Biomedical Engineering Reference
In-Depth Information
Ultimate
strength
x
Yield point
x
Metal
stress-strain
curve
Skin stress-
strain curve
Strain
3.2
Stress-strain curve for a typical material such as a metal along
with that for skin. The Young's moduli for the two are very different.
The figure is used to illustrate only the trend in the stresses with
increasing strains. Skin shows a positive second derivative - it be-
comes stiffer as it is stretched.
study deforms under applied stresses. The yield point occurs when the material
will no longer deform elastically. In other words, it will not go back to its original
length or conformation after the stress is removed. It will have undergone plastic
deformation (there will be some deformation in the material even after all stresses
or forces have been removed). The tensile strength of the material is the maximum
stress the material can withstand and occurs at the point of rupture of the material.
Figure 3.2 also shows the stress-strain curve for skin. As skin is stretched it
shows increasing stiffness (it has a positive second derivative). This is because
with increased stretch the fibers in skin orient in the same direction, thereby
increasing its resistance to the applied stretch.
3.4
Wounded skin contraction
Skin can be damaged under the action of various mechanical, chemical and other
stresses. Because the skin serves such an important role in the body, wounded skin
needs to be replaced quickly. There are essentially two types of healing responses.
One is healing by first intention and the other is healing by second intention.
4
In the
former reparative process, after the wounding agent is removed, the edges of the
wound bed are in very close proximity. This type of a reparative process involves
little or no contraction of the wound bed. However, in the latter type of wound
healing, the edges of the wound bed are not in close proximity and thus in order to
bring them closer, fibroblasts occur at the edge of the wound.
4
These fibroblasts
