Dissection Manual
Numerous trials were conducted to develop the procedure for the rat dissection and lung casting. Under the guidance of Dr. Frederick, Interim Head and Professor in the RIT Biological Sciences Department, the team devised a casting process that resulted in detailed and accurate solid models of rat lung geometry.
The main steps in the final casting procedure are as follows:
• I. Obtain rat specimen and determine weight using triple-beam balance.
• II. Restrain rat with tail exposed and place under heat lamp to increase circulation.
• III. Inject anesthetizing dose of Sodium Pentobarbital in main tail vein; verify loss of reflexes.
• IV. Place rat in dissection tray, pinning feet if necessary.
• V. Expose trachea by cutting down through ribcage, carefully avoiding lungs and arteries.
• VI. Make small incision in 3rd-5th tracheal ring, and insert tubing.
• VII. Inflate lungs several times with CO2.
• VIII. Inject 0.35% body mass of degassed saline into lungs using syringe pump at predetermined flow rate.
• IX. Prepare 0.35% body mass of Silastic E casting agent; inject into lungs with syringe pump at predetermined flow rate.
• X. Cover rat and allow casting agent to cure overnight.
• XI. Excise lungs and digest tissue by placing in 4M NaOH solution.
• XII. After 24 hours, neutralize solution with 4M HCl; clean lungs with mild detergent.
Once the casting procedure was finalized, a lab manual was created that utilized the procedure. The manual was developed to be a user friendly guide for engineering students with little biology background. Color photos from actual dissections and detailed diagrams were used to help guide the students through the procedure. An accompanying video using footage from actual dissections was also produced to help introduce students to the procedure.
An instructor's supplemental guide was also developed to aid the laboratory setup. The intention of this manual was not to reiterate the procedure, but provide future instructors with the resources needed to run the lab. A list of materials required for the lab, key personnel, and safety precautions were all detailed in the instructor manual.
Solid Model
From 3-D CAD drawing the team produced a human lung replica solid model using stereolithography. This process allowed to increase the scale of the solid model to more accurately represent the human lung.
Molding Material
Polyester resin was ultimately chosen for the hollow models, because it was relatively inexpensive, locally available and easy to work with. This material is a two part liquid that is commonly used to make fiberglass. Its refractive index is dependent on the amount of hardener used, but the optimal mix resulted in a value of 1.334. Luminous transmittance is approximately 80%.
Hollow Model Fabrication
- Pour liquid resin into mold
- Coat solid model with polyvinyl alcohol (PVA)
- Half submerge solid model in liquid resin
- Allow to cure, remove and coat with PVA
- Pour another mix of resin into mold
- Place 1st half on top of liquid resin
- Remove after curing
- Extract solid model
- Rejoin halves
PIV Validation
The hollow model was connected to PIV system. Immersion liquid mixed with red fluorescent microspheres was pumped through the model. Oxford laser illuminated fluorescent particles seeded in the flow and a high speed digital camera captured images at 500 frames per second and shutter speed of 1/5000 of a second.
