ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

experiment are presented here. Prior to this experiment seven trial experiments were
conducted. They showed results consistent with those we report here (Fig.2).
Reaction Force
0.4
0.3
0.2
0.1
0
0 1 2 3 4 5
Displacement (mm)
Figure 2. Indentation of sheep brain in-situ: experimental result for the reaction force-displacement
relationship during trial experiments (each curve represents one experimental result)
4. DETERMINING SUBJECT-SPECIFIC PROPERTIES OF THE BRAIN TISSUE
Following Miller and Chinzei (1997), the constitutive properties of brain tissue were
determined through semi-confined uniaxial compression of a tissue sample (Fig. 3).
Only one sample could be extracted due to relatively small size of the sheep brain. The
sample was compressed between two metal plates covered with sandpaper to ensure noslip
boundary conditions. The constant loading speed of 4 mm/min was used.
Moving Plate
Tissue Sample
Fixed Plate
Figure 3. Uniaxial compression of brain tissue in vitro using the Instron 5948 Microtester
The brain tissue constitutive behaviour was modelled using an Ogden-type (1976)
Hyperelastic model as proposed by Miller and Chinzei (2002):
2μ
α α α
W= ( λ1
+ λ2
+ λ3
− 3)
(1)
2
α
where W is the strain energy potential, λi are principal stretches, µ is the relaxed shear
modulus, and α is a material coefficient. Constants µ and α of equation (1) were varied
to obtain the calculated moving plate reaction force-time history close to the
relationship measured from the experiments (Fig. 4). For the analysed brain, these
constants were determined as µ = 720 Pa and α = -4.7.
Reaction Force (N)
1
0.8
0.6
0.4
0.2
Experiment
Simulation
0
0 20 40 60 80
Time (Seconds)
Figure 4. Uniaxial compression of sheep brain tissue sample: comparison of modelling and experimental
results of the indentor reaction force-time history