The objective of this study was to define the constitutive response of brainstem undergoing finite shear deformation. Brainstem was characterized as a transversely isotropic viscoelastic material and the material model was formulated for numerical implementation. Model parameters were fit to shear data obtained in porcine brainstem specimens undergoing finite shear deformation in three directions: parallel, perpendicular, and cross sectional to axonal fiber orientation and determined using a combined approach of finite element analysis (FEA) and a genetic algorithm (GA) optimizing method. The average initial shear modulus of brainstem matrix of 4-week old pigs was , and therefore the brainstem offers little resistance to large shear deformations in the parallel or perpendicular directions, due to the dominant contribution of the matrix in these directions. The fiber reinforcement stiffness was , indicating that brainstem is anisotropic and that axonal fibers have an important role in the cross-sectional direction. The first two leading relative shear relaxation moduli were 0.8973 and 0.0741, respectively, with corresponding characteristic times of 0.0047 and , respectively, implying rapid relaxation of shear stresses. The developed material model and parameter estimation technique are likely to find broad applications in neural and orthopaedic tissues.
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e-mail: margulie@seas.upenn.edu
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December 2006
Technical Papers
A Transversely Isotropic Viscoelastic Constitutive Equation for Brainstem Undergoing Finite Deformation
Xinguo Ning,
Xinguo Ning
Department of Bioengineering,
University of Pennsylvania
, Philadelphia, PA 19104-6382
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Qiliang Zhu,
Qiliang Zhu
Department of Bioengineering,
University of Pennsylvania
, Philadelphia, PA 19104-6382
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Yoram Lanir,
Yoram Lanir
Department of Bioengineering,
University of Pennsylvania
, Philadelphia, PA 19104-6382
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Susan S. Margulies
Susan S. Margulies
Department of Bioengineering,
e-mail: margulie@seas.upenn.edu
University of Pennsylvania
, Philadelphia, PA 19104-6382
Search for other works by this author on:
Xinguo Ning
Department of Bioengineering,
University of Pennsylvania
, Philadelphia, PA 19104-6382
Qiliang Zhu
Department of Bioengineering,
University of Pennsylvania
, Philadelphia, PA 19104-6382
Yoram Lanir
Department of Bioengineering,
University of Pennsylvania
, Philadelphia, PA 19104-6382
Susan S. Margulies
Department of Bioengineering,
University of Pennsylvania
, Philadelphia, PA 19104-6382e-mail: margulie@seas.upenn.edu
J Biomech Eng. Dec 2006, 128(6): 925-933 (9 pages)
Published Online: June 29, 2006
Article history
Received:
September 15, 2005
Revised:
June 29, 2006
Citation
Ning, X., Zhu, Q., Lanir, Y., and Margulies, S. S. (June 29, 2006). "A Transversely Isotropic Viscoelastic Constitutive Equation for Brainstem Undergoing Finite Deformation." ASME. J Biomech Eng. December 2006; 128(6): 925–933. https://doi.org/10.1115/1.2354208
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