TY - JOUR
T1 - Are in vivo and in situ brain tissues mechanically similar?
AU - Gefen, Amit
AU - Margulies, Susan S.
N1 - Funding Information:
The authors are thankful to Mr. John Noon for designing and building the indentor, Ms. Brittany Coats for her technical assistance in preparing the indentation apparatus for the present study and Ms. Jill Ralston for handling of animals. These studies were supported by NIH-R01-NS-39679 and CDC-R49-CCR-312712 grants (SSM) and by the Dan David Foundation (AG).
PY - 2004/9
Y1 - 2004/9
N2 - Brain tissue mechanical properties have been well-characterized in vitro, and were found to be inhomogeneous, nonlinear anisotropic and influenced by neurological development and postmortem time interval prior to testing. However, brain in vivo is a vascularized tissue, and there is a paucity of information regarding the effect of perfusion on brain mechanical properties. Furthermore, mechanical properties are often extracted from preconditioned tissue, and it remains unclear if these properties are representative of non-preconditioned tissue. We present non-preconditioned (NPC) and preconditioned (PC) relaxation responses of porcine brain (N = 10) obtained in vivo, in situ and in vitro, at anterior, mid and posterior regions of the cerebral cortex during 4mm indentations at either 3 or 1mm/s. Material property characteristics showed no dependency on the site tested, thus revealing that cortical gray matter on the parietal and frontal lobes can be considered homogenous. In most cases, preconditioning decreased the shear moduli, with a more pronounced effect in the dead (in situ and in vitro) brain. For most conditions, it was found that only the long-term time constant of relaxation (τ > 20 s) significantly decreased from in vivo to in situ modes (p<0.02), and perfusion had no effect on any other property. These findings support the concept that perfusion does not affect the stiffness of living cortical tissue.
AB - Brain tissue mechanical properties have been well-characterized in vitro, and were found to be inhomogeneous, nonlinear anisotropic and influenced by neurological development and postmortem time interval prior to testing. However, brain in vivo is a vascularized tissue, and there is a paucity of information regarding the effect of perfusion on brain mechanical properties. Furthermore, mechanical properties are often extracted from preconditioned tissue, and it remains unclear if these properties are representative of non-preconditioned tissue. We present non-preconditioned (NPC) and preconditioned (PC) relaxation responses of porcine brain (N = 10) obtained in vivo, in situ and in vitro, at anterior, mid and posterior regions of the cerebral cortex during 4mm indentations at either 3 or 1mm/s. Material property characteristics showed no dependency on the site tested, thus revealing that cortical gray matter on the parietal and frontal lobes can be considered homogenous. In most cases, preconditioning decreased the shear moduli, with a more pronounced effect in the dead (in situ and in vitro) brain. For most conditions, it was found that only the long-term time constant of relaxation (τ > 20 s) significantly decreased from in vivo to in situ modes (p<0.02), and perfusion had no effect on any other property. These findings support the concept that perfusion does not affect the stiffness of living cortical tissue.
KW - Brain injury
KW - Constitutive properties
KW - Indentation
KW - Shear modulus
KW - Stress relaxation
KW - Viscoelasticity
UR - http://www.scopus.com/inward/record.url?scp=3242688027&partnerID=8YFLogxK
U2 - 10.1016/j.jbiomech.2003.12.032
DO - 10.1016/j.jbiomech.2003.12.032
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C2 - 15275841
AN - SCOPUS:3242688027
SN - 0021-9290
VL - 37
SP - 1339
EP - 1352
JO - Journal of Biomechanics
JF - Journal of Biomechanics
IS - 9
ER -