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Home / Exhibits
Plastination
Plastination is a process at the interface of the medical discipline of anatomy and modern polymer chemistry. Plastination makes it possible to preserve individual tissues and organs that have been removed from the body of the deceased as well as the entire body itself. Like most inventions, plastination is simple in theory: in order to make a specimen permanent, decomposition must be halted. Decomposition is a natural process triggered initially by cell enzymes released after death and later completed when the body is colonized by putrefaction bacteria and other microorganisms. By removing water and fats from the tissue and replacing these with polymers, the plastination process deprives bacteria of what they need to survive. Bodily fluids cannot, however, be replaced directly with polymers, because the two are chemically incompatible. Dr. Gunther von Hagens found a way around this problem: In the initial fluid-exchange step, water in the tissues (which comprises approximately 70% of the human body) and fatty tissues are replaced with acetone, a solvent that readily evaporates. In the second step, the acetone is replaced with a polymer solution.
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The trick that first proved to be critical for pulling the liquid polymer into each and every cell is what he calls “forced vacuum impregnation.” A specimen is placed in a vacuum chamber and the pressure is reduced to the point where the solvent boils. The acetone is suctioned out of the tissue at the moment it vaporizes, and the resulting vacuum in the specimen causes the polymer solution to permeate the tissue. This exchange process is allowed to continue until all of the tissue has been completely saturated—while a matter of only a few days for thin slices, this step can take weeks for whole bodies. | The second trick is selecting the right polymer. For this purpose, “reactive polymers” are used, i.e., polymers that cure (polymerize) under specific conditions, such as the presence of light, heat, or certain gases.
Their viscosity must be low, i.e., they have to be very thin liquids; they must be able to resist yellowing; and, of course, they must be compatible with human tissue. The polymer selected determines the look and feel of the finished specimen.
Special Technical Subtleties
What makes plastination complicated is the large number of variations that have become possible since the invention of this process and that are essential for obtaining the best results. Indeed, these variations represent the very strengths of the process. A large number of factors need to be taken into consideration: foremost among these is the degree of decomposition, but the list also includes the distribution of fatty tissue and the amount of blood in the veins. As a result, each individual specimen requires its own unique, carefully and precisely planned plastination program if it is to be preserved perfectly. Improvements and nuances in the process have understandably been linked to the development of suitable polymers. Today, the following four primary classes of polymer are used in a variety of formulations, each with its own distinctive properties and appropriate for specific types of specimens:
- Epoxide resins, which become transparent when heat-cured, have become the material of choice for preparing body slices.
- Light-cured polyester resin blends yield excellent results for slices of the brain.
- Polymer emulsions that turn white when cured are primarily suitable for thicker slices, as these emulsions make fatty tissue look more natural.
- Silicone rubber cures in gas and remains relatively soft and pliable, lending specimens an especially life-like appearance. Very low-viscosity silicone achieves the best results with complete organ systems. Silicone-based processes are now the most frequently used (in over 40 countries).
Through the use of silicone rubber, Dr. Gunther von Hagens was able to solve the greatest problem posed by plastination: the long periods of time required for complete preservation of large tissue specimens and whole bodies. In 1990 he completed his first whole-body plastination. Other milestones along the way have included, for instance, “perfusion plastination,” which makes it possible to purge organ systems of blood, fix them in place, and then permeate them first with acetone and then with silicone. The vascular system is then evacuated before curing the specimen via gas perfusion. These plastinates are pliable and lightweight because their vascular systems are empty—only their cells are saturated with plastic. A number of key experiences have been integrated into what has become a 25-year-long process of development and optimization of the preservation and dissection methods used.
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