Biomedical Engineering Reference
In-Depth Information
7 Mechanical Properties of Adipose Tissues
Several studies examined mechanical properties of adipose tissues extracted from
different species and/or different anatomical sites [ 23 - 25 , 34 , 39 , 59 , 65 , 71 , 79 ].
Gefen and Haberman [ 24 ], for example, found that the short-term elastic modulus
of adipose tissues covering the gluteus muscles of sheep was in the range of
0.53-0.85 kPa under confined compression. The long-term elastic modulus of
these tissues was 0.3 kPa under the same mechanical testing protocol. The short-
term elastic modulus under swift indentation experiments however was in the
range of 15.8-22.6 kPa. Subcutaneous adipose tissues from pigs and rats were
examined in the studies of Geerligs et al. [ 23 ] and Iatridis et al. [ 34 ], respectively.
Shear experiments on a rotational rheometer indicated that the shear modulus of
the subcutaneous porcine tissues was 7.5 kPa [ 23 ]. The long-term shear modulus
of the tissues was 1.5-15 kPa [ 22 ]. By means of uniaxial tension with incremental
stress relaxation experiments, the instantaneous and long-term tensile moduli of
the subcutaneous rat tissues were 4.77 and 2.75 kPa, respectively [ 34 ]. Other
studies focused on human breast adipose tissues [ 39 , 59 , 71 ]. Compression loading
of these tissues indicated that their elastic modulus was in the range of 18-24 kPa
[ 39 ]. When examined using magnetic resonance elastography and indentation
techniques, the shear and elastic moduli of breast tissues were 1 and 3.25 kPa,
respectively [ 59 , 71 ]. Magnetic resonance elastography was also used in the study
of Weaver et al. [ 79 ] for determining mechanical properties of adipose tissues
from heel pads of humans. The shear modulus in their study was in the range of
8-12 kPa. The compression modulus of fat pads however, which was evaluated
in vivo using a digital radiographic fluoroscopy/contact pressure display method,
was found to be much greater, in the range of 105-306 kPa [ 25 ]. To summarize,
even though it is rather difficult to compare tissue mechanical properties across
literature reports considering the diversity in measurement techniques and proto-
cols, it appear that the stiffness of adipose tissues depends on the anatomical site
and hence on the physiological function [ 65 ].
8 Mechanical Properties of Adipocytes
Characterizing the mechanical properties of adipocytes is technically challenging
but extremely important since these properties directly determine the extent of
cellular deformations and stresses when adipose tissues are weight-bearing. Hence,
adipogenesis and the macroscopic-scale increase in fat tissue mass, which are
mechanosensitive processes (as described earlier), are influenced by the distribu-
tion of cell stiffnesses in the adipose tissues. Mechanical properties of adipocytes
were examined in a limited number of studies so far [ 13 , 80 , 81 ]. Using atomic
force microscopy (AFM), Young-Nam et al. [ 80 ] found that the stiffnesses of 3T3-
L1 adipocytes negatively correlate with the time of differentiation. This result
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