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

Biomechanics of Human Gluteal Tissue:
In Vivo Characterization and Loading Simulation
C. Then 1 , J. Menger 2 , T. J. Vogl 3 , F. Hübner 4 , G. Silber 5,*
KEY WORDS: Adipose and skeletal muscle tissue; Hyperelasticity; Finite deformations; Quasilinear
viscoelasticity; Relaxation; Tissue interaction simulation;
1. ABSTRACT
The most common complication associated with immobilization is pressure sores
caused by sustained localized tissue strain and stress. Computational simulations have
provided insight into tissue stress-strain distribution, subject to loading conditions and
thus can contribute to designing more efficient devices interacting with the tissue. In the
simulation process, a suitable material model as well as adequate soft tissue material
parameters are indispensable. Tissue specific mechanical in vivo behaviour, separating
human gluteal adipose and passive skeletal muscle tissue compressed with finite strain
has, however, been sparsely characterized.
Measurements to characterize deep human soft tissue regions in vivo do not permit a
classical experimental set-up employing isolated test specimens such as those used in
tensile or shear testing. A method is presented to investigate the time-dependent
properties of in vivo gluteal adipose and passive skeletal muscle tissue, utilizing a
combined experimental and numerical approach. Specifically, displacement-controlled
ramp-and-hold indentation relaxation tests were performed and documented with
magnetic resonance imaging. Employing a finite element model, a time domain quasilinear
viscoelasticity formulation with Prony series valid for finite strains was used in
conjunction with a hyperelastic model formulation for soft tissue constitutive model
parameter identification and calibration of the relaxation test data.
Distinct non-linear elastic but linear viscoelastic tissue material behaviour was apparent
at finite strains for both passive skeletal muscle and adipose mechanical properties with
orthogonal skin and cross muscle fibre loading. The employed material model was
found to be well suited to fit the experimental data. Separate characterization of in vivo
gluteal adipose and cross-fibre muscle tissue could thus be established and used for
simulation of tissue loading employing the finite element method.
Gluteal tissue was used in the presented approach. Similarly, human heel and cheek
tissue were characterized for tissue stress-strain analysis during gait loading and virtual
shaving simulation, respectively.
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1
PhD, LOEWE-research focus Preventive Biomechanics PreBionics, Frankfurt/M. and Institute for
Materials Science, University of Applied Sciences Frankfurt/M., Germany.
2
M. Eng., LOEWE-research focus Preventive Biomechanics PreBionics, Frankfurt/M. and Institute for
Materials Science, University of Applied Sciences Frankfurt/M., Germany.
3
Professor, Director of the Department of Diagnostic and Interventional Radiology, Hospital of the
Johann Wolfgang Goethe University Frankfurt/M., Germany.
4
M. Eng., Department of Diagnostic and Interventional Radiology, Hospital of the Johann Wolfgang
Goethe University Frankfurt/M., Germany.
5
Professor, LOEWE-research focus Preventive Biomechanics PreBionics, Frankfurt/M. and Institute for
Materials Science, University of Applied Sciences Frankfurt/M., Germany. Scientific Director of the
federal state government PreBionics-LOEWE program funded by the state of Hesse (Germany), by the
Ministry of Higher Education, Research and the Arts (HMWK). *Corresponding author.