Biomedical Engineering Reference
In-Depth Information
Fig. 5.7 a Electrospun elastin (bovine ligamentum nuchae) showing 1.1 ± 07lm fibre
diameter (magnification 4,300X with the inserted scale bar at 1 micron), b (top) Electrospun
type I collagen (calf skin) showing 100 ± 40 nm fibre diameter (magnification 8,000X with the
inserted scale bar at 1 micron), (bottom). Electrospun type I collagen (calf skin) showing
4.62 ± 2.09 lm fibre diameter (magnification 500X with the inserted scale bar at 10 microns),
(Boland et al. 2004)
A distinction is made between collagen of type I to type III where type II
predominantly exists in cartilage, and type I and III in ligaments, tendons and skin.
5.1.1.2 Elastin
Elastin (formerly: tropoelastin) consits of interlinked elastin-units forming a
network of very fine protein fibres, cf. Figs.
5.5
,
5.6a
, b and
5.7
.
Elastin represents the major protein of elastic fibres in almost all vertebrate
connective tissue. It belongs to the group of structural proteins since it is
responsible for shape, resilience and elasticity. In contrast to collagen, elastin
protein fibres can stretch several times their normal length under loading. Elastin is
predominantly found in elastic tissues such as arterial walls, lungs, intestines and
skin. It is secreted by cells in a soluble form and interconnected by the enzyme
lysyloxidase (LOX) and the amino acid lysine.
Mechanically, elastin fibres can be characterized by elastic spring behaviour
and they fully recoil to their original shape when unloaded. Collagen fibres, in
contrast, are characterized by extreme tensile strength, thus exhibiting viscous and
damping characteristics. Under tension loading, however, collagen fibres behave
almost linearly elastic, with little energy dissipation.
5.1.1.3 Ground Substance
Ground Substance is an unstructured substance and is found in connective tissue.
Its chemical consistency depends on the chemical composition and can be liquid to
gel-like. Intercellular components such as collagen and elastin are embedded in the
ground substance. The ground substance consists largely of water (60 to [90 %).
