Department of Comparative Medicine, College of Veterinary Medicine, University of Tennessee, Knoxville, TN, USA.
The development of the Biodur™ S10 low-temperature plastination process thirty years ago has sparked development of similar methodologies and products. The Dow/Room temperature process used silicone chemicals similar to the Biodur™ products . However, Dow changed the order in which the basic Biodur™ S10 plastination chemicals were combined. This combination renders the impregnation-mix non-reactive and hence deep freezers are not needed or used for impregnation. Recently, both the North Carolina and Biodur™ chemicals both have been shown to be compatible for use as a room-temperature format. The North Carolina Room-temperature technique combines the cross-linker and polymer for impregnation , but uses chain extender prior to using the catalyst after impregnation .
plastination; silicone; polymer; NCSX; NCSXI; NCSIII; NCSV; NCSVI
R.W. HENRY - Department of Comparative Medicine, College of Veterinary Medicine, University of Tennessee, Knoxville, TN, USA. Telephone: (865) 974 5822; Fax: (865) 974 5822; E-mail : email@example.com
Silicone plastination replaces tissue fluid with a curable polymer. Besides the Biodur™ products, other silicone polymers and chemicals, all well-known in the silicone industry (Henry et al., 2002a), have been developed for use in the plastination process (Henry et al., 2002b). Forced impregnation of silicone polymer into biological specimens is the common thread for all of the generic plastination products . Impregnation uses the same intermediary solvent (acetone) along with a decrease in pressure to extract the acetone (von Hagens, 1979a; 1979b; 1986; von Hagens et al., 1987; Henry, 2004). This resultant tissue void allows the impregnation-mix to be drawn into the specimen. Each generic product produces a durable, high quality plastinated specimen.
Chemicals used in the various "alternate" silicone plastination processes need to be similar to the Biodur™ SlO plastination technique :
The general steps of silicone plastination are described earlier in this volume. This manuscript will highlight the differences with respect to this alternate process which occurs with room-temperature impregnation and curing of the plastinated specimens.
The basic steps of plastination are utilized for each plastination process:
Specimen preparation dehydration and defatting
Specimen preparation, dehydration and defatting are the same for all plastination methods . Please refer to: "The S10/15 cold-temperature plastination technique" for that information . As well, refer to the "Dow room temperature technique" for additional information.
North Carolina products for silicone plastination : NCSX (lowest viscosity): silicone polymer NCSXI (low viscosity): silicone polymer NCSIII: catalyst
NCSV: chain extender NCSVI: cross-linker
Replacing the volatile solvent (acetone or methylene chloride) in a specimen with a curable polymer. For this to happen, the products must meet the same conditions as for the Biodur™ S10 plastination process .
Impregnation equipment: Similar to Biodur™ S10 requirements [vacuum pump (oil preferred) and chamber with see through port and specimen basket, vacuum gauge, manometer , needle valves]. However, no deep freezer is required or used for impregnation. Deep freezers are necessary and strongly recommended for dehydration.
Preparing the impregnation-mixture: NCSX or NCSXI polymer is mixed with NCSVI (Cross-linker) at 100:8 to prepare the impregnation-mixture and stirred thoroughly. The main difference in this room temperature methodology is handling of the resultant reaction-mixture. This mixture is stable (does not become viscous) when stored and/or used at room temperature for an indefinite period of time as is the case with other generic room-temperature polymers.
Adjusting the vacuum: Speed of lowering the pressure in the vacuum chamber is fast when compared to the Biodur™ S10 Cold-temperature Technique. The NCSX and NCSXI polymers have a much lower viscosity than Biodur™ S10 or DowTM PR 10. The impregnation mixture is not reactive, provided it is not exposed to catalyst. There-fore the polymer-mix remains fluid at impregnation (room) temperatures As well, since there is no increase of viscosity which results from placement in a cold environment. When monitoring bubble formation, a rapid boil is recommended. Remember the plastination principal , if in doubt, decrease pressure slower, to prevent incomplete impregnation which can result in shrinkage.
|Day 1||Load specimens and allow to equilibrate over night.|
|Day 2||Start pump: Decrease pressure until rapid boil is produced (around 30 to 25cm/13.5 to 13in Hg pressure). Maintain rapid boil - Decrease pressure (incrementally, close needle valves) as needed.|
|Day 3||Maintain rapid boil - Decrease pressure (close needle valve incrementally).|
|Day 4a||Small specimens: Maintain rapid boil until boiling ceases (4-5mm Hg) or when l -2cm bubbles cease to form, tum off pump, return to atmosphere, allow specimens to equilibrate overnight and proceed to Step 4: Curing, the next day.|
|Day 4b||Large specimens: Maintain rapid boil - Decrease pressure as necessary.|
|Day 5+X||Maintain rapid boil until l-2cm bubbles cease and/or 5mm Hg pressure is reached. Tum off pump, return to atmosphere and proceed to Step 4 - Curing.|
Day 1: The dehydrated and degreased specimens are removed from the solvent (acetone or methylene chloride). Excess solvent is drained and the dehydrated, solvent-filled specimens are placed in the room-temperature polymer impregnation-mixture. Submerge the specimens immediately to prevent solvent evaporation from their surface and hence, drying. The port (glass) on ·the vacuum chamber is closed and the specimens allowed to accommodate/ equilibrate in the polymer-mix overnight.
Day 2: The vacuum pump is warmed briefly. Close the needle valves and lower pressure (apply vacuum) to seal the chamber. Lower the pressure until bubble formation becomes rapid (decrease to around 30- 25cm/13 .5-13in Hg pressure) . When a rapid boil is achieved, maintain this pressure by opening the vacuum adjustment valves slowly until pressure is stabilized. The vapor pressure of acetone at room temperature (+25°C) is 22cm/10in Hg and MeCl is 43cm/17in Hg. Continue to monitor the pressure and decrease the pressure as needed to maintain a rapid boil by closing the needle valves incrementally . Likely adjustment will be every one half hour for the first three or four hours.
Day 3: Continue to monitor bubble production (solvent extraction) and keep a rapid boil by decreasing pressure (closing the valves) as needed.
Day 4a: Small specimens - Impregnation will be complete as noted by cessation or reduction in number of l-2cm size bubbles forming and/or reaching < lcm Hg of pressure. Note: When pressure goes below 4 or 5 mm Hg, larger bubbles will rise and burst if the chamber is tilted or shaken. These are not likely the solvent (acetone) but likely water vapor or the cross linker, NCSVI vaporizing . Vacuum should be turned off when this occurs. Tum off pump and bring specimens to atmospheric pressure . Allow the impregnated specimens to sit in the polymer-mix over night at atmospheric pressure.
Day 5: Proceed to Step 4 - "Curing".
Day 4b: Large specimens or a large quantity of specimens . Continue to monitor solvent extraction by watching bubble formation and by reading and adjusting pressure to maintain a rapid boil (extraction of the solvent).
Day 5 or plus X: Continue to monitor solvent extraction (watch bubble formation) and maintain a rapid boil. If impregnation is completed , as noted by cessation or reduction of 1-2 cm size bubble formation and/or reaching 5mm Hg of pressure, tum off pump and bring specimens to atmospheric pressure (see note in Day 4a). Proceed to Step 4 - "Curing".
Rule: If 1-2 cm bubbles are actively rising to the top of the polymer and bursting, impregnation is not finished! Impregnation will be complete when both needle valves are closed, pressure has reached <5mm Hg and/or l- 2cm diameter bubble production is greatly diminished. Note, once the 1-2cm bubbles have subsided, larger 4-5 cm bubbles will explode to the top if you shake the vacuum chamber. These are likely not acetone bubbles but either water vapor or cross-linker (NCSVI) vaponzing. 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 chamber|
|Day 2||Empty polymer-mix from hollow organs. Place specimens on absorbent toweling to drain polymer-mix. Wipe excess polymer from the surface.|
|Day 3 and 4||Manicure specimen surface, dilate and/or position anatomically. Chain extend: Vaporize the NCSV m an enclosed environment.|
|Day 5||Wipe excess polymer-mix from surface of specimens. Apply NCSIII to specimen surface and wrap in foil/plastic wrap.|
|Day 6||Unwrap specimen and examine curing rate. If necessary, apply more NCSIII and rewrap with foil. If the curing is complete, specimen is ready to use.|
|Day 7||Unwrap specimen and examine curing rate. If necessary , apply more NCSIII. If curing is complete, specimen is ready to use.|
|Day 8||Use specimen as desired.|
Specimen removal and drainage of surface polymer impregnation-mix: Follow the S10 protocol. Since the impregnation-mixture is stable, drain specimens into the room-temperature plastination chamber.
Curing (hardening or cross-linking)
Equipment for curing:
Curing of the impregnation-mixture within the specimen is a three-step process:
Drain: Drain the excess impregnation polymer-mix from the specimens.
Chain elongation: Chain elongation of the siliconepolymer molecules by end to end alignment of the molecules. Chain elongation occurs as the NCSV vapor is applied to the surface of the specimen. NCSV is vaporized in an enclosed chamber by using an aquarium pump or ventilator for a few minutes once a day for one to three days. This process is similar to the cross-linking application in the Biodur™ S10 Cold- or Ambient temperature technique.
Catalyzing and cross-linking: Catalyzing and cross linking of the silicone polymer molecules. This reaction occurs when the catalyst (NCSIII) is applied to the surface of the impregnated specimen. It enables the NCSX or XI molecules in the impregnation-mix to react with the NCSVI which is in the impregnated specimen. Cross-linkage changes the polymer from a liquid to a solid. Mist or wipe NCSIII onto the surface of the specimen, wrap specimen with foil and leave over night. Wrapping in foil (plastic wrap) is necessary to facilitate cross-linking.
The NCSX or XI impregnated and cured specimens are dry and durable. Thin specimens exhibit some flexibility. The room-temperature plastinates are not models but real specimens (Figs. 1, 2, 3, 4). They make excellent teaching and public relation aids.
As with all plastination processes, the room temperature plastination produces real specimens and not models. The specimens are dry and odorless. Only time will reveal if the NCSX develops a less than transparent surface which conceals intricate surface cellular detail as seen with the Dow™/Corcoran chemicals (Henry et al., 2004; Smodlaka et al., 2005a; 2005b). Room-temperature technique specimens are used as teaching aids (Latorre et al., 2001). They have been used to compile a library of specimens for normal, exotic (Fig. 2) and pathological anatomy (Henry, 2005) and is useful in research (Raoof, 2001).
Henry RW. 2004: Principles of plastination. J Int Soc Plastination 19:5-6.
Henry RW. 2005: Teaching with plastinated specimens in veterinary medicine. J Int Soc Plastination 20:38- 39.
Henry RW, Reed RB, Henry CL. 2001: "Classic" silicone processed specimens vs "New formula" silicone plastinated specimens: A two year study. J Int Soc Plastination 16:33.
Henry RW, Seamans G, Ashburn RJ. 2002a: Polymer chemistry in silicone plastination. J Int Soc Plastination 17:5-6.
Henry RW, Reed RB, Henry CL. 2002b: Naked silicone impregnation. J Int Soc Plastination 17:5.
Henry R W, Reed R B, Latorre R, Smodlaka H. 2004: Continued studies on impregnation with silicone polymer and no additives. J Int Soc Plastination 19:47.
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 room-temperature plastination technique in assessing prenatal changes in the human spinal cord. J Int Soc Plastination 16:5-8.
Smodlaka H, Latorre R, Reed RB, Gil F. Ramirez G, Vaquez-Auton JM, L6pez-Albors 0, Ayala MaD, Orenes M, Cuellar R, Henry RW. 2005a: surface detail comparison of specimens ipregnated using six plastination regimens. J Int soc Plastination 20:20-30.
Smodlaka H, Reed RB, Latorre R, Hervas JM, Cuellar R, Henry RW. 2005b: Comparison of plastinated specimens prepared using six regimens. J Int soc Plastination 21:22-23.
von Hagens G. 1979a: Impregnation of soft biological specimens with thermosetting resins and elastomers. Anat Rec 194(2):247-255.
von Hagens G. 1979b: Emulsifying resins for plastination. Der Praparator 25(2):43-50.
von Hagens G. 1986: Heidelberg Plastination Folder: Collection of technical leaflets for plastination. Biodur Products, Rathausstrasse 18, Heidelberg, 69126. pp 2:1-6, 3:1-13, 4:1-20, 5:1-17.
von Hagens G, Tiedemann K, Kriz W. 1987: The current potential of plastination. Anat Embryol 175(4):411-421.
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.