Tuesday, 18 July 2017

THE HUMAN PLASTINATION PROCESS


The 


Plastination 


Process




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. We will first present the process in a general, comprehensible manner; for those with an interest, we will then go into more detail regarding the chemicals and chemical processes used.


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. Gunther von Hagens found a way around this problem: In the initial fluidexchange 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. 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.

                      The Method of Plastination


Plastination is a relatively simple process designed to preserve the body for educational and instructional purposes.

Plastination, like many revolutionary inventions, is simple in concept:

1. Embalming and Anatomical Dissection
The first step of the process involves halting decay by pumping formalin into the body through the arteries.

Formalin kills all bacteria and chemically stops the decay of tissue.


Using dissection tools, the skin, fatty and connective tissues are removed in order to prepare the individual anatomical structures.



2.           Removal of Body Fat and Water
In the first step, the body water and soluble fats are dissolved from the body by placing it into a solvent bath (e.g., an acetone bath).




3. Forced Impregnation
This second exchange process is the central step in Plastination. During forced impregnation a reactive polymer, e.g., silicone rubber, replaces the acetone. To achieve this, the specimen is immersed in a polymer solution and placed in vacuum chamber.

 The vacuum removes the acetone from the specimen and helps the polymer to penetrate every last cell.



4. Positioning
After vacuum impregnation, the body is positioned as desired. Every single anatomical structure is properly aligned and fixed with the help of wires, needles, clamps, and foam blocks.


5. Curing (Hardening)
In the final step, the specimen is hardened. Depending on the polymer used, this is done with gas, light, or heat. Dissection and Plastination of an entire body requires about 1,500 working hours and normally takes about one year to complete.


    

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Preservation by Plastination
                       The study of biological specimens is significantly impeded by processes of decay. Thus, for centuries, people have been looking for appropriate methods of preservation. Thanks to the method of plastination, biological specimens can be prepared for research, teaching, and demonstration purposes in a lifelike and durable manner. To this end, in a vacuum process, specimens are impregnated with special reactive polymers. The mechanical (flexible or rigid) and optical (translucent or opaque) properties of the polymers used determine the characteristics of the preserved objects. Plastinated specimens are dry and odorless; they maintain their original surface relief and are identical to their state prior to preservation, down to the cellular level. Even histological studies can be performed on them.The method of plastination is based on replacing the water and fat contained in tissues with a reactive polymer such as silicone rubber, epoxy, or polyester resins: In a solvent bath, initially the tissue water is replaced by freeze substitution, and later, at room temperature, the tissue fats are gradually replaced by acetone. The dehydrated and degreased specimen subsequently is placed into the polymer solution. Under vacuum conditions, the solvent, in its gaseous state, is then continuously extracted from the specimen, creating a negative pressure that causes the polymer to gradually enter into the tissue. Following this process of “forced impregnation,“ the specimen is cured with gas, light, or heat, depending on the polymer used.
A special variation of plastination is “sheet plastination.“ With this method, specimens such as individual organs or entire bodies, mostly in a deep frozen state, first are cut or sawed into slices of 2 mm to 8 mm (about 1/12 inch to 1/3 inch) thickness. These slices, placed between polymer nettings, are then dehydrated, degreased, and eventually impregnated with polymer under vacuum conditions. In order to give the specimens a smooth surface, the impregnated slices are either cured between foil or in a flat chamber are casted with additional resin. The refractive index of the resin used determines the optical properties of the plastinated body slices: Epoxy resin yields translucency and good coloration of the various tissues; polyester resin, which is used for plastinating brain slices, allows for particularly good discrimination between white and gray brain matter.
Plastinated slices of organs and bodies constitute excellent teaching materials in cross-sectional anatomy, a field of ever increasing importance, and they correlate well with radiographic images. Serial sections of translucent body slices are useful in various scientific research approaches. In addition, they are a suitable diagnostic aid in pathology because they allow for quick macroscopic-diagnostic screening of entire organs and organ specimens. Pathologically modified tissue areas can then be selectively analyzed with conventional histological methods. Plastination was invented at the Anatomical Institute of Heidelberg University by Gunther von Hagens in 1977 and has been further refined since. By now, it has been generally recognized as a valid method of preservation and is practiced at more than 400 institutions in 40 countries. The main reasons for this wide-spread popularity of the method are the toughness, the durability, and the lifelikeness of the plastinates and the associated high teaching value.                 
   
   

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