Kb. Arbogast et Ss. Margulies, MATERIAL CHARACTERIZATION OF THE BRAIN-STEM FROM OSCILLATORY SHEAR TESTS, Journal of biomechanics, 31(9), 1998, pp. 801-807
Traumatic damage to the brainstem occurs frequently when the brain-sku
ll complex experiences injurious loading especially during those traum
atic situations that produce diffuse axonal injury (DAI). DAI has been
shown to be dependent on load direction and correlated with regional
tissue deformation in response to rotational inertial loads. Possible
mechanisms for the selective vulnerability of the brainstem are (1) th
e geometry of the central nervous system is responsible for producing
high tissue strains in these regions, (2) regional differences in over
all material stiffness result in larger deformations at these sites, a
nd (3) the anisotropic mechanical properties of these regions lead to
a sensitivity to the rotational load direction and magnitude. This pap
er investigates the latter two hypotheses by performing oscillatory sh
ear tests on adult porcine brainstem in three mutually perpendicular d
irections. The complex shear moduli were calculated over a range of fr
equencies (20-200 Hz), for three levels of peak engineering strain (2.
5%, 5.0%, and 7.5%). The directional data demonstrated that the brains
tem exhibits significant transversely isotropic behavior. Both compone
nts of the complex modulus in which the axonal fibers are oriented par
allel to the plane of shear but transverse to the shear direction were
significantly higher than those of the other two, mutually indistingu
ishable test cases across the range of strains tested. By comparison w
ith similar tests on cerebral tissue, these data demonstrated that the
brainstem displays a stiffer biomechanical response. These difference
s were present for both components of the complex shear modulus and we
re greater as the magnitude of the applied strain increased. The regio
nal stiffness and anisotropic response of the brainstem coupled with i
ts location as a narrow bridge between CNS regions interact to result
in the selective vulnerability of this region in rotational loading. (
C) 1998 Elsevier Science Ltd. All rights reserved.