1 Anatomy Division, Plastination Lab, University of Michigan Medical School, Ann Arbor, MI, USA.
2 Department of Comparative Medicine, College of Veterinary Medicine, University of Tennessee, Knoxville, TN, USA.
With the development of the superior Biodur® S10/low-temperature plastination process nearly thirty years ago, it would not be unusual for similar silicone products to be developed as well as alternate techniques. VisDocta, Hoffen, Preservation Specialities and North Carolina low temperature products use similar methods and chemicals as the Biodur® S10 process. Most silicone products on the market could be used in either methodology , therefore nothing being truly unique. However, there is uniqueness with the Dow™/Corcoran/Room-temperature methodology. Dow changes the sequence in which basic plastination chemicals are added such that the impregnation mixture (polymer plus cross-linker) is stable at room temperature . Recently , the North Carolina and Biodur® chemicals have also been used successfully in this room-temperature format.
plastination; silicone; PR10; PR14; Ct30; Ct32; Cr20; Cr22
A. Raoof: Anatomy Division, Plastination Lab, University of Michigan Medical School, Ann Arbor, MI, USA. Telephone: (734) 615 2597 ; Fax: (734) 615 8191; E-mail: email@example.com
A curable polymer replaces tissue fluid in silicone plastination . Silicone polymers and chemicals, other than the Biodur™ products , have been developed to carry out the silicone plastination process (Henry et al., 2001; Smodlaka et al., 2005a). The basic components are common products of the silicone industry and may be used to some degree interchangeably with caution (Henry et al., 2002). Principally, methods of placing the silicone into the biological specimen are the same: an intermediary solvent (acetone/methylene chloride) is removed by a decrease in pressure to extract the solvent (von Hagens, 1979a; 1979b; 1986; von Hagens et al., 1987; Henry and Nel, 1993). Hence a tissue void is produced and the polymer-mix is drawn into the cells. Each variant produces high quality durable plastinates.
The basic difference in methodology, excluding the polymers , is the sequence in which polymer, catalyst chain extender and cross-linker are combined. The basic cold S10 process combines the silicone polymer with the catalyst and chain extender to serve as the impregnation-mixture (von Hagens, 1986). This yields an unstable impregnation-mixture which commences to thicken upon mixing. Therefore, it is prudent to keep the mix in the cold to prevent premature thickening (increased viscosity) . As noted in the earlier manuscript on S10, impregnation with this mix may be done also at ambient-temperature . However, the pot-life of the mix is greatly reduced. Uniquely , the Dow™/Corcoran/ Room-temperature method combines the silicone polymer with the cross-linker (Glover et al., 1998). This mix yields a stable impregnation-mix even when kept at room temperature. Therefore, there is no need to keep the impregnation-mix in the freezer for storage or for impregnation . Recent experience has demonstrated that both the Biodur™ and the North Carolina products may also be used with this methodology.
Chemicals used in these "generic" silicone plastination techniques are the same or at least similar to those used in the classic Biodur™ S 10 Cold temperature plastination process:
The sequence of combination of these products is the difference in these two methodologies. The general steps of silicone plastination are described earlier in this volume. This manuscript will highlight the differences with respect to this variant process which occur during impregnation and curing of the plastinated specimens.
The basic steps of plastination are used for each plastination technique:
Steps I and 2 (Specimen preparation and Dehydration) are the same for all plastination methods, even with the Dow methodology. Please refer to: "The Sl0/ 15 Plastination Cold-temperature Technique" for this information . Adequate specimen preparation and thorough cold dehydration are essentials for producing good plastinates.
The more common Dow™ products for silicone plastination are:
PR10 and PR14 (lower viscosity): Silicone polymer Ct30 and Ct32 : Catalyst and chain extender, premix Cr20 and Cr22: Cross-linker
Step 3. Forced Impregnation:
Replacing the volatile solvent (acetone) in a biological specimen with a curable polymer. For this to occur, the same criteria as for the classic Biodur™ S10 plastination process must be met, including thorough cold dehydration.
Impregnation equipment: Similar to the Biodur™ S10 requirements - Vacuum chamber and pump (oil or dry); Specimen basket; Vacuum gauge; Bennert manometer; Needle valves. One exception: no deep freezer is needed for impregnation or storage of impregnation mixture. However for dehydration , freezers are highly recommended.
Preparing reaction-mixture: Dow™ PR 10 or PR14 polymer is mixed with Cr20 or Cr22 (Cross-linker and Chain extender) at 100:10 to prepare the reaction- mixture. Thorough stirring is recommended. One of the two main differences is how the reaction-mixture is to be handled. The reaction-mixture is stored and used at room temperature (Glover et al., 1998; Glover, 2004; Raoof, 2004). It is stable (does not become viscous) for at least ten years at room temperature .
|Day 1||Load specimens and allow equilibration over night.|
|Day 2||Start pump, Decrease pressure until rapid boil IS produced (around 28crn/13in Hg). Maintain rapid boil - by decreasing pressure (close needle valves incrementally).|
|Day 3||Maintain rapid boil by decreasing
pressure (close needle valve incrementally).
|Day 4a||Small specimens: Maintain rapid boil until boiling ceases. When boiling ceases, turn off pump, return to atmosphere and proceed to Step 4 - "Curing".|
|Day 4b||Large specimens: Maintain rapid boil - Decrease pressure incrementally as necessary .|
|Day5 +X||Maintain rapid boil until boiling ceases. When boiling ceases, turn off pump, return to atmosphere and proceed to Step 4 - Curing.|
Adjusting vacuum: The speed for lowering of pressure in the vacuum chamber is very fast when compared to the Biodur™ S10 Cold-temperature Technique. The viscosity of the PR10 polymer is 20% less than the viscosity of S10 polymer. The impregnation-mixture is not reactive, as long as it is not exposed to catalyst. Therefore, the polymer-mix remains fluid. As well, it is used at room temperature so there is no increase of viscosity from placing the mixture in a cold environment. When monitoring bubble formation, a rapid boil is the standard. If in doubt, go slower, to prevent incomplete impregnation with resulting shrinkage. Pressure is decreased by closing the air intake valves.
Day 1: The dehydrated and degreased specimens are removed from the solvent (acetone), excess solvent is drained and the dehydrated, solvent-filled specimens are placed m the room-temperature polymer impregnation-mixture. Submerge the specimens immediately to prevent solvent evaporation from their surface and hence, surface drying. Close the port of the vacuum chamber with the glass and let the specimens accommodate/equilibrate over night.
Day 2: Warm the vacuum pump a few minutes. Seal the vacuum chamber and lower pressure (around Yi atmosphere) until bubble formation becomes rapid. Stabilize pressure at the level which maintains a rapid boil. Monitor pressure and decrease the pressure as needed to maintain a rapid boil.
Day 3: Continue to monitor bubble formation (solvent extraction) maintaining a rapid boil by decreasing pressure (incrementally close needle valves) as needed.
Day 4a: Small specimens will likely finish impreg nation as noted by cessation of bubble formation. Tum off pump and bring specimens to atmospheric pressure. Proceed to Step 4 - "Curing/hardening".
Day 4b: Large specimens or a large quantity of specimens. Continue to monitor solvent extraction (watch bubble formation) and maintain a rapid boil by incrementally closing the needle valves.
Day 5 or plus X: Continue to monitor solvent extraction (watch bubble formation) and maintain a rapid boil. When impregnation is completed, as noted by cessation of bubble formation, tum off pump and bring specimens to atmospheric pressure.
Rule: If bubbles are actively rising to the top of the polymer and bursting, impregnation is not finished! Impregnation will be complete when needle valves are closed and no more rapid bubbling is noted and when pressure reaches <5mmHg. Nearly complete evacuation of acetone/solvent is necessary to avoid incomplete impregnation of the specimen with the polymer-mix which may lead to shrinkage.
|Day 1||Bring specimens to atmospheric pressure and allow to drain into the plastination chamber.|
|Day 2||Place specimens on absorbent toweling. Allow excess polymer-mix to drain. Wipe excess polymer from the surface. Blow polvmer-mix from hollow organs.|
|Day 3||Wipe excess polymer-mix from surface of specimen. Apply Ct30 or Ct32 to specimens and wrap in plastic wrap.|
|Day 4||Unwrap specimen and examine curing rate. If specimen is wet, apply more Ct30 or Ct32 and rewrap with foil. If curing is complete, specimen is ready to use.|
|Day 5||Unwrap specimen and examine curing rate. If necessary apply more Ct30 or Ct32, etc. If curing IS complete, specimen is ready to use.|
|Day 6||Use specimen as desired.|
Specimen removal and drainage of polymer-mix : Follow SIO protocol. Since keeping the reaction-mix cold is not necessary , specimens are drained for an extended period directly into the room-temperature plastination chamber.
Step 4. Curing (Hardening or Cross-linking) of the impregnation-mix within the specimen to make it dry: Equipment for curing:
Curing/Cross-linking is a two-step process:
a. Drainage of the excess silicone-mix. Drain excess polymer-mix from the specimens into the plastination chamber.
b. Catalyzing, cross-linking of the silicone polymer molecules . This reaction occurs because as the catalyst (Ct30 or Ct32) is applied to the impregnated specimen, it prepares the PR10 or PR14 silicone molecules in the impregnation-mix to react with the cross-linker (Cr20 or Cr22) in the impregnated specimen. Catalyst is applied to the specimen surface via a mist bottle or brush. Then the catalyst covered specimen is wrapped in The next day foil is removed and the specimen checked to see if cured (dry). If not completely cured, the specimen surface is wiped and catalyst is applied to the specimen . The specimen is rewrapped with foil. The following day the specimen is checked for complete curing. If curing is complete, the specimen is ready for use. If curing is not complete, more catalyst is applied and the specimen is wrapped again in foil, etc.
The PR10/PR14 specimens are durable and some flexibility is exhibited by thinner specimens (Glover et al., 1998; Glover, 2004). The specimens are dry and odorless. They are not models but the actual specimens. Numerous specimens and whole cadavers have been successfully plastinated using the room-temperature technique
Plastinated specimens are the real specimen and not a model (Figs. 1-6). All specimens are free of offensive odor and dry (Latorre et al., 2001). One feature of the finished product is a less than transparent surface which conceals intricate surface cellular detail (Henry et al., 2004; Smodlaka et al., 2005a; 2005b). Room temperature specimens may be used as teaching aids both in the class room and the clinical setting (Latorre et al., 2001; Raoof et al., 2006). They may be compiled and used as a library of specimens for normal , exotic and pathological anatomy (Henry, 2005) and in research (Raoof, 2001).
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Henry RW, Nel PPC. 1993: Forced impregnation for the standard S10 method. J Int Soc Plastination 7(1):27-31.
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Latorre R, Vaquez JM, Gil F, Ramirez G, L6pez-Albors 0, Orenes M, Martinez-Gomariz F, Arencibia A. 2001: Teaching anatomy of the distal equine thoracic
limb with plastinated slices. J Int Soc Plastination 16:23-30.
Raoof A. 2001 : Using a room-temperature plastination technique in assessing prenatal changes in the human spinal cord. J Int Soc Plastination 16:5-8.
Raoof A, Liu L, Zhao H, Falk K, Bodnar T, Dueke E. 2006: Plastinated specimens as an adjunct to dissection: Are they really helpful? J Int Soc Plastination 21:35.
Smodlaka H, Latorre R, Reed RB, Gil F, Ramirez G, Vaquez-Auton JM, L6pez-Albors 0, Ayala MD, Orenes M, Cuellar, Henry RW. 2005a: Surface detail comparison of specimens impregnated using six current plastination regimes. J Int Soc Plastination 20:20-30.
Smodlaka H, Reed RB, Latorre R, L6pez-Albors 0, Hervas JM, Cuellar R, Henry RW. 2005b: Comparison of plastinated specimens prepared using six regimens. J Int soc Plastination 21:22-23.
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von Hagens G, Tiedemann K, Kriz W. 1987: The current potential of plastination. Anat Embryol 175(4):411-421.
Corcoran Laboratories , Inc., Daniel Corcoran, Corcoran Laboratories, Inc. P. 0. Box 3251, Traverse City, MI 49685-3251, Tel. (231) 922-8044.
Silicones Inc., High Point, NC, USA. Distributed by: RW Henry, 1455 A. R. Davis Road, Seymour, TN, 37865, USA. firstname.lastname@example.org , Ph: (865) 982 - 4354 .