Quantification of mechanical behavior of rat tail under compression

Specimen preparation

• Eighteen male Sprague-Dawley cadaver rat tails with an average tail length of 172 mm were used for this study.
• The tails were obtained from control groups that were a part of several inhalation studies and all procedures performed on the animals were approved by the NIOSH Morgantown Animal Care and Use Committee in those studies.
• The tails were collected after the rats were euthanized, put in aluminum foil to limit air/water exposure, then put on ice, and immediately after were delivered to our mechanical testing lab for experimentation.
• The tails were kept at 5° C to avoid the onset of rigor mortis and freezing, and were removed an hour prior to testing to adjust to room temperature which was checked using a thermometer.
• All testing took place on a 7.5-mm-diameter section for each tail, which was measured and marked prior to testing to ensure the tail diameter was consistent for all tests.

Experimental set up and testing

• All compression testing was completed using the Mach1Motion micromechanical system equipped with a displacement sensor with a resolution of 0.5 µm and a 98 N (10 kg) load cell with a resolution of 4.90 mN (500 mg). Max sampling rate of machine was 50 Hz.
• During testing each tail was only used once and the tails were placed in a rigid plastic base platen that was 2-3 times that of the tail to ensure it did not touch the sides during compression (unconfined).
• A platen (57 mm in length and 25 mm in width) was attached to the indenter, which was used to compress the tail.
• For all compression tests the deformation magnitude and deformation velocity were specified using the machine, and the time histories of force and deformation were measured.

Design of compression tests

• The indenter platen was centered over the 7.5-mm-diameter-loaction on the tail and the indenter platen was applied directly to the top surface of the rat tail during the compression testing.
• Three tails were tested at each of the three selected deformation velocities (0.15 mm/s, 0.05 mm/s, and 0.015 mm/s), and all tails were compressed to a deformation magnitude of 1.875 mm (25% compression ratio).
• A pre-conditioning compression cycle process was used to obtain a steady state, a total of ten compression cycles were completed, and the 9^th cycle was used for data analysis as it was consistently the most representative of the steady state for all tails tested.
• For the fastest deformation velocity (0.15 mm/s), an 11^th cycle was completed for the three tails in which an 11-minute hold was executed immediately after the deformation to evaluate the force-relaxation response of the tail.

Contact width testing

• For the contact width testing three tails were tested at each of the three deformation magnitudes (0.75 mm, 1.35 mm, and 1.875 mm or 10%, 18%, 25% compression ratio, respectively), all at a deformation velocity of 0.015 mm/s.
• To determine the contact width of the tails during the compression tests a light coat of baby oil and then baby powder was applied to tail.
• After the oil and powder was applied to the tail a plexiglass piece identical in size to the indenter platen was carefully placed on top of the tail.
• The indenter platen, the plexiglass, and the 7.5-mm-diameter-location were all centered over one another and then the tail was compressed.
• After the compression test the baby powder left an accurate and detailed outline of the tail on the plexiglass piece that had been placed on top of the tail.
• The plexiglass piece was then careful removed and photographed with a reference scale in frame.
• The contact widths were then measured and recorded using the pictures taking during testing.