Impact Acceleration Tests and Material Properties of Rat Brain

1. Impact Acceleration Tests and Material Properties of Rat Brain Investigators: Kurosh Darvish Temple University Jeff Crandall Center for Applied Biomechanics James Stone and David Okonkwo Department of Neurosurgery University of Virginia, Charlottesville, VA December 2006

2. Accurate TBI Model Enhanced Numerical Algorithms Improved Constitutive Models Accumulation of Experimental Data Objectives Characterization of Changes in Brain Tissue Material Properties in • Live vs. Dead Tissue • Injured vs. Intact Tissue

3. Live vs. Dead Tissue Material Properties

4. load cell actuator 2 mm spherical indenter load cell spherical indenter In Situ Sectioned Indentation Tests for Live vs. Dead Tissue Material Properties actuator In Vivo

5. In Vivo Test Results 2.7 s breathing Two Oscillations: 0.28 s heart beat

6. In Situ and Sectioned Test Results

7. P m 8 D = e 3 / 2 P h sn= P/A - n 3 ( 1 ) 2 D t ¶ ¶ ie P h h ò = - t t P ( t ) G ( t ) d ¶ ¶ t h 0 m = m + m ( h ) h 0 1 Modeling Based on Elastic Spherical Indentation Theory 1. Elastic Solution 2. Viscoelastic Approximation 3. Material Nonlinearity

8. 3 5 = + ie P ah bh 2 2 Instantaneous Elastic Response

9. 4 å - b = + t G ( t ) G G e i ¥ i = i 1 Reduced Relaxation Function 0 < G(t) ≤ 1

10. Injured vs. Intact Tissue Material Properties

11. Injury Model: Impact Accel. Tests Lab Reference Frame y x z

12. The Head Kinematics from Accelerometers

13. Traumatic Axonal Injury (TAI) in Rat Brain Stem Corticospinal tract (CSpT): a motor pathway Inferior View P1: ponto-medullary junction P2: pyramidal decussation 10 mm Sagittal section

14. Quantification of TAI TAI was identified using antibodies to the amyloid precursor protein (APP). n = 40

15. Indentation Tests for Injured vs. Intact Tissue Material Properties load cell P1 P2 0.78 mm radius flat indenter

16. m 4 = k e P a h - n 1 t ¶ ¶ ie P h ò = - t t P ( t ) G ( t ) d ¶ ¶ t h 0 m = m + m 2 ( h ) h 0 2 Modeling Based on Elastic Flat Indentation Theory P 1. Elastic Solution sn= P/A 2a 2. Viscoelastic Approximation h t 3. Material Nonlinearity

17. Modeling Procedure

18. Variable Time Constants Are two models different?

21. Range of Shear Modulus

22. Modeling Multiple Steps 2002-T1-In-P1

23. Step 2

24. Step 3

25. Limitation of the QLV Assumption

27. More Recent Activities • Mild/Moderate Rat Brain Injury Model • Dynamic Impact System • Nano-indentaiton Test System Goal • Modeling the evolution of changed in material properties (damage model) • Development of an injury model in which the severity of injury can be easily controlled and mechanical parameters be measured • Model can be used on pigs

28. Mild/Moderate Brain Injury Model Impactor connected to the Pneumatic Piston Posterior Accelerometer Anterior Accelerometer Custom-made Harness to Hold the Sensors 5% Gelatin Support Bed Front view of the experimental setup

30. Impact Test Dynamic Parameters Table 1: Video Analysis data Table 2: Max vertical velocity and acceleration of the head Marmarou’s Test: Maximum Displacement = 100 mm Maximum Velocity = 6 m/s

31. Rat Impact Tests NURBS Model of Rat

32. Urethane Casing for Linear and Angular Head Motion

33. Crash Pulse 10 m/s = 22.4 mph Stops in 10 cm distance Average Acceleration = 50 g

34. Specimen Mounted in Vertical Position (Aorta Model)

37. Thank you! Temple Biomechanics Laboratory

39. Number of Samples