Biomedical Engineering Reference
In-Depth Information
Fig. 5.12
Schematic
representation
of
the
test
design
for
evaluation
of
mechanical
and
physiological tissue data in the gluteal region
experiments. This is due to a paucity of information on human in vivo material
parameters characterizing human long-term gluteal fat and muscle tissue proper-
ties. Therefore, no calibration with human tissue properties has been performed to
judge the adequacy of the employed animal data.
A more or less distinct anisotropic and/or viscoelastic material behaviour can
principally be assumed for all tissues. Determining tissue anisotropy most likely
constitutes the major problem involving the living human organism (aside from
prerequisite ethical approval) since experiments require a different approach than
handling ex vivo tissue samples in the lab. Simplified material experiments must
be
performed
on
humans
which,
at
minimum,
provide
information
on
the
qualitative material behaviour of the body site under investigation.
The isotropic assumption is admissible with respect to the fat-muscle tissue
compound in the human gluteal region. This is particularly true for adipose tissue
as the substructure on a macroscopic scale in Fig.
5.2
a indicates. In a first
approximation, the muscle groups involved in the gluteal region exhibit
predominantly passive behaviour during static sitting or laying down. The loading
during the experiments in this approximation was conducted in a cross fibre
direction, i.e. orthogonal to the fibre direction.
To evaluate the viscoelastic material behaviour of human soft tissues, an
established procedure is described (cf.
Sects. 5.2.4
and
5.2.5
), similar to the
experimental procedure employed in soft foam material characterization
(cf.
Sect. 4.2.1
). Furthermore, an approach is presented to separate the mechanical
behaviour of both ''sub-systems'', i.e. fat and muscle. Both procedures rely on the
use of (medical) imaging procedures and are quite rigorous (volunteers are
required to remain several hours in an almost unchanged body position).
Figure
5.12
illustrates the schematic assembly of the test design for mechanical
tissue property evaluation (force-displacement-data) together with some physio-
logical data (O
2
-values and micro-perfusion) of the gluteal tissue.
