Biomedical Engineering Reference
In-Depth Information
Fig. 7.50 Direct tissue stress
progression from skin level
(0.0 mm) to ischial bone
surface (43 mm) using block-
shaped cushion and
optimized cushion shape
foam support geometry is shown. Lateral foam shape/stiffness controls the vertical
displacement of the lateral buttock tissue as indicated previously in conjunction
with shear stress minimization, Fig.
7.46
.
Any approach towards tissue stress and strain minimization should thus aim to
control tissue displacement. Such control includes tissue displacement relative to
bone structures as well as displacement of fat tissue relative to adjacent muscle
tissue.
To acquire an additional impression of existing gluteal tissue displacement
resulting from numerical simulation, Fig.
7.51
a and b, were superimposed.
Figure
7.52
depicts the deformed tissue configuration (shaded) and the unde-
formed configuration, borderline.
Vector plots of the displacement fields of gluteal tissue (relative to the bone)
under maximum loading of the optimized transversal cushion shape and the block-
shaped cushion shape show that the area beneath the ischial tuberosity differs
significantly, Fig.
7.53
. Whereas the block-shaped cushion causes the tissue to
displace ''around'' the ischial bone, the optimized support shape predominantly
causes lateral tissue displacement. Displacement towards the body center nearly
vanishes.
7.2.5 Discussion
The previous sections present a possible approach towards generating body
supports which reduce mechanical tissue peak stress at defined body sites. The
described approach is based on automated optimizing techniques in conjunction
with numerical modelling and simulation of tissue-support interaction. The process
is exemplarily performed aiming to minimize direct stress beneath the ischial
tuberosity. In the same manner, support shape optimization can readily be
performed to reduce any stress or strain quantity, singularly or simultaneously at
