This article details a protocol for conducting nanoindentation experiments on mouse brain tissue to assess its mechanical properties. The method involves precise alignment and measurement techniques to evaluate tissue stiffness and elasticity.
Take a thick mouse brain tissue slice secured to the sample holder. Place an immersion chamber over the holder and fill it with carbon dioxide-independent media to maintain tissue hydration.
Mount the holder onto the calibrated instrumented nanoindenter's stage.
Align the immersion chamber so the spherical probe attached to the pendulum arm is directly
above the chamber.
Raise the chamber until the probe is submerged in the media and aligned with the tissue surface.
Bring the probe into contact with the tissue surface, then retract slightly to allow free pendulum motion and ensure precise force application.
Begin the nanoindentation experiment, where the pendulum swings forward and strikes the tissue. This impact penetrates the surface and initiates an oscillatory motion due to damped
harmonic behavior.
Measure the pendulum displacement and the velocity to assess penetration depth, energy dissipation, and damping. These measurements reveal the tissue's mechanical properties, such as stiffness and elasticity.
When the impact indentation setup is fully complete, aspirate the medium and dry the brain slice. Then use a thin layer of cyanoacrylate adhesive to secure the sliced brain to the aluminum sample post.
Then slide the liquid cell over the second O-ring on the sample post. And fill the liquid cell with 5 milliliters of carbon dioxide-independent medium to fully immerse the tissue.
Move the bath in the negative x direction until the tip on the lever arm is properly located above the bath. Next, move in the positive z direction until the tip is fully submerged in the bath and is in front of the sample.
Using the Sample Stage control window, carefully make contact, and then back the stage away from the sample surface by about 30 micrometers.
Under the Experiment menu, click Impact and set up an impact experiment. Choose a specific impulse load that will relate directly to the resulting impact velocity based on the swing distance calibration. And then run the scheduled experiment.
When the pendulum swings back and the sample surface continues to move to the measurement plane, turn the bottom limit switch off. The displacement of the probe as a function of time will be recorded by the software.
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