The Plastination process
In the university training of doctors and medical professions, the preparation of corpses and the associated production of anatomical teaching specimens is an essential process. Various preservatives and manufacturing processes have been developed over the last few centuries.
The technique of plastination is a recognized preparation process in which tissue water is replaced by a plastic (silicone, polyester, epoxy resin). Plastination was introduced at the University of Heidelberg in the late 1970s by Dr. Gunther von Hagens.
To date, there are numerous institutes and companies worldwide that use the technique of plastination to preserve organic tissue.
Application of plastination
Wherever organic tissue not only needs to be protected from decay, but is also subject to certain practical applications, the technique of plastination is used.
Anatomical teaching specimens that are no longer subject to constant humidification, that are exposed to mechanical stress and that should be odorless must ideally be plastinates. Various techniques within the plastination process allow detailed preparations that meet the respective presentation requirements and are important even in clinical research.
Plastination
Plastination is a “replacement” drying process. Water is not just removed. It is replaced by a substance that takes the place of the tissue water and hardens there. During replacement drying, the object to be dried must never actually dry. One could figuratively say that the places on which the water sits must never be unoccupied, otherwise they will close and cannot be used again. In order to keep these seats free, you place a "paid" sub-tenant in every free seat and wait until the final seater takes his place.
More precisely: Drying is done by dewatering with a water-soluble, organic solvent, for example acetone or ethanol or similar variants. In order to avoid shrinkage caused by too rapid dewatering, the preparations are frozen at sub-zero temperatures (-25°C). At these temperatures, the frozen water (ice) is only slowly released from the solvent. Daily circulation of the acetone prevents the released tissue water from forming its own layer in the solvent bath and thus reduces the efficiency of the solvent during freeze exchange.
Daily monitoring of the water content in the solvent bath ensures that a water content of 10% is not exceeded. The dewatering times are between 2 - 4 weeks, depending on the mass of the fabric and the ratio to the solvent (optimally 1:10).
If the solvent is passively warmed to room temperature after the dewatering has been completed by switching off the freezers, the degreasing phase begins. The function of the solvent is not limited to frozen tissue water, but also includes the lipids (fats) in organic tissues. Although degreasing also occurs during dewatering in freeze exchange, the solvent achieves its highest degreasing efficiency at positive temperatures. Due to the risk of shrinkage if dewatering occurs too quickly, dewatering must first be completed at low temperatures before degreasing begins. Degreasing is complete when the warm solvent no longer turns yellow. Tissues and organs with a high fat content (liver, brain) must quickly leave the degreasing phases at high temperatures as they usually shrink significantly. Incomplete degreasing or a long solvent phase at low temperatures is recommended here.
The plastic imersion that follows the solvent phases is comparable to the paraffinization of histological sections, which are dehydrated through an ascending series of ethanol at room temperature and cast into a paraffin block. In order to avoid shrinkage, dewatering is not carried out through complex freeze exchange, but rather through ethanol-water mixtures at room temperature. Paraffin is not suitable for the production of permanent microscopic preparations, which is why Dr. Gunther von Hagens focused on the use of silicone (whole body plastination), epoxy resins (disc plastination) and polyester resins (disc plastination). The dewatered and defatted preparations are brought back to sub-zero temperatures or pre-cooled and transferred (imerized) into -25 °C plastic (deviations in detail are possible, depending on the preparation and the plastination technique).
The next most important step in the overall process is forced impregnation. While the immersion of the preparation in the respective plastic is referred to as passive, forced impregnation enables complete plasticization of the tissue. A vacuum is applied to the already iterated preparations and all solvent components are removed from the preparation under constant observation. At the same time, plastic is sucked into the vacant spaces. The “paid sub-tenant” Acetone is relieved of his sitting duties and the permanent guest silicone, epoxy resin or polyester resin is allowed to take a seat. The constant danger of tissue shrinkage during plastination takes on particular importance here. Vacuuming too quickly is a common source of errors. Solvent bubbles visibly rise from the preparations lying in liquid plastics. Only experience can generate the right method and provide guidance. The general rule is: too fast and the preparation will be destroyed.
The subsequent steps depend on the process, but are of less importance in the structure of the plastination steps. Positioning, hardening and post-processing of the finished plastinates depend on the purpose of the desired preparation. Anatomical peculiarities must be taken into account as well as stability and color.