Biomedical Engineering Reference
In-Depth Information
Fig. 11.6
Experimental setup for indentation-based mechanical testing of cheek and tongue tissue
ing tissue mechanics are much less routine than medical imaging for morphology.
Our reference models incorporate average material properties from cadaver studies
and previously published literature. Recently, we have worked with collaborators
to develop new experimental protocols to measure subject-specific material proper-
ties in vivo [
25
,
26
]. Our general approach for representing soft-tissue mechanics
is to combine a passive matrix for tissue elasticity together with along-fiber muscle
mechanics using an uncoupled strain energy formulation [
27
,
28
].
11.2.2.1 Isotropic Indentation Measurements
The initial material properties for our FE models were taken from literature data in
combination with mechanical testing with fresh cadaveric cheek and tongue tissues
[
29
]. The mechanical testing involved uniaxial indentation tests using an EnduraTEC
indentation device (Bose Corporation, Framingham, MA). The experimental setup
is pictured in Fig.
11.6
. Indentation measurements characterized the relationship be-
tween the local force applied to the external surface of the tissue and the resulting
displacement. These measurements were used to fit parameters in a isotropic, non-
linear, hyperelastic material—a fifth-order Mooney-Rivlin material [
30
,
31
],
+
2
(
2
2
W
=
C
10
(
I
1
−
3
)
+
C
20
(
I
1
−
3
)
ln
J
)
,
2
term enforces tissue incompressibility. Other terms in the
Mooney-Rivlin material were omitted, i.e. c
01
=
where the
κ/
2
(
ln
J
)
c
11
=
c
02
=
0. For the face tissue,
=
,
=
material coefficients were found of c
10
2500 Pa
c
20
1175 Pa [
20
]. For the
tongue tissue, material coefficients were found of c
10
=
1037Pa, c
20
=
486 Pa
