Biomedical Engineering Reference
In-Depth Information
Fig. 7.9 Comparison of tissue normal stress S
33
along a node path 1 and b node path 2 (see
Fig.
7.6
) for the selected systems LS1 to LS3
Fig. 7.10 Comparison of
tissue shear stress S
23
along
node path 1 (see Fig.
7.6
) for
the selected systems LS1 to
LS3
7.1.3.4 Deformation Analysis and Additional Selection Criteria
Variation LS1 caused a large deformation of the mattress foam material at the
tailbone region, thus creating a critical zone between the buttocks and T-beams, cf.
Fig.
7.11
(top), thereby excluding this system as a favorable candidate. The three
chamber system LS3 in contrast, caused large curvatures of the mattress
membrane between some T-beams [Fig.
7.11
(bottom)] making membrane
material failure likely to occur, thus excluding this particular variation as an ideal
bedding system. The system LS2 represents the most promising model to be
further optimized, since the disadvantages of the other two systems are not present.
7.1.3.5 Comparison with Two Reference Systems
The system LS2 was compared with two commonly employed bedding systems to
judge the effects on tissue. Reference system (a) was a plain soft foam mattress and
system (b) was the Thevo Vital-system (TV), from T
HOMASHILFEN
GmbH.
Figures
7.12
and
7.13
depict tissue mechanical normal stress component S
33
along
node paths 1 and 2 (see Fig.
7.6
) and shear stress component S
23
along path 1.
Both stress components were significantly lower in system LS2. The foam mattress
showed high tissue normal stress along path 2 towards the bone surface.
