Specimen can easily be stored and handled by students according to their needs. Currently a set of plastinated sections is collected at our learning resource center for correlation with x-ray anatomy.

Plastination has been developed for teaching as well as for research. It had been invented about 20 years ago at Heidelberg by Dr. von Hagens and proved to be the superior method for preservation of gross specimen. Vienna was the first place to introduce this new method in the late 70ies. Nowadays the method is applied in more than 200 institutes for Human Anatomy, Clinical Pathology, Biology and Zoology worldwide. The ,,International Society for Plastination" was founded in 1986, the first issue of Journal of the International Society of Plastination appeared in 1987.

Plastination allows for preservation of specimen with completely visible surface and high durability. Plastinated specimen are odorless, not toxic and mechanically resistant to a high degree. Plastination is a procedure, during which water and fat of gross specimen are replaced by a polymerisable resin. First, specimen are dehydrated in an intermedium (f.e. acetone) with a boiling point below that of the resin. Than the intermedium is continuously evaporated under vacuum conditions. In this phase the resin replaces the intermedium. Finally, the resin is polymerised. Optical properties - opaque or transparent - and mechanical properties - smooth and flexible or hard - can be chosen by appropriate composition of plastination resins.

The three most important resins and hence plastination techniques are Silicone (S-10), Epoxy (E-12) and Polyesther (P-40).

           Principle of the Plastination Procedure

 Fixation and dehydration 

 Most plastinated specimens start from fixed material and every established fixation method is applicable. We use formaIin in
 concentrations between 5 and 20%. To enhance color preservation, the Kaiserling solution is suitable. Perfusion-fixed animals and
 arterially injected human cadavers yield well fixed organs in their correct anatomical positions. Organs removed at autopsy are fixed by
 immersion and infiltration, taking care to restore their natural shape. Hollow organs have to be dilated during fixation, a step essential
 in heart plastination. All embalming fluids containing long chain alcohol (e.g., glycerol) have to be removed before dehydration, as they
 easily spoil the final specimens. Fixation can be omitted when epoxy resins are used (epoxy resins have fixing properties), resulting in
 better color preservation. However, care should be taken with respect to possible infections. 

 Dehydration and defatting are mandatory since water and lipids can not be exchanged directly against polymers. As known from
 histology, a proper dehydration procedure must avoid shrinkage. The degree of defatting is essential in plastination The two methods
 used are stepwise dehy-dration in graded ethanol and freeze substitution with acetone. 

 Ethanol dehydration is used when a histological exami-nation of the plastinated specimen is intended, The disadvantage of ethanol is
 its need for replacement by a low boiling intermediary solvent (acetone or methylene chloride). In addition, stepwise ethanol
 dehydration causes con-siderable shrinkage (roughly 50%) and is time consuming. Ethanol dehydration is advantageous for embalmed
 specimens, because it easily removes (especially after addition of H202) the long chain alcohol contained in the embalming fluid. 
 The standard dehydration procedure for plastination is freeze substitution in acetone at -25°C. This method saves time, requires less
 labor compared with ethanol dehydration, and causes only minor tissue shrinkage. It is the only way to dehydrate brain tissue with a
 tolerable (less than 10%) shrinkage. During freeze substitution, specimens (precooled to + 5°C) freeze immediately on immersion into
 the ice cold acetone (technical grade), thereby stabilizing the specimens shape instantly. Within the next 3-5 weeks (including 2-3
 changes of the acetone), the specimens become completely dehydrated. The only disadvantage of freeze substitution is theformation  of ice crystals in specimens which will also be used for histology. This can be overcome by processing specimens containing 20-100%
 formalin which acts as a freeze protecting agent. 

 In ethanol dehydration, the defatting is accomplished simultaneously with the dehydration procedure. In freeze substitution, defatting
 requires an additional acetone bath at room temperature. For lipid-rich specimens (containing bones, subcutaneous or subserous
 adipose tissue), defatting may be achieved in a final bath of methylene chloride. For plastination purposes, acetone is ideal because it
 acts as dehydration agent, defatting agent and intermediary solvent all at the same time and readily mixes with all the different resins
 used for plastination. 

 Forced impregnation 

 The central and most important step in plastination is re-placement of the intermediary solvent (which occupies the spaces originally
 filled with water and lipids) by curable polymers. This is achieved by means of a vacuum during forced impregnation. The specimen,
 soaked within a vola-tile intermediary solvent (acetone or methylene chloride), is placed into the polymer solution. The intermediary
 sol-vent has a high vapor pressure and a low boiling point (acetone: + 56°C, methylene chloride: + 40°C), while the polymer solution has
 a low vapor pressure and a high boiling point. Therefore, when a vacuum is applied, only the intermediary solvent is continuously
 extracted out of the specimen and through the surrounding polymer solution in the form of gaseous bubbles. The surrounding resin is
 also eventually cleared completely of the intermediary solvent, and therefore only one impregnation bath is needed. Thus, the quantity
 of polymer consumed is very small and approximates, for silicone, at most to the volume of the specimens. 

 The speed of impregnation depends both, on the specimen and on the class of polymer used. Generally, polymers with a higher viscosity
 require a longer impregnation time than polymers of lower viscosity. The larger and denser the specimen, the slower an impregnation
 should be  preferably with a low viscosity resin. To accomplish impregnation, any small oil driven vacuum vane pump is sufficient, speed
 must be adjusted by varying the vacuum by means of an air bypass valve. Gas bubble formation, easily observed through a window, is a
 useful indicator of the speed of impregnation. A too rapid extraction of the intermediary solvent causes a collapse of the structural
 framework of the specimens (i.e., shrinkage) and must be prevented. Very delicate specimens are preferably processed via methylene
 chloride. Its high specific gravity (1.3) ensures that the specimens will sink to the bottom of the impregnation bath (specific gravity
 about 1) and therefore they must not be weighted down. 

 Forced impregnation is carried out either at room tem-perature when using epoxy and polyester resin or at - 25°C in a deep freezer
 when working with silicone rubber. In the cold, the gas bubbles will rise slowly to the surface, without splashing. A final vacuum in the
 range between 2 and 15 mm Hg is necessary. At room temperature forced impregnation generally goes faster and with strong bubbling,
 since the polymers are less viscous and have a shorter processing time. 
 Curing (hardening) 

 The curing of the specimens is carried out after removal from the impregnation bath; the residual polymer of the bath should stay fluid
 for reuse. Three specific techniques are applied, which differ markedly from the usual curing of polymers cast in molds. 

 A gas curing procedure, specially developed for plastination is used for silicone specimens. In this technique, the decisive crosslinking
 curing agent is not a constituent of the impregnation bath, but is applied later to the specimens in a gaseous form. In a closed chamber, the impregnated specimens are exposed to an atmosphere which is continuously saturated with the gaseous hardener evaporating from a stock solution inside the chamber. Continuous evaporation and circulation of the gas is achieved by a small membrane pump speeding up the curing process. 

 The curing of specimens impregnated with epoxy resin (E 12) or polymerizing emulsion (PEM) takes advantage of the tissue amines
 contained within the specimens. Amines are effective accelerators. Together with anhydrides, used as hardeners for epoxy resins or
 PEM impregnation mixtures, they are sufficient to fully cure the specimens at+50°C. 

 Curing of polyester-copolymers can be initiated by UVA-light followed by a heat treatment (+50°C). The inherent advantages are a long
 manfacturing time in the dark, and a lower temperature peak during their markedly exothermic curing.